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SBI3U_RP Module #8

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As soon as you put food into your mouth digestion begins. Your first impulse is to chew up that pizza. This is considered mechanical digestion, where your body physically breaks down the food into smaller pieces that are more easy to chemically digest. Now, as soon as you thought of tasty, steaming hot pizza you probably started to salivate. Saliva, or spit, contains an enzyme called amylase that helps break down starches, and mucus to moisten your food for swallowing, and gather it all together into a bolus or ball of food. All of this is sped up by your tongue which helps control the mechanical digestion and combine it with saliva. It also tastes the food which can alert your body to what sorts of chemicals are in the food and certain tastes may make you vomit.

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As the tongue pushes the newly formed bolus of food to the back of your mouth, the Pharynx at the top of your esophagus swallows the food which is a voluntary muscle movement ( a muscle movement we consciously make), and then it begins to travel through the esophagus towards the stomach with involuntary muscle movements that squeeze the bolus downwards. The muscle contractions are called peristalsis. This can take 5-10 seconds which is probably longer than you thought. We don't sense it moving that slowly because it is harder to detect involuntary muscle movements.

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<----- this is an image of a real esophagus

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In One End, Out The Other, A Complete Description Of The Digestion Process

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In One End, Out The Other, A Complete Description Of The Digestion Process

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Swallowing Reflex, Phases and Overview of Neural Control, Animation.

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The digestive system is a critical part of our body. In order to grow, have energy, and for cells to be repaired we need nutrients to build with and energy to burn. When we ingest food (pizza for example) our body is capable of breaking that food down into small specific pieces called macro-molecules. We can separate the macro-molecules into four basic groups.

Carbohydrates: Both simple and complex, this group contains starches, sugars, and fibers in our food. Shortened comfortably to carbs, we need an awful lot of carbs in our diet according to the Canadian food guide.

Protein: Protein molecules are taken from certain foods like eggs, meat, and beans.  The amino acids within the proteins are very important for our body.

Fats (lipids):  This group can be found in foods like oil and butter. Because lipids don't break down too well in water the body has a special way of breaking it into fatty acids and glycerol.

Vitamins (nucleic acids): This group is found in almost everything fresh that we consume. Some vitamins can be lost over time in some foods though.

With all of these important macro-molecule groups combined into say, a slice of meat-lovers pizza, our body has an important task of breaking up this food into pieces it can consume, and disposing of what it cannot use. This amazing process is carried out by the one and only, digestive system. We could call the digestive system the  disassembly line.  If it was a piece of pizza there would be many carbohydrates in the dough, some proteins if there were pieces of meat like pepperoni, lipids in the oils/butter that are used in the cooking process and in the dough, and nucleic acids throughout the slice; but without the carefully organized, amazingly efficient digestive system we have then the pizza would be of no use to our body. Here is the journey of a slice of pizza you have eaten.

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6 Major Events That Occur During Digestion

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6 Major Events That Occur During Digestion

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Ingestion

Secretion

Mixing and movement

Digestion

Absorption

Excretion

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Our teeth are specially made of Enamel to grind and tear up food. they help us break it down into small enough pieces to swallow and for the enzymes to digest as fully as possible.

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The tongue is considered the strongest muscle in our body, and while some of you probably thought it was because we talk too much, it's actually because our tongue gets a real workout every time you eat. It is constantly moving your food around and aiding the chewing process and helping cover the food in saliva. It also helps gather the food into a bolus and then shove it to that back of the mouth to be swallowed.

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The small intestine is 4.6-9.8 meters long. It averages at 6.9m for men and 7.1m for women. That means your intestine could be 15-32 feet long! Can you imagine that all coiled up in your body? No wonder it can take over 16 hours for food to move into the next section!

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The small intestine is a long circular tube of tissue that is coiled up in your mid-section. inside each section there are small fingers of tissue called villi that absorb available nutrients out of the Gastric chyme. This is also where the rest of digestion takes place. It has three main sections that host the different stages of digestion and absorption. Food is moved along the intestine with smooth muscle movements that slowly squish the food along.

Duodenum: The duodenum is the first 20-25cm long C-shaped section of bowel. In this section some very important enzymes are released into the Gastric Chyme. In the side of the intestine there is a Common Bile Duct that separates forks into two ducts. These two ducts (the Cystic Duct which leads to the gall and the Common Hepatic Duct which leads to the liver and splits into bile ducts) The liver releases bile into the Duodenum through a duct and the gall bladder recycles bile for reuse. Bile is composed of water, bile salts, bilirubin, and fats such as cholesterol and fatty acids. The bile is used to surround the lipids in the food that do not bond with water and emulsify them with the water and keep them from rejoining together into larger lipid groups. The pancreatic duct is directly after the common bile duct and it releases all manner of enzymes to digest the various food groups as completely as possible so that the nutrients can be absorbed and used. The enzymes released together are called pancreatic jiuces and these juices are composed of Trypsinogen, Chymotrypsinogen,  Elastase, Carboxypeptidease, Pancreatic Lipase, Nucleases, and Amylase. Each of these enzymes has a specific purpose that is detailed in the list to the left. The duodenum also has short villi that line the walls and absorb some of the nutrients.

