# data[].attributes.body
The two primary vascular tissues are xylem, which transports water and dissolves minerals from the roots to the leaves, and phloem, which conducts food from the leaves to all parts of the plant.

# data[].attributes.body
Our organism that we chose was a butter weed. Butter weed is known to be an important early spring source of nectar for bees and other pollinators. The flowers are borne at the ends of thick, erect, deeply ridged green stems that are sometimes streaked in reddish-purple.

# data[].attributes.attachment_link.readable_text
Albert's quote captures perfectly the dichotomous nature of native Butterweed ( Packera glabella; syn. Senecio glabellus). On one hand, a sea of yellow flowers carpeting farm fields flanking Ohio's interstates in the spring provides welcome relief from highway monotony. On the other hand, upright 2 - 3' tall plants bolting seemingly out of nowhere in Ohio landscapes presents a weed management challenge.

The flowers are borne at the ends of thick, erect, deeply ridged green stems that are sometimes streaked in reddish-purple. Seedheads look like miniature dandelion puff-balls which is no accident; dandelions ( Taraxacum spp.) also belong to the aster family.

Don't Rocket Towards a M isidentification

Yellow-flowering Garden Yellowrocket ( Barbarea vulgaris) is a non-native invasive biennial weed that is also on the rise at this time of the year and may be found mixed with butterweed. Yellowrocket belongs to the mustard family (Brassicaceae), so it is a prolific seed producer.

# data[].attributes.attachment_link.title
Butterweed / Cressleaf Groundsel: Beauty is in the Eye of the Beholder

# data[].attributes.attachment_link.description
The dichotomous nature of Butterweed may test the tolerance of lovers of native wildflowers. On one hand, a sea of yellow flowers carpeting farm fields flanking Ohio's interstates in the spring provides welcome relief from highway monotony. On the other hand, upright 2 - 3' tall plants bolting seemingly out of nowhere in Ohio landscapes presents a weed management challenge.

# data[].attributes.attachment_link.readable_text
Senecio glabellus

Asteraceae (Sunflower Family)

Butterweed is a cool-season annual that usually grows to 18 to 20 inches tall. On rare occasions it grows to 40 inches. The basal leaves, up to 4 inches long, are deeply lobed, with oblong, lateral lobes having wavy margins.

Although the plant usually has one stalk, it occasionally has a few. It can be unbranched or branched above, depending upon moisture and soil fertility.

Numerous yellow flowers stand on short stalks, forming a large terminal cluster.

Butterweed may be found in many of the areas of Texas, but large populations are usually present only in the eastern third of the state. It is often found in clay or heavy loam soils in disturbed areas, stream bottoms, ditches and flood plains.

These plants contain pyrrolizidine alkaloids that cause progressive liver cirrhosis. Consumption of large amounts of the plant can result in acute liver necrosis. However, in most instances, several months elapse between consumption and the appearance of clinical signs. Horses, cattle and llamas have died of liver cirrhosis after being on pastures containing butterweed.

Sudden death has been seen in some cases in which horses were placed on almost pure butterweed paddocks with no hay or feed.

Most animals are clinically normal for several months after consuming the plant and then demonstrate signs of poisoning, which are all related to loss of liver function and can include: Anorexia; Depression; Weight loss; Aggression; Death.

Animals should not be forced to consume these unpalatable plants. Poisoning has not been observed in species other than llamas if there is adequate pasture or good quality hay and feed available. Llamas may be more sensitive to the pyrrolizidine alkaloids or less discriminating in their eating habits.

Sheep are more resistant to pyrrolizidine alkaloid poisoning and may be used to "clean" the pastures while the plants are young. Severe infestations may be controlled with broadleaf herbicides such as 2,4-D or Grazon P+D® at 0.5 to 1.0 pound a.i./acre in the spring with good growing conditions.

Flower Color: Yellow

Seed Type: Non-Encapsulated

Duration: Annual

Stem Texture: Hairless/Smooth

Growth Habit: Forbs/Broadleaf

Leaf Shape : Simple with Pinnate or Parallel Venation

Season: Cool

Distribution : 01 - Pineywoods, 02 - Gulf Prairies and Marshes, 03 - Post Oak Savannah, 04 - Blackland Prairies, 05 - Cross Timbers and Prairies

Collection: Toxics, Wild Flowers

# data[].attributes.attachment_link.description
Senecio glabellus Asteraceae (Sunflower Family) Butterweed is a cool-season annual that usually grows to 18 to 20 inches tall. On rare occasions it grows to 40 inches. The basal leaves, up to 4 inches long, are deeply lobed, with oblong, lateral lobes having wavy margins.

# data[].attributes.body
plants grow through a combination of cell growth and cell division.

# data[].attributes.body
How flowering plants help the environment! ^^^

# data[].attributes.body
Plants do not need a digestive system because they get their energy through photosynthesis and their nutrients through their roots!

# data[].attributes.attachment_link.readable_text
Packera glabella (formerly Senecio glabellus)

Asteraceae (daisies, sunflowers, asters)

Butterweed, one of Missouri's seven species of ragworts or groundsels, is the only one that is an annual, has fibrous roots (lacking rhizomes or stolons), usually has only a single, unbranched stalk that is smooth (without hairs), and typically grows in colonies (at times covering acres of floodplain). The stems are heavily ridged and usually inflated or hollow. It usually has no basal leaves at flowering time; the stem leaves, however, are largest at the base of the plant and get gradually smaller up the stem. The blades are deeply pinnately lobed, with toothed margins. Flowers abundant, with rich golden heads with few ray flowers. Blooms April-June.

Learn more about Missouri's ragworts.

Similar species: Seven Packera species occur in Missouri, plus a number of hybrids having intermediate characteristics that make identification tricky. Generally, the best characters for distinguishing among Missouri's ragwort species are the leaves, especially the basal leaves, if they are present at flowering time. Butterweed, being the only one that is annual and lacking a basal whorl of leaves at flowering time, stands apart from the others.

From a distance, colonies of blooming butterweed may be misidentified as colonies of yellow rocket (a type of mustard). Indeed, one common name for butterweed, "cressleaf groundsel," recognizes the foliage's similarity to cresses and other mustards.

About Wildflowers, Grasses and Other Nonwoody Plants in Missouri

A very simple way of thinking about the green world is to divide the vascular plants into two groups: woody and nonwoody (or herbaceous). But this is an artificial division; many plant families include some species that are woody and some that are not. The diversity of nonwoody vascular plants is staggering! Think of all the ferns, grasses, sedges, lilies, peas, sunflowers, nightshades, milkweeds, mustards, mints, and mallows - weeds and wildflowers - and many more!

# data[].attributes.attachment_link.description
Butterweed, one of Missouri's seven species of ragworts or groundsels, is the only one that is an annual, has fibrous roots (lacking rhizomes or stolons), usually has only a single, unbranched stalk that is smooth (without hairs), and typically grows in colonies (at times covering acres of floodplain).

# data[].attributes.headline
Does it reproduce using meiosis or mitosis

# data[].attributes.subject
Does it reproduce using meiosis or mitosis

# data[].attributes.body
It Uses Mitosis to reproduce.

# data[].attributes.body
The three basic organs of plants or flowers are roots, stems and leaves. Roots help take in water and nutrients,Stems help transport water and nutrients up from the roots all the way to the leaves, And lastly leaves change sunlight into energy through photosynthesis.

# data[].attributes.body
The exchange of gases in the leaves during respiration takes place through stomata.

# data[].attributes.body
This is a image describin the different parts of the circulatory system

# data[].attributes.body
our organism does not have a skeletal system the stem is hollow

# data[].attributes.attachment_caption
Another important part of the circulatory system 

# data[].attributes.body
This shows you the heart wich help pump the blood through out to the body

# data[].attributes.attachment_caption
The heart pumping blood through the body

# data[].attributes.body
This is a image of the heart doing it job in the circulatory system.

# data[].attributes.attachment_caption
Heart pumping blood and with other with disorders 

# data[].attributes.body
In this image you can see hoe the heart pumps blood and what it would look like with issues.

# data[].attributes.body
This is a image of a blood clot where your blood cells get stuck together and can harm the body

# data[].attributes.headline
pt 1 of circulatory system - Ms. Coble- circulatory system

# data[].attributes.subject
pt 1 of circulatory system - Ms. Coble- circulatory system

# data[].attributes.attachment_link.title
Blood Flow through the Heart in 2 MINUTES

# data[].attributes.headline
pt 2 of circulatory videos - Ms. Cobles - Circulatory system

# data[].attributes.subject
pt 2 of circulatory videos - Ms. Cobles - Circulatory system

# data[].attributes.attachment_link.title
The Circulatory System - Learning the Human Body

# data[].attributes.body
this is a article on the circulatory system

# data[].attributes.attachment_link.readable_text
Listen

Play Stop Volume mp3 Settings Close Player

Larger text size Large text size Regular text size

What Does the Heart Do?

The heart is a pump, usually beating about 60 to 100 times per minute. With each heartbeat, the heart sends blood throughout our bodies, carrying oxygen to every cell. After delivering the oxygen, the blood returns to the heart. The heart then sends the blood to the lungs to pick up more oxygen. This cycle repeats over and over again.

What Does the Circulatory System Do?

The circulatory system is made up of blood vessels that carry blood away from and towards the heart. Arteries carry blood away from the heart and veins carry blood back to the heart.

The circulatory system carries oxygen, nutrients, and

hormonesto cells, and removes waste products, like carbon dioxide. These roadways travel in one direction only, to keep things going where they should.

What Are the Parts of the Heart?

The heart has four chambers - two on top and two on bottom:

The two bottom chambers are the right ventricle and the left ventricle. These pump blood out of the heart. A wall called the interventricular septum is between the two ventricles.

The two top chambers are the right atrium and the left atrium. They receive the blood entering the heart. A wall called the interatrial septum is between the atria.

The atria are separated from the ventricles by the atrioventricular valves:

The tricuspid valve separates the right atrium from the right ventricle.

The mitral valve separates the left atrium from the left ventricle.

Two valves also separate the ventricles from the large blood vessels that carry blood leaving the heart:

The pulmonic valve is between the right ventricle and the pulmonary artery, which carries blood to the lungs.

The aortic valve is between the left ventricle and the aorta, which carries blood to the body.

What Are the Parts of the Circulatory System?

Two pathways come from the heart:

The pulmonary circulation is a short loop from the heart to the lungs and back again.

The systemic circulation carries blood from the heart to all the other parts of the body and back again.

In pulmonary circulation:

The pulmonary artery is a big artery that comes from the heart. It splits into two main branches, and brings blood from the heart to the lungs. At the lungs, the blood picks up oxygen and drops off carbon dioxide. The blood then returns to the heart through the pulmonary veins.

In systemic circulation:

Next, blood that returns to the heart has picked up lots of oxygen from the lungs. So it can now go out to the body. The aorta is a big artery that leaves the heart carrying this oxygenated blood. Branches off of the aorta send blood to the muscles of the heart itself, as well as all other parts of the body. Like a tree, the branches gets smaller and smaller as they get farther from the aorta.

At each body part, a network of tiny blood vessels called capillaries connects the very small artery branches to very small veins. The capillaries have very thin walls, and through them, nutrients and oxygen are delivered to the cells. Waste products are brought into the capillaries.

