Introduction to the Digestive System

Chemical digestion, through a process called hydrolysis, uses water and digestive enzymes to break down the complex molecules. Digestive enzymes speed up the hydrolysis process, which is otherwise very slow. Most chemical digestion takes place in the duodenum by chemicals secreted by the liver, pancreas and small intestine.

These muscles allow the stomach to squeeze and churn the food during mechanical digestion. Also known as the gastrointestinal (GI) tract, the digestive system begins at the mouth, includes the esophagus, stomach, small intestine, large intestine (also known as the colon) and rectum, and ends at the anus. The entire system – from mouth to anus – is about 30 feet (9 meters) long, according to the American Society of Gastrointestinal Endoscopy (ASGE).

This enzyme breaks the bonds between the monomeric sugar units of disaccharides, oligosaccharides, and starches. The salivary amylase breaks down amylose and amylopectin into smaller chains of glucose, called dextrins and maltose. The increased concentration of maltose in the mouth that results from the mechanical and chemical breakdown of starches in whole grains is what enhances their sweetness. Only about five percent of starches are broken down in the mouth. (This is a good thing as

How each of these components is digested is discussed in the following sections. Digestion starts when food enters the mouth and ends when feces are excreted.

The powerful muscles of the gizzard churn and mix the mass of food and dirt. When the churning is complete, the glands in the walls of the gizzard add enzymes to the thick paste, which helps chemically breakdown the organic matter. By peristalsis, the mixture is sent to the intestine where friendly bacteria continue chemical breakdown. This releases carbohydrates, protein, fat, and various vitamins and minerals for absorption into the body. The small intestine also produces enzymes that plays part in the digestive process of reducing the complex food compounds eaten to the simple compounds or building blocks that can be absorbed across the intestinal wall for transport to the organ or location where either they will be further processed, stored or used.

  • The inside surfaces of the intestine are covered with projections called villi.
  • The process of emesis is regulated by the medulla.
  • Some of the remaining indigestible carbohydrates are broken down by enzymes released by bacteria in the large intestine.
  • The bile salts surround long-chain fatty acids and monoglycerides, forming tiny spheres called micelles.

It is stimulated by distension of the stomach, presence of food in stomach and decrease in pH. Distention activates long and myenteric reflexes. This activates the release of acetylcholine, which stimulates the release of more gastric juices.

Gastric inhibitory peptide (GIP) and enteroglucagon decrease both gastric motility and secretion of pepsin. Other than gastrin, these hormones act to turn off the stomach action. This is in response to food products in the liver and gall bladder, which have not yet been absorbed. The stomach needs only to push food into the small intestine when the intestine is not busy. While the intestine is full and still digesting food, the stomach acts as a storage for food.

3. Structures of the Alimentary Canal Ingest Food and Propel It on a Journey Through the Body

The partially digested food enters the duodenum as a thick semi-liquid chyme. In the small intestine, the larger part of digestion takes place and this is helped by the secretions of bile, pancreatic juice and intestinal juice. An earthworm’s digestive system consists of a mouth, pharynx, esophagus, crop, gizzard, and intestine. The mouth is surrounded by strong lips, which act like a hand to grab pieces of dead grass, leaves, and weeds, with bits of soil to help chew.

the body's process of eliminating indigestible

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