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Digestion ,Absorption ,& metabolism - body food component travel together ,through GIT into the cell. *basic principles of digestion: -digestion: • prepares the food for the body use ,under effect of muscular &chemical reaction. • -muscular layer of the elementary system (serosa,submucosa,&mucosa),&fiber layer longitudinal or circular layer, help in the movement of food &push it forward ,this movement called peristalsis. • -chyme:fluid secreted by GIT to help in digestion . • -the action of food is under control of nervous system at GIT wall called intramural nervous plexus extend from esophagus to anus responsible for regulation of the rate &intensity of muscle contraction with coordination in various movement. *definition of digestion: • -the process of break down food to release its nutrients for absorption & transport to the cell for use in the body . • *peristalsis: • Wave like progression of contraction & relaxation . **types of GIT secretion: • -1-Enzymes: chemical action e.g. lipase ,amylase . • -2-hydro-choloric acid & buffer ions : necessary ph . • -3-mucous:protect the inside wall tissue of GIT,lubricate &facilitate food mass passage . • • -4-water & electrolyte. Mouth& esophagus: preparation &delivery: • -1*mastication: • -chewing break-down food into smaller particles by teeth & jaw muscle with tongue. • -2*swallowing: • -occur at mouth & pharynx. • -rapid less than one second . • -coordination &swallowing comes from(swallowing centre area) in the brain stem. • -gravity &muscle at the base of the tongue ,help in the movement of the food down to esophagus ,in the up-right position . • -in the stomach food enter by opening of the sphincter to prevent reflux ,&occurrence of heart burn . • ** chemical or secretary digestion : 3 pairs of salivary glands ,parotid ,sub-maxillary , sub-lingual ,secrete salivary amylase this enzyme is specific for starch digestion - : • • *factors affect salivary secretion :• 1-sight . 2-smell. 3-taste. 4-touch. 5thought of like & dis-like of food. • -normal range of daily saliva secretion between 800-1500ML,pH neutral 6.0 7.4 -stomach : storage & initial digestive process . • -as the food enter the stomach ,the muscle of the stomach mix the food ,storage ,&control emptying . • -when the food mixed with chyme ,the pyloric sphincter constrict & relax for control of emptying at duodenum. • **types of stomach secretion : • a-acid : HCL hydro chloric acid . • b-mucous : protect the wall of lining stomach & lubricant . • c- enzymes: pepsin ,break down of protein (pepsinogen converted to pepsin under HCL secretion ),gastric lipase for fat , rennin in child-hood aid in co-agulation of milk ,but absent in adult . الخضار • -control process of gastric secretion under effect of : • 1-nervous stimulus in response to sense ,ingested food & emotions ,e.g. anger & hostility increase secretion , while fear & depression ,decrease secretion . • 2-hormonal stimulus in response to entrance of food into stomach ,e.g. gastric enterogastrone -small intestine: major digestion & absorption • -under control of nervous plexuses or hormonal stimulation ,the wall stretch from pressure of food . • -small intestine is chemical digestion by secrete large number of enzymes & assistance of pancreatic enzyme . ** types of secretion : • a- enzymes . • b-mucous from glands near the duodenum to protect the mucosa of intestine . • c-hormones that stimulate pancreas to secrete alkaline juice . • d-bile secreted from liver &store by gall bladder to dissolve fat . Absorption • • • • • -end product of digestion . -CHO (glucose, fructose, galactose ). -fat (fatty acid ,glycerides). -protein (amino-acid ). -villi: finger like projection seen under microscope help in absorption *Routes of absorption : • -proteins &CHO become water soluble ,enter to blood stream ,go to liver ,&other tissue ,while fat is not water soluble ,bile secreted in intestine ,help in digestion of fat . • Large intestine : final absorption & waste elimination . • Water absorption take side at colon . • As much as 25% of meal may remain in rectum up to 7 hrs الفواكه Mineral absorption : • • • • • • Essential minerals as Na & K go to blood stream . Bacteria in the colon syntheses vit K . -intestinal bacteria affect color & odor of the stool . Brown stool comes from bile pigment . Intestinal gas or flatus produced by bacteria . Fiber does not digested so it contribute to form bulk of the stool . • Normal feces contain 75% water, 25% solids . • Solids ( fiber ,bacteria ,minerals ,small amount of fat , mucous). Metabolism • 1-CHO metabolism : • Source of blood glucose *CHO &non CHO substances * • *CHO sources: • -dietary starch & sugars . • -glycogen from liver & muscle tissue , by hydrolysis glycogen to glucose . *non CHO sources: • -from protein & fat . • -indirect source of glucose . • *in case of protein glycogenic amino-acid could be used in energy , if insufficient CHO . • *in case of fat broken to fatty acid &glycerol ,glycerol converted to glycogen in the liver . • -the process of production of glucose from protein or fat is called gluconeogenesis. • • • • -normal blood glucose level 70-120mg \dl. 1- energy production . 2-energy storage : Glucose converted to glycogen , stored in liver 7 muscle tissue . • Excess glucose converted to fat & stored in adipose tissue (fat tissue ). • 3- glucose product : • Glucose enter in DNA &RNA building . الحمضيات **hormonal controls • -blood sugar lowering hormones • a- insulin decrease blood sugar ,produced by beta cells in the pancreas. • -convert glucose in the liver to glycogen by process called glycogen sis . • -convert glucose to fat & storage in adipose tissue . • b-blood sugar raising hormones : • *1-glycogen -produced from alpha cells of pancreas, opposite action of insulin . • • • • • • *2-somatostatin: -delta cells of pancreas . -anti insulin effect *3-steroid hormones : -secreted from adrenal gland . -anti insulin effect *4-Epinephrine : • • • • • • • -secreted from adrenal medulla . -break down glycogen in the liver to glucose . *5-grouth hormone : -secreted from anterior pituitary gland . -anti insulin effect . *6-thyroxine : -increase glucose absorption from intestine