Capillaries then lead into small veins. Small veins lead to larger and larger veins as the blood approaches the heart. Valves in the veins keep blood flowing in the correct direction. Two large veins that lead into the heart are the superior vena cava and inferior vena cava. (The terms superior and inferior don't mean that one vein is better than the other, but that they're located above and below the heart.)

Once the blood is back in the heart, it needs to re-enter the pulmonary circulation and go back to the lungs to drop off the carbon dioxide and pick up more oxygen.

How Does the Heart Beat?

The heart gets messages from the body that tell it when to pump more or less blood depending on a person's needs. For example, when you're sleeping, it pumps just enough to provide for the lower amounts of oxygen needed by your body at rest. But when you're exercising, the heart pumps faster so that your muscles get more oxygen and can work harder.

How the heart beats is controlled by a system of electrical signals in the heart. The sinus (or sinoatrial) node is a small area of tissue in the wall of the right atrium. It sends out an electrical signal to start the contracting (pumping) of the heart muscle. This node is called the pacemaker of the heart because it sets the rate of the heartbeat and causes the rest of the heart to contract in its rhythm.

These electrical impulses make the atria contract first. Then the impulses travel down to the atrioventricular (or AV) node, which acts as a kind of relay station. From here, the electrical signal travels through the right and left ventricles, making them contract.

One complete heartbeat is made up of two phases:

1. The first phase is called systole (pronounced: SISS-tuh-lee). This is when the ventricles contract and pump blood into the aorta and pulmonary artery. During systole, the atrioventricular valves close, creating the first sound (the lub) of a heartbeat. When the atrioventricular valves close, it keeps the blood from going back up into the atria. During this time, the aortic and pulmonary valves are open to allow blood into the aorta and pulmonary artery. When the ventricles finish contracting, the aortic and pulmonary valves close to prevent blood from flowing back into the ventricles. These valves closing is what creates the second sound (the dub) of a heartbeat.

2. The second phase is called diastole (pronounced: die-AS-tuh-lee). This is when the atrioventricular valves open and the ventricles relax. This allows the ventricles to fill with blood from the atria, and get ready for the next heartbeat.

How Can I Help Keep My Heart Healthy?

To help keep your heart healthy:

Get plenty of exercise.

Eat a nutritious diet.

Reach and keep a healthy weight.

If you smoke, quit.

Go for regular medical checkups.

Tell the doctor about any family history of heart problems.

Let the doctor know if you have any chest pain, trouble breathing, or dizzy or fainting spells; or if you feel like your heart sometimes goes really fast or skips a beat.

Date reviewed: September 2023

More on this topic
For Teens

View more

# data[].attributes.attachment_link.title
Heart and Circulatory System (for Teens)

# data[].attributes.attachment_link.description
The heart and circulatory system (also called the cardiovascular system) make up the network that delivers blood to the body's tissues.

# data[].attributes.body
And one last time another article on the circulatory system.

# data[].attributes.attachment_link.readable_text
The blood circulatory system (cardiovascular system) delivers nutrients and oxygen to all cells in the body. It consists of the heart and the blood vessels running through the entire body. The arteries carry blood away from the heart; the veins carry it back to the heart. The system of blood vessels resembles a tree: The "trunk" - the main artery (aorta) - branches into large arteries, which lead to smaller and smaller vessels. The smallest arteries end in a network of tiny vessels known as the capillary network.

There isn't only one blood circulatory system in the human body, but two, which are connected: The systemic circulation provides organs, tissues and cells with blood so that they get oxygen and other vital substances. The pulmonary circulation is where the fresh oxygen we breathe in enters the blood. At the same time, carbon dioxide is released from the blood.

Blood circulation starts when the heart relaxes between two heartbeats: The blood flows from both atria (the upper two chambers of the heart) into the ventricles (the lower two chambers), which then expand. The following phase is called the ejection period, which is when both ventricles pump the blood into the large arteries.

In the systemic circulation, the left ventricle pumps oxygen-rich blood into the main artery (aorta). The blood travels from the main artery to larger and smaller arteries and into the capillary network. There the blood drops off oxygen, nutrients and other important substances and picks up carbon dioxide and waste products. The blood, which is now low in oxygen, is collected in veins and travels to the right atrium and into the right ventricle.

This is where pulmonary circulation begins: The right ventricle pumps low-oxygen blood into the pulmonary artery, which branches off into smaller and smaller arteries and capillaries. The capillaries form a fine network around the pulmonary vesicles (grape-like air sacs at the end of the airways). This is where carbon dioxide is released from the blood into the air inside the pulmonary vesicles, and fresh oxygen enters the bloodstream. When we breathe out, carbon dioxide leaves our body. Oxygen-rich blood travels through the pulmonary veins and the left atrium into the left ventricle. The next heartbeat starts a new cycle of systemic circulation.

Sources

Menche N (Ed). Biologie Anatomie Physiologie. Munich: Urban und Fischer; 2016.

Pschyrembel. Klinisches Wörterbuch. Berlin: De Gruyter; 2017.

Schmidt R, Lang F, Heckmann M. Physiologie des Menschen: mit Pathophysiologie. Berlin: Springer; 2017.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

# data[].attributes.attachment_link.title
How does the blood circulatory system work?

# data[].attributes.attachment_link.description
The blood circulatory system (cardiovascular system) delivers nutrients and oxygen to all cells in the body. It consists of the heart and the blood vessels running through the entire body.

# data[].attributes.body
This yet again another article on the digestive system.

# data[].attributes.attachment_link.readable_text
The human gastrointestinal tract, also called the alimentary canal, is around 30 feet (9 meters) long in adults.

It of the following:

the mouth, or oral cavity

the esophagus

the stomach

the small intestine

the large intestine, or colon

the rectum

In addition, the following organs support digestion, for example, by chewing or adding enzymes and other secretions that enable the body to absorb nutrients:

Together, these organs provide mechanical processing, the secretion of enzymes and bile to help break down compounds, and the excretion of waste.

Some terms to describe these functions include:

ingestion, which includes chewing and swallowing

the secretion of substances that enable food and nutrients to move through the body effectively

propulsion, where muscles move the contents of the canal forward

digestion, the breakdown of food, for example, through chewing and secretions

the absorption of nutrients, which mainly occurs in the small intestine

defecation and urination, the removal of waste products through the rectum and the bladder, respectively

The mouth

Digestion begins even before the food enters the mouth.

When a person smells or thinks of food or eating, the salivary glands begin producing saliva.

Once the food is inside of the mouth:

saliva moistens it.

the teeth and tongue break it down mechanically.

an enzyme in the saliva, salivary amylase, breaks it down into starch.

Chewing and amylase digestion will convert the food into a small, round blob, or bolus. This enables a person to swallow it easily.

The esophagus

After swallowing, the bolus enters the esophagus, where gravity and muscle contractions help move it down to the stomach through a process called peristalsis.

Peristalsis is the slow contraction of smooth muscles along and around the digestive system.

As the bolus moves through the esophagus, these contractions push it toward the stomach.

What is esophageal achalasia, and how does it affect digestion?

The stomach

The bolus enters the stomach through a ring-like muscle called the lower esophageal sphincter. This sphincter relaxes, allowing the bolus to enter the stomach.

In the stomach, the following processes occur:

The stomach stores the food temporarily.

Cells in the stomach secrete gastric juices. These include hydrochloric acid, which maintains the pH of the stomach between .

The stomach has three muscular layers that churn and mix its contents.

These processes turn the food into a thick paste, known as chyme.

Hydrochloric acid is essential for:

destroying microorganisms, such as bacteria

breaking down proteins and plant fibers

activating pepsin, an enzyme that helps digest proteins

The acid, however, can harm the stomach lining, so some cells produce mucus to protect the lining from damage.

The stomach does not absorb many nutrients from the chyme into the bloodstream, so the chyme enters the small intestine through the pyloric sphincter.

How can you increase stomach acid naturally?

The small intestine

The small intestine is around 20 ft (6 m) long and absorbs around of the nutrients from food into the bloodstream.

There are three sections:

The duodenum: This receives chyme from the stomach and digestive enzymes from the liver and pancreas.

The jejunum: Most of the chemical digestion and absorption occur here.

The ileum: This contains the ileocecal valve, a sphincter through which food passes to the large intestine.

Once the food is fully broken down, the villi absorb the nutrients, which enter the bloodstream.

Villi are tiny, finger-like projections that line the walls of the small intestine. Within the villi are tiny capillaries called lacteals. By increasing their surface area, the villi maximize their absorption of nutrients.

How do the intestines work?

The large intestine

Any unabsorbed food and nutrients now pass to the large intestine, or colon. The material is now feces.

The large intestine is around long and consists of the:

cecum, a pouch through which food enters from the small intestine

ascending colon

transverse colon

descending colon

sigmoid colon

From the large intestine, the body absorbs water and electrolytes.

Food travels slowly through the colon to allow the body to absorb water, and of gut bacteria break down any undigested food.

Next, peristalsis moves the feces toward the rectum.

The rectum

As the digested food moves into the rectum, nerves in the wall of the rectum known as stretch receptors detect when the chamber is full and stimulate the desire to defecate.

Defecation involves of muscle movement.

The first happens automatically, and a person cannot control it. This is a relaxation of the smooth muscles in the internal anal sphincter.

The second, a person can control and is a conscious relaxation of the skeletal muscles in the external anal sphincter. If a person wishes to delay defection, they can avoid relaxing their muscles to move the feces back into the colon.

The longer feces stay in the colon, the more water the body will absorb. This can lead to dry, hard feces, constipation, and possibly impaction. For this reason, a person should defecate as soon as is convenient.

A person should seek medical advice if they are unable to defecate for about 3 days or if they have abdominal or rectal pain or bleeding

What are some home remedies for constipation?

Here are some answers to questions people often ask about digestion.

What are the stages of the digestive system?

During digestion, food passes through the following stages:

1. the mouth

2. the esophagus

3. the stomach

4. the small intestine

5. the large intestine, or colon

6. the rectum

How does digestion work, step-by-step?

First, the teeth, tongue, and saliva turn food into a bolus, which is small and liquid enough to pass through the esophagus.

Next, the bolus enters the stomach, where muscular action, acids, and enzymes turn it into a paste called chyme. The chyme enters the small intestine.

Here, about of absorption occurs. Nutrients enter the bloodstream through capillaries in villi. From there, the nutrients travel to various body cells. Any remaining food passes into the large intestine, or colon.

The body absorbs water as the food passes through to the rectum, ready for defecation.

How can I keep my digestion healthy?

Tips include:

drinking plenty of water

eating a varied diet with plenty of fresh vegetables and whole foods

establishing regular bowel habits

seeking medical help for any unexplained changes in digestion or bowel habits

# data[].attributes.attachment_link.title
Digestion: Anatomy, physiology, and chemistry

# data[].attributes.attachment_link.description
The human gastrointestinal tract, also called the alimentary canal, is around 30 feet (9 meters) long in adults.

# data[].attributes.body
This is a image of the digestive system and the important parts of the system

# data[].attributes.body
This is another article on the digestive system

# data[].attributes.attachment_link.readable_text
Abstract

It is crucial to replicate or mimic the human digestive system conditions closely in model systems to have the food digestion-related data as accurate as possible. Thus, the data obtained could contribute to studies like those on the relationship between health and nutrition. This review aims to express the human digestion system's role in food digestion and compare the capability of the models used in simulations, especially the dynamic in vitro models. Activities of the human digestive system governing food digestion and the food matrix's disintegration mechanism in the digestive system were discussed. Dynamic in vitro models and their relevance to the human digestive system were described. Advancements in the last 20 years, as well as limitations of those artificial systems, with prospects, were discussed. Extensive use and improvement on these models will extend our knowledge of the food matrix and digestive system's complex interaction. Thus, it will be possible to design next-generation foods with improved health benefits.

