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Homeostasis-the monitoring and adjusting that goes on in the human body at any given time-is astounding. Your body continually makes adjustments to the body systems you use during everyday activities. In this interactive, make adjustments in respiration or heart rate or energy delivery in response to changing activities, and anticipate how a change in one system changes the balance in another system.

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Homeostasis - What Is Homeostasis - What Is Set Point For Homeostasis- Homeostasis In The Human Body

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The Brain Is the Boss

When you're taking a big math test, you know that your brain is hard at work. But your brain is doing a lot more than just remembering formulas. Those sweaty palms you get as the test starts? That's your brain at work. The relief you feel when you know an answer's right? That's your brain too. And yes, your brain is even in charge when you take a minute to daydream about the big party on Friday night.

The brain may simply be the bossiest part of the body: It tells virtually every other part of your body what to do, all the time, whether you're aware of it or not. It controls what you think and feel, how you learn and remember, and the way you move. It also controls things you might not think about - like the beating of your heart and whether you feel sleepy or awake.

The Brain & Nervous System in Everyday Life

If the brain is like a central computer that controls all the functions of your body, then the nervous system is like a network that sends messages back and forth from the brain to different parts of the body. It does this via the spinal cord, which runs from the brain down through the back and contains threadlike nerves that branch out to every organ and body part.

When a message comes into the brain from anywhere in the body, the brain tells the body how to react. For example, if you accidentally touch a hot stove, the nerves in your skin shoot a message of pain to your brain. The brain then sends a message back telling the muscles in your hand to pull away. Luckily, this neurological relay race takes a lot less time than it just took to read about it!

How the Brain Works

Considering everything it does, the human brain is incredibly compact, weighing just 3 pounds. Its many folds and grooves, though, provide it with the additional surface area necessary for storing all of the body's important information.

The spinal cord, on the other hand, is a long bundle of nerve tissue about 18 inches long and ¾ inch thick. It extends from the lower part of the brain down through spine. Along the way, various nerves branch out to the entire body. These make up the peripheral nervous system.

Both the brain and the spinal cord are protected by bone: the brain by the bones of the skull, and the spinal cord by the set of ring-shaped bones called vertebrae that make up the spine. They're both cushioned by layers of membranes called meninges as well as a special fluid called cerebrospinal fluid. This fluid helps protect the nerve tissue, keep it healthy, and remove waste products.

The brain is made up of three main sections: the forebrain, the midbrain, and the hindbrain.

The Forebrain

The forebrain is the largest and most complex part of the brain. It consists of the cerebrum - the area with all the folds and grooves typically seen in pictures of the brain - as well as some other structures beneath it.

The cerebrum contains the information that essentially makes us who we are: our intelligence, memory, personality, emotion, speech, and ability to feel and move. Specific areas of the cerebrum are in charge of processing these different types of information. These are called lobes, and there are four of them: the frontal, parietal, temporal, and occipital.

The cerebrum has right and left halves, called hemispheres, which are connected in the middle by a band of nerve fibers (the corpus callosum) that enables the two sides to communicate.

Although these halves may look like mirror images of each other, many scientists believe they have different functions. The left side is considered the logical, analytical, objective side. The right side is thought to be more intuitive, creative, and subjective. So when you're doing a math problem you're using the left side, and when you're listening to music you're using the right side. Scientists think that some people are more "right-brained" or "left-brained" while others are more "whole-brained," meaning they use both halves of their brain to the same degree.

The outer layer of the cerebrum is called the cortex (also known as "gray matter"). Information collected by the five senses comes into the brain from the spinal cord to the cortex. This information is then directed to other parts of the nervous system for further processing. For example, when you touch the hot stove, not only does a message go out to move your hand but one also goes to another part of the brain to help you remember not to do that again.

In the inner part of the forebrain sit the thalamus, hypothalamus, and pituitary gland. The thalamus carries messages from the sensory organs like the eyes, ears, nose, and fingers to the cortex. The hypothalamus controls body temperature, thirst, appetite, sleep patterns, and other processes in our bodies that happen automatically. It also controls the pituitary gland, which makes the hormones that control our growth, metabolism, water and mineral balance, sexual maturity, and how we respond to stress.

The Midbrain

The midbrain, located underneath the middle of the forebrain, acts as a master coordinator for all the messages going in and out of the brain to the spinal cord.

The Hindbrain

The hindbrain sits underneath the back end of the cerebrum, and it consists of the cerebellum, pons, and medulla. The cerebellum - also called the "little brain" because it looks like a small version of the cerebrum - is responsible for balance, movement, and coordination. The pons and the medulla, along with the midbrain, are often called the brainstem. The brainstem takes in, sends out, and coordinates all of the brain's messages. It is also controls many of the body's automatic functions, like breathing, heart rate, blood pressure, swallowing, digestion, and blinking.

How the Nervous System Works

The basic functioning of the nervous system depends a lot on tiny cells called neurons. The brain has billions of them, and they have many specialized jobs. For example, sensory neurons take information from the eyes, ears, nose, tongue, and skin to the brain. Motor neurons carry messages away from the brain and back to the rest of the body.

All neurons relay information to each other through a complex electrochemical process, making connections that affect the way we think, learn, move, and behave.

Intelligence, Learning, and Memory

When you learn things, messages travel from one neuron to another, over and over. Then the brain creates connections (or pathways) between the neurons, so things become easier and you can do them better and better.

In young children, the brain is highly adaptable. In fact, when one part of a young child's brain is injured, another part may learn to take over some of the lost function. But as we age, the brain has to work harder to make new neural pathways, making it more difficult to master new tasks or change established behavior patterns. That's why many scientists believe it's important to keep challenging your brain to learn new things and make new connections - it helps keep the brain active over the course of a lifetime.

Memory is another complex function of the brain. The things we've done, learned, and seen are first processed in the cortex, and then, if we sense that this information is important enough to remember permanently, it's passed inward to other regions of the brain (such as the hippocampus and amygdala) for long-term storage and retrieval. As these messages travel through the brain, they create pathways that serve as the basis of our memory.

Movement

Different parts of the cerebrum are responsible for moving different body parts. The left side of the brain controls the movements of the right side of the body, and the right side of the brain controls the movements of the left side of the body. When you kick a soccer ball with your right foot, for example, it's the left side of your brain that sends the message allowing you to do it.

Basic Body Functions

A part of the peripheral nervous system called the autonomic nervous system is responsible for controlling many of the body processes we almost never need to think about, like breathing, digestion, sweating, and shivering. The autonomic nervous system has two parts: the sympathetic and the parasympathetic nervous systems.

The sympathetic nervous system prepares the body for sudden stress, like if you see a robbery taking place. When something frightening happens, the sympathetic nervous system makes the heart beat faster so that it sends blood more quickly to the different body parts that might need it. It also causes the adrenal glands at the top of the kidneys to release adrenaline, a hormone that helps give extra power to the muscles for a quick getaway. This process is known as the body's "fight or flight" response.

The parasympathetic nervous system does the exact opposite: It prepares the body for rest. It also helps the digestive tract move along so our bodies can efficiently take in nutrients from the food we eat.

The Senses

Your eyes may watch as your best friend walks toward you - but without the brain, you wouldn't even recognize her. Pepperoni pizza sure is delicious - but without the brain, your taste buds wouldn't be able to tell if you were eating pizza or the box it came in. None of your senses would be useful without the processing that occurs in the brain.

Sight. Sight probably tells us more about the world than any other sense. Light entering the eye forms an upside-down image on the retina. The retina transforms the light into nerve signals for the brain. The brain then turns the image right-side up and tells us what we are seeing.

Hearing. Every sound we hear is the result of sound waves entering our ears and causing our eardrums to vibrate. These vibrations are then transferred along the tiny bones of the middle ear and converted into nerve signals. The cortex then processes these signals, telling us what we are hearing.

Taste. The tongue contains small groups of sensory cells called taste buds that react to chemicals in foods. Taste buds react to sweet, sour, salty, and bitter. Messages are sent from the taste buds to the areas in the cortex responsible for processing taste.

Smell. Olfactory cells in the mucous membranes lining each nostril react to chemicals we breathe in and send messages along specific nerves to the brain - which, according to experts, can distinguish between more than 10,000 different smells. With that kind of sensitivity, it's no wonder research suggests that smells are very closely linked to our memories.

Touch. The skin contains more than 4 million sensory receptors - mostly concentrated in the fingers, tongue, and lips - that gather information related to touch, pressure, temperature, and pain and send it to the brain for processing and reaction.

Things That Can Go Wrong With the Brain

Because the brain controls just about everything, when something goes wrong, it's often serious and can affect many different parts of the body. Inherited diseases, brain disorders associated with mental illness, and head injuries can all affect the way the brain works and upset the daily activities of the rest of the body.

Here are some of the problems that can affect the brain:

Brain tumors. A tumor is an abnormal tissue growth in the brain. A tumor in the brain may grow slowly and produce few symptoms until it becomes large. Or a tumor can grow and spread rapidly, causing severe and quickly worsening symptoms.

Brain tumors can be benign or malignant. They usually grow in one place and may be curable through surgery if they're located in a place where they can be removed without damaging the normal tissue near the tumor. A malignant tumor is cancerous and more likely to grow rapidly and spread.

