1. Ingestion of food
GIT
GIT Secretions
Dr.Rashid Mahmood

2. Activation of Pepsinogen
Proteins in food
Nervous system
Gastrin
HCl
Causes proteolysis
Pepsinogen
Pepsin
Contd…..

3. Pepsinogen activation in stomach lumen

4. Types of Pepsinogen
Pepsinogen I
Pepsinogen II

5. 3. Pyloric glands Structurally similar to oxyntic glands but
Few peptic cells
Almost no parietal cells
Mostly mucous cells
Small amount of Pepsinogen
Mucus
Lubrication
Protection
Gastrin
Secreted by G cells located in pyloric glands

6. Nervous system
HCl
Causes proteolysis
Pepsinogen
Pepsin

7. Pepsinogen activation in stomach lumen

8. Types of Pepsinogen
Pepsinogen I
Pepsinogen II

9. Intrinsic factor Parietal cells Absorption of B-12 in ileum
Chronic gastritis→ Achlorhydria→ Pernicious Anemia

10. 3. Pyloric glands Structurally similar to oxyntic glands but
Few peptic cells
Almost no parietal cells
Mostly mucous cells
Small amount of Pepsinogen
Mucus
Lubrication
Protection
Gastrin
Secreted by G cells located in pyloric glands

11. Stimulation of Gastric Acid Secretion
Food in stomach
(Proteins)
Nervous signals
Gastrin
cells
Endocrine signals
ECL (Enterochromafin-like cells) in
oxyntic glands in body of stomach
Gastrin
Stimulation
of Gastric
Acid Secretion H2
Receptors
(in Parietal cells)
Histamine

12. Stimulation of Gastric Acid Secretion

13. Gastrin Secreted by G cells located in pyloric glands Polypeptide
2 forms (both important)
G-34
G-17 (More abundant)
Stimulated by proteins
Secreted into stomach
Carried to ECL cells in body of stomach by MIXING movements of the stomach

14. Phases of gastric secretion
Three phases
Cephalic phase
Before food enters stomach
Sight, smell, thought
Taste, food being eaten
Gastric phase
When food in in stomach
Intestinal phase
When food reaches upper portion of small intestine

15. Phases of Gastric Secretion1
20% 1
Cerebral cortex &
Appetite center
of lower brain 2
Sight
Smell
Thought
Taste
70% 3
10%

16. Intestinal phase of Gastric Secretion
All these factors also
↓the gastric motility
Hormones:
Secretin
CCK
GIP
VIP
Somatostatin
Initially slight stimulation

17. Gastric secretion during inter digestive period
Small amount
Mainly mucus
Little pepsin
No acid
↑ by emotional stress → Peptic ulcer

18. For digestion of Proteins (Trypsin, Chymotrypsin, Elastase, Carboxypeptidase)
Inactive (Proenzymes)
Trypsinogen, chymotrypsinogen, procarboxypolypeptidase
Trypsin, Chymotrypsin, Elastase → Endopeptidases
Carboxypolypeptidase → Exopeptidases
Mechanism of stimulation of proenzymes
Chyme
Enterokinase
Intestinal mucosa
Activation of Proenzymes
inside lumen of intestine
Contd…..

19. Secretion of Bicarbonate by Pancreas5 4 2 3 1 6

20. Functions of HCO3-- Neutralize acid pH of stomach
Optimum pH for pancreatic enzymes
Blockage of digestive action of digestive enzymes (because digestive enzymes of stomach become inactivated at pH>3-4.5

21. Rate of Pancreatic secretion

22. Diseases of pancreas Pancreatic failure
Causes
Pancreatitis
Acute
Chronic
Causes of Pancreatitis:
Alcohol
Blockage of Ampulla of Vater by Gall Stone
Blockage of Pancreatic duct by at Ampulla of Vater by Gall Stone
Removal of head of Pancreas due to malignancy

23. Effects of Pancreatic failure
Effect on Pancreas
Effect on digestion
Effects on absorption

24. Effects of Pancreatic failure
Effect on Pancreas
Blockage → accumulation of Pancreatic enzymes → overcoming the Trypsin Inhibitor → activation of Trypsinogen → formation of Trypsin and other Proteolytic enzymes →digestion of Pancreas itself
Effect on digestion
Loss of digestive enzymes
Copious fatty feces
½ to 1/3 effect on carbohydrate & protein digestion
Undernutrition

25. 3. Effects of Pancreatic failure on absorption
More effect on Fats absorption
Steatorrhea
Acid inhibits lipase
↓ alkaline secretion by pancreas → ↓ pH
Impaired absorption of
Carbohydrates
Proteins
Calcium
Vitamin K

26. Summary Slide Pancreatic Secretion
Components of Pancreatic secretion
Pancreatic Digestive Enzymes
For digestion of Proteins, Carbohydrates and Fats
Bicarbonate and water
Functions of HCO3--
Regulation/ control of Pancreatic Secretion (Factors affecting)
Phases of Pancreatic secretion
Diseases of pancreas
Pancreatic failure