Lec 5. GIT 12 March 14
StomachObjectives 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 regionb. Fundic---filled with swallowed airc. Body regiond. The pyloric region ( antrum)Blood and lymphatic supply. Gastric Innervation----para & symp
Gastric SecretionComposition 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 enzymesOxyntic 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/dayPH is 0.8 highly acidicBasic 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 secretionHistamine: 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 mucusmucus alkaline.Lubrication1 millimeter thick, thus providing a major shell of protectionSubstances 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 gastrinPhases of Gastric Secretion
Cephalic phase .. Gastric Phase . Intestinal Phase
Cephalic phasebefore food enters the stomachsight, 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 secretionAccount 20% of gastric secretion.
Gastric phase
A.Distention ---1.vagovagal---MO—vagus--stomach2. local enteric reflexes, 3.GRP---. gastrin SECRETION---acid secretionFood ,caffein,low acid--- G – cells--gastrin secretionB,stress,high acid ----gastric secretionby 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