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 secretionK+
ATP
Na+

6. control of acid secretionM3
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
cytokines

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