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Physiological functions of the stomach

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1 Physiological functions of the stomach
Digestive Physiology By: M.H.Dashti Lecture 4 Physiological functions of the stomach

2 Anatomy of Stomach cardia fundus---air in x-ray body
Size when empty? large sausage stretches due to rugae Parts of stomach cardia fundus---air in x-ray body pylorus---starts to narrow as approaches pyloric sphincter

3 Physiological functions of the Stomach - secretions
By Oxyntic and Pyloric glandular cells exocrine Gastric juice-2-3 L/day Water & electrolytes enzymes Mucus Endocrine: Gastrin Paracrine Histamine Somatostatin

4 Gastric glandular cells & their secretions
surface mucous cells & mucous neck cells Alkaline Mucin Parietal cell Hydrochloric acid and Intrinsic factor Chief ,peptic or zymogene cell Gastric lipase, pepsinogen and rennin G cell Gastrin hormone ,rennin Entrochromafin cells produce paracrine secretions of Histamine & D cells Somatostatin

5 Mechanisms of acid secretion
K+ ATP Na+

6 control of acid secretion
M3 CckB Histamine Ach Gastrin Somatostatin Prostaglandins EGF PGE2 cAMP - IP3


8 Ionic concentrations of gastric juice as a function of secretion rate
.At low flow rates the juice is hypotonic At high flow rates it approaches isotonicity and contains predominantly H+ and Cl-

9 Gastric alkaline mucosal barrier

10 Factors affecting Gastric alkaline mucosal barrier
stimulation Prostaglandins parasympathetic inhibition Sympathetic Bile salts Alcohol Citric acid pH~7 at Cell surface

11 Helicobacter pylori & Gastritis

12 Control of the chief cells
Secretin , VIP & β-adrenergic agonists act via CAMP Ach Gastrin & cck act via IP3 & Ca2+ Mechanism for Potentiation effect of H+ is not known Pepsinogen & Gastric lipase


14 type II & III are stimulated by Ach & Gastrin and inhibited by NE
Gastric motility : type I type II typeIII Gentle mixing waves (type I) every 20 seconds (BER) mixes bolus with 2 .5 L/day of gastric juice to turn it into chyme More vigorous waves (type II) travel from body of stomach to pyloric region Intense waves (type III ) open the pylorus and squirt out 3ml of chyme with each wave type II & III are stimulated by Ach & Gastrin and inhibited by NE

15 Gastric motility: Mechanical Digestion

16 Pyloric sphincter & Pyloric pump
Myenteric plex Sub mucosal plexus Circular muscle layer Longitudinal muscle layer duodenum antrum

17 Control of Gastric functions Three Phases

18 Cephalic Phase = “Stomach Getting Ready”
Sight, smell, taste & thought stimulate parasympathetic nervous system Vagus nerve increases stomach muscle and glandular activity Receptive relaxation

19 Gastric Phase = “Stomach Working”
Nervous control via stretch receptors & chemoreceptor keeps stomach active vigorous peristalsis and glandular secretions continue chyme is released into the duodenum Endocrine gastrin hormone increases stomach churning and pyloric sphincter relaxation

20 Intestinal Phase = “Stomach Emptying”
Stretch receptors in duodenum slow stomach activity & increase intestinal activity Distension, fatty acids or sugar signals medulla sympathetic nerves slow stomach activity Hormonal influences (from SI) secretin hormone decreases stomach secretions cholecystokinin(CCK) decreases stomach emptying Takes 2-4 hrs to completely empty the stomach Hormones ,short & Inhibit gastric function

21 Regulation of Gastric Emptying

22 Chemical Digestion in the Stomach
Protein digestion begins HCl denatures (unfolds) protein molecules HCl transforms pepsinogen into pepsin that breaks peptides bonds between certain amino acids (aromatics) Rennin in infants Fat digestion continues gastric lipase splits the triglycerides in milk fat most effective at pH 5 to 6 (infant stomach)

23 Absorption of Nutrients by the Stomach
Water especially if it is cold Electrolytes Some drugs (especially aspirin) & alcohol

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