Cerebral palsy (CP). Cerebral palsy is the result of a developmental defect or damage to the brain before or during a child's birth, or during the first few years of life. CP affects the motor areas of the brain. A person with cerebral palsy may have average intelligence or can have severe developmental delays or mental retardation.

Cerebral palsy can affect body movement in many different ways. In mild cases, a person may have minor muscle weakness in the arms and legs. In other cases, there may be more severe motor impairment - a person may have trouble talking and performing basic movements like walking.

Epilepsy. Epilepsy is a condition of the nervous system that can lead people to have seizures. Partial seizures involve specific areas of the brain, and symptoms vary depending on the location of the seizure activity. Other seizures, called generalized seizures, involve a larger area of the brain and usually cause uncontrolled movements of the entire body and loss of consciousness. Although in many cases doctors don't know what causes it, epilepsy can be related to brain injury, tumors, or infections. The tendency to develop epilepsy may be inherited in families.

Headaches. Of the many different types of headaches, some of the more common are:

tension headache (the most common type) is caused by muscle tension in the head, neck, and shoulders

migraine is an intense, recurring headache with an unclear cause

cluster headache is often considered to be a form of migraine

Migraines happen with or without warning and may last for a few hours or up to several days. The tendency to develop migraines may be inherited in families. A person who has migraines may get one after being exposed to a "trigger" (such as a particular food), and may feel dizzy, numb, nauseated, and sensitive to light, and may see flashing zigzag lines before their eyes.

Meningitis and encephalitis. These are infections of the brain and spinal cord that are usually caused by bacteria or viruses. Meningitis is an inflammation of the coverings of the brain and spinal cord, and encephalitis is an inflammation of the brain tissue. Both conditions may result in permanent injury to the brain.

Mental illness. Mental illnesses involve a wide range of problems in how people think and function. Experts now know that certain mental illnesses are linked to structural or chemical problems in the person's brain. Some mental illnesses are inherited, but even though researchers know that these illnesses run in families, they often can't pinpoint what causes them in the first place. Injuries to the brain and chronic drug or alcohol abuse also can trigger some mental illnesses.

Signs of chronic mental illnesses such as bipolar disorder or schizophrenia may first show up in childhood. Mental illnesses that can be seen in teens include depression, eating disorders such as bulimia or anorexia nervosa, obsessive-compulsive disorder (OCD), and phobias.

Head injuries. Head injuries fit into two categories: external (usually scalp) injuries and internal injuries. Internal injuries may involve the skull, the blood vessels within the skull, or the brain. Fortunately, most falls or blows to the head usually injure the scalp only, which is usually more frightening than threatening. An internal head injury is usually more serious because the skull serves as the protective helmet for the delicate brain.

Concussions are a type of internal head injury that causes the temporary loss of normal brain function. Repeated concussions can lead to permanent brain injury. Playing sports is one of the most common ways teens get concussions. The right protective gear, worn the right way, can help people avoid concussions. But even helmets don't prevent all concussions. If you get hit on the head while playing sports and think there's a chance you have a concussion, stop playing right away and let a coach or parent know what's going on.

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If the brain is a central computer that controls all the functions of the body, then the nervous system is like a network that relays messages back and forth to different parts of the body. Find out how they work in this Body Basics article.

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Why We Need It

Just about everyone knows that we can't live without blood. And that the blood in our bodies is pumped by the heart through a network of arteries and veins. But beyond those blood basics, what do you know about that red stuff beneath your skin?

Blood is essential for good health because the body depends on a steady supply of fuel and oxygen to reach its billions of cells. Even the heart couldn't survive without blood flowing through the vessels that bring nourishment to its muscular walls. Blood also carries carbon dioxide and other waste materials to the lungs, kidneys, and digestive system; from there they are removed from the body.

Without blood, we couldn't keep warm or cool off, we couldn't fight infections, and we couldn't get rid of our own waste products.

So how exactly does blood do these things? How is it made, and what's in it? How does blood clot? It's time to learn a little about the mysterious, life-sustaining fluid called blood.

What Is Blood and What Does It Do?

Two types of blood vessels carry blood throughout our bodies: The arteries carry oxygenated blood (blood that has received oxygen from the lungs) from the heart to the rest of the body. The blood then travels through the veins back to the heart and lungs, so it can receive more oxygen to be sent back to the body via the arteries. As the heart beats, you can feel blood traveling through the body at your pulse points - like the neck and the wrist - where large, blood-filled arteries run close to the surface of the skin.

The blood that flows through this network of veins and arteries is called whole blood. Whole blood contains three types of blood cells:

In babies and young children, blood cells are made in the bone marrow of many bones throughout the body. But as kids get older, blood cells are made mostly in the bone marrow of the vertebrae (the bones that make up the spine), ribs, pelvis, skull, sternum (the breastbone), and parts of the humerus (the upper arm bone) and femur (the thigh bone).

Blood cells travel through the circulatory system suspended in a yellowish fluid called plasma. Plasma is 90% water and contains nutrients, proteins, hormones, and waste products. Whole blood is a mixture of blood cells and plasma.

Red Blood Cells

Red blood cells (RBCs, and also called erythrocytes, pronounced: ih-RITH-ruh-sytes) are shaped like slightly indented, flattened disks. RBCs contain an iron-rich protein called hemoglobin (pronounced: HEE-muh-glow-bun). Blood gets its bright red color when the hemoglobin in RBCs picks up oxygen in the lungs. As the blood travels through the body, the hemoglobin releases oxygen to the tissues.

The body contains more RBCs than any other type of cell, and each has a life span of about 4 months. Each day, the body produces new RBCs to replace those that die or are lost from the body.

White Blood Cells

White blood cells (WBCs, and also called leukocytes, pronounced: LOO-kuh-sytes) are a key part of the body's immune system, which is the body's defense system against infection. WBCs can move in and out of the bloodstream to reach affected tissues. The blood contains far fewer white blood cells than red cells, although the body can increase production of WBCs to fight infection.

There are several types of white blood cells, and their life spans vary from a few days to months. New cells are constantly being formed in the bone marrow.

Several different parts of blood are involved in fighting infection. White blood cells called granulocytes (pronounced: GRAN-yuh-low-sytes) and lymphocytes (pronounced: LIM-fuh-sytes) travel along the walls of blood vessels. They fight germs such as bacteria and viruses and may also attempt to destroy cells that have become infected or have changed into cancer cells.

Certain types of WBCs produce antibodies, special proteins that recognize foreign materials and help the body destroy or neutralize them. Someone with an infection will often have a higher white cell count than when he or she is well because more WBCs are being produced or are entering the bloodstream to battle the infection. After the body has been challenged by some infections, lymphocytes "remember" how to make the specific antibodies that will quickly attack the same germ if it enters the body again.

Platelets

Platelets (also called thrombocytes, pronounced: THROM-buh-sytes) are tiny oval-shaped cells made in the bone marrow. They help in the clotting process. When a blood vessel breaks, platelets gather in the area and help seal off the leak. Platelets survive only about 9 days in the bloodstream and are constantly being replaced by new cells.

Blood also contains important proteins called clotting factors, which are critical to the clotting process. Although platelets alone can plug small blood vessel leaks and temporarily stop or slow bleeding, the action of clotting factors is needed to produce a strong, stable clot.

Platelets and clotting factors work together to form solid lumps to seal leaks, wounds, cuts, and scratches and to prevent bleeding inside and on the surfaces of our bodies. The process of clotting is like a puzzle with interlocking parts. When the last part is in place, the clot happens - but if only one piece is missing, the final pieces can't come together.

When large blood vessels are severed (or cut), the body may not be able to repair itself through clotting alone. In these cases, dressings and stitches are used to help control bleeding.

In addition to the cells and clotting factors, blood contains other important substances, such as nutrients from the food that has been processed by the digestive system. Blood also carries hormones released by the endocrine glands and carries them to the body parts that need them.

An interesting thing about blood is that blood cells and some of the special proteins blood contains can be replaced or supplemented by giving a person blood from someone else. This process is called a transfusion. In addition to receiving whole-blood transfusions, people can also receive transfusions of a particular component of blood that they need. For example, someone can receive only platelets, red blood cells, or a clotting factor. When people donate blood, the whole blood can be separated into its different parts and used in this way.

Things That Can Go Wrong With Blood

Most of the time, blood functions normally, but sometimes, blood disorders or diseases can cause problems. Diseases of the blood that commonly affect young people can involve any or all of the three types of blood cells (red blood cells, white blood cells, or platelets) or the proteins and chemicals in the plasma that are responsible for clotting.

Some of the diseases and conditions involving the blood include:

Diseases of the Red Blood Cells

The most common condition affecting the red blood cells of teens is anemia, a lower-than-normal number of red cells in the blood. Anemia is accompanied by a decrease in the amount of hemoglobin present in the blood. Anemia symptoms - such as pale skin, weakness, and a fast heart rate - happen because of the blood's reduced capacity for carrying oxygen. Causes of anemia can be grouped into two categories: anemia caused by insufficient RBC production and anemia caused by RBCs being destroyed too soon.