Keywords: In vitro, food digestion; Dynamic model; Food matrix

Graphical abstract

Higlights

Digestion is a combination of versatile and multiple scales physicochemical processes.

Food composition, structure, and processing affect food digestion.

There are many dynamic in vitro models used in food digestion studies.

Results from the models should be interpreted with care.

1. Introduction

Understanding the outcome of the ingested food components in the human digestive system is an area of interest for researchers because of its relation to nutrition and health. Foods contain components that can have either beneficial or adverse effects on human health. Consumed foods are combinations of diverse phases and structures depending on their sources, formulations, and processes used for their production. The digestive system must physically and chemically break down ingested food to release its components, which will be further metabolized to be used by the body.

The foods' composition and structure have a significant role in their nutritional and functional performances during digestion ( Bornhorst & Singh, 2012, 2013; Bornhorst et al., 2014; Bornhorst, 2017; Mackie, 2017; Dupont et al., 2018). The food matrix affects the release of nutrients and their journey to the body's target sites during digestion. Therefore, it is essential to understand the underlying mechanisms affecting the release of the food components during digestion for health benefit.

Digestion of food in the human digestive system is a complex combination of versatile and multiple-scale physicochemical processes that steer the food intake, disintegration to suitable forms, absorption of the basic units, transportation to related organs, and purging the remaining waste. The human digestive system consists of the digestive tract and the accessory organs controlled by the neural network and the hormones ( Saladin, 2017). The digestive tract can be described as an open-ended tube with a total length of about 8-9 ​m, extending from mouth to anus, consisting of the pharynx, esophagus, stomach, and small and large intestines ( Fig. 1 ). Accessory organs are the teeth, tongue, salivary glands, liver, gall bladder, and pancreas ( Bender et al., 2005; Saladin, 2017). Each part of the digestive tract has a specific function, where altogether, they perform the extraction of the digested products and the disposal of wastes.

Increased interest in modifying the matrix and structural characteristics of foods to optimize their digestion and absorption behavior for health benefit requires implementing many food digestion studies in the digestive tract. However, studying human digestion's intricate process is complicated, costly, varies from person to person, and constrained by ethical considerations (Directive 2001/20/EU, 2001). The usage of animal models as an alternative should also be avoided as much as possible ( Directive, 2010/63/EU, 2010). Therefore, these limitations and considerations have led researchers to design and use in vitro models to simulate the human digestive system for research.

The interaction between the food and human digestive systems controlling the disintegration of foods and releasing nutrients is quite complicated. This review describes the physiological processes of the human digestive system steering food digestion. The disintegration mechanism of the food matrix in the digestive system was discussed. Models used to simulate the digestion, and their relevance to the human digestive system was analyzed.

2. Effect of food matrix on digestion

The disintegration mechanism differs among foods and is related to the original food structure and how it changes during digestion. Although most of the breakdown process for the solid foods happens in the mouth, the rest of the disintegration occurs while transiting the digestive system, especially in the stomach ( Bornhorst and Singh, 2013; Bornhorst et al., 2013; Drechsler and Ferrua, 2016). Forces that food particles experience in the stomach are less than those applied by the teeth in the mouth. The maximum force that the human jaw can apply is about 400 ​N, while the force that the walls of the stomach (antrum) can apply is about 0.2-2 ​N depending on the subjects ( Ferrua et al., 2011; Lentle and Janssen, 2010, Lentle and Janssen, 2011; Lentle, 2018a).

Fragmentation, abrasion, and dissolution behaviors of the food in the digestive system determine their effect on human health. Fragmentation (cleavage into smaller pieces) and abrasion (erosion of the surface by shear stress) are the two primary disintegration mechanisms of the food ( Brandstaeter et al., 2019). When the forces received by the food due to contractions and peristaltic movements in the stomach are higher than the critical value for the internal forces holding the food matrix together, fragmentation will be the dominant mechanism, and the food will be broken down into relatively larger pieces ( Ferrua et al., 2011). When the applied stresses are smaller, surface abrasion will be dominant, and the smaller fragments leave the surface ( Ferrua et al., 2011; Drechsler and Ferrua, 2016). The acidic environment and the digestive system's enzymes also contribute to the leaching of solids to the digestion medium.

The kinetic of food disintegration is affected by the physiological conditions in the digestive system like mechanical forces, pH, temperature, and enzymes, as well as by the meal properties such as composition, amount, texture, structure, and viscosity ( Kong and Singh, 2008a, Kong and Singh, 2008b; 2009; 2010; Ferrua and Singh, 2010, Ferrua and Singh, 2011; Ferrua et al., 2011; Bornhorst et al., 2015; Drechsler and Ferrua, 2016; Mulet-Cabero et al., 2019). Some foods are more susceptible to fragmentation than other foods under similar mechanical forces ( Kong and Singh, 2008a; Ferrua et al., 2011). Water absorption, acid hydrolysis, and enzymatic reactions may cause softening of the ingested foods. Cohesive forces holding the food matrix together may attenuate, leading to a shift in the disintegration mode from erosion to fragmentation ( Kong and Singh, 2008a; Ferrua et al., 2011). For example, cereal products like bread and snacks become very soft after mixing and absorption of saliva in the mouth, and then they fragment easily. On the other hand, for foods with a rigid and hard texture like carrots and nuts, erosion is the dominant disintegration mechanism ( Kong and Singh, 2008a; Ferrua et al., 2011). Moreover, diffusion processes inside the chyme are affected by physiological conditions such as pH, temperature, viscosity, and degree of mixing as well as by the structure and content of the food. One of the studies attempting to explain and quantify the disintegration mechanisms, Bornhorst et al. (2016), suggested a classification system for the food breakdown similar to the one used by the pharmaceutical industry as a tool to be used for product development. Therefore, all modes of transport phenomena, mass, heat, and momentum, should be considered together in analyzing and simulating the digestive system.

3. Food digestion in the human digestive system

The digestive tract that begins at the mouth continues as the throat (pharynx), the esophagus, the stomach, the small intestine (duodenum, jejunum, and ileum), the large intestine (cecum, ascending colon, transverse colon, descending colon, and sigmoid colon) and rectum, ending at the anus where the wastes are excreted ( Fig. 1 ). Digestive juices are secreted by the salivary glands, gastric glands, pancreas, and liver with its adjuncts (the gallbladder and bile ducts). Secretions from the digestive organs alter the physical properties of the digested meal by dilution ( Fig. 1 ). On average, humans can produce 1.5 ​L saliva, 2 ​L stomach secretions, and 0.5 ​L bile solution.

3.1. Mouth

Food enters the digestion system through the mouth and is broken down into small pieces while mixed with saliva to speed its progression through the digestive system. Textural and rheological properties of foods as well as age, gender, and eating ability of individuals affect the oral processing behavior ( Chen, 2009; Ketel et al., 2019).

The mechanical digestion of foods starts by chewing. The teeth in the human mouth are responsible for different tasks like cutting, tearing, grinding, and shearing ( Rogers, 2011; Mosca and Chen, 2016). Biting force can range approximately from 100 to 400 ​N depending on the individual ( Mosca and Chen, 2016; Marze, 2017a, Marze, 2017b). Solid foods are more difficult to manipulate. Therefore, the amount of food taken in by the mouth decreases from liquid foods to solids ( Chen, 2009; Bornhorst et al., 2016; Aguayo-mendoza et al., 2019; Ketel et al., 2019). Moreover, the bolus' mean particle size depends on the physical properties of the food, smaller for hard and larger for softer foods ( Chen, 2009).

Bolus formation in the mouth includes deformation, deterioration, and disintegration processes, which are accomplished by the coordinated effort of the teeth, tongue, and saliva secretion mechanism ( Rogers, 2011; Mosca and Chen, 2016). Saliva, which is about 99% water, contains sodium, potassium, calcium, bicarbonate, mucin, and enzymes (amylase, lingual lipase). The saliva secreted by the salivary glands moistens and starts to dissolve the food with the amylase enzyme action that splits starch into disaccharide molecules of maltose ( Table 1 ). The bolus is propelled from mouth to esophagus by the pharynx during the swallowing process. The pressure of 10 ​kPa can be generated on the tongue's surface during swallowing ( Chen, 2009).

Table 1

Section

Physical Process

Chemical Process

Conditions (adult)

References

Mouth

Food breakdown

Mixing

pH: 5-7
Transit time: 5s −2 ​min
Saliva flow rate:

0.042-1.83 ​mL/min (unstimulated),

0.77-4.15 ​mL/min (stimulated)

Biting force: 100-400 ​N
( Chen, 2009, Marze, 2017a, Marze, 2017b, Mosca and Chen, 2016, Rogers, 2011)

Esophagus

Bolus transport

-

Transit time: 8-10 ​s solid1-2 liquid

( Bender et al., 2005, Buettner et al., 2001, Rogers, 2011)

Stomach

Food breakdown

Mixing

Gastric transport

Gastric sieving

Acid hydrolysis

Food softening and dissolution (gastric acid)

pH: 1-3
Transit time: 15 ​min - 4 ​h
Gastric juice secretion: 1-3 ​L/day
Contraction frequency: 3 cycles/min

( Boland et al., 2014, Chen et al., 2011, Miftahof, 2017, Rogers, 2011, Sullivan, 2009)

Small Intestine

Chyme transport

Starch breakdown (pancreatic amylase, dextrinase, sucrose, maltase, lactase, amyloglucosidase)

Protein breakdown (trypsin, chymotrypsin, carboxypeptidase, elastase)

Lipid breakdown (pancreatic lipases, phospholipase)

Nucleic acid breakdown (nucleases, nucleosidases and phosphatases)

Segmentation

Monosaccharides (glucose, galactose, fructose)

Amino acids, peptides Monoacylglycerides, glycerol, free fatty acids

Phosphates, nitrogenous bases, pentose sugars

Minerals and vitamins

pH: 6-7.5
Transit time: 1-5 ​h
Pancreatic juice secretion: ~1.5 ​L/day

( Rogers, 2011, Saladin, 2017, Smith and Morton, 2010, Sullivan, 2009)

Large Intestine

Chyme transport

Segmentation Absorption

Water, ions, minerals, vitamins, fats and organic molecules

pH: 5-7
Transit time: 12-24 ​h
Microbiota: ~10 ¹¹-10 ¹² (>1000 different species)

( Rogers, 2011, Saladin, 2017, Smith and Morton, 2010, Sullivan, 2009)

Peristaltic contractions of the esophagus transfer the bolus to the stomach ( Buettner et al., 2001; Rogers, 2011; Bornhorst et al., 2016). Transport of material through the esophagus (length: ~ 25 ​cm and diameter: 1.5-2 ​cm) takes approximately 8-10 ​s ( Buettner et al., 2001; Bender et al., 2005; Rogers, 2011). When the bolus arrives at the stomach junction, the bolus can enter the stomach by the relaxed esophageal sphincter (a muscular cuff). Even though the transport of liquids through the esophagus may be faster than solids due to the gravity, they wait (8-10 ​s) for the arrival of the peristaltic relaxation before entering into the stomach ( Rogers, 2011).