Jejunum: The Duodenum passes upwards to join the jejunum where much of digestion finishes and the nutrients are absorbed. This section of the intestine is often around 2.5m long and is covered with small mucosa called villi. Villi are pretty amazing, They greatly increase the surface area of your intestine which means more area to absorb the many nutrients that are now broken into usable pieces. And on these villi are even smaller finger-like tentacles that are called micro-villi. These villi use passive transport to transfer sugar fructose to the blood and active transport for amino acids, small peptides, vitamins, and most types of glucose. Although the jejunum is very similar to the Ilium and there is no exact line of distinction, the jejunum has a few differences. The jejunum has less fat inside it's mesentery and is larger in diameter than the ilium. There is lymphatic tissue all along the small intestine, but only the Jejunum has such abundant Peyer's Patches (encapsulated lymphoid nodules). There is a fair amount of lymphatic action in the Jejunum and also more intensive peristalsis (smooth muscle contractions that move the contents of the intestine via muscle contractions) compared to other sections of the intestine.

Ileum: This section of the small intestine is usually about 3m long and it is the final section before the nutrient-bare waste enters the large intestine. It's primary function is to absorb any remaining nutrients, Vitamin B12, and bile acids. The many large circular folds present in the Jejunum are now much smaller and disappear altogether at the very end of the ilium. Digestion is not completely complete, the ilium releases protease and carbohydrase enzymes to complete the digestion of protein and carbohydrates, and it also has villi although they are progressively smaller. The food will complete the journey through the small intestine and move on into the large intestine. Hardly any usable material is left in the watery waste.

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Pancreatic Juices: Enzymystery!     Get it? (End the mystery... ) :P

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Pancreatic Juices: Enzymystery!     Get it? (End the mystery... ) :P

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Trypsinogen, carboxypeptidease, and chymotrypsenogen are activated and work together to break down the peptide bonds of amino acids in proteins. Elastase also breaks down proteins. The resulting amino acids are used to build new cells all over the body

Pancreatic lipase breaks down fat molecules , they are able to digest the non-soluble fats because the bile salts have already emulsified them and allow the lipase to convert it to monoglycerides and free fatty acids that are used by the body.

Nucleases and Nucleosidases are secreted to break down certain bonds in the subunits of nucleic acids. They help prepare them to be used for DNA replication.

Amylase is once again released to break down the starches in the food even further. There is a lot more amylase in the duodenum than in the mouth. It breaks starch into disaccharides and trisaccharides which will later be transformed into glucose to supply the body with energy. It is also a bit more potent, (basic not neutral like Salivary Amylase)

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The rectum is a straight section of the intestine that is directly linked to the anal canal (in humans). These are both used for the elimination of fully digested, dehydrated, nearly nutrient-bare feces which and are controlled by internal and external sphincter muscles that are extremely strong. The Anus is the final opening through which the feces are pushed (formed with a strong sphincter muscle), into the great outdoors. This is the final stage of the digestive system. Your pizza slice, or it's remains, have reached their destination.

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Wow! You Made It, But most of that Pizza didn't . . . 

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Wow! You Made It, But most of that Pizza didn't . . . 

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As you can see, the digestive system is complex, efficient, and quite simply incredible! Because of the way we are designed, none of us could live without it. It may seem like a simple function that you barely have to think about and most of which occurs beyond your conscious control, but it is the gopher of nutrients, the food disassembly line of your body. The products it provides are in every cell in your body. look at your skin, every part of you contains something you ate at one time or another, that's pretty darn amazing right?

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The villi in the above picture work together to absorb enourmous amounts of nutrients into the blood. The circulatory system is intertwined with the digestive system and nutrients would be useless without it.

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Below you can see a somewhat messy illustration of everything that is going on with that food you eat (she's even eating pizza!!!) Try clicking on the image to enlarge it and to get a better view.

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Ever get that awful burning sensation in your chest or sharp stabs of pain? We call it heart burn or indigestion. It occurs when the LES doesn't close fully or your stomach is so full that acid is pushed into your esophagus. It can also be a result of the over production of HCl. The esophagus is not lined with protective mucous and so it begins to burn your tissue. Some people have it so bad that they are restricted to very specific diets and pills to control the acid levels in the stomach.

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The liver is similar to a triangle in shape and it sits beside the stomach above the main part of the small intestine (in humans). It's main function in digestion is to produce bile which is released by way of ducts into the duodenum. It also filters out and destroys toxins and old cells from the blood and stores nutrients and biological molecules for later use. These functions only brush the surface of this organ.

The gall bladder stores recycled bile and is nestled into the liver. It is usually a green colour. It attaches to it with membranes and tissues and has a duct that joins with the liver's bile duct and then joins to the duodenum.