Anemia due to inadequate red blood cell production:
Several conditions can cause a reduced production of red blood cells, including:

Iron deficiency anemia. Iron deficiency anemia is the most common type of anemia and can affect people who have a diet low in iron or who've lost a lot of RBCs (and the iron they contain) through bleeding. Premature babies, infants with poor nutrition, menstruating teenage girls, and those with ongoing blood loss due to illnesses such as inflammatory bowel disease are especially likely to have iron deficiency anemia.

Anemia due to chronic disease. People with chronic diseases (such as cancer or human immunodeficiency virus infection [HIV]) often develop anemia as a complication of their illness.

Anemia due to kidney disease. The kidneys produce erythropoietin, a hormone that stimulates production of red cells in the bone marrow. Kidney disease can interfere with the production of this hormone.

Anemia due to unusually rapid red blood cell destruction:
When red blood cells are destroyed more quickly than normal by disease (this process is called hemolysis, pronounced: hih-MOL-uh-sus), the bone marrow will make up for it by increasing production of new red cells to take their place. But if RBCs are destroyed faster than they can be replaced, a person will develop anemia.
Several causes of increased red blood cell destruction can affect teens:

G6PD deficiency. G6PD is an enzyme that helps to protect RBCs from the destructive effects of certain chemicals found in foods and medications. When the enzyme is deficient, these chemicals can cause red cells to hemolyze, or burst. G6PD deficiency is a common hereditary disease among people of African, Mediterranean, and Southeast Asian descent.

Hereditary spherocytosis (pronounced: sfeer-o-sye-TOE-sus). In this inherited condition, RBCs are misshapen (like tiny spheres, instead of disks) and especially fragile because of a genetic problem with a protein in the structure of the red blood cell. This fragility causes the cells to be easily destroyed.

Autoimmune hemolytic anemia. Sometimes - because of disease or for no known reason - the body's immune system mistakenly attacks and destroys red blood cells.

Sickle cell disease. Most common in people of African descent, sickle cell disease (also called sickle cell anemia) is a hereditary disease that results in the production of abnormal hemoglobin. The RBCs become sickle shaped, cannot carry oxygen adequately, and are easily destroyed. The sickle-shaped cells also tend to abnormally stick together, causing obstruction of blood vessels. This blockage in the blood vessels can seriously damage organs and cause bouts of severe pain.

Diseases of the White Blood Cells

Neutropenia (pronounced: new-truh-PEE-nee-uh) occurs when there aren't enough of a certain type of white blood cell to protect the body against bacterial infections. People who take certain chemotherapy drugs to treat cancer may develop neutropenia. These people are at higher risk of bacterial infection.

Human immunodeficiency virus (HIV) attacks certain types of white blood cells (lymphocytes) that work to fight infection. Infection with the virus can result in AIDS (acquired immunodeficiency syndrome), leaving the body prone to infections and certain other diseases. Teens and adults can get the disease from sexual intercourse with an infected person or from sharing contaminated needles used for injecting drugs or tattoo ink.

Leukemias are cancers of the cells that produce white blood cells. These cancers include acute myeloid leukemia (AML), chronic myeloid leukemia (CML), acute lymphocytic leukemia (ALL), and chronic lymphocytic leukemia (CLL). The most common types of leukemia affecting kids are ALL and AML. Scientists have made great advances in treating several types of childhood leukemia, most notably certain types of ALL.

Diseases of Platelets

Thrombocytopenia (pronounced: throm-buh-syte-uh-PEE-nee-uh), or a lower than normal number of platelets, is usually diagnosed because a person has abnormal bruising or bleeding. Thrombocytopenia can happen when someone takes certain drugs or develops infections or leukemia or when the body uses up too many platelets. Idiopathic thrombocytopenic purpura (ITP) is a condition in which the immune system attacks and destroys platelets.

Diseases of the Clotting System

The body's clotting system depends on platelets as well as many clotting factors and other blood components. If a hereditary defect affects any of these components, a person can have a bleeding disorder. Common bleeding disorders include:

Hemophilia (pronounced: hee-muh-FIL-ee-uh), an inherited condition that almost exclusively affects guys, involves a lack of particular clotting factors in the blood. People with severe hemophilia are at risk for excessive bleeding and bruising after dental work, surgery, and trauma. They may experience episodes of life-threatening internal bleeding, even if they haven't been injured.

von Willebrand disease, the most common hereditary bleeding disorder, also involves a clotting-factor deficiency. It affects both guys and girls.

Other causes of clotting problems include chronic liver disease (clotting factors are produced in the liver) and vitamin K deficiency (the vitamin is necessary for the production of certain clotting factors).

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Without blood, our organs couldn't get the oxygen and nutrients they need, we couldn't keep warm or cool off, we couldn't fight infections, and we couldn't get rid of our own waste products. Find out about the mysterious, life-sustaining fluid called blood.

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Our bodies produce several kinds of wastes, including sweat, carbon dioxide gas, feces (also known as stool or poop), and urine (pee).

These wastes exit the body in different ways: Sweat is released through pores (tiny holes) in the skin. Water vapor and carbon dioxide are exhaled (breathed out) from the lungs. And undigested food materials are formed into feces in the intestines and excreted from the body as solid waste in bowel movements.

Urine, which is produced by the kidneys, contains the by-products of our body's metabolism - salts, toxins, and water - that end up in our blood. The kidneys and urinary tract (which includes the ureters, bladder, and urethra) filter and eliminate these waste substances from our blood. Without the kidneys, waste products and other toxins would soon build up in the blood to dangerous levels.

In addition to eliminating wastes, the kidneys and urinary tract also regulate many important body functions. For example, the kidneys monitor and maintain the body's balance of water, ensuring that our tissues receive enough water to function properly and be healthy.

When you're asked to give a urine sample during a doctor's visit, the results reveal how well your two kidneys are working. For example, blood, protein, or white blood cells in the urine may indicate injury, infection, or inflammation of the kidneys, and glucose in the urine might be a sign of diabetes.

What the Kidneys and Urinary Tract Do

Although the two kidneys work together to perform many vital functions, people can live a normal, healthy life with just one kidney. In fact, some people are born with just one of these bean-shaped organs. If one kidney is removed, the remaining one will enlarge within a few months to take over the role of filtering blood on its own.

Every minute, more than 1 quart (about 1 liter) of blood passes through the kidneys, adding up to about 425 gallons (1,609 liters) of blood each day. About a quarter of our blood is in our kidneys at any one time, and the kidneys cleanse all of the blood in the body about every 50 minutes.

In addition to filtering blood, producing urine, and ensuring that body tissues receive enough water, the kidneys also regulate blood pressure and the level of vital salts in the blood. By regulating salt levels through production of an enzyme called renin (as well as other substances), the kidneys ensure that blood pressure is regulated.

The kidneys also secrete a hormone called erythropoietin (pronounced: eh-rith-ro-PO-uh-ten), which stimulates and controls the body's red blood cell production (red blood cells carry oxygen throughout the body). In addition, the kidneys help regulate the acid-base balance (or the pH) of the blood and body fluids, which is necessary for the body to function normally.

Where They Are and How They Work

The kidneys are located just under the ribcage in the back, one on each side. The right kidney is located below the liver, so it's a little lower than the left one. Each adult kidney is about 5 inches (127 millimeters) long, 3 inches (76 millimeters) wide, and 1 inch (25 millimeters) thick. Each has an outer layer called the cortex, which contains the filtering units.

The center part of the kidney, the medulla (pronounced: meh-DUH-luh) has 10 to 15 fan-shaped structures called pyramids. These drain urine into cup-shaped tubes called calyxes (pronounced: KAY-luh-seez). A layer of fat surrounds the kidneys to cushion and help hold them in place.

Here's how the kidneys filter blood: Blood travels to each kidney through the renal artery, which enters the kidney at the hilus (pronounced: HY-luss), the indentation in middle of the kidney that gives it its bean shape. As it enters the cortex, the artery branches out; each branch envelops the nephrons (pronounced: NEH-fronz) - 1 million tiny filtering units in each kidney that remove the harmful substances from the blood.

Each of the nephrons contains a filter called the glomerulus (pronounced: gluh-MER-yuh-lus), which contains a network of tiny blood vessels known as capillaries. The fluid filtered from the blood by the glomerulus then travels down a tiny tube-like structure called a tubule (pronounced: TU-byool) that adjusts the level of salts, water, and wastes that are excreted in the urine.

Filtered blood leaves the kidney through the renal vein and flows back to the heart.

The continuous blood supply entering and leaving the kidneys gives the kidneys their dark red color. While the blood is in the kidneys, water and some of the other blood components (such as acids, glucose, and other nutrients) are reabsorbed back into the bloodstream. Left behind is urine. Urine is a concentrated solution of waste material containing water, urea (pronounced: yoo-REE-uh, a waste product that forms when proteins are broken down), salts, amino acids, byproducts of bile from the liver, ammonia, and any substances that cannot be reabsorbed into the blood. Urine also contains urochrome (pronounced: YUR-uh-krome), a pigmented blood product that gives urine its yellowish color.

The renal pelvis, located near the hilus, collects the urine flowing from the calyxes. From there, urine leaves the kidneys through the ureters (pronounced: YUR-uh-ters), tubes that carry the urine to the bladder (a muscular sac in the lower abdomen).