3.2. Stomach

In the stomach, which is a J-shaped muscular pouch, the digested food goes through a mechanical and chemical disintegration ( Table 1 ). The stomach where the digested food is diluted with the gastric juice works like a container, mixer, and sieve ( Bornhorst and Paul Singh, 2014, Brandstaeter et al., 2019). The stomach is the main digestion region. Even though digestion of the starch and triglycerides can start in the mouth due to amylase and lingual lipase in the saliva, protein digestion starts in the stomach ( Sullivan, 2009).

The concave border of the human stomach on the right is named as the lesser curvature, and the convex border to the left is named as the greater curvature ( Fig. 2 ). The section that the stomach is connected to the esophagus is called the cardia ( Miftahof, 2017). Fundus, body (corpus), and antrum ( Fig. 2 ) are the main sections of the stomach ( Brandstaeter et al., 2019). The stomach's proximal region regulates the pressure for food storage, and the distal stomach functions as a gastric pump ( Liu et al., 2019a). After a meal, the fundus, which sticks out like a dome, usually stores swallowed air. The largest section of the stomach, the body, serves as a reservoir for the ingested meal ( Fig. 2 ). The antrum has a conical shape and is between the lower section of the body and the pyloric canal. The pylorus is the stomach's slimmest portion and has enclosed by thick, smooth muscle layers ( Miftahof, 2017, Rogers, 2011).

The sphincters, connecting the stomach to the esophagus and the duodenum ( Fig. 2 ), are tightly controlled by the nervous system and responsible for the flow of chymus by rhythmic relaxation of the ring of smooth muscles from time to time, allowing partially digested food to pass through ( Bender et al., 2005). The pyloric sphincter is more potent than the esophageal sphincter ( Fig. 2 ).

Layers of the stomach wall (~ 3-4 ​mm thick) such as gastric mucosa and muscles are responsible for gastric secretions to dissolve the food and for contractions to grind and push the food through to the pyloric sphincter. In the stomach, the change of pH is controlled, and the bolus from the mouth is mixed with the digestive enzymes. Gastric contractions mix food particles and digestive juice by grinding action and reduce particle sizes (<1-2 ​mm) to form the fluidized mixture called chyme ( Ferrua and Singh, 2011; Ferrua et al., 2011; Rogers, 2011; Bornhorst, 2017). Chyme progresses into the small intestine at small amounts and regular intervals.

The mucosal lining of the stomach forms countless wrinkles and folds, known as rugae when it is empty. These folds disappear when the stomach expands. The empty human stomach has a volume of about 25-50 ​mL, and the volume becomes 1-1.5 ​L after an average meal, while the geometry can vary depending on the individual, body position, surrounding organs, ingested meal, and digestion time ( Ferrua and Singh, 2010; Saladin, 2017). Stomach volume can increase up to 4 ​L when full by unfolding and stretching ( Saladin, 2017; Marieb and Keller, 2018; Brandstaeter et al., 2019).

The digestion process in the stomach involves physical and chemical processes ( Table 1 ). Physical parameters like contractions affect particle sizes, while chemical parameters such as secretion of acid and digestive enzymes have an impact on the softening of the food and hydrolysis of nutrients ( Kong and Singh, 2008a). The acidic environment activates the secreted pepsin and causes denaturation of food. Gastric pH in the fasted state is in the range of 1-3; after the ingestion of a meal, it will rise to 5.5-7, and after the half emptying time, it will go down to 4-5, and after the stomach emptied it will turn to its basal value ( Boland et al., 2014).

The fundus is the region where the food stays until some space becomes available for digestion. Some of the food that entered the stomach by relaxation of the esophageal sphincter stays in the fundus region, and the rest mixes with the gastric juice and moves toward the pylorus ( Fig. 2 ). Vigorous mixing takes place near the pyloric sphincter. Because small amounts of chyme are allowed to pass through by the relaxed and opened pyloric sphincter, most of the material remains in the stomach for further mixing. As chyme is transferred to the small intestine, the food in the fundus region moves down for digestion ( Fig. 2 ).

Gastric contractions are complex systems controlled by interrelated combinations of the body's neural and hormonal systems and depend on the amount, composition, and physicochemical parameters of the ingested meal ( Ferrua and Singh, 2010). In the antrum, generated compressive forces can be about 0.65 ​N for soft and 1.89 ​N for hard solids ( Lentle, 2018). According to calculations based on magnetic resonance imaging (MRI) measurements, the maximum pressure experienced by the food particle surfaces is about 30-40 ​Pa ( Lentle and Janssen, 2011; Lentle, 2018b).

The stomach wall consists of three layers of smooth muscle; longitudinal, circular, and oblique layers ( Fig. 2 ). This combination of muscles lets the stomach not only push but mix and grind so the ingested meal can disintegrate into smaller particles. Gastric motility ( Fig. 3 a) can be defined as the contractions or relaxations of the smooth muscles in the stomach wall to coordinate the gastric accommodation, gastric mixing and emptying through antral contraction waves, and migrating motor complexes. ( Brandstaeter et al., 2019). Gastric accommodation is the expansion of the stomach, especially in the proximal stomach, due to the reflex after ingestion of the meal to allow food storage. Antral peristalsis, or contraction waves, are ring-shaped muscular contractions propagating through the stomach wall and are in charge of mixing and emptying. Migrating motor complexes can be observed in the fasted state between meals ( Brandstaeter et al., 2019).

Tonic or sustained contractions of all the stomach muscles coordinate the stomach's accommodation to varying volumes of gastric content ( Ferrua and Singh, 2010). During tonic contraction, the stomach wall contracts as a whole; thus, the lumen size decreases. The tonic contraction is independent of the mixing and peristaltic contractions; but, mixing and peristaltic contractions co-occur with the tonic contraction ( Rogers, 2011).

A small contraction wave that produces slight indentations on the stomach wall starts in the upper part and slowly moves down toward the pyloric sphincter ( Fig. 3 a). Backward waves sweep back from the pyloric sphincter through the antrum. These contractions cause a pressure build-up and a retropulsive backflow in the antrum region ( Chen et al., 2011). This combination of back and forth flow causes mixing, grinding, and erosion of food particles.

Another contracting wave, which is peristaltic in nature, originates in the corpus and slowly propagates toward the pyloric sphincter ( Ferrua and Singh, 2010). This peristaltic contraction starts with small indentations, and indentations deepen as it goes down. When this peristaltic wave reaches the antrum, the indentation completely blocks and divides the lumen ( Boland et al., 2014). This wave propelling the chymus moves over the antrum. These peristaltic antral contractions function as a pump for emptying the contents through the pyloric sphincter at a constant rate ( Boland et al., 2014, Rogers, 2011).

Contractions in the antrum are more potent because the muscles are thicker than other regions of the stomach ( Smith and Morton, 2010). The pyloric sphincter governs the passage of the stomach content to the duodenum and inhibits the content of the duodenum from going back to the stomach. Tiny food particles are pushed through a momentarily opened pyloric sphincter providing the duodenum to taste the gastric content. About 3 ​mL of chyme is purged to the duodenum at each contraction regularly ( Saladin, 2017).

The mixing and the peristaltic contractions are produced at a regular rate of 2-3 cycles per minutes as a response to the ingested meal ( Chen et al., 2011; Rogers, 2011; Bornhorst and Singh, 2014; Ferrua and Singh, 2015; Bornhorst et al., 2016; Lentle, 2018a). Migrating peristaltic waves move indigestible fractions from the stomach to the intestine every 120 ​min ( Brandstaeter et al., 2019).

The inner surface of the stomach contains the gastric mucosa, which is a mucous membrane layer. The mucosa secretes 1.2-1.5 ​L gastric juice per day, which contains water, hydrochloric acid, electrolytes (sodium, potassium, calcium, phosphate, sulfate, and bicarbonate), mucus, enzymes (lipase and pepsinogen), hormones (gastrin, serotonin) and the intrinsic factor ( Bender et al., 2005, Rogers, 2011). The stomach walls are protected from this highly acidic juice by the membrane adjacent to the stomach's lumen. In the area bordering the epithelium, the acidity of the mucous layer is almost neutral (pH 7) because of the secreted bicarbonate from the mucosa, whereas the acidity at the lumen side is very high (pH 2).

The gastric mucosa is covered by mucus-secreting epithelial cells and other types of cells, such as mucoid cells, chief cells, gastrin cells, parietal cells, and other endocrine cells ( Rogers, 2011). Mucoid cells secrete gastric mucus. Chief cells secrete gastric lipase and pepsinogen, which is converted to the active digestive enzyme pepsin by the stomach's acidic conditions. Gastrin (G) cells secrete the acid-stimulating hormone gastrin as a response to meal intake, which reduces the pH and extends the stomach wall. Gastrin hormone, which binds the receptor sites of the parietal cells, triggers hydrogen ion production in the parietal cells. The secreted hydrogen ions form hydrochloric acid (HCl) by combining with chloride ions ( Sullivan, 2009). Most of the water in the gastric juice is produced by the parietal cells, which produce an intrinsic factor (glycoprotein) that is essential for the absorption of B ₁₂ through the small intestine as well as the appetite-regulating hormone ghrelin. The serotonin hormone secreted from endocrine cells stimulates the contraction of stomach muscles ( Bender et al., 2005).

The gastric secretion processes that consist of cephalic, gastric, and intestinal phases are complex coordination of neural and hormonal factors, which overlap ( Rogers, 2011). The cephalic phase starts before food reaches the stomach; seeing, smelling, and tasting food stimulates the secretion of gastrin hormone ( Bender et al., 2005). The gastric phase starts with the presence of food. The intestinal phase starts when food starts to leave the stomach after one to 3 ​h. With the help of receptors, the duodenal bulb (the juncture between the duodenum and the stomach) and the next section of the duodenum relax to allow fluidized chyme with sufficiently small particles to enter the small intestine. The intestinal phase involves complex simulatory and inhibitory processes. When acidic chyme coming from the stomach enters the duodenum, it triggers the secretion of hormones that slow or inhibit gastric secretion in order to prevent more acidic chyme from entering the small intestine ( Bender et al., 2005).

3.3. Small intestine

Most of the processes that convert the food into suitable forms that the body can use happen in the small intestine, where the nutrients are absorbed ( Lentle and Janssen, 2010, Lentle and Janssen, 2011; Tharakan, Norton, Fryer and Bakalis, 2010; Rogers, 2011). The small intestine is the longest (6-7 ​m) part of the gastrointestinal tract and folded to fit in the abdominal cavity ( Fig. 2 ). It is joined to the stomach by the pylorus and to the colon by the ileocecal valve. The duodenum, jejunum, and ileum are the small intestine's main segments, respectively ( Fig. 1 ). The duodenum (23-28 ​cm long) is where the canals secrete pancreatic juice and bile open up. The jejunum (~ 2 ​m) is the first 40% of the small intestine beyond the duodenum. The remaining 60% is the ileum (~ 3 ​m), which joins the large intestine through the ileocecal valve.

Most of the secretions controlled by nerves and hormones occur in the duodenum; the secretions are minimal in the other parts of the small intestine. The pancreas is a large gland that produces enzymes and hormones. The pancreatic juice and the bile flow through the duodenal papilla (rounded projection into the duodenum) to enter the duodenum ( Rogers, 2011).

