The Digestive System
Your body needs food to survive. Each of your cells needs a supply of food (to provide chemical energy) and other nutrients. The first part of the journey is through the digestive system. The second part is through the circulatory system. The digestive system is the organ system that takes in food, digests it, and excretes the remaining waste. The digestive system is made up of the
digestive tract and the accessory organs.
Your body needs food to survive. Each of your cells needs a supply of food (to provide chemical energy) and other nutrients. The first part of the journey is through the digestive system. The second part is through the circulatory system. The digestive system is the organ system that takes in food, digests it, and excretes the remaining waste. The digestive system is made up of the
digestive tract and the accessory organs.
The Digestive Tract
The digestive tract in most animals is essentially one long tube with two openings, one at either end. This structure is very apparent in an earthworm,
where the tube varies only slightly in diameter along its length (a). In humans, the digestive tract is much more complex. It includes the mouth, esophagus, stomach, small intestine, large intestine, and anus. The accessory organs include the liver, gall bladder, and pancreas (b).
The digestive tract in most animals is essentially one long tube with two openings, one at either end. This structure is very apparent in an earthworm,
where the tube varies only slightly in diameter along its length (a). In humans, the digestive tract is much more complex. It includes the mouth, esophagus, stomach, small intestine, large intestine, and anus. The accessory organs include the liver, gall bladder, and pancreas (b).
(a) In an earthworm, food passes through the esophagus
and is stored in the crop. The gizzard grinds the food to break it into
pieces. Nutrients are absorbed in the intestine. (b) In a human, the
breakdown of food starts in the mouth and continues until nutrient
absorption occurs in the small intestine.
The entire length of the digestive tract is lined with epithelial tissue. This tissue is made up of many different types of cells, including goblet cells that secrete mucus. The mucus serves two functions: it protects the digestive tube from digestive enzymes, and it allows the material to pass smoothly along the tube. The digestive tube also includes layers of muscle tissues and nerves.
If you eat spoiled food, your body recognizes the presence of toxins produced by bacteria. Your digestive tract responds by attempting to remove
the toxins rapidly, which you experience as vomiting or diarrhea. This can also happen as a result of too much alcohol or other poisonous substances.
The Mouth
The mouth starts the process of breaking down food. It does this in two ways: mechanically (with the teeth and tongue) and chemically (with
chemicals called enzymes that break apart the molecules of food). The mouth adds saliva—a mixture of water and enzymes—to the food in the
mouth. Saliva is produced by cells in the epithelial tissue that lines the mouth. Once the food is broken up and softened with saliva, it is swallowed
and passed into the esophagus.
The Esophagus
The esophagus is a muscular tube connecting your mouth to your stomach. The muscles are a special type, called smooth muscle tissue, which can
contract and relax without conscious thought. This movement is controlled by nerve tissue. The contractions slowly move the food along the stomach.
Stomach
One of the major organs in the animal digestive system is the stomach. The main function of the stomach is to hold food and churn it
to continue the process of digestion. The stomach lining contains cells that produce digestive enzymes and acids. Smooth muscle tissue contracts to
mix the stomach contents. The stomach is richly supplied with nerves that signal when we have had enough to eat.
the toxins rapidly, which you experience as vomiting or diarrhea. This can also happen as a result of too much alcohol or other poisonous substances.
The Mouth
The mouth starts the process of breaking down food. It does this in two ways: mechanically (with the teeth and tongue) and chemically (with
chemicals called enzymes that break apart the molecules of food). The mouth adds saliva—a mixture of water and enzymes—to the food in the
mouth. Saliva is produced by cells in the epithelial tissue that lines the mouth. Once the food is broken up and softened with saliva, it is swallowed
and passed into the esophagus.
The Esophagus
The esophagus is a muscular tube connecting your mouth to your stomach. The muscles are a special type, called smooth muscle tissue, which can
contract and relax without conscious thought. This movement is controlled by nerve tissue. The contractions slowly move the food along the stomach.
Stomach
One of the major organs in the animal digestive system is the stomach. The main function of the stomach is to hold food and churn it
to continue the process of digestion. The stomach lining contains cells that produce digestive enzymes and acids. Smooth muscle tissue contracts to
mix the stomach contents. The stomach is richly supplied with nerves that signal when we have had enough to eat.
The Intestine
The part of the digestive tract between the stomach and the anus is the intestine. The lining of the intestine has cells that produce mucus.
It also has many fine blood vessels interlaced through the other tissues. Like the esophagus and stomach, the intestines contain smooth muscles that
contract and relax without our conscious thought. There are two parts to the intestine: the small intestine and the large intestine. The small intestine, which is about 6 m long and relatively narrow, is where most digestion occurs. Goblet cells release mucus, and nutrients diff use through the wall of the small intestine and enter the bloodstream. The large intestine, or colon, is about 1.5 m long but larger in diameter than the small intestine. Its lining absorbs water from the indigestible food. The remaining solid matter is excreted as feces from the anus. Sometimes the epithelial tissue lining the colon can become inflamed and stop working properly. This disease is known as colitis. There are several causes of colitis, including viruses, bacteria, narrowed blood vessels, and failure of the body’s disease-fighting mechanism. Colitis is diagnosed with the aid of an endoscope and microscopic examination of tissue samples taken from the colon.
Accessory Organs
The liver, pancreas, and gall bladder all help with the digestion of food by supplying digestive enzymes. The liver also produces a fluid called bile, which
helps in the breakdown of fats in our food. These substances are delivered into the digestive tract, where they mix with the partially digested food. The pancreas produces an important enzyme called insulin. Insulin regulates the concentration of glucose (a sugar) in the blood. Diabetes is a disease in which the pancreas produces too much or too little insulin. A person with diabetes can experience weakness and dizziness due to too low or too high blood glucose levels. Some forms of diabetes can be controlled by diet.
The part of the digestive tract between the stomach and the anus is the intestine. The lining of the intestine has cells that produce mucus.
It also has many fine blood vessels interlaced through the other tissues. Like the esophagus and stomach, the intestines contain smooth muscles that
contract and relax without our conscious thought. There are two parts to the intestine: the small intestine and the large intestine. The small intestine, which is about 6 m long and relatively narrow, is where most digestion occurs. Goblet cells release mucus, and nutrients diff use through the wall of the small intestine and enter the bloodstream. The large intestine, or colon, is about 1.5 m long but larger in diameter than the small intestine. Its lining absorbs water from the indigestible food. The remaining solid matter is excreted as feces from the anus. Sometimes the epithelial tissue lining the colon can become inflamed and stop working properly. This disease is known as colitis. There are several causes of colitis, including viruses, bacteria, narrowed blood vessels, and failure of the body’s disease-fighting mechanism. Colitis is diagnosed with the aid of an endoscope and microscopic examination of tissue samples taken from the colon.
Accessory Organs
The liver, pancreas, and gall bladder all help with the digestion of food by supplying digestive enzymes. The liver also produces a fluid called bile, which
helps in the breakdown of fats in our food. These substances are delivered into the digestive tract, where they mix with the partially digested food. The pancreas produces an important enzyme called insulin. Insulin regulates the concentration of glucose (a sugar) in the blood. Diabetes is a disease in which the pancreas produces too much or too little insulin. A person with diabetes can experience weakness and dizziness due to too low or too high blood glucose levels. Some forms of diabetes can be controlled by diet.