The bladder expands as it fills and can hold about half a liter (2 cups) of urine at any given time (an average adult produces about 1½ liters, or 6 cups, of urine per day). Producing too much or not enough urine may be a sign of illness.

When the bladder is full, nerve endings in its wall send impulses to the brain. When a person is ready to pee, the bladder walls contract and the sphincter (pronounced: SFINK-ter, a ring-like muscle that guards the exit from the bladder to the urethra) relaxes. The urine leaves the bladder and goes out of the body through the urethra (pronounced: yoo-REE-thruh), another tube-like structure. The male urethra ends at the tip of the penis; the female urethra ends just above the vaginal opening.

Things That Can Go Wrong

Like other systems in the body, the entire urinary tract is subject to diseases and disorders. In kids and teens, the more common kidney and urinary tract problems include:

Congenital problems of the urinary tract. As a fetus develops in the womb, any part of the urinary tract can grow to an abnormal size or in an abnormal shape or position. One of the more common congenital abnormalities (meaning abnormalities that exist at birth) is duplication of the ureters, in which a kidney has two ureters instead of one. This defect occurs in about one out of every 125 births and can cause the kidney to develop problems with infection and scarring over time.

Another congenital problem is horseshoe kidney, where the two kidneys are fused (connected) into one arched kidney that usually functions normally, but is more prone to develop problems later in life. This condition is found in 1 out of every 500 births.

Glomerulonephritis is an inflammation of the glomeruli, the parts of the filtering units (nephrons) of the kidney that contain a network of capillaries (tiny blood vessels). The most common form of this condition is post-streptococcal glomerulonephritis, which usually occurs in young children.

Hypertension (high blood pressure) can result when the kidneys are impaired by disease. They also produce the enzyme renin that, along with other substances, controls the constriction of muscle cells in the walls of the blood vessels, which affects a person's blood pressure.

Kidney (renal) failure can be acute (which means sudden) or chronic (happening over time and usually long lasting or permanent). In either form of kidney failure, the kidneys slow down or stop filtering blood effectively, causing waste products and toxic substances to build up in the blood.

Acute kidney failure may be due to bacterial infection, injury, shock, heart failure, poisoning, or drug overdose. Treatment includes correcting the problem that led to the failure and sometimes requires surgery or dialysis (which involves using a machine or other artificial device to remove the excess salts and water and other wastes from the body when the kidneys aren't able to perform this function).

Chronic kidney failure involves a deterioration of kidney function over time. In kids and teens, it can result from acute kidney failure that fails to improve, birth defects of the kidney, chronic kidney diseases, or chronic severe high blood pressure. If diagnosed early, chronic kidney failure can be treated, but usually not reversed, and may require a kidney transplant at some point in the future.

Kidney stones (or nephrolithiasis) result from the buildup of crystallized salts and minerals such as calcium in the urinary tract. Stones (also called calculi) can also form after an infection. If kidney stones are large enough to block the kidney or ureter, they can cause severe abdominal pain. But the stones usually pass through the urinary tract on their own. In some cases, they may need to be removed surgically.

Nephritis is any inflammation of the kidney. It can be caused by infection, an autoimmune disease (such as lupus), or it may be idiopathic (which means the exact cause may not be known or understood). Nephritis is generally detected by high levels of protein and blood in the urine.

Nephrotic syndrome is a type of kidney disease that leads to loss of protein in the urine and swelling of the face (often the eyes) or body (often around the genitals). It is most common in children younger than 6 years old and is more common in boys. Nephrotic syndrome is often treated with steroids.

Urinary tract infection (UTI) is infection of a part of or throughout the urinary tract, usually caused by bacteria. UTIs are most commonly caused by intestinal bacteria, such as E. coli, that are normally found in feces. These bacteria can cause infections anywhere in the urinary tract, including the kidneys. Most UTIs occur in the lower urinary tract, especially in the bladder and urethra. Teen girls are more likely to develop UTIs than boys; one of the reasons this may be is because girls have shorter urethras than boys.

Vesicoureteral reflux (VUR) is a condition in which urine abnormally flows backward (or refluxes) from the bladder into the ureters. It may even reach the kidneys, where infection and scarring can occur over time. VUR occurs in 1% of children and tends to run in families. It's often detected after a young infant or child has a first UTI.

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Our bodies produce several kinds of wastes, including sweat, carbon dioxide gas, feces (also known as stool or poop), and urine (pee). These wastes exit the body in different ways: Sweat is released through pores (tiny holes) in the skin. Water vapor and carbon dioxide are exhaled (breathed out) from the lungs.

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The Brain for Kids | Learn cool facts about the human brain

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No matter what we're doing - even when we're sleeping - our brains depend on glucose to function. Glucose is a sugar that comes from the foods we eat, and it's also formed and stored inside the body. It's the main source of energy for the cells of our body, and it's carried to each cell through the bloodstream.

The blood glucose level is the amount of glucose in the blood. When blood glucose levels (also called blood sugar levels) drop too low, it's called hypoglycemia (pronounced: hi-po-gly-SEE-me-uh). Very low blood sugar levels can cause severe symptoms that need to be treated right away.

Low Blood Sugar Levels in Diabetes

People with diabetes can have low blood sugar levels because of the medicines they have to take to manage their diabetes. They may need a hormone called insulin or diabetes pills (or both) to help their bodies use the sugar in their blood. These medicines help take the sugar out of the blood and get it into the body's cells, which makes the level of sugar in the blood go down. But sometimes it's a tricky balancing act and blood sugar levels can get too low.

People with diabetes need to keep their blood sugars from getting too high or too low. Part of keeping blood sugar levels in a healthy range is having good timing, and balancing when and what they eat and when they exercise with when they take medicines.

Some things that can make low blood sugar levels more likely to happen are:

skipping meals and snacks

not eating enough food at a meal or snack

exercising longer or harder than usual without eating some extra food

getting too much insulin

not timing the insulin doses properly with meals, snacks, and exercise

Also, certain things may increase how quickly insulin gets absorbed into the bloodstream and can make hypoglycemia more likely to occur. For example, taking a hot shower or bath right after having an insulin injection increases blood flow through the blood vessels in the skin, which can cause the insulin to be absorbed more quickly than usual.

Other things that can cause insulin to be absorbed more quickly include injecting the shot into a muscle instead of the fatty layer under the skin and injecting the insulin into a part of the body most used in a particular sport (like injecting the leg right before soccer practice). All of these situations increase the chances that a person may get hypoglycemia.

Signs and Symptoms

Different people may feel low blood sugar levels differently. People with low blood sugar may:

feel hungry or have "hunger pains" in their stomach

feel shaky or like they're trembling

have a rapid heart rate

feel sweaty or have cold, clammy skin

have pale, gray skin color

have a headache

feel moody, cranky, or irritable

feel drowsy, weak, or dizzy

be unsteady or stagger when walking

have blurred or double vision

feel confused

have seizures or convulsions

lose consciousness (pass out)

If you have diabetes, try to remember how your body reacts when your blood sugar levels are low. It may help you figure out when you're having a low blood sugar level more quickly the next time.

Checking for Low Blood Sugar Levels

The warning signs of hypoglycemia are the body's natural response to low blood sugar levels. When blood sugar levels fall too low, the body releases the hormone adrenaline, which helps get stored glucose into the bloodstream quickly. Becoming pale, sweating, shaking, and having an increased heart rate are early signs of the adrenaline being released. If the hypoglycemia isn't treated, more severe symptoms may develop, including drowsiness, confusion, seizures, and loss of consciousness.

The only way to know for sure if you're having a low blood sugar level is to test. Blood sugar levels can be tested with a glucose meter, which is a computerized device that measures and displays the amount of glucose in a blood sample. However, if you can't quickly check your blood sugar level, it's important to treat yourself for hypoglycemia immediately to prevent symptoms from getting worse.

Sometimes a person with diabetes may have symptoms of low blood sugar levels, but blood sugar levels are not actually low. This is a called a false reaction. The hormone adrenaline (mentioned above) is not just released when blood sugar drops too low - it's also released when blood sugar levels fall quickly when they're too high. If you're having a false reaction, you might actually have blood sugar levels in a healthy range but feel as if you have low blood sugar. Testing blood sugar levels before treating yourself for hypoglycemia can help you figure out if you're having a false reaction.

Some people with diabetes don't actually notice the typical signs of low blood sugar levels. For them it's even more important to check blood glucose levels often and take extra precautions to prevent low blood sugar (see our prevention tips below). If you're having trouble feeling the symptoms of low blood sugar, let your diabetes health care team know.

Treating Low Blood Sugar Levels

Your diabetes health care team will give you guidelines for treating low blood sugar levels, depending on your symptoms. If you can, try to test your blood sugar levels to make sure that your symptoms are because of hypoglycemia. If you can't test blood sugar immediately, don't delay in treating your symptoms - you can always check your blood sugar after you've taken steps to get your blood sugar back up into the normal range.