When the chyme enters the duodenum, gastric secretions within the chyme continue their digestive processes for a short time in the small intestine. Incoming chyme stimulates the pancreas to release concentrated bicarbonate solution that neutralizes the highly acidic gastric juice ( Sullivan, 2009). Other secretions from the pancreas, gallbladder, and glands in the intestinal wall increase the total volume of chyme. Pancreatic secretion includes many enzymes, proteases (trypsin and chymotrypsin), pancreatic lipase, and pancreatic amylase. Bile is an aqueous solution produced by the liver and stored in the gallbladder facilitates digestion and absorption of lipids, acting as an emulsifier. Bile consists of bile salts, phospholipids, cholesterol, bilirubin (a breakdown product of red blood cells), electrolytes, and water. Here, digestion enzymes break down proteins, carbohydrates, triglycerides, and nucleic acids to smaller sizes. Pancreatic amylase can split starch into disaccharides such as maltose, but, here, disaccharides such as sucrose (from sugar and fruits) and lactose (from milk) can not be broken down into their monomers yet.

The motor activities observed in the small intestine are segmenting and peristaltic contractions that provide mixing and transport of chyme ( Fig. 3 b). Segmenting contractions, which are the predominant motor action, mix and separate the intestinal chyme. A short segment of the intestinal wall (<1-2 ​cm) contracts and constricts the lumen to divide its contents. The number of segmenting contractions decreases gradually from 11 to 12 cycles per minute in the duodenum to 8-9 cycles per minute in the ileum ( Boland et al., 2014, Rogers, 2011). Peristaltic contraction is an advancing wave of contraction that can propel the chyme at a rate of 2-2.5 ​cm/s ( Tharakan et al., 2010; Bornhorst and Singh, 2014). These contractions provide the movement of the intestinal content by creating a pressure difference between the adjacent segments.

The small intestine's diameter is 3-4 ​cm in diameter, but its total absorptive surface area is approximately 4500 square meters ( Rogers, 2011, Sullivan, 2009; Capuano, 2017; Lambeau and McRorie, 2017; Saladin, 2017). Numerous concentric folds of the mucosa (plicae circulares) provide this large absorptive surface. The brush border, which is the specialized surface of the epithelial cells, is richer in proteins and lipids than the plasma membrane on the epithelial cells. The final breakdown of digestion products happens on the surface of the brush border. It consists of microvilli that secrete the enzymes (maltase-glucoamylase, sucrase-isomaltase, lactase, brush border peptidases, lipase) that hydrolyze disaccharides, peptides, and nucleotides to their basic units suitable for absorption, such as monosaccharides and amino acids. These monomers are absorbed by the intestinal wall and transported to the bloodstream. Solutes and water move through the surface epithelium of the mucosa. Most of the absorption happens in the proximal small intestine, but a few substances (vitamin B ₁₂ and bile salts) are absorbed in the ileum ( Smith and Morton, 2010). The absorption rate of water and nutrients are different in the jejunum and the ileum because, in the proximal region, the villi are large, and the available brush border surface area increases.

3.4. Large intestine

The large intestine has a large diameter (~ 6 ​cm), but it is shorter (~ 150 ​cm) than the small intestine. The ileocecal valve joining the small and large intestine shields the opening of the ileum into the cecum. The large intestine absorbs water into the body, and the remaining thick waste is ejected to complete the digestion. Each day about 1.5-2 ​L of chyme passes through the ileocecal valve. The chyme volume becomes about 150 ​ml after the water absorption in the colon ( Fig. 1 b).

The large intestine has an anaerobic environment and is colonized by an involved community of microorganisms (~ 10 ¹¹/g) formed mainly by obligate anaerobic bacteria. The microbiota produces a variety of enzymes that breakdown dietary fibers not digested in the small intestine. The bacteria also metabolize the bile salts and pancreatic enzymes that reach the colon. The colon also contains bacteria that synthesize some essential vitamins (niacin, vitamin B1, and vitamin K) ( Rogers, 2011). The free fatty acids (by-products of fermentation) content increases from about 6 to 8 ​mM in the ileum to 32-29 ​mM in the cecum. Chyme content affects the composition of the microbiota and metabolites produced, which can impact health.

Contractions and reverse movements in the large intestine mix the chyme and push the contents toward the walls. Slow-wave contractions sweep at a frequency of 11 cycles per minute from the ascending colon to the descending colon, then decrease to 6 cycles per minute in the sigmoid colon and rectum. Local contractions migrate at a rate of 4 ​cm per second through the colon. Reverse movements are seen mainly in the upper (proximal) colon.

4. In vitro digestion models

Digestion models are tools that can be used to design novel food products for human health. The models can be instrumental in consciously designing food products by estimating the in vivo behavior after meals. In vitro digestion models have been developed since the 1990s to be used in food digestion studies ( Ferrua and Singh, 2010).

It is possible to study food digestion by in vivo (human or animal) or in vitro methods. Both methods have their advantages and disadvantages. Even though in vivo studies can give direct results due to their high cost, the requirement of ethical evaluation and variation of the digestive system from person to person, in general, in vitro models are used. In vitro models are preferred in food, nutrition, and medical research because of their speed, cost, and reproducibility due to used standardized conditions compared to in vivo studies ( Kong and Sing 2008a, 2008b, 2010; Ferrua et al., 2011; Hur, Lim, Decker and McClements, 2011; Vardakou et al., 2011; Lafond et al., 2015; Egger et al., 2016; Guerra et al., 2016). Bioaccessibility determinations can be conducted in vitro or ex vivo by use of tissues, cell cultures and artificial membranes to measure permeability or absorption of small molecules ( Vega-Rojas et al., 2021; Caicedo-Lopez et al., 2019).

Many in vitro digestion systems are designed to work in static conditions using glass containers to mimic human digestion. These systems can not produce the mechanical forces and dynamic conditions that foods experience in the digestive system. Static models can be practical, inexpensive, and feasible choices to assess many experimental conditions and a large number of samples; however, dynamic models are the ones that can come closest to in vivo conditions.

In food digestion, substrate-enzyme ratio, pH profiles, and transport of digested products are important parameters. Therefore, in vitro, static models that lack dynamic and mechanic actions have limitations for accurately predicting accessible nutrients or food behavior during digestion. Therefore, different dynamic systems have been developed to mimic the human digestive system's physiological conditions with reproducibility necessary for scientific studies. They can be either mono-compartmental or multi-compartmental ( Guerra et al., 2012; Dupont et al., 2019; Liu et al., 2019a, 2019b).

These dynamic systems have the challenge of competition between technological complexity and biological significance ( Guerra et al., 2012). Multi-compartmental systems usually have gastric and small intestinal compartments, but few include the colon. Dynamic models can simulate the change in pH, enzyme secretion, peristaltic forces, and microbial fermentation continuously ( Liu et al., 2019b). A list of in vitro dynamic models developed, especially for food digestion studies, is presented below ( Table 2 ). Not all dynamic in vitro models mimic mechanic, kinetic, and chemical physiological conditions of the digestive system altogether. Some only simulate chemical conditions, some primarily focus on mechanical conditions, and very few include all mechanical, dynamic, and chemical conditions ( Table 2 ). In this review, models developed for pharmaceutical and medicinal products were not included due to different digestion mechanisms of food, pharmaceuticals, and drugs.

Table 2

SYSTEM

Mouth

Stomach

Small Intestine

Colon

System
Temperature
Control

References with images of the systems

Mixing pH
Saliva

Secretions

Mixing

Emptying

Secretions

Mixing

Absorption

Microbiota
Mixing
Absorption

TIM
Prepared as a bolus

Syringe pumps

Peristaltic pumps

Peristaltic pumps

Syringe pumps

Peristaltic pumps

Dialysis (Hallow fibers)

TIM-2
Feces
Anaerobic conditions Peristaltic pumps
Dialysate system

Heating elements connected with temperature sensors for each compartment

( Bellmann et al., 2016, Lafond et al., 2015)

SHIME
Prepared as suspension

Fill and draw

Magnetic stirrer

Fill and draw

Fill and draw

Magnetic stirrer

-

Feces
Anaerobic conditions
Magnetic stirrer

Heater and Thermostat

( Molly et al., 1993, Vissenaekens et al., 2017)

DIDGI
Prepared as a bolus

Peristaltic pumps

Agitation with a rotating blade actuated by a motor

Peristaltic pumps

Peristaltic pumps

Agitation with a rotating blade actuated by a motor

-

-

Water bath

( de La Pomélie et al., 2019, Ménard et al., 2014)

SIMGI
Prepared as a bolus

Peristaltic pumps

Peristaltic pumps

Peristaltic pumps

Peristaltic pumps

Magnetic stirrer

-

Feces
Anaerobic conditions
Magnetic stirrer

Water bath

( Barroso et al., 2015, Miralles et al., 2018)

DGM
Prepared as a bolus
Can be loaded in real time

Through perforated hoop
Peristaltic pumps

Piston and barrel up and down movement

Piston and cyclical movement

-

-

-

-

Water bath

( Vardakou et al., 2011, Wickham et al., 2012)

c-GDS
Prepared as a bolus
<5 ​mm cube particle size solids

Diaphram pump

Plastic rollers

Syringe pump

-

-

-

-

Heater with a temperature controller

( Kobayashi et al., 2017, Kozu et al., 2017)

AGDS
As a suspension

Roller peristalsis

Driving wheels, belts, compression rollers

Flow pump

-

-

-

-

Computer controlled incubator

( Liu et al., 2019a, Liu et al., 2019b)

ARCOL
-

-

-

-

-

-

-

Feces
Anaerobic conditions
Magnetic stirrer
Dialysate system

Heater

( Cordonnier et al., 2015, Thévenot et al., 2013)

In order to reproduce the conditions of the human digestive system, especially for food systems, the mechanic, dynamic and chemical conditions of each organ in the digestive system should be acquired. Usually, data obtained in vivo from human or animal subjects were used in simulations. These conditions can be outlined as transit times of ingested meal, pH profiles, temperature, contractions, and peristaltic movements, digestive secretion rates, and absorption of water and nutrients through the surface of the organs. Each model uses a protocol specific to their food sample and research interest. Protocols can be specialized to an individual (healthy adult, elderly, infant, or person with specific needs) as well as the properties of the meal (solid, liquid). In the protocols used for dynamic models, chyme transfer is controlled according to a power exponential curve given below. The curve allows the description of two-component emptying patterns for solid and liquid foods. The constants of the equation are determined by using observed in vivo data according to the properties of the meal (solid or liquid) and used in simulation models.

Where.

f: the fraction of remaining chyme

t 1/2: half-time (time to empty 50% of the chyme)

β: coefficient describing the shape of the curve

Several dynamic in vitro models used in food digestion studies were described briefly below.

4.1. TNO gastrointestinal model (TIM)

The in vitro gastrointestinal model (TIM) was developed at TNO Nutrition and Food Research Center (Zeist, The Netherlands) in the early 1990s. TIM is a computer-controlled multi-compartmental dynamic system that simulates the gastrointestinal system ( Table 2 ). The system aimed to simulate the main physiological conditions that change with time and location, such as contractions, transit time, pH, composition, and secretion rate of digestive fluids, absorption of nutrients, and water in a reproducible and controllable manner. In the system, computer simulations used the protocols that were prepared with valid in vivo data. Specialized protocols depending on age and health status, as well as on the type of food, can be generated.

