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Digestion
The third chapter of the Human Nutrition
| Term | Definition |
|---|---|
| digestion | process that breaks down food into individual molecules small enough to be absorbed through the intestinal wall |
| absorption | process of moving nutrients from the GI tract into the circulatory system |
| elimination | excretion of undigested and unabsorbed food through the feces |
| gastrointestinal (GI) tract | tubular organ system including the mouth, pharynx, esophagus, stomach, and small and large intestines, by means of which food is digested, nutrients absorbed, and wastes expelled |
| lumen | channel or inside space of a vessel such as the intestine or artery |
| propulsion | process that moves food along the GI tract during digestion |
| sphincters | circular rings of muscle that open and close in response to nerve input |
| chemical digestion | breaking down food through enzymatic reactions |
| mechanical digestion | breaking down food by chewing, grinding, squeezing, and moving it through the GI tract by peristalsis and segmentation |
| mastication | chewing food |
| saliva | secretion from the salivary glands that softens and lubricates food and begins the chemical breakdown of starch |
| ingestion | food enters the GI tract via the mouth |
| bolus | soft mass of chewed food |
| pharynx | area of the GI tract between the mouth and the esophagus |
| esophagus | tube that connects the mouth to the stomach |
| epiglottis | cartilage at the back of the tongue that closes off the trachea during swallowing |
| upper esophageal sphincter | muscular ring located between the base of the esophagus and the stomach |
| stomach | J-shaped muscular organ that mixes and churns food with digestive juices and acid to form chyme |
| goblet cells | cells throughout the GI tract that secrete mucus |
| parietal cells | specialized cells in the stomach that secrete the gastric juices hydrochloric acid and intrinsic factor |
| chief cells | specialized cells in the stomach that secrete pepsinogen, an inactive form of the protein-digesting enzyme pepsin |
| mucus | secretion produced throughout the GI tract that moistens and lubricates food and protects membranes |
| chyme | semiliquid, partially digested food mass that leaves the stomach and enters the small intestine |
| small intestine | long coiled chamber that is the major site of food digestion and nutrient absorption |
| villi | small, fingerlike projections that line the lumen of the small intestine |
| enterocytes | absorptive epithelial cells that line the lumen of the small intestine |
| microvilli | tiny projections on the villi in the small intestine |
| crypts | glands at the base of the villi; they contain stem cells that manufacture young cells to replace the cells of the villi when they die |
| large intestine | lowest portion of the GI tract, where water and electrolytes are absorbed, and waste is eliminated |
| cecum | pouch at the beginning of the large intestine that receives waste from the small intestine |
| ileocecal valve | sphincter that separates the small intestine from the large intestine |
| colon | another name for the large intestine |
| GI flora | microorganisms that live in the GI tract of humans and animals |
| ferment | to metabolize sugar into carbon dioxide and other gases |
| probiotics | live microorganisms that, when consumed in adequate amounts, confer a health benefit on the host |
| prebiotics | nondigestible starch found in plant foods that promote the growth and health of your GI flora |
| stool | waste produced in the large intestine |
| rectum | Final 8-inch portion of the large intestine |
| anus | opening of the rectum, or end of the GI tract |
| salivary glands | cluster of glands located underneath and behind the tongue that release saliva in response to the sight, smell, and taste of food |
| liver | accessory organ of digestion located in the upper abdomen and responsible for the synthesis of bile, the processing of nutrients, the metabolism of alcohol, and other functions |
| gallbladder | pear-shaped organ that stores and concentrates bile produced by the liver and secretes it through the common bile duct into the small intestine |
| pancreas | large gland located behind the stomach that releases digestive enzymes and bicarbonate after a meal. Also secretes the hormones insulin and glucagon, which control blood glucose |
| peristalsis | forward, rhythmic muscular contractions that move food through the GI tract |
| segmentation | muscular contractions of the small intestine that move food back and forth, breaking the mixture into smaller and smaller pieces and combining it with digestive juices |
| mass movement | strong, slow peristaltic movements, occurring only three or four times a day within the colon, that force waste toward the rectum |
| enzymes | substances, mostly proteins, that increase the rate of chemical reactions |
| hydrolysis | chemical reaction that breaks the bond between two molecules with water. A hydroxyl group is added to one molecule and hydrogen ion is added to the other molecule |
| substrate | substance or compound that is altered by an enzyme |
| pH | measure of the acidity or alkalinity of a solution |
| hydrochloric acid (HCl) | strong acid produced in the stomach that aids in digestion |
| proteases | classification of enzymes that catalyze the hydrolysis of proteins |
| pepsinogen | inactive proteases secreted by the chief cells in the stomach; it is converted to the active enzyme pepsin in the presence of HCl |
| pepsin | active proteases that begin the digestion of proteins in the stomach |
| bile | secretion produced by the liver, stored in the gallbladder, and released into the duodenum to emulsify dietary fat |
| emulsify | to break large fat globules into smaller droplets |
| enterohepatic circulation | process of recycling bile from the large intestine back to the liver to be reused during fat digestion |
| bicarbonate | negatively charged alkali ion produced from bicarbonate salts; during digestion, bicarbonate ions released from the pancreas neutralize HCl in the duodenum |
| intestinal permeability | condition in which the junctions between enterocytes allow large molecules to enter the bloodstream; also called leaky gut syndrome |
| passive diffusion | movement of substances across a cell membrane along their concentration gradient |
| facilitated diffusion | movement of substances across a cell membrane with the help of a carrier protein along their concentration gradient |
| active transport | movement of substances across a cell membrane against their concentration gradient with the help of a carrier protein and energy expenditure |
| endocytosis | type of active transport in which the cell membrane forms an indentation, engulfs the substance to be absorbed, and releases it into the interior of the cell |
| enteric nervous system | section of the peripheral nervous system that directly controls the gastrointestinal system |
| enterogastrones | group of GI tract hormones, produced in the stomach and small intestine, that controls gastric motility and secretions |
| gastrin | hormone released from the stomach that stimulates the release of the acid |
| secretin | a hormone secreted from the duodenum that stimulates the stomach to release pepsin, the liver to make bile, and the pancreas to release digestive juices |
| cholecystokinin (CCK) | hormone released by the duodenum that stimulates the gallbladder to release bile |
| gastric inhibitory peptide (GIP) | hormone produced by the small intestine that slows the release of chyme from the stomach |
| ghrelin | hormone produced in the stomach that stimulates hunger |
| peptide YY | hormone produced in the small intestine that reduces hunger |
| hepatic portal vein | large vein that connects the GI tract to the liver and transports newly absorbed water-soluble nutrients |
| hepatic vein | vein that carries the blood received from the hepatic portal vein away from the liver |
| lymphatic system | system of interconnected vessels that contains lymph fluid in which fat-soluble nutrients are carried; also includes bone marrow, lymph nodes, and other tissues and organs that produce and store defensive cells |
| gastroesophageal reflux disease (GERD) | chronic condition characterized by the backward flow of stomach contents into the esophagus, resulting in heartburn |
| gastroenteritis | inflammation of the lining of the stomach and intestines; stomach flu |
| ulcer | sore or erosion of the stomach or intestinal lining |
| gallstones | stones formed from cholesterol in the gallbladder or bile duct |
| celiac disease | genetic disease in which a hyperimmune response damages the villi of the small intestine when gluten is consumed |
| non-celiac gluten sensitivity (NCGS) | reaction to eating foods that contain gluten when celiac disease has been ruled out. symptoms may vary but include abdominal pain, fatigue, headaches, rashes, or mental confusion |
| flatulence | production of excessive gas in the stomach or the intestines |
| diarrhea | abnormally frequent passage of watery stools |
| constipation | infrequent passage of dry, hardened stools |
| hemorrhoid | swelling in the veins of the rectum and anus |
| irritable bowel syndrome (IBS) | intestinal disorder resulting in abdominal discomfort, pain, diarrhea, constipation, and bloating |
| inflammatory bowel disease (IBD) | chronic inflammation throughout the GI tract |
| ulcerative colitis | chronic inflammation of the colon that results in ulcers forming in the lining |
| Crohn's disease | forms of ulcerative colitis in which ulcers form throughout the GI tract and not just in the colon |
| salivary amylase | the primary enzyme in saliva |
| organs of the GI tract | mouth, pharynx, esophagus, stomach, small intestine, large intestine, and rectum |
| accessory organs | salivary glands, liver, gallbladder, pancreas |
| muscles of the stomach | longitudinal, circular, diagonal |
| pyloric sphincter | prevents chyme from exiting the stomach too soon and blocks the intestinal contents from returning to the stomach |
| parts of the small intestine | duodenum, jejenum, and the ileum |
| parts of the large intestine | cecum, colon, rectum |
Created by:
bsauveur
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