When blood sugar levels are low, the goal is to get them back up quickly. To do that, you should take in sugar or sugary foods, which raise the blood sugar level quickly. Your health care team might suggest that you:

Eat, drink, or take something that contains sugar that can get into the blood quickly. Your doctor may tell you to have really sugary foods or drinks (like regular soda, orange juice, or cake frosting) or might give you glucose tablets or gel to take - all of these can help to raise your blood sugar level fast, which is what you need to do when it's low.

Wait about 10 minutes to let the sugar work.

Recheck your blood sugar level with a glucose meter to see if blood sugar levels are back to normal.

Get a glucagon shot (see below), if your symptoms are severe or get worse after you eat, drink, or take glucose.

Sometimes, blood sugar levels can get so low that you may not be awake enough to eat or drink something to get them back up. When this happens, you may need a glucagon shot.

Glucagon (pronounced: GLOO-kuh-gon) is a hormone that helps raise blood sugar levels quickly. Your parents, teachers, and coaches should all know how to give glucagon shots in case of a low blood sugar emergency or at least know to call 911. Your doctor can prescribe a glucagon kit, which should be kept in a place where the people who are close to you can easily find it.

Also, you should always wear a medical identification bracelet or necklace and/or carry an ID that says you have diabetes. Then, if you are not feeling well, whoever's helping you - even if the person doesn't know you - will know to call for medical help. This medical identification also can also include your doctor's phone number or a parent's phone number.

Preventing Low Blood Sugar Levels

By knowing what causes low blood sugar levels and being prepared, you can lessen the chance that you'll have low blood sugar levels. But no matter how well they take care of themselves, people with diabetes will sometimes have low blood sugar levels.

Here are some additional tips to help you avoid low blood sugar levels:

Eat all your meals and snacks on time and try not to skip any.

Take the right amount of insulin.

If you exercise longer or harder than usual, have an extra snack.

Don't take a hot bath or shower right after an insulin shot.

Stick to your diabetes management plan.

Check your blood sugar levels regularly, so you can tell if your blood sugars are running too low and your treatment plan needs adjustment.

Carry something containing sugar with you at all times and take it right away if you have symptoms. Don't wait to see if the symptoms will go away - they may get worse!

Alcohol and drugs can cause major problems with your blood sugar levels, so avoiding them is another way to prevent diabetes problems. Drinking can be particularly dangerous - even deadly - for people with diabetes because it messes up the body's ability to keep blood glucose in a normal range. This can cause a very rapid drop in blood glucose in people with diabetes. Drug or alcohol use is also dangerous because it may impair someone's ability to sense low blood sugar levels.

You should also check your blood sugar - and treat hypoglycemia, if needed - before you drive. Make sure you have some form of sugar handy in the car to use if you get low at any time while driving. If you do feel low, immediately pull over safely to the side of the road and treat your hypoglycemia - and don't start to drive again until your symptoms are gone. You also should test your blood sugar before doing other activities during which a low blood sugar reaction could be especially dangerous, such as skiing, swimming, or rock climbing.

Learning how to recognize the signs of low blood sugar levels and get them back to normal is an important part of caring for diabetes. Keeping track of your blood sugar levels and recording lows when they occur will help you and your diabetes health care team keep your blood sugar levels in a healthy range.

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No matter what we're doing - even when we're sleeping - our brains depend on glucose to function. Glucose is a sugar that comes from the foods we eat, and it's also formed and stored inside the body. It's the main source of energy for the cells of our body, and it's carried to each cell through the bloodstream.

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The purpose of homeostasis is to maintain a normal balance within the body regarding its temperature, salt concentration, water concentration, and food intake. The human body functions normally with a narrow range of variation for each of these factors. The body has ways of detecting changing levels of these factors ...

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Regulation of glucose in the body is done autonomically and constantly throughout each minute of the day. Normal BG levels should be between 60 and 140 mg/dL in order to supply cells of the body with its required energy. Brain cells don't require insulin to drive glucose into neurons; however, there must still be normal amounts available. Too little glucose, called hypoglycemia, starves cells, and too much glucose ( hyperglycemia) creates a sticky, paralyzing effect on cells. Euglycemia, or blood sugar within the normal range, is naturally ideal for the body's functions. A delicate balance between hormones of the pancreas, intestines, brain, and even adrenals is required to maintain normal BG levels.

Fuels of the Body

To appreciate the pathology of diabetes, it is important to understand how the body normally uses food for energy. Glucose, fats, and proteins are the foods that fuel the body. Knowing how the pancreatic, digestive, and intestinal hormones are involved in food metabolism can help you understand normal physiology and how problems develop with diabetes.

Throughout the body, cells use glucose as a source of immediate energy. To keep the body running smoothly, a continuous concentration of 60 to 100 mg/dL of glucose in blood plasma is needed. During exercise or stress the body needs a higher concentration because muscles require glucose for energy (Basu et al., 2009). Of the three fuels for the body, glucose is preferred because it produces both energy and water through the Krebs cycle and aerobic metabolism. The body can also use protein and fat; however, their breakdown creates ketoacids, making the body acidic, which is not its optimal state. Excess of ketoacids can produce metabolic acidosis.

Functioning body tissues continuously absorb glucose from the bloodstream. For people who do not have diabetes, a meal of carbohydrates replenishes the circulating blood glucose about 10 minutes after eating and continues until about 2 hours after eating. A first-phase release of insulin occurs about 5 minutes after a meal and a second phase begins at about 20 minutes. Because the duration of insulin's effect is only about 2 hours, taking a 2-hour postprandial (after meal) BG shows how well insulin was released and used by the body. The food is broken down into small components including glucose and is then absorbed through the intestines into the bloodstream. Glucose (potential energy) that is not immediately used is stored by the body as glycogen in the muscles, liver, and fat.

Your body is designed to survive and so it stores energy efficiently, as fat. Most Americans have excess fat because they replenish the glucose stores by eating before any fat needs to be broken down.

When blood glucose levels fall after 2 hours, the liver replenishes the circulating blood glucose by releasing glycogen (stored glucose). Glycogen is a polysaccharide, made and stored primarily in the cells of the liver. Glycogen provides an energy reserve that can be quickly mobilized to meet a sudden need for glucose.

Hormones of the Pancreas

Regulation of blood glucose is largely done through the endocrine hormones of the pancreas, a beautiful balance of hormones achieved through a negative feedback loop. The main hormones of the pancreas that affect blood glucose include insulin, glucagon, somatostatin, and amylin.

Insulin (formed in pancreatic beta cells) lowers BG levels, whereas glucagon (from pancreatic alpha cells) elevates BG levels.

Somatostatin is formed in the delta cells of the pancreas and acts as the "pancreatic policeman," balancing insulin and glucagon. It helps the pancreas alternate in turning on or turning off each opposing hormone.

Amylin is a hormone, made in a 1:100 ratio with insulin, that helps increase satiety, or satisfaction and state of fullness from a meal, to prevent overeating. It also helps slow the stomach contents from emptying too quickly, to avoid a quick spike in BG levels.

As a meal containing carbohydrates is eaten and digested, BG levels rise, and the pancreas turns on insulin production and turns off glucagon production. Glucose from the bloodstream enters liver cells, stimulating the action of several enzymes that convert the glucose to chains of glycogen-so long as both insulin and glucose remain plentiful. In this postprandial or "fed" state, the liver takes in more glucose from the blood than it releases. After a meal has been digested and BG levels begin to fall, insulin secretion drops and glycogen synthesis stops. When it is needed for energy, the liver breaks down glycogen and converts it to glucose for easy transport through the bloodstream to the cells of the body (Wikipedia, 2012a).

In a healthy liver, up to 10% of its total volume is used for glycogen stores. Skeletal muscle cells store about 1% of glycogen. The liver converts glycogen back to glucose when it is needed for energy and regulates the amount of glucose circulating between meals. Your liver is amazing in that it knows how much to store and keep, or break down and release, to maintain ideal plasma glucose levels. Imitation of this process is the goal of insulin therapy when glucose levels are managed externally. Basal-bolus dosing is used as clinicians attempt to replicate this normal cycle.

While a healthy body requires a minimum concentration of circulating glucose (60-100 mg/dl), high chronic concentrations cause health problems and are toxic:

Acutely: Hyperglycemia of >300 mg/dl causes polyuria, resulting in dehydration. Profound hyperglycemia (>500 mg/dl) leads to confusion, cerebral edema, coma, and, eventually, death (Ferrante, 2007).

Chronically: Hyperglycemia that averages more than 120 to 130 mg/dl gradually damages tissues throughout the body and makes a person more susceptible to infections. The glucose becomes syrupy in the bloodstream, intoxicating cells and competing with life-giving oxygen.

When blood glucose concentrations are low, the liver is signaled to add glucose to the circulation.

When blood glucose concentrations are high, the liver and the skeletal muscles are signaled to remove glucose from the circulation.

The concentration of glucose in the blood is determined by the balance between the rate of glucose entering and the rate of glucose leaving the circulation. These signals are delivered throughout the body by two pancreatic hormones, insulin and glucagon (Maitra, 2009). Optimal health requires that:

Test Your Knowledge

1. A hormone produced in the pancreas.

2. A polysaccharide that is stored in the liver.

3. Produced in the striated muscles when exercising.

4. An energy reserve that is slow to mobilize in an emergency.

Glycogen is:

Apply Your Knowledge

If you want to lose weight, what fuel would you decrease in your diet and what fuels would you increase?