TIM is one of the successful in vitro dynamic systems and has been widely used in food and pharmacology research to investigate the release and absorption behavior of nutrients and drug components ( Ferrua et al., 2011). The TIM system consists of glass units for the stomach, duodenum, jejunum, and ileum. Each unit has a glass jacket with a flexible inner membrane to allow expansion and contraction of the walls. Pressures and the temperature of the water pumped through the glass jackets can be adjusted to simulate peristaltic contractions and body temperature. Peristaltic valves are used to connect each unit. Computer simulation controls the flow of the digested food through and between the compartments.

This group has TIM-1, TIM-2, Tiny TIM, and TIM-agc models ( Bellmann et al., 2016). TIM-1 is the most used one with four compartments. TIM-2 is the system designed for the large intestine using fecal donations from volunteers ( Liu et al., 2019b). TinyTIM is a simplified and higher capacity version of TIM-1. The stomach section is the same as TIM-1, whereas the small intestine has one compartment instead of three and has no ileum exit. TIMagc has an advanced gastric model ( Bellmann et al., 2016). TIM, with its computer-controlled simulations of peristaltic contractions and membrane technologies, offers flexibility to be used for different groups (babies, adults, elderly, and animal species), including health and disease conditions. Even though TIM-1 and TIM-2 complement each other as the upper and lower sections of the gastrointestinal tract, they do not run jointly ( Liu et al., 2019b).

4.2. Simulator of the human intestinal microbial ecosystem (SHIME®)

Simulator of the human intestinal microbial ecosystem (SHIME®, Ghent University-Prodigest, Belgium) has been developed to simulate the microbial ecosystem of the gastrointestinal tract ( Molly et al., 1993). The system ( Table 2 ) that contains five reactor stages simulates the stomach, the small intestine, and the regions of the large intestine together ( Liu et al., 2019b). The first two reactors simulate the acidity and pepsin digestion of the stomach and digestive process of the small intestine by fill and draw principle, where the stomach was simulated by reactor 1, and the small intestine by reactor 2. Peristaltic pumps were used for the controlled transfer of the vessel contents and digestive juices. The last three vessels, which were stirred continuously with a magnetic stirrer, were used to simulate the sections of the large intestine, ascending, transverse, and descending colons. Transit time of the contents and pH values in the vessels can be controlled to mimic in vivo data ( Molly et al., 1993; Douny et al., 2019). System temperature kept at 37 ​°C, and N ₂ is flushed every day for 15 ​min to secure anaerobic conditions ( Possemiers et al., 2004). Fecal microbiota is used to simulate the metabolic fate of food.

The group has other new models for different purposes. M-SHIME® (Mucus-SHIME) contains a mucosal compartment integrated to the colonic regions of SHIME® to evaluate the fraction of microorganisms that can selectively adhere to the mucous layer that covers the gut wall and play an essential role as a barrier against pathogens ( AbbeeleVan Den et al., 2013). Evaluating the changes in the bacterial adhesion for several reasons is crucial in investigating host-microbiota interactions and resulting health effects. Another model developed by the group is TWINSHIME®. In this system, two identical SHIME® systems run in parallel under identical conditions to be able to have a direct comparison of two different samples at the same time ( Vissenaekens et al., 2017). Diseased conditions such as inflammatory bowel disease have also been simulated with specific protocols ( Dupont et al., 2019). This model's strength is the incorporation of the human microbiota. However, it lacks the dialysis modules in the small and large intestines. Furthermore, using magnetic stirrers for mixing of the vessels is not as good as peristaltic movements ( Liu et al., 2019b).

4.3. Engineered stomach and small intestinal (ESIN) system

Engineered stomach and small intestinal (ESIN) system have been developed at the University of Auvergne (Clermont-Ferrand, France). This dynamic system ( Table 2 ) has been reported to aim to overcome some limitations of otherwise complex and useful models like TIM and SHIME ( Guerra et al., 2012). Limitations were expressed as using ground food rather than a close imitation of real food bolus with realistic size particles at the stomach entrance and not representing the differential emptying of liquids and solids in the stomach seen in vivo ( Dupont et al., 2019; Guerra et al., 2016). This dynamic model includes a patented (WO2009087314 A1) design for the stomach section ( Dupont et al., 2019).

The ESIN model has six vessels, a meal reservoir, salivary container, the stomach, and the small intestine, duodenum, jejunum, and ileum segments. Food particles are advanced gradually into the stomach via the meal reservoir. Solid particles can pass the pylorus only if their sizes are reduced to 1-2 ​mm. The passage of the small particles (<2 ​mm) and liquids into the second vessel was achieved by an indentation inside the stomach vessel ( Guerra et al., 2016). Solid particles larger than 2 ​mm stay in the gastric vessel for further digestion.

Liquids and solids particles are emptied by two peristaltic pumps that are programmed to follow an exponential model separately. Liquid fractions follow the exponential model without a lag phase period, while the solid factions have a 30 ​min lag phase ( Guerra et al., 2016). In vivo data were used to simulate temperature, variations in pH values, flow rates of secretions, retention times, and absorption of nutrients in the digestive system.

4.4. In vitro dynamic system (DIDGI ®)

This dynamic digestion system ( Table 2 ), which is developed at the French National Institute for Agricultural Research (INRA, Rennes, France) simulates the stomach and the small intestine with two glass jacketed vessels. The jackets are filled with water that is pumped from a temperature-controlled water bath. A Teflon membrane with 2 ​mm holes is placed before the transfer pump between the gastric and the intestinal compartment mimicking the sieving effect of the pylorus in humans. The temperature, pH, flow rate of the meal, digestive secretions and emptying rate for each compartment are controlled by computer simulation designed with the data obtained from in vivo observations ( Ménard et al., 2014; de La Pomélie et al., 2019).

4.5. Simulator of the gastrointestinal tract (Simgi®)

This dynamic simulator ( Table 2 ) has been developed to reproduce gastrointestinal digestion and colonic fermentation at the Institute of Food Science Research (Madrid, Spain). The simgi® model consists of five compartments simulating the stomach, small intestine, and the ascending, transverse, and descending colon ( Barroso et al., 2015; Mackie et al., 2017; Miralles, del Barrio, Cueva, Recio & Amigo, 2018; Tamargo et al., 2018). The stomach section has two transparent and rigid plastic vessels that cover a flexible silicone container. Water at 37 ​°C pumped through the jacket between the plastic modules, and the flexible container is used to simulate peristaltic movements ( Barroso et al., 2015). Flow rates of the digestive secretions, temperature, and pressure values are controlled through a computer program to follow the defined values. Emptying curves are controlled according to an exponential equation described by Elashoff et al.. The remaining four compartments, the small intestine, the ascending, transverse and descending colon are continuously stirred reactors operating under anaerobic conditions and controlled pH. The system has collecting points in each of the compartments to carry out the biochemical and microbiological analysis. This system combines peristaltic contractions and chyme transit behaviour for gastric and small intestine compartments ( Liu et al., 2019b).

4.6. Dynamic gastric model (DGM)

The model (DGM) has been developed at the Institute of Food Research (Norwich, UK). This computer-controlled model ( Table 2 ) simulating only the stomach can process real size chewed meals and simulates the physiological conditions such as mixing, the transit of meals, and forces observed in the stomach ( Wickham et al., 2012; Dupont et al., 2019). This model simulates three stages of the in vivo conditions: 1. stage: the proximal stomach for ingestion and mixing; 2. stage: the antrum for higher shear rate; 3. stage: the duodenum, first part of the small intestine ( Bornhorst and Singh, 2012). In the model, the disintegration of the food particles was obtained by a stationary outer and mobile inner tube ( Wickham et al., 2012; Ferrua et al., 2011). Temperature, transit time, and flow rates of acid, salts, and enzymes are controlled and adjusted to desired physiological rates. The model produces a cyclical (0.05 ​Hz) mixing in the body of the stomach and preferential antral sieving ( Wickham et al., 2012). In the system, with the collection of data obtained by the samples delivered from the antrum over time, emptying profiles, particle size reduction, and mass transfer data can be obtained but, peristaltic movement is not accurately simulated ( Liu et al., 2019b).

4.7. Human gastric simulator (HGS)

Human gastric simulator (HGS) is designed at the University of California, Davis, USA ( Kong and Singh, 2010). The model ( Table 2 ) simulates peristaltic contractions, secretions and emptying rates seen in the stomach. The mechanical driving system composed of rollers, a latex reservoir, secretion, emptying and temperature control systems ( Kong and Singh, 2010). The latex stomach vessel can be filled with food and digestive fluids, and peristaltic contractions were created by the 12 rollers steered by a motor assembly. The flow rates of secretions and temperature can be adjusted, and stomach contents can be emptied through pylorus simulating in vivo conditions ( Kong and Singh, 2010). Two generations of the HGS model exists ( Kong and Singh 2010; Dupont et al., 2019). The model called IHGS (improved human gastric simulator) has a better capability of simulating the shape, contour, contractions, and other physical parameters of the human stomach.

4.8. Dynamic gastric simulation model (DGSM)

This is a design based on the dynamic gastric simulation model proposed by Chen et al. (2011) at the University of Leeds (Leeds, UK). The model ( Table 2 ) simulates compressive forces, secretions, and gastric emptying to remove digest to simulate digestion in the stomach. The model has an acrylic vessel insulated with water. A PVC probe attached to a texture analyzer is used to measure the forces observed. Up and down movements of the probe attached to a texture analyzer produces the gastric contractions. The probe moves down to the bottom of the vessel until leaving a 2 ​mm gap to compress and generate food particles <2 ​mm at the bottom, then cycles back up (at a rate of 3 cycles/min). Variable flow mini pumps are used for gastric secretions and emptying ( Tran Do et al., 2016).

4.9. Near real dynamic in vitro human stomach (new DIVHS) system

This dynamic in vitro human stomach (new DIVHS) model is an advanced design based on the previous models DIVRS-I, DIVRS-II, and RD-IV-HSM at the Suzhou Key Laboratory of Green Chemical Engineering, Soochow University (Suzhou, China) ( Wang et al., 2019). The new DIVHS ( Table 2 ) includes a stomach and duodenum vessel, a driving instrument, a system for secreting and emptying, and a box with temperature control. J-shaped soft elastic silicone vessel is produced by 3D-printing technology to have a similar dimension and folded inner morphology of the human stomach. Contractions are simulated by a series of motors, rollers, and eccentric wheels. A separate roller-added system improves the disintegration and sieving ability. An auxiliary emptying device controls the gastric emptying rate by adjusting the tilting angles ( Wang et al., 2019). An exponential model was used to generate gastric emptying rates for the solid and liquid fractions where the solid fractions had a lag phase, whereas the liquid fractions did not have a lag phase.

4.10. Human gastric digestion simulator (GDS)

This human gastric digestion simulator (GDS) was designed to simulate the antrum at the Food Research Institute, NARO (Ibaraki, Japan). The GDS ( Table 2 ) consists of a gastric compartment, a roller system, and a temperature control system with a transparent parallel window to view the food disintegration mechanism ( Kozu et al., 2014; Kobayashi et al., 2017). The simplified antrum geometry has a trapezoidal shape resembling the human antrum with a smaller diameter toward the pylorus. The deformable sidewalls allow the simulation of progressive antral contraction waves by pushing a pair of rollers. The rollers move down at a speed of several mm/s at a frequency of a few cycles/min. The digestion process, which can last for up to 180 ​min can be followed with a video camera to analyze the changes in the food particles. This group also developed a continuous GDS (c-GDS) equipped with gastric secretion and emptying systems ( Kozu et al., 2017).

