DIGESTIVE AND EXCRETORY SYSTEMS

The body needs food products for energy and to provide fuel for the cells to perform their individual functions.  The digestive system takes the food a person eats, breaks it down into tiny particles, and absorbs the important nutrients and water. 

These particles are then passed into the blood supply for transportation to all the cells.  The organs of the digestive system are automatic, meaning they are controlled by the brain, with no conscious control by the person. 

There are several organs that combine to make the digestive system. They include the stomach, pancreas, liver, gall bladder, spleen, and the large and small intestines.   

The salivary glands, tongue, and teeth are part of the mechanical digestion system. 

As food is ingested, or eaten, it is chewed into smaller pieces by the teeth in the mouth. It mixes with saliva and is swallowed. As chewed food heads for the stomach, it travels in a long, smooth tube called the esophagus.

The esophagus is located in the throat behind the trachea, which is the tube that carries oxygen to the lungs. It is lined with a slippery mucus coating. The esophagus consists of rings of muscles that contract in a series of waves called peristalsis, which moves food down the esophagus to the stomach.

You can swallow while standing on your head because of peristalsis. 

The stomach is a small sac that can hold over four quarts of food.  It can easily expand to 50 times its empty size. 

Although the stomach appears smooth on the outside, the inside consists of many ridges. These ridges help move the food slowly back and forth in a wave-like effect, causing it to break up into smaller and smaller pieces. These waves generally occur at a rate of three per minute. On an average, a meal takes about 2-4 hours to be completely ingested by the stomach.

barium study of upper intestinal tract

The sphincter is a muscle located where the stomach meets the esophagus.  The sphincter muscle contracts and closes so the stomach contents do not go back up the esophagus.   

It is usually closed and opens only when food enters the esophagus and peristalsis occurs. Other sphincter muscles include the mouth and rectum. 

The diaphragm also helps break up the food by rubbing against the stomach as it moves up and down. This contact stimulates the stomach to release extremely powerful hydrochloric acid secretions. This acid along with an enzyme called pepsin, breaks food into protein and then into simple amino acids that the body can absorb.

The acid would be strong enough to actually burn holes through the lining of the stomach if the stomach did not constantly replace destroyed cells with new ones. People who develop certain types of ulcers have areas where the cells are not replaced fast enough to prevent the tissue of the stomach lining to be damaged. If left untreated, these ulcers would become deep enough to eat their way through the lining of the stomach, causing its contents to be spilled into the abdominal cavity and create a life threatening infection known as peritonitis. 

These secretions mix with the food and turn it into a liquid called chyme.

Nutrients are not absorbed through the stomach, but are passed from the stomach as chyme into the small intestines. Digestion actually takes place in the small intestines, not the stomach!

Once it leaves the stomach as a liquid, food enters the small intestines.   

Muscle contractions force the food along its 15 - 20 foot length. As it travels, it mixes with special digestive juices called enzymes that are secreted by the liver and the pancreas. These enzymes shatter the chemical bonds that link the food molecules together. This breaks food into simpler and simpler units.  

Lining the small intestines are millions of microscopic hairs called villi. These hairs absorb all the nutrients from the food mixture and send it directly into the bloodstream and to the cells. After all the nutrients have been removed from the food by the villi, the food exits the small intestines and enters the large intestines.   

magnified view of intestinal villi

Although it is shorter than the small intestines with a length of only 5 feet, it is called the large intestines because its diameter is much larger. 

The large intestines is divided into 6 sections.  

The top section, called the cecum, is where the small fingerlike projection called the appendix is located. There appears to be no known use for the appendix. At one time in man’s history, however, it may have performed an important function that is longer required for survival. It often can become diseased and is frequently removed today. 

In the large intestines all the moisture left within the food is absorbed and a hard waste product is passed along its length until it is removed from the body through the rectum.   

barium study of lower intestinal tract

The liver is a large reddish-purple organ that sits on the right side of the body, directly under the diaphragm. Blood passes through the liver to be filtered at a rate of about 3 pints per second.  

At any time, the liver contains about 10 percent of the body’s total blood supply. This makes it a very serious location for a tearing injury, as a person would quickly bleed to death. 

The liver has over 500 known functions. Among these are to filter poisonous materials from the blood, store glycogen - a blood sugar, breaks down cholesterol, make carbohydrates and fat that it stores and releases as the body needs it, and store vitamins, including vitamin D which is needed for blood clotting.  

The liver also produces bile that it releases into the small intestines to aid digestion and controls the temperature of blood, keeping it at 98.6 degrees. 

Hepatitis is a disease of the liver. It is often characterized by a yellow tint to the nails and eyes. There are different types of hepatitis. Some have vaccines to prevent them, and some are fatal. 

Cirrhosis of the liver causing scar tissue and is usually a result of alcoholism. Diabetes mellitus is a result of fat deposits that accumulate on the liver. 

The gall bladder is a small sac that is only about 3 inches long and an inch wide. It is located under the liver. It serves as a reservoir, or storage area for extra bile that the liver has produced. When this bile is needed for digestion, the gall bladder empties into the small intestines. 

As a person ages, salts build-up in the gall bladder. These salts can form stones called gallstones. These can range in size from a pea to the size of a pear. If they cannot be chemically broken apart, surgery is needed to remove them. 

The spleen is a flat, oblong organ wrapped around the stomach. It is about 5 inches long and 3 inches wide. Its function is to remove disease-producing bacteria and worn-out red blood cells. It also produces antibodies (lymphocytes) against various disease organisms and produces a variety of blood cells. 

If removed because of disease or injury, a person can function well without a spleen as other organs also produce antibodies. They are, however, at a greater risk of catching certain diseases and infections. 

The pancreas is about 6 inches long. It is located in the center of the upper abdomen, behind the stomach and the small intestines. It not only produces enzymes to help break down food, but it more importantly produces insulin which helps to keep the blood sugar level in balance.    

When the pancreas malfunctions, a disease called diabetes results. Usually people with diabetes require daily insulin injections to keep their sugar balance equalized. Without treatment, they would lapse into a coma and die. 

The kidneys and bladder are part of the excretory system. The job of the excretory system is to remove carbon dioxide, nitrogen, heat, and water. 

Located near the vertebrae are a pair of small bean-shaped organs called the kidneys. There is one on each side of the body. They are about 4 inches long and 2 inches wide. Their function is to filter blood and remove the waste products. They also remove excess water and salts from the blood. 

The kidneys remove the wastes from the urine which it sends to the bladder for removal from the body. They produce about 3 pints of urine and filter about 47 gallons of blood per day. 

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