Online Resource

Video [2:36]

https://www.youtube.com/watch?v=OlHez8gwMgw

Answer: B

The Role of Insulin

Insulin is a peptide hormone made in the beta cells of the pancreas that is central to regulating carbohydrate metabolism in the body (Wikipedia, 2016). After a meal, insulin is secreted into the bloodstream. When it reaches insulin-sensitive cells-liver cells, fat cells, and striated muscle-insulin stimulates them to take up and metabolize glucose. Insulin synthesis and release from beta cells is stimulated by rising concentrations of blood glucose. Insulin has a range of effects that can be categorized as anabolic, or growth-promoting.

Test Your Knowledge

1. Is only available by injection or orally to treat T2DM.

2. Is a hormone that acts on the liver to convert excess glucose into glycogen.

3. Inhibits the uptake and use of glucose by skeletal muscles.

4. Is manufactured and secreted by the alpha cells of the pancreas.

Insulin:

Apply Your Knowledge

How would you explain the function of insulin to your patient with diabetes? What does it turn on and what does it turn off?

Answer: B

The Role of Glucagon

Glucagon, a peptide hormone secreted by the pancreas, raises blood glucose levels. Its effect is opposite to insulin, which lowers blood glucose levels. When it reaches the liver, glucagon stimulates glycolysis, the breakdown of glycogen, and the export of glucose into the circulation. In these ways, the effects of glucagon are catabolic, breaking down cells-the opposite of insulin's anabolic effects (Drucker, 2008).

The pancreas releases glucagon when glucose levels fall too low. Glucagon causes the liver to convert stored glycogen into glucose, which is released into the bloodstream. High BG levels stimulate the release of insulin. Insulin allows glucose to be taken up and used by insulin-dependent tissues, such as muscle cells. Glucagon and insulin work together automatically as a negative feedback system to keeps BG levels stable.

Glucagon is a powerful regulator of BG levels, and glucagon injections can be used to correct severe hypoglycemia. Glucose taken orally or parenterally can elevate plasma glucose levels within minutes, but exogenous glucagon injections are not glucose; a glucagon injection takes approximately 10 to 20 minutes to be absorbed by muscle cells into the bloodstream and circulated to the liver, there to trigger the breakdown of stored glycogen.

People with type 2 diabetes have excess glucagon secretion, which is a contributor to the chronic hyperglycemia of type 2 diabetes. The amazing balance of these two opposing hormones of glucagon and insulin is maintained by another pancreatic hormone called somatostatin, created in the delta cells. It truly is the great pancreatic policeman as it works to keep them balanced.

After you've eaten, the concentration of glucose in your blood rises. When it goes too high the pancreas releases insulin into the bloodstream. This insulin stimulates the liver to convert the blood glucose into glycogen for storage. If the blood sugar goes too low, the pancreas release glucagon, which causes the liver to turn stored glycogen back into glucose and release it into the blood. Source: Google Images.

Test Your Knowledge

1. Is a peptide hormone that is stored in the pancreas.

2. Is used to treat hyperglycemia by increasing the uptake of glucose in muscles.

3. Is a hormone that acts on the liver to convert glycogen back into glucose.

4. Stimulates the production of insulin.

Glucagon:

Apply Your Knowledge

How is glucagon available by injection?

Answer: C

The Role of Amylin

Amylin is a peptide hormone that is secreted with insulin from the beta cells of the pancreas in a 1:100 ratio. Amylin inhibits glucagon secretion and therefore helps lower BG levels. It also delays gastric emptying after a meal to decrease a sudden spike in plasma BG levels; further, it increases brain satiety (satisfaction) to help someone feel full after a meal. This is a powerful hormone in what has been called the brain-meal connection.

People with type 1 diabetes have neither insulin nor amylin production. People with type 2 diabetes seem to make adequate amounts of amylin but often have problems with the intestinal incretin hormones that also regulate BG and satiety, causing them to feel hungry constantly. Amylin analogues have been created and are available through various pharmaceutical companies as a solution for disorders of this hormone.

The Role of Incretins

Incretins are glucagon-like peptides (hormones) made in cells of the small intestine and secreted into the circulation in response to food intake (Cernea & Raz, 2011). Incretins go to work even before blood glucose levels rise following a meal. They also slow the rate of absorption of nutrients into the bloodstream by reducing gastric emptying, and they may also help decrease food intake by increasing satiety.

People with type 2 diabetes have lower than normal levels of incretins, which may partly explain why many people with diabetes state they constantly feel hungry. After research showed that BG levels are influenced by intestinal hormones in addition to insulin and glucagon, incretin mimetics became a new class of medications to help balance BG levels in people who have diabetes.

Two types of incretin hormones are GLP-1 (glucagon-like peptide) and GIP (gastric inhibitory polypeptide). Each peptide is broken down by naturally occurring enzymes called DDP-4, (dipeptidyl peptidase-4).

Exenatide (Byetta), an injectable anti-diabetes drug, is categorized as a glucagon-like peptide (GLP-1) and directly mimics the glucose-lowering effects of natural incretins upon oral ingestion of carbohydrates. The administration of exenatide helps to reduce BG levels by mimicking the incretins. Both long- and short-acting forms of GLP-1 agents are currently being used.

Stimulate insulin secretion

Suppress glucagon secretion

Slow gastric emptying to prevent spike in BG levels

Increase satiety after a meal to signal to the brain to stop eating

The functions of incretins are as follows:

Incretins are deactivated quickly by enzymes called DPP-4, in the bloodstream and on the surface of endothelial cells; thus, the glucose-lowering effects of incretins last only a few minutes (Drucker & Nauck, 2006). A new class of medications, called DPP4 inhibitors, block this enzyme from breaking down incretins, thereby prolonging the positive incretin effects of glucose suppression. An additional class of medications called dipeptidyl peptidase-4 (DPP-4 inhibitors-note hyphen), are available in the form of several orally administered products. These agents will be discussed more fully later.

Source: Wikimedia Commons.

Poor Regulation of Blood Glucose

People with diabetes have frequent and persistent hyperglycemia, which is the hallmark sign of diabetes. For people with type 1 diabetes, who make no insulin, glucose remains in the blood plasma without the needed BG-lowering effect of insulin. Another contributor to this chronic hyperglycemia is the liver. When a person with diabetes is fasting, the liver secretes too much glucose, and it continues to secrete glucose even after the blood level reaches a normal range (Basu et al., 2009).

Another contributor to chronic hyperglycemia in diabetes is skeletal muscle. After a meal, the muscles in a person with diabetes take up too little glucose, leaving blood glucose levels elevated for extended periods (Basu et al., 2009).

The metabolic malfunctioning of the liver and skeletal muscles in type 2 diabetes results from a combination of insulin resistance, beta cell dysfunction, excess glucagon, and decreased incretins. These problems develop progressively.

Early in the disease the existing insulin resistance can be counteracted by excess insulin secretion from the beta cells of the pancreas, which try to address the hyperglycemia. The hyperglycemia caused by insulin resistance is met by hyperinsulinemia. Eventually, however, the beta cells begin to fail. Hyperglycemia can no longer be matched by excess insulin secretion, and the person develops clinical diabetes (Maitra, 2009).

Test Your Knowledge

1. Insulin sensitivity, which is an over-reaction of cells to insulin.

2. No beta cells in their pancreas and no circulating insulin at all.

3. Chronic hypoglycemia.

4. Insulin resistance, which is a decreased response of cells to insulin.

People with type 2 diabetes have:

Apply Your Knowledge

How would you explain to your patient what lifestyle behaviors create insulin resistance?

Answer: D

The Problem of Insulin Resistance

In type 2 diabetes, many patients have body cells with a decreased response to insulin known as insulin resistance. This means that, for the same amount of circulating insulin, the skeletal muscles, liver, and adipose tissue take up and metabolize less glucose than normal. Being less sensitive to insulin, the liver does not react to the usual signal of insulin, so the liver manufactures and secretes more glucose than is needed (Huether & McCance, 2012).

Insulin resistance can develop in a person over many years before the appearance of type 2 diabetes. People inherit a propensity for developing insulin resistance, and other health problems can worsen the condition. For example, when skeletal muscle cells are bathed in excess free fatty acids, the cells preferentially use the fat for metabolism while taking up and using less glucose than normal, even when there is plenty of insulin available. In this way, high levels of blood lipids decrease the effectiveness of insulin; thus, high cholesterol and body fat, overweight and obesity increase insulin resistance.

Physical inactivity has a similar effect. Sedentary overweight and obese people accumulate triglycerides in their muscle cells. This causes the cells to use fat rather than glucose to produce muscular energy. Physical inactivity and obesity increase insulin resistance (Monnier et al., 2009).

The Problem of Beta Cell Dysfunction

For people with type 1 diabetes, no insulin is produced due to beta cells destruction. Research shows this is an autoimmune response gone awry, attacking the body's own cells. Triggers of that autoimmune response have been linked to milk, vaccines, environmental triggers, viruses, and bacteria.

For people with type 2 diabetes, a progressive decrease in the concentration of insulin in the blood develops. The continuously decreasing availability of insulin in type 2 diabetes is the direct result of a progressive worsening of the beta cells' ability to produce enough insulin when it is needed (Huether & McCance, 2012).

