digestion [L. digestio, a taking apart]
The process by which food is broken down mechanically and chemically in the gastrointestinal tract and converted into absorbable forms. Salts (minerals), water, and monosaccharides can be absorbed unchanged, but starches, fats, and proteins must be broken down into smaller molecules. This is brought about by enzymes, each of which acts on a specific type of food and requires a specific pH to be effective. See: table
Hormones released by the gastrointestinal mucosa stimulate the secretion of digestive enzymes and bile and influence the motility (peristalsis) of the stomach and intestines. Starches and disaccharides are digested to monosaccharides; fats are digested to fatty acids and glycerol; proteins are digested to amino acids. During digestion vitamins and minerals are liberated from these large organic molecules. See: intestinal hormone
Digestion occurring outside the living organism by an enzyme.
The conversion of complex food molecules into simpler molecules by digestive enzymes. See: table
That part of digestion that occurs in the duodenum where stomach contents mix with biliary and pancreatic secretions. The duodenum absorbs iron, vitamin B12, and other essential nutrients. See: duodenum
Digestion outside a cell, as of tissue by bacterial enzymes (toxins).
That part of digestion that takes place in the stomach. See: stomach
That part of digestion that occurs in the intestine. See: absorption; large intestine; small intestine
The consumption and chemical degradation of materials ingested by cells (e.g., bacteria, viruses, or large molecules) within vacuoles in the cytoplasm.
The conversion of neutral fats by hydrolysis into fatty acids and glycerol; fat splitting.
The conversion of food into small pieces by chewing, churning of the stomach, or the emulsifying action of bile salts, exposing more surface area to digestive enzymes.
That part of digestion that takes place in the mouth. It includes the physical process of chewing food and the chemical process of starch splitting by the enzyme amylase, present in the saliva.
The digestion of proteins and fats by pancreatic enzymes released into the intestine.
The digestion of foreign substances by body cells as opposed to enteral digestion, which occurs in the alimentary canal.
Digestion of starches by salivary amylase.
|Food Component||Enzyme||Secretion||Site of Action|
|Proteins||Pepsin||Gastric juice, acid||Stomach|
|Trypsin||Pancreatic juice, alkaline||Small intestine|
|Peptidases||Intestinal juice||Small intestine|
|Pancreatic juice||Small intestine|
|Carbohydrates||Salivary amylase||Saliva, alkaline||Mouth|
|Pancreatic amylase||Pancreatic juice||Small intestine|
|Sucrase, maltase, lactase||Intestinal juice||Small intestine|