Lec 5. GIT 12 March 14

Stomach Objectives 1.Physiological anatomy 2.blood supply 3.innervation 4.Gastic secretion

Physiological Anatomy The stomach is a j – shaped. ( rugae) stomach to change size and adapt its content. Anatomically the stomach is divided into a. Cardiac region b. Fundic---filled with swallowed air c. Body region d. The pyloric region ( antrum)

Blood and lymphatic supply. Gastric Innervation----para & symp

Gastric Secretion

Composition of normal gastric juice (fasting state hydrochloric acid---- intrinsic factor pepsinogen mucus, hormone gastrin cations and ( such as Na+ ,K+ , Mg2+ , H+ ) , anions ( Cl- , HCO3- , So42-,Hpo42-) digestive enzymes

chief cells ----- pepesinogen. Oxyntic Glands -------HCL ,intrinsic factor, pepsinogen, , and mucus. composed of three types cells : chief cells ----- pepesinogen. b. parietal ( or oxyntic cells ) -----HCl and intrinsic factor c. mucous neck cells----- mucus .

Basic mechanism of HCL Secretion HCL--150–160 mmol/L in amounts of 1–2 L/day PH is 0.8 highly acidic Basic steps for HCl formation

Q: Any factor inhibits the enzyme carbonic acid anhydrase (CA) or H-K ATPase will abolish the secretion of HCL from oxyntic cells. Why?

Postprandial(enteroprandial) alkaline tide:. Increase in H secretion ----increase HCO3- To blood -----increase PH ( Alkaline)---alkaline urine

Q.explain why a slight increase in blood PH may occur following a heavy meal?.

Stimulation of gastric acid secretion Histamine: Acid secretion is stimulated by histamine via H2 receptors acetylcholine . by acetylcholine via M3 muscarinic receptors GASTRIN----GASTRIN RECEPTOS EITHER: directly by gastrin receptors indirectly ---- ECL cells---Gastrin is the major regulator of the ECL cells. .

2.Pepsinogen inactive precursor pepsinogen--- intragastric pH lower than 5 -------- active enzyme pepsin Pepsinogen detected in the plasma and in the urine, where it is called uropepsinogen 3.Intrinsic factor ----with dietary vitamin B12----- absorption distal ileum,

3. Intrinsic factor Intrinsic factor is secreted by the parietal cells. It combines with dietary vitamin B12, forming a complex necessary for the absorption of the vitamin in the distal ileum.

4.Surface Mucous Cells viscid mucus mucus alkaline. Lubrication 1 millimeter thick, thus providing a major shell of protection Substances cause gastric irritation are : ethanol , vinegar , bile salts , aspirin , and other non steroidal anti – inflammatory drugs ( NSAIDs).

4.Digestive Enzymes Gelatinase---liquefies gelatin . lingual lipase---for partial digestion of fats.. gastric lipase----for partial digestion of fats..

Pyloric Glands no parietal cells mucus neck cells---mucus ,small amount of pepsinogen Secrete hormones gastrin

Phases of Gastric Secretion Cephalic phase . . Gastric Phase . Intestinal Phase

Cephalic phase before food enters the stomach sight, thought----cerebral cortex----hypothalamus &MO---para.vagal---gastric secretion smell,, or taste of food, tactile sensation ---hypo &MO-----Para. Vagal---gast.secre. Loss of appetite –---gastric secretion Account 20% of gastric secretion .

Gastric phase A.Distention ---1.vagovagal---MO—vagus--stomach 2. local enteric reflexes, 3.GRP---. gastrin SECRETION---acid secretion Food ,caffein,low acid--- G – cells--gastrin secretion B,stress,high acid ----gastric secretion

by vagal stimulation about 500ml of HCl is secret daily),while by gastrin release about 200ml /day is released

Q. What happens when Surgeon cuts the vagal nerve(parasympathetic cranial nerve) to the stomach

Intestinal phase 1.Entergastric inhibitory reflex : 1.myenteric nervous system 2.extrinsic sympathetic and vagus nerves-----inhibits gastric secretion 2.Hormonal . inhibitory hormones (VIP CCK,GIP,secretin)—inhibit gastric and motility secretion