Not only do the beta cells release less insulin as type 2 diabetes progresses, they also release it slowly and in a different pattern than that of healthy people (Monnier et al., 2009). Without sufficient insulin, the glucose-absorbing tissues-mainly skeletal muscle, liver, and adipose tissue-do not efficiently clear excess glucose from the bloodstream, and the person suffers the damaging effects of toxic chronic hyperglycemia.

At first, the beta cells manage to manufacture and release sufficient insulin to compensate for the higher demands caused by insulin resistance. Eventually, however, the defective beta cells decrease their insulin production and can no longer meet the increased demand. At this point, the person has persistent hyperglycemia. In type 2 diabetes, beta cells seemingly exhaust their capacity to adapt to the long-term demands of peripheral insulin resistance (Huether & McCance, 2012).

A downward spiral follows. The hyperglycemia and hyperinsulinemia caused by the over-stressed beta cells create their own failure. In type 2 diabetes, the continual loss of functioning beta cells shows up as a progressive hyperglycemia.

Test Your Knowledge

1. Beta cells in the pancreas cannot compensate for insulin resistance.

2. The pancreas is attacked by the body's immune system, resulting in pancreatitis.

3. The liver becomes overly sensitive to insulin.

4. Glucose cannot be used as fuel by any cells in the body.

In type 2 diabetes:

Apply Your Knowledge

How would you explain insulin resistance differently to someone with type 1 diabetes and someone with type 2 diabetes?

Online Resource

Video [11:46]

https://www.youtube.com/watch?v=iTjDi2ZO0n8

Answer: A

Cell Damage in DM

Together, insulin resistance and decreased insulin secretion lead to hyperglycemia, which causes most of the health problems in diabetes. The acute health problems-diabetic ketoacidosis and hyperosmolar hyperglycemic state-are metabolic disorders that are directly caused by an overload of glucose. In comparison, the chronic health problems-eye, heart, kidney, nerve, and wound problems-are tissue injury, a slow and progressive cellular damage caused by feeding tissues too much glucose (ADA, 2015).

Over time, excess glucose attaches to proteins in a process called glycosylation. For example, glycosylated hemoglobin (HbA1c), is the laboratory measure to monitor average glycemic levels. Glycosylated proteins trigger inflammatory reactions, which injure the lining of blood vessels. In addition, glycosylated proteins stick together on the basement membranes of capillaries, thickening the endothelial layers and disrupting their normal function.

Excess intracellular glucose activates an enzyme called protein kinase C, which encourages the growth of unnecessary blood vessels, leads to blood vessel constriction, thickens basement membranes, and releases pro-inflammatory molecules such as C-reactive protein and homocysteine.

Excess intracellular glucose reduces the effectiveness of the intracellular activities that protect against oxidants and oxidative stress. This leads to oxidative damage, especially in neurons. (Maitra, 2009)

Hyperglycemic damage to tissues is the result of glucose toxicity. There are at least three distinct routes by which excess glucose injures tissues:

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Regulation of glucose in the body is done autonomically and constantly throughout each minute of the day. Normal BG levels should be between 60 and 140 mg/dL in order to supply cells of the body with its required energy. Brain cells don't require insulin to drive glucose into neurons; however, there must still be normal amounts available.

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It's going to be hot over there.

At this summer's Olympic Games in Athens, temperatures will soar into the 90s. The air will be humid, sticky, and laden with pollution. It'll be hard to breathe, hard to stay cool, hard to keep hydrated. And that's just what the fans will have to face. Imagine trying to race a bicycle or run a marathon under such harsh conditions.

For months, elite athletes have been preparing for the heat in Athens. Their coaches hope that a fine-tuned balance of training techniques and technology will help them perform as efficiently as possible without overheating.

Some athletes have practiced their sport in heated rooms. Many will wear clothes, helmets, and other gear that's specially designed to keep them cool. They'll drink fluids before, during, and after their events.

The games run from Aug. 13 to Aug. 29, 2004.

Warming up

Exercising in any kind of weather warms you up. That's because muscles release heat as they work. Think about how hot you get when you walk up a steep hill or run around for a while.

For every 15 to 30 minutes of consistent exercise, an athlete's core body temperature rises about half a degree, says Mark Verstegen. He's founder and director of Athletes' Performance, a training facility in Tempe, Ariz.

Such a temperature rise can feel good if it's cool outside. When it's hot, though, exercise can be a drag for many people.

Your body functions best with a core temperature of about 98.6 degrees F., and it works hard to stay there. You shiver when it's cold, and the motion helps warm you up. You sweat when it's hot, and the evaporation cools you off.

But this system works only up to a certain point, says engineer Christian DiBenedetto. He leads a research team in Portland, Ore., at the headquarters of Adidas, an athletic gear company.

The body's cooling system is at its best when your body glistens with sweat but no droplets form. "When droplets run down your body, taking layers of sweat with them, you're not dissipating heat as effectively," DiBenedetto says. "You aren't as cool as you could be."

In many hot places, people nap during the heat of the afternoon, or they sit on the porch drinking lemonade. For Olympic athletes, relaxation is not an option. Rain, shine, or oppressive heat, they must run, jump, and play as hard as they can. Glory is at stake.

Marathon runners may face some of the biggest challenges in Athens. After more than 2 hours of heavy exertion, their core temperatures can easily reach 103 or 104 degrees, Verstegen says. "It can be almost like having the flu," he adds. "It can be really dangerous."

Learning to cope

When the Olympic Games were held in Mexico City in 1968, athletes had a different concern. Mexico City sits at 7,349 feet above sea level, where the air is thinner and oxygen more scarce than at sea level. To prepare, competitors had to acclimate to, or get used to, the conditions by training at altitude or traveling to Mexico City weeks before the games. With enough time, their bodies started to work better with less oxygen.

Acclimation will be important in Athens, too, not to the altitude but to the heat.

It takes between 3 and 60 days for the body to adapt to new climates, Verstegen says. Then, physical changes happen. Blood vessels begin to deliver more oxygen to muscle cells. The cells themselves use energy more efficiently to produce less heat. The body gets better at cooling itself.

Without acclimation, the results can be ugly.

"It's brutal," Verstegen says. "Your legs feel all mushy and wobbly. It's the sensation that you can't dissipate enough heat. You're using all your energy to cool your body, and you don't have enough left over to perform."

Granted, athletes who already live in hot places will have a slight advantage, as will people whose bodies naturally deal well with heat. Training in warm rooms and getting to Athens early will have to do for everyone else.

When it comes time for their events, athletes will have to work hard to stay hydrated. The human body is made up mostly of water, which keeps the body running smoothly. The more people sweat, the more water they lose, and the harder it becomes to perform well.

Athletes will have to drink plenty of water and sports drinks the night before they compete to make sure they begin with a full tank. If their sports allow it, they'll also try to drink liquids every 10 to 15 minutes during their events.

New technology

Training, acclimation, and keeping hydrated can take an athlete only so far. To push the human body beyond these limits, technology often takes over.

One of the most important decisions athletes will have to make in Athens is about what to wear. And it's not a question of fashion.

Clothing companies have put years of research into developing gear that helps the body deal with particular weather conditions. At Adidas, for instance, researchers use infrared cameras to study how both men's and women's body temperatures change with exercise. Scientists have identified several places on the body that release a lot of heat. These hotspots include the head, neck, shoulders, and back of the knee.

Based on their studies, Adidas engineers invented a fabric called ClimaCool, which is designed to manage sweat and help the body get rid of heat. ClimaCool is a three-dimensional mesh so that much of the fabric rides above the skin.

This creates a layer of air between the body and the fabric, DiBenedetto says. Where it touches the body, the fabric picks up sweat. The extra ventilation makes the sweat evaporate more quickly, and athletes stay cooler than they would with, say, a cotton T-shirt.

ClimaCool shirts, shoes, and other gear will make appearances in Athens. Some athletes will wear similar fabrics designed by other companies.

Believe it or not, lots of science can go into the clothes you wear, DiBenedetto says.

"Kids sit in science class and learn about heat, but they don't understand how it actually applies to anything they might be interested in," he says. "We take those same principles and apply them to the way we build apparel and footwear."

There'll be other types of heat-specific equipment in Athens besides clothing, Verstegen says.

For example, some athletes may end up taking advantage of the Game Ready Accelerated Recovery System for cooling the body. Inspired by NASA spacesuit technology, it consists of specially designed, computer-controlled body wraps made from a flexible fabric. The system, used in place of ice packs and elastic bandages, allows athletes to recover more quickly from sprains, strains, and other injuries.

To get rid of surplus heat, athletes can also use what is basically a personal air-conditioning unit. They wear a device that fits around the hand like a glove. Called the Rapid Thermal Exchange (RTX), it contains a water-cooled metal plate that draws excess heat from the palm of the hand. It can make an athlete's core temperature drop in just a few minutes.

The RTX was invented by scientists at Stanford University. It has already been used by football players to cope with high temperatures when competing in places such as Arizona. Cyclists, runners, and other athletes can take advantage of it during a timeout or whenever they take a break to cool down to avoid heat exhaustion.

