Gastric secretion

1. Gastric secretions -1
Dr. Sai Sailesh Kumar G
Associate Professor
Department of Physiology
RDGMC
DR Sai Sailesh Kumar G 1

2. Learning objectives
 List the different types of gastric glands and
indicate their secretions
 List the composition and functions of gastric juice
 Outline the steps involved in the formation of
gastric acid
 Describe the regulation of gastric acid secretion
 List different phases of gastric acid secretion and
factors influencing them
 Outline the basis of various forms of treatment for
acid peptic disease DR Sai Sailesh Kumar G 2

3. Gastric secretion
 Type of glands
 Stomach mucosa has two important types of
tubular glands
1. Oxyntic glands (gastric glands)
2. Pyloric glands
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4. Oxyntic glands
 Acid forming glands
 Location: inside surface of body and fundus of
stomach
 Secretes
1. Hydrochloric acid,
2. Pepsinogen
3. Intrinsic factor
4. Mucus
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5. Anatomical regions of stomach
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6. Oxyntic glands
 Acid forming glands
 Location: inside surface of body and fundus of
stomach
 Secretes
1. Hydrochloric acid,
2. Pepsinogen
3. Intrinsic factor
4. Mucus
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7. Oxyntic glands
 Composed of three types of cells
1. Mucous neck cells – secrete mucus
2. Peptic or chief cells – secrete pepsinogen
3. Parietal or oxyntic cells – secrete hydrochloric
acid and intrinsic factor
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8. Oxyntic glands
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9. Pyloric glands
 Structurally similar to oxyntic glands
 But have few peptic cells and no parietal cells
 Location: Antral portion of stomach
 Secretes mucus
 Mucus offers protection to pyloric