When a person swallows, food pushes into the esophagus, the muscular tube that carries food and liquids from the mouth to the stomach. Once swallowing begins, it becomes involuntary and proceeds under the control of the esophagus and brain.
The lower esophageal sphincter, a ringlike muscle at the junction of the esophagus and stomach, controls the passage of food and liquid between the esophagus and stomach.
As food approaches the closed sphincter, the muscle relaxes and lets food pass through to the stomach. The stomach stores swallowed food and liquid, mixes the food and liquid with digestive juice it produces, and slowly empties its contents, called chyme, into the small intestine.
The muscle of the upper part of the stomach relaxes to accept large volumes of swallowed material from the esophagus. The bile acids produced by the liver dissolve fat into tiny droplets and allow pancreatic and intestinal enzymes to break the large fat molecules into smaller ones.
Some of these small molecules are fatty acids and cholesterol. The bile acids combine with the fatty acids and cholesterol and help these molecules move into the cells of the mucosa. In these cells the small molecules are formed back into large ones, most of which pass into vessels called lymphatics near the intestine. These small vessels carry the reformed fat to the veins of the chest, and the blood carries the fat to storage depots in different parts of the body.
Another vital part of food that is absorbed through the small intestine are vitamins. The two types of vitamins are classified by the fluid in which they can be dissolved: water-soluble vitamins all the B vitamins and vitamin C and fat-soluble vitamins vitamins A, D, E, and K.
Fat-soluble vitamins are stored in the liver and fatty tissue of the body, whereas water-soluble vitamins are not easily stored and excess amounts are flushed out in the urine. Water and salt.
Most of the material absorbed through the small intestine is water in which salt is dissolved. The salt and water come from the food and liquid you swallow and the juices secreted by the many digestive glands. The major hormones that control the functions of the digestive system are produced and released by cells in the mucosa of the stomach and small intestine. These hormones are released into the blood of the digestive tract, travel back to the heart and through the arteries, and return to the digestive system where they stimulate digestive juices and cause organ movement.
Both of these hormones work on the brain to help regulate the intake of food for energy. Together, nerves, hormones, the blood, and the organs of the digestive system conduct the complex tasks of digesting and absorbing nutrients from the foods and liquids you consume each day. Search temple health. Your Digestive System. Why Is Digestion Important? How Is Food Digested?
Movement of food through the system. Production of digestive juices. Starch is digested in two steps. First, an enzyme in the saliva and pancreatic juice breaks the starch into molecules called maltose. Then an enzyme in the lining of the small intestine splits the maltose into glucose molecules that can be absorbed into the blood. Glucose is carried through the bloodstream to the liver, where it is stored or used to provide energy for the work of the body.
Sugars are digested in one step. An enzyme in the lining of the small intestine digests sucrose, also known as table sugar, into glucose and fructose, which are absorbed through the intestine into the blood.
Milk contains another type of sugar, lactose, which is changed into absorbable molecules by another enzyme in the intestinal lining. How Is the Digestive Process Controlled? Hormone regulators The major hormones that control the functions of the digestive system are produced and released by cells in the mucosa of the stomach and small intestine. The main hormones that control digestion are gastrin, secretin, and cholecystokinin CCK : Gastrin causes the stomach to produce an acid for dissolving and digesting some foods.
The digestive tract is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. It consists of the following:. Click Image to Enlarge. Parts of other organ systems, such as nerves and blood, also play a major role in the digestive process. Muscles propel food and liquid along the digestive tract in a wave-like movement. This movement is called peristalsis.
In general, there are 6 steps in the process of moving food and liquid through the digestive system:. The first step in the digestive process occurs in the mouth.
An adult's digestive tract is about 30 feet about 9 meters long. Digestion begins in the mouth, well before food reaches the stomach. When we see, smell, taste, or even imagine a tasty meal, our salivary glands in front of the ear, under the tongue, and near the lower jaw begin making saliva spit. As the teeth tear and chop the food, spit moistens it for easy swallowing. A digestive enzyme in saliva called amylase pronounced: AH-meh-lace starts to break down some of the carbohydrates starches and sugars in the food even before it leaves the mouth.
Swallowing, done by muscle movements in the tongue and mouth, moves the food into the throat, or pharynx pronounced: FAIR-inks. The pharynx is a passageway for food and air. A soft flap of tissue called the epiglottis pronounced: ep-ih-GLAH-tus closes over the windpipe when we swallow to prevent choking.
From the throat, food travels down a muscular tube in the chest called the esophagus pronounced: ih-SAH-fuh-gus. Waves of muscle contractions called peristalsis pronounced: per-uh-STALL-sus force food down through the esophagus to the stomach.
A person normally isn't aware of the movements of the esophagus, stomach, and intestine that take place as food passes through the digestive tract. At the end of the esophagus, a muscular ring or valve called a sphincter pronounced: SFINK-ter allows food to enter the stomach and then squeezes shut to keep food or fluid from flowing back up into the esophagus. The stomach muscles churn and mix the food with digestive juices that have acids and enzymes, breaking it into much smaller, digestible pieces.
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