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Third Stage: A Stomach's Role In Digestion

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Third Stage: A Stomach's Role In Digestion

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At the bottom of the esophagus there is a sphincter muscle that is kept tightly closed to keep acid and food from coming up, it relaxes to allow food inside the stomach and then tightens up again. Once inside, the food becomes mixed with the digestive juices, also called gastric juices. The digestive juices are made up of HCl (hydrochloric acid), mucus, and pepsinogen secreted by special cells. Mucus lines the inner walls of the stomach to prevent the stomach from digesting itself, the stomach would not be able to exist safely in the body without the mucus layer that covers the lining. The HCl is secreted by parietal cells in the stomach lining and is responsible for killing pathogens and helping turn pepsinogen into pepsin. Pepsin is an acidic enzyme secreted by cells in the stomach called chief cells. Pepsin is secreted to digest proteins by breaking up the long chains of amino acids into smaller chains. Chemical digestion isn't the only thing going on in your stomach. Around the stomach there are three layers of extremely strong smooth muscles. These muscles are involuntarily contracted and pulsed to help the stomach swish the contents around. In this way the stomach performs mechanical digestion as well as a great deal of chemical digestion. Finally the food within the stomach moves on in it's journey escaping out the Pyloric sphincter into the very beginning of the small intestine, it is now called Gastric Chyme

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Fifth Stage: The Large Intestine (Colon)

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Fifth Stage: The Large Intestine (Colon)

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The large intestine is like the desert of the body. Nearly every other part of the body needs lubrication, but this section of the body dehydrates the waste that comes out of the small intestine via the ileocecal valve. Compared to the small intestine, the large intestine is relatively short with a general length of 4.9ft. In this large diameter tube of tissue the water is dehydrated out of the waste and, along with salts, absorbed into the body. The remains are called feces and are eventually eliminated from the body. In a healthy bowel, the colon is right full of bacteria. Not just any bacteria, these are good microflora that help release certain vitamins that our body can use. After an average total of 16 hours in the colon, the waste in the form of feces is eliminated via the rectum and anus. There are several sections of the large intestine as it circles around the small intestine in the midsection area of your body.

Cecum and Appendix: The cecum is the very first section of the bowel, and at the very back it has a little finger-shaped extension that is known as the appendix (also the mystery organ). Science has yet to fully understand the appendix, but it does host a rather large storehouse of gut flora and scientists think it may be used to repopulate the gut if too much of the gut flora are eliminated.
Ascending Colon: This is where the dehydration begins, as the waste moves through this section the gut flora also begin to release various vitamins in the waste and the waste has become slightly more solid.
Transverse Colon: The transverse colon is unique in that it is mobile unlike the Ascending colon and descending colon. The waste continues to dehydrate and solidify.
Descending Colon: The gut flora is the most proficient in this section of the large intestine. It often stores feces that will eventually be emptied into the rectum.
Sigmoid Colon: This section of the bowel has powerful muscles that push feces into the rectum. It is S-shaped as it's name implies and is the last section of large intestine before the rectum. Some people include the rectum as part of the colon, but we will discuss it in connection with the anus

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Digestion inside the mouth: Salivary Glands

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Digestion inside the mouth: Salivary Glands

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The salivary glands are responsible for secreting saliva. Saliva is made up of mucus and amylase enzymes that break down starch into maltose and glucose. There are various salivary glands located all over the mouth and with various purposes. The two largest glands are called the Parotid glands (see picture to the left) and they secrete saliva mostly to facilitate chewing and swallowing. The submandibular glands are responsible for 65-70% of the saliva in your mouth and the sublingual glands produce only about 5%. There are also many minor glands located around the mouth that contribute also. Very special glands called the Von Ebner glands secrete a serous liquid that begins the breakdown of lipids by starting hydrolysis and also helps activate the taste buds. Salivary glands are activated even before food enters the mouth then the brain sends messages from what it sees, smells, or anticipates.

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"Digestive System." EMedTV: Health Information Brought To Life. N.p., n.d. Web. 17 Apr. 2016. <http://digestive-system.emedtv.com/digestive-system/digestive-system.html>.

The Editors of Encyclopædia Britannica. "Digestion." Encyclopedia Britannica Online. Encyclopedia Britannica, n.d. Web. 17 Apr. 2016. <http://www.britannica.com/science/digestion-biology>.

N.p., n.d. Web. <http://kidshealth.org/en/parents/digestive.html>.

N.p., n.d. Web. <https://www.nlm.nih.gov/medlineplus/digestivesystem.html>.

"Your Digestive System and How It Works." Your Digestive System and How It Works. N.p., n.d. Web. 17 Apr. 2016. <http://www.niddk.nih.gov/health-information/health-topics/Anatomy/your-digestive-system/Pages/anatomy.aspx>.

Zimmermann, By Kim Ann. "Digestive System: Facts, Function & Diseases." LiveScience. TechMedia Network, 11 Mar. 2016. Web. 17 Apr. 2016. <http://www.livescience.com/22367-digestive-system.html>.

N.p., n.d. Web. <http://www.webmd.com/heartburn-gerd/your-digestive-system>.

N.p., n.d. Web. <http://www.innerbody.com/image/digeov.html>.

N.p., n.d. Web. <https://www.nlm.nih.gov/medlineplus/digestivesystem.html>.

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