Digestion is the process whereby food is broken down into smaller parts,chemically changed, and moved through the gastrointestinal system. The gas-trointestinal (GI) tract consists of the body structures that participate indigestion. Digestion begins in the mouth and ends at the anus. Along the entire GI tract secretions of mucus lubricate and protect the mucosal tissues.
Digestion occurs through two types of action—mechanical and chemical.
During mechanical digestion,food is broken into smaller pieces by the teeth. It is then moved along the gastrointestinal tract through the esophagus, stomach, and intestines. This movement is caused by a rhythmic contraction of the muscular walls of the tract called peristalsis. Mechanical digestion helps to prepare food for chemical digestion by breaking it into smaller pieces.
During chemical digestion, the composition of carbohydrates, pro-teins, and fats is changed. Chemical changes occur through the addition of water and the resulting splitting, or breaking down, of the food molecules. This process is calledhydrolysis. Food is broken down into nutrients that the tissues can absorb and use. Hydrolysis also involves digestive enzymes that act on food substances, causing them to break down into simple compounds.
Digestion in the Mouth
Digestion begins in the mouth, where the food is broken into smaller pieces by the teeth and mixed with saliva. At this point, each mouthful of food that is ready to be swallowed is called a bolus. Saliva is a secretion of the salivary glands that contains water, salts, and a digestive enzyme called salivary amylase (also called ptyalin), which acts on complex carbohydrates (starch).
The Esophagus
The esophagus is a 10-inch muscular tube through which food travels from the mouth to the stomach. When swallowed, the bolus of food is moved down the esophagus by peristalsis and gravity. At the lower end of the esophagus, the cardiac sphincter opens to allow passage of the bolus into the stomach. The cardiac sphincter prevents the acidic content of the stomach from flowing back into the esophagus.
Digestion in the Stomach
The stomach consists of an upper portion known as the fundus, a middle area known as the body of the stomach, and the end nearest the small intestine called the pylorus.Food enters the fundus and moves to the body of the stomach, where the muscles in the stomach wall gradually knead the food, tear it, and mix it with gastric juices, and with the intrinsic factor necessary for the absorption of vitamin B12, before it can be propelled forward in slow, controlled movements.
Digestion in small intestine
When food reaches the small intestine, the hormone secretin causes the pancreas to release sodium bicarbonate to neutralize the acidity of the chyme. The gallbladder is triggered by the hormone cholecystokinin (CCK), which is produced by intestinal mucosal glands when fat enters, to releasable. Bile is produced in the liver but stored in the gallbladder. Bile emulsifies fat after it is secreted into the small intestine. This action enables the enzymes to digest the fats more easily.
The Large Intestine
The large intestine, or colon,consists of the cecum, colon, and rectum. The cecum is a blind pouchlike beginning of the colon in the right lower quadrant of the abdomen. The appendix is a diverticulum that extends off the cecum. Thececum is separated from the ileum by the ileocecal valve and is considered to be the beginning of the large intestine (colon).
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Digestion occurs through two types of action—mechanical and chemical.
During mechanical digestion,food is broken into smaller pieces by the teeth. It is then moved along the gastrointestinal tract through the esophagus, stomach, and intestines. This movement is caused by a rhythmic contraction of the muscular walls of the tract called peristalsis. Mechanical digestion helps to prepare food for chemical digestion by breaking it into smaller pieces.
During chemical digestion, the composition of carbohydrates, pro-teins, and fats is changed. Chemical changes occur through the addition of water and the resulting splitting, or breaking down, of the food molecules. This process is calledhydrolysis. Food is broken down into nutrients that the tissues can absorb and use. Hydrolysis also involves digestive enzymes that act on food substances, causing them to break down into simple compounds.
Digestion in the Mouth
Digestion begins in the mouth, where the food is broken into smaller pieces by the teeth and mixed with saliva. At this point, each mouthful of food that is ready to be swallowed is called a bolus. Saliva is a secretion of the salivary glands that contains water, salts, and a digestive enzyme called salivary amylase (also called ptyalin), which acts on complex carbohydrates (starch).
The Esophagus
The esophagus is a 10-inch muscular tube through which food travels from the mouth to the stomach. When swallowed, the bolus of food is moved down the esophagus by peristalsis and gravity. At the lower end of the esophagus, the cardiac sphincter opens to allow passage of the bolus into the stomach. The cardiac sphincter prevents the acidic content of the stomach from flowing back into the esophagus.
Digestion in the Stomach
The stomach consists of an upper portion known as the fundus, a middle area known as the body of the stomach, and the end nearest the small intestine called the pylorus.Food enters the fundus and moves to the body of the stomach, where the muscles in the stomach wall gradually knead the food, tear it, and mix it with gastric juices, and with the intrinsic factor necessary for the absorption of vitamin B12, before it can be propelled forward in slow, controlled movements.
Digestion in small intestine
When food reaches the small intestine, the hormone secretin causes the pancreas to release sodium bicarbonate to neutralize the acidity of the chyme. The gallbladder is triggered by the hormone cholecystokinin (CCK), which is produced by intestinal mucosal glands when fat enters, to releasable. Bile is produced in the liver but stored in the gallbladder. Bile emulsifies fat after it is secreted into the small intestine. This action enables the enzymes to digest the fats more easily.
The Large Intestine
The large intestine, or colon,consists of the cecum, colon, and rectum. The cecum is a blind pouchlike beginning of the colon in the right lower quadrant of the abdomen. The appendix is a diverticulum that extends off the cecum. Thececum is separated from the ileum by the ileocecal valve and is considered to be the beginning of the large intestine (colon).
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