To win in Athens this summer, Olympic athletes will need more than skill, training, determination, and fancy fabrics. More than anything else, they'll need to keep their cool.

Going Deeper:

Word Find: Athens Olympics

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It's going to be hot over there. At this summer's Olympic Games in Athens, temperatures will soar into the 90s. The air will be humid, sticky, and laden with pollution. It'll be hard to breathe, hard to stay cool, hard to keep hydrated. And that's just what the fans will have to face.

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Modern humans evolved in the warm tropics of Africa. Eventually, our species began to scatter into cooler climes more than two million years ago. Yet even after all that time, we still need a lot of help surviving where it is bitterly cold.

Luckily, our enlarged brains helped us create technology that can keep us as warm as a woolly mammoth, even where it's extremely cold. But that doesn't mean we should take our comfort for granted. Thick gloves and puffy jackets can't protect us against every frigid environment.

Our species "is a tropical animal," says Michael Tipton. He's a physiologist at the University of Portsmouth in England. There, he studies how the body responds to extremely cold air and water. What he has learned helped him advise the makers of clothing and equipment for polar explorers. It also informed part of the book he co-wrote: Essentials of Sea Survival. "We have used our intellect [and] technology to move out of the tropics," he says. Way out.

You may not be planning an expedition to the North Pole in the foreseeable future. Or to Antarctica or Mount Everest, for that matter. But explorers and winter Olympians aren't the only ones in danger of frostbite, hypothermia and other cold-related illnesses. You can get very sick - even die - from exposure to cold temperatures, even when it's well above freezing outside.

Whether skiing in the backcountry or jumping in a frigid mountain lake during a sweaty summertime hike, you can risk serious injury from the cold. Knowing your body's limits is essential to having healthy outdoor adventures.

In recent years, scientists have learned a lot about how our bodies respond to extreme cold. Their knowledge is helping doctors better understand and treat symptoms of cold injuries. And that's helping us all to stay safer.

Know the risks

There are several types of cold-related injuries and illnesses. Frostbite is the most obvious. Indeed, you can see it.

Frostbite occurs when exposure to very cold temperatures makes blood vessels shrink. This slows the flow of blood and oxygen. Air temperature, wind speed and wetness all add to the risk of frostbite.

At first the skin will redden and turn very cold. Then it will go numb, harden and turn pale. In extreme cases, ice crystals can form in affected body parts. Most often, these will be the fingers, toes, ears, nose, cheeks or chin. In the worst cases, frostbit tissues will blacken and die. This may lead to the loss of that body part.

That's what happened to the polar explorer Sir Ranulph Fiennes in 2000. He lost all the fingertips of his left hand to frostbite while trying to survive a solo walk to the North Pole. The expedition failed when his sleds fell through the ice and he had to pull them out by hand. This froze his fingers. It also brought an end to his mission. (Tipton and his colleagues tested and advised on some of the gear that Fiennes had used.)

Much less dramatic, but sometimes still severe, are non-freezing cold injuries, or NFCIs. These can develop in less than freezing temperatures. The most common NFCI is known as trench foot. Its name comes from soldiers who fought in soggy trenches during World War I. The painful condition is caused by feet remaining in cold water or mud for long periods. Affected tissues can turn blue or blacken as they die from a lack of blood supply. Feet may give off a stinky, decaying odor as tissue death sets in.

NFCIs like trench foot can be hard for doctors to spot in time. There's no great way to test for trench foot. "You know when someone has it severely because he'll be struggling to walk," Tipton says. But he and other researchers are hoping to change that. They're still trying to figure out how trench foot starts and what makes it turn severe.

At the other end of the scariness spectrum is hypothermia, which can kill. As its name implies, the body is losing heat faster than it can produce more. That makes the body's core temperature drop dangerously low. Hypothermia typically comes from exposure to cold weather, or being dunked in very cold water.

The normal temperature for a human body is roughly 37° Celsius (98.6° Fahrenheit). Hypothermia sets in when the body falls below 35 °C (95 °F). At first, people will shiver. Then their breathing will turn slow and shallow. The victim can become sleepy or feel exhausted. As the brain fails to get enough oxygen, a person might become confused or show memory loss and become uncoordinated. The victim's pulse also will slow and weaken. As their condition turns extreme, people can lose consciousness and appear to stop breathing.

Generally, hospitals treat hypothermia by warming the body back to a normal temperature.

But how low can the core body temperature drop before it's too late to save someone? That's the big question. And the answer has changed in recent years. That's because medical experts have made new discoveries about how the human body responds to extreme cold. There also have been new advances in medical technology.

The brink of death

It turns out that the line between life and death is rather blurry.

A major milestone came in May 1999. That's when a 28-year-old skier and medical intern named Anna Bågenholm was essentially brought back from the dead. Her body temperature had dropped to 14 °C (57 °F). That was the lowest body temperature a living person had ever been known to survive. To this day it remains a world record. (Not that she was trying to win a medal!) Until that time, doctors thought that once the core body temperature fell below roughly 15 °C (59 °F), you were a goner.

Mads Gilbert fights back tears as he describes the intensity and horror of that day nearly 18 years ago - and then the seeming miracle. He is a physician who heads the emergency medicine department at the University Hospital of North Norway in Tromsø. Gilbert led the team that rescued Bågenholm from the brink of death.

While skiing with two friends down a steep, icy gully, Bågenholm fell into freezing water. She got trapped there between rocks under a thick slab of ice. The ice had a small pocket of air. And that's what allowed her to breathe. But her friends couldn't pull her out, and within an hour Bågenholm stopped moving. By the time the rescue team arrived and cut her out of the water, she was no longer breathing. They could not find her pulse.

"She was clinically dead," explains Gilbert. "No [breathing]. No circulation. Ice-cold. Dilated pupils. No signs of life."

A helicopter carried Bågenholm to Gilbert's hospital, where his team anxiously awaited her. Along the way, paramedics desperately performed CPR (cardiopulmonary resuscitation) on her. That's when someone pushes down with the hands onto the victim's chest (to push air out of the lungs) and then periodically blows air into the person's mouth. "We didn't know who this lady was," Gilbert recalls. "We saw a dead body coming out of helicopter. I mean dead. Ice cold. She looked like a candle - stiff skin, waxy white."

Gilbert and his team tried an advanced life-support procedure on Bågenholm. Doctors had only recently starting using the procedure to save the lives of patients with hypothermia. It's called extracorporeal membrane oxygenation, or ECMO. Extracorporeal (EX-tra-KOR-por-EE-uhl) means "outside the body." Oxygenation (OX-uh-gen-AY-shun) refers to providing oxygen, which a body's cells need to survive. A machine sucks the blood out of the body, then filters it, warms it and pumps oxygen into it before sending it back into the vessels. With this technique, Bågenholm's body gradually warmed.

More surprisingly, her heart started beating again.

Despite the icy ordeal, Bågenholm's brain was fine. After many months of physical therapy, the woman was back on the mountains, hiking and skiing. She is now a radiologist, working alongside those who saved her at the hospital in Tromsø. Since her incident, several other frozen people have similarly been brought back from the brink of death as she was.

Gilbert says there's a key lesson in that stunning "resurrection," as he calls it. It's a well-known saying in medicine: "You're not dead until you're warm and dead." Tipton explains that especially when you're out in the mountains, far from hospital equipment, it's hard to diagnose death in a very cold person. That person might look dead, with a very slow heart rate, shallow breathing and no reflexes. But until you warm him or her back up you won't know for sure.

The bottom line for us all, Gilbert advises, is to never give up.

Staying safe

You may never completely eliminate the risk of frostbite, hypothermia or some other cold-related injury - unless you stay indoors during your vacation, safely glued to your smartphone. And who wants to do that?

But you can keep your risks low by being prepared.

"There's an old adage," says John Castellani. "There's no bad weather, just bad equipment. Castellani is a research physiologist at the U.S. Army's Research Institute of Environmental Medicine in Natick, Mass. He studies how soldiers - and ultimately athletes and the rest of us - can perform well and stay safe in extreme environments.

I can vouch for the importance of good equipment. In late November 2010, I jumped into the ice-sprinkled, -0.56 °C (31 °F) Southern Ocean. I was on a reporting trip to Palmer Station, a small U.S. research site off the Western Antarctic Peninsula. I wouldn't be alive to tell you this story if not for the gear I was wearing - a suit specially built for cold water.

I wasn't diving in for fun. I was taking part in a safety drill. All scientists and other visitors there must do search-and-rescue training before venturing onto the ocean in inflatable boats. Despite the initial shock of hitting the frigid water, I eventually felt as comfortable as a seal. I stayed happily insulated while rolling around in the water until I was "rescued."

"We never want to tell anybody that they can't go out into the environment and do something," Castellani says. "In fact, there's no environment that people don't go into. You just have to have the right gear."

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Extreme survival: Managing the deadly cold

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Modern humans evolved in the warm tropics of Africa. Eventually, our species began to scatter into cooler climes more than two million years ago. Yet even after all that time, we still need a lot of help surviving where it is bitterly cold.

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Insulin is a hormone that lowers the level of glucose (a type of sugar) in the blood.

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Glucose is the main type of sugar in the blood and is the major source of energy for the body's cells.