4.11. Artificial gastric digestive system (AGDS)

This artificial gastric digestive system (AGDS) is developed at the School of Food Science and Biotechnology, Zhejiang Gongshang University (Zhejiang, China). Size, shape, and the folds of the stomach wall are generated by using 3D printing technology in the silicone stomach model ( Table 2 ) ( Liu et al., 2019b). Peristaltic contractions of the stomach were produced by two sets of symmetrical rollers and one set of contrary rollers. A computer program controlled the forces, temperature, pH, gastric juice secretions, and gastric emptying. The mechanical forces exerted on the external wall of the silicone stomach were measured by a texture analyzer to estimate the forces experienced by the chyme ( Liu et al., 2019b).

4.12. Artificial colon (ARCOL)

The artificial colon (ARCOL) is a fermenter (Applikon, Schiedam, The Netherlands) that simulates the human colonic environment ( Cordonnier et al., 2015; Thévenot et al., 2013). The system ( Table 2 ) simulates the pH, body temperature, supply of ileal effluents, retention time, anaerobic conditions, and absorption of water and fermentation metabolites ( Blanquet-Diot et al., 2012; Cordonnier et al., 2015). Feces from healthy volunteers are used in the reactor. Fecal suspension prepared under anaerobic conditions flushed with O ₂-free N ₂ gas.

The temperature of 37 ​°C, pH of 6.3, and mean retention time of 36 ​h were used in the model. Mixtures consisting of carbohydrate, protein, lipid, mineral, and vitamins consecutively introduced into the reactor to mimic the ileal effluents. After inoculation, the flushing with O ₂-free N ₂ gas is ceased to allow the fermentative process to maintain anaerobic conditions in the reactor. A dialysis system with hollow fiber membranes (cut-off 30 ​kDa) is used to simulate the electrolyte and metabolite concentrations in vivo.

Only a few (TIM, SHIME, ESIN, DIDGI, and SIMGI) of the above dynamic models ( Table 2 ) simulate both the stomach and small intestine compartments as interconnected modules. SHIME and SIMGI models also simulate the fermentation of the large intestine connected to the small intestine. While TIM, ESIN, and DIDGI are highly sophisticated systems and focus on reproducing the mechanical, dynamic, and chemical physiological conditions in the stomach and small intestine close to reality, SHIME and SIMGI are systems that focus entirely on the large intestine fermentation and cannot accurately mimic the contractions of the stomach and small intestine ( Table 2 ). The meal chamber in the ESIN model allows meals to be delivered to the stomach as mixtures of particles of realistic size, progressively. DIDGI does not have a dialysis system as TIM and ESIN to simulate the absorption of the digested nutrients in the small intestine.

The other group, DGM, HGS, DGSM, DIVHS, c-DGS, and AGDS, are models aiming to simulate the mechanical, dynamic, and chemical conditions of the stomach only ( Table 2 ). These successful and sophisticated models simulating the stomach have differences. DGM model focused on the representation of the mechanical forces by using piston and barrel, but peristalsis and dynamic conditions of the stomach were not considered. Due to its windowed design, the GDS model allows the monitoring of stomach contents during digestion. In DIVHS and AGDS systems, stomach geometry is modeled very close to reality. Finally, ARCOL is a reactor that simulates fermentation in the large intestine only ( Table 2 ). TIM-2 is also an independent module that simulates the large bowel fermentation only ( Table 2 ).

The surge of articles published in the area indicates the requirement of engineering physiologically relevant in vitro models to use to understand the food digestion mechanism and use in the development of novel foods ( Jin, Ou, Decker, McClements, 2011; Guerra et al., 2012; Alminger et al., 2014; Bornhorst et al., 2016; Marze, 2017a; Shani-Levi et al., 2017; Bohn et al., 2018; Lucas-González, Viuda-Martos, Perez-Alvarez and Fernandez-Lopez, 2018; Pimentel, Burton, Vergeres & Dupont, 2018; Bellmann et al., 2019; Brodkorb et al., 2019; Costa and Ahluwalia, 2019; Dupont et al., 2019; Keppler, O'Meara, Bakalis, Fryer and Bornhorst, 2020). Digestion is regulated by nerves and hormones that facilitate acid release, and increase muscular movements in the stomach ( Rogers, 2011). There is no definitive model to use for the interactions of the digestive system's simulatory and inhibitory effects with food intake. As we gain information on these interactions, it will be possible to fine-tune the simulations. As an example of such improvement, to improve the prediction behavior of the existing models, TIM group used TIMagc with an in silico artificial neural network to estimate the appetite parameters after consumption of different meals. They have achieved a reasonable prediction for appetite in humans. Other improvement areas would be related to simulation of the large intestine. Although many large intestine models use human feces bacteria, challenges still exist. Variations in the ratio of bacterial populations from the feces and inadequate simulation of the real shape and movements of the large intestine can limit the simulation studies ( Liu et al., 2019b). The role of gut microbiota in digestion also needs further exploration. Even though the results obtained from these complex models should be analyzed with care and require confirmation with human studies, their contribution to the accumulation of scientific data is substantial.

5. Conclusions

Many in vitro simulation tools have been designed to reproduce the complexity of the human digestive system. Many of them are very complex systems with their sometimes in-house computer control and the mechanic or dynamic systems designs. They attempt to reproduce the physiological conditions of the human digestive system as close as possible by the use of observed in vivo data obtained from human subjects. They use complex computer control systems to adjust the dynamics of pH, transit time, and digestive secretions. Sophisticated roller or piston systems or application of regulated pressure waves by peristaltic pumps have been used to simulate the fluid dynamics and mechanical forces in the digestive system. Carrier-mediated transport and passive diffusion through the small intestine epithelial cells were simulated as passive diffusion by using a filter medium or by exposing the digested samples to cell lines. The systems sometimes used a texture analyzer to measure and control the applied forces in the stomach. Even individual organs can be modeled to close perfection in anatomy and physiology. There are examples of early models like a human duodenum model by Wright et al. (2016). Even though it was not possible to perfectly match the complex human digestive system, it was possible to simulate the digestive system's critical mechanical, dynamic, and biochemical processes in a robust, repeatable manner. The models have been improved extensively over the years, and some have been used by the food, nutrition, and medical industry widely. Still, new models show up, as seen in a recent real-size stomach model developed by Li et al. (2019).

CRediT authorship contribution statement

Ilkay Sensoy: Conceptualization, Investigation, Writing - orginal draft, Writing - review & editing.

Declaration of competing interest

The author declares no conflicts of interest.

References

AbbeeleVan Den P., Venema K., WieleVan T.De, Verstraete W., Possemiers S. Different human gut models reveal the distinct fermentation patterns of Arabinoxylan versus inulin. J Agric Food Chem. 2013 doi: 10.1021/jf4021784. [[PubMed] [CrossRef] Google Scholar]

Boland M., Golding M., Singh H., editors. Food Structures, Digestion and Health. Elsevier Inc; New York: 2014. [[CrossRef] Google Scholar]

Bornhorst G.M., Rutherfurd S.M., Roman M.J., Burri B.J., Moughan P.J., Singh R.P. Gastric pH distribution and mixing of soft and rigid food particles in the stomach using a dual-marker technique. 2014. 292-300. [CrossRef]

Directive 2001/20/EU No 2010/63/EU of the European Parliament and of the Council of 4 April 2001 on the approximation of the laws, regulations and administrative provisions of the Member States relating to the implementation of good clinical practice in the conduct of clinical trials on medicinal products for human use. Off. J. Eur. Communities. 2001:L121/34-44. [http://data.europa.eu/eli/dir/2001/20/oj [PubMed] Google Scholar]

Dupont D., Alric M., Bornhorst G., Cueva C., Deglaire A., Denis S., Ferrua M., Havenaar R., Lelieveld J., Mackie A.R., Marzorati M., Minekus M., Miralles B., Recio I., Abbeele P. Van Den. Can dynamic in vitro digestion systems mimic the physiological reality ​? Crit. Rev. Food Sci. Nutr. 2019:1-17. doi: 10.1080/10408398.2017.1421900. 0(0) [[PubMed] [CrossRef] Google Scholar]

Lentle R.G. 2018. Function digestion : reductionist approaches may; pp. 4069-4084. [[PubMed] [CrossRef] Google Scholar]

Lentle R.G., Janssen P.W.M. Springer; New York: 2011. The Physical Process of Digestion. [Google Scholar]

Lucas-González R., Viuda-Martos M., Pérez-Alvarez J.A., Fernández-López J. vol. 107. 2018. pp. 423-436. (Vitro Digestion Models Suitable for Foods: Opportunities for New Fields of Application and Challenges). [[PubMed] [CrossRef] Google Scholar]

Marieb E.N., Keller S.M. 12[th. Pearson Education Limited; England: 2018. Essentials of Human Anatomy and Physiology. Google Scholar]

Marze S. Ch. 14 Modeling of Food Digestion. In: Becker S.M., editor. [Modeling of Microscale Transport in Biological Processes. Academic Press, Elsevier Inc; New York: 2017. pp. 353-374. [CrossRef] Google Scholar]

Ménard O., Cattenoz T., Guillemin H., Souchon I., Deglaire A., Dupont D., Picque D. Validation of a new [in vitro dynamic system to simulate infant digestion. Food Chem. 2014;145:1039-1045. doi: 10.1016/j.foodchem.2013.09.036. [PubMed] [CrossRef] Google Scholar]

Miftahof R.N. [Biomechanics of the Human Stomach. Springer International; New York: 2017. [CrossRef] Google Scholar]

Articles from Current Research in Food Science are provided here courtesy of Elsevier

# data[].attributes.attachment_link.title
A review on the food digestion in the digestive tract and the used in vitro models

# data[].attributes.attachment_link.description
It is crucial to replicate or mimic the human digestive system conditions closely in model systems to have the food digestion-related data as accurate as possible. Thus, the data obtained could contribute to studies like those on the relationship between ...

# data[].attributes.body
It produces Asexually

# data[].attributes.headline
Katherine Monroy- How our organism grows in comparison to humans.

# data[].attributes.subject
Katherine Monroy- How our organism grows in comparison to humans.

# data[].attributes.body
at 7 seconds i meant butter weeds but said buts to shorten it idk why but i was sick so yeah.

# data[].attributes.headline
does the organism have a nervous system?

# data[].attributes.subject
does the organism have a nervous system?

# data[].attributes.body
Our organism does NOT have a nervous system

# data[].attributes.headline
Katherine Monroy- Respiratory System of a plant.

# data[].attributes.subject
Katherine Monroy- Respiratory System of a plant.

# data[].attributes.headline
Katherine Monroy- Respiratory System of a Human.

# data[].attributes.subject
Katherine Monroy- Respiratory System of a Human.

# data[].attributes.body
this is a link to I digestive system article

# data[].attributes.attachment_link.provider_name
National Institute of Diabetes and Digestive and Kidney Diseases

# data[].attributes.attachment_link.readable_text
What is the digestive system?

The digestive system is made up of the gastrointestinal tract-also called the GI tract or digestive tract-and the liver, pancreas, and gallbladder. The GI tract is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. The hollow organs that make up the GI tract are the mouth, esophagus, stomach, small intestine, large intestine, and anus. The liver, pancreas, and gallbladder are the solid organs of the digestive system.

The small intestine has three parts. The first part is called the duodenum. The jejunum is in the middle and the ileum is at the end. The large intestine includes the appendix, cecum, colon, and rectum. The appendix is a finger-shaped pouch attached to the cecum. The cecum is the first part of the large intestine. The colon is next. The rectum is the end of the large intestine.

The digestive system

Bacteria in your GI tract, also called gut flora or microbiome, help with digestion. Parts of your nervous and circulatory systems also help. Working together, nerves, hormones, bacteria, blood, and the organs of your digestive system digest the foods and liquids you eat or drink each day.

Why is digestion important?

Digestion is important because your body needs nutrients from food and drink to work properly and stay healthy. Proteins, fats, carbohydrates, vitamins, minerals, and water are nutrients. Your digestive system breaks nutrients into parts small enough for your body to absorb and use for energy, growth, and cell repair.

Proteins break into amino acids

Fats break into fatty acids and glycerol

Carbohydrates break into simple sugars

MyPlate offers ideas and tips to help you meet your individual health needs.

Your digestive system breaks nutrients into parts that are small enough for your body to absorb.

How does my digestive system work?

Each part of your digestive system helps to move food and liquid through your GI tract, break food and liquid into smaller parts, or both. Once foods are broken into small enough parts, your body can absorb and move the nutrients to where they are needed. Your large intestine absorbs water, and the waste products of digestion become stool. Nerves and hormones help control the digestive process.

The digestive process

How does food move through my GI tract?

Food moves through your GI tract by a process called peristalsis. The large, hollow organs of your GI tract contain a layer of muscle that enables their walls to move. The movement pushes food and liquid through your GI tract and mixes the contents within each organ. The muscle behind the food contracts and squeezes the food forward, while the muscle in front of the food relaxes to allow the food to move.

The digestive process starts when you put food in your mouth.

Mouth. Food starts to move through your GI tract when you eat. When you swallow, your tongue pushes the food into your throat. A small flap of tissue, called the epiglottis, folds over your windpipe to prevent choking and the food passes into your esophagus.

Esophagus. Once you begin swallowing, the process becomes automatic. Your brain signals the muscles of the esophagus and peristalsis begins.

Lower esophageal sphincter. When food reaches the end of your esophagus, a ringlike muscle-called the lower esophageal sphincter -relaxes and lets food pass into your stomach. This sphincter usually stays closed to keep what's in your stomach from flowing back into your esophagus.

Stomach. After food enters your stomach, the stomach muscles mix the food and liquid with digestive juices. The stomach slowly empties its contents, called chyme, into your small intestine.

Small intestine. The muscles of the small intestine mix food with digestive juices from the pancreas, liver, and intestine, and push the mixture forward for further digestion. The walls of the small intestine absorb water and the digested nutrients into your bloodstream. As peristalsis continues, the waste products of the digestive process move into the large intestine.

Large intestine. Waste products from the digestive process include undigested parts of food, fluid, and older cells from the lining of your GI tract. The large intestine absorbs water and changes the waste from liquid into stool. Peristalsis helps move the stool into your rectum.

Rectum. The lower end of your large intestine, the rectum, stores stool until it pushes stool out of your anus during a bowel movement.

Watch this video to see how food moves through your GI tract.

How does my digestive system break food into small parts my body can use?

As food moves through your GI tract, your digestive organs break the food into smaller parts using:

motion, such as chewing, squeezing, and mixing

digestive juices, such as stomach acid, bile, and enzymes

Mouth. The digestive process starts in your mouth when you chew. Your salivary glands make saliva, a digestive juice, which moistens food so it moves more easily through your esophagus into your stomach. Saliva also has an enzyme that begins to break down starches in your food.

Esophagus. After you swallow, peristalsis pushes the food down your esophagus into your stomach.

Stomach. Glands in your stomach lining make stomach acid and enzymes that break down food. Muscles of your stomach mix the food with these digestive juices.

Pancreas. Your pancreas makes a digestive juice that has enzymes that break down carbohydrates, fats, and proteins. The pancreas delivers the digestive juice to the small intestine through small tubes called ducts.

Liver. Your liver makes a digestive juice called bile that helps digest fats and some vitamins. Bile ducts carry bile from your liver to your gallbladder for storage, or to the small intestine for use.

Gallbladder. Your gallbladder stores bile between meals. When you eat, your gallbladder squeezes bile through the bile ducts into your small intestine.

Small intestine. Your small intestine makes digestive juice, which mixes with bile and pancreatic juice to complete the breakdown of proteins, carbohydrates, and fats. Bacteria in your small intestine make some of the enzymes you need to digest carbohydrates. Your small intestine moves water from your bloodstream into your GI tract to help break down food. Your small intestine also absorbs water with other nutrients.

Large intestine. In your large intestine, more water moves from your GI tract into your bloodstream. Bacteria in your large intestine help break down remaining nutrients and make vitamin K. Waste products of digestion, including parts of food that are still too large, become stool.

What happens to the digested food?

The small intestine absorbs most of the nutrients in your food, and your circulatory system passes them on to other parts of your body to store or use. Special cells help absorbed nutrients cross the intestinal lining into your bloodstream. Your blood carries simple sugars, amino acids, glycerol, and some vitamins and salts to the liver. Your liver stores, processes, and delivers nutrients to the rest of your body when needed.

The lymph system, a network of vessels that carry white blood cells and a fluid called lymph throughout your body to fight infection, absorbs fatty acids and vitamins.

Your body uses sugars, amino acids, fatty acids, and glycerol to build substances you need for energy, growth, and cell repair.

How does my body control the digestive process?

Your hormones and nerves work together to help control the digestive process. Signals flow within your GI tract and back and forth from your GI tract to your brain.

Hormones

Cells lining your stomach and small intestine make and release hormones that control how your digestive system works. These hormones tell your body when to make digestive juices and send signals to your brain that you are hungry or full. Your pancreas also makes hormones that are important to digestion.

Nerves

You have nerves that connect your central nervous system-your brain and spinal cord-to your digestive system and control some digestive functions. For example, when you see or smell food, your brain sends a signal that causes your salivary glands to "make your mouth water" to prepare you to eat.

You also have an enteric nervous system (ENS)-nerves within the walls of your GI tract. When food stretches the walls of your GI tract, the nerves of your ENS release many different substances that speed up or delay the movement of food and the production of digestive juices. The nerves send signals to control the actions of your gut muscles to contract and relax to push food through your intestines.

Clinical Trials

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) and other components of the National Institutes of Health (NIH) conduct and support research into many diseases and conditions.

What are clinical trials, and are they right for you?

Watch a video of NIDDK Director Dr. Griffin P. Rodgers explaining the importance of participating in clinical trials.

What clinical trials are open?

Clinical trials that are currently open and are recruiting can be viewed at www.ClinicalTrials.gov.

# data[].attributes.attachment_link.title
Your Digestive System & How it Works - NIDDK

# data[].attributes.attachment_link.description
Overview of the digestive system-how food moves through each part of the GI tract to help break down food for energy, growth, and cell repair.

# data[].attributes.body
And here is another article on the circulatory system

# data[].attributes.attachment_link.title
Circulatory System: Anatomy and Function

# data[].attributes.attachment_link.description
The circulatory system includes the heart and blood vessels. Your heart sends blood to the lungs for oxygen. It pumps oxygen-rich blood to the rest of the body.

# data[].attributes.headline
Digestive system videos - Ms. Cobles- Digestive system

# data[].attributes.subject
Digestive system videos - Ms. Cobles- Digestive system

# data[].attributes.body
Here is a video on the digestive system

# data[].attributes.attachment_link.title
The Digestive System - Learning the Body for kids

# data[].attributes.headline
pt 2 on the digestive system videos- Ms. Cobles- Digestive system

# data[].attributes.subject
pt 2 on the digestive system videos- Ms. Cobles- Digestive system

# data[].attributes.body
And here is another video on the digestive system but its a song

# data[].attributes.headline
Katherine Monroy- Integumentary System of a Plant

# data[].attributes.subject
Katherine Monroy- Integumentary System of a Plant

# data[].attributes.body
Learn more about the Integumentary System of a Plant!

https://www.encyclopedia.com/medicine/anatomy-and-physiology/anatomy-and-physiology/integumentary-system#:~:text=The%20integumentary%20system%20of%20plants,%2C%20feathers%2C%20hair%20and%20glands.

# data[].attributes.body
https://www.khanacademy.org/science/ap-biology/cellular-energetics/photosynthesis/a/intro-to-photosynthesis#:~:text=Photosynthesis%20is%20the%20process%20in,is%20released%20as%20a%20byproduct.

# data[].attributes.headline
Katherine Monroy- Integumentary System of a Human 

# data[].attributes.subject
Katherine Monroy- Integumentary System of a Human 

# data[].attributes.body
Learn more about the Integumentary System of a Human!

https://www.ncbi.nlm.nih.gov/books/NBK554386/#:~:text=The%20integumentary%20system%20includes%20the,D%2C%20and%20detection%20of%20stimuli.

# data[].attributes.attachment_caption
The difference between the growth of humans and dandelions - Ms. Coble - Growth differences

# data[].attributes.headline
The difference how a dandelion grows and how a human grows.

# data[].attributes.subject
The difference how a dandelion grows and how a human grows.

# data[].attributes.body
This video explains the growth difference between humans and dandelions

# data[].attributes.attachment_caption
Circulatory and Digestive system of the butter weed- Ms. Coble-Butter Weed

# data[].attributes.attachment_link.title
What is the Nervous System | Nervous System Basics

# data[].attributes.attachment_link.description
Reproductive plant parts produce seed; they include flower buds, flowers, fruit, and seeds.

# data[].attributes.body
A song explaining the different parts of a plant.

# data[].attributes.body
A video explaining the reproduction of a plant.

# data[].attributes.attachment_link.title
Plant sexual reproduction | Educational Video for Kids

# data[].attributes.body
flowers reproduce through a process called pollination!

# data[].attributes.body
Plants do NOT have a muscular system, but they do have something like it.

# data[].attributes.attachment_link.readable_text
The muscular system is composed of specialized cells called muscle fibers. Their predominant function is contractibility. Muscles, attached to bones or internal organs and blood vessels, are responsible for movement. Nearly all movement in the body is the result of muscle contraction. Exceptions to this are the action of cilia, the flagellum on sperm cells, and amoeboid movement of some white blood cells.

The integrated action of joints, bones, and skeletal muscles produces obvious movements such as walking and running. Skeletal muscles also produce more subtle movements that result in various facial expressions, eye movements, and respiration.

In addition to movement, muscle contraction also fulfills some other important functions in the body, such as posture, joint stability, and heat production. Posture, such as sitting and standing, is maintained as a result of muscle contraction. The skeletal muscles are continually making fine adjustments that hold the body in stationary positions. The tendons of many muscles extend over joints and in this way contribute to joint stability. This is particularly evident in the knee and shoulder joints, where muscle tendons are a major factor in stabilizing the joint. Heat production, to maintain body temperature, is an important by-product of muscle metabolism. Nearly 85 percent of the heat produced in the body is the result of muscle contraction.

# data[].attributes.attachment_link.description
The muscular system is composed of specialized cells called muscle fibers. Their predominant function is contractibility. Muscles, attached to bones or internal organs and blood vessels, are responsible for movement. Nearly all movement in the body is the result of muscle contraction.

# data[].attributes.body
A song describing the muscular system.

# data[].attributes.body
A video describing the muscular system.

# data[].attributes.attachment_link.title
Muscles, Part 1 - Muscle Cells: Crash Course A&P #21

# data[].attributes.body
Plants "Muscular" System

# data[].attributes.body
Human Muscular System