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 intra-mural 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

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*factors affect salivary secretion :- 1-sight . 2-smell. 3-taste. 4-touch. 5-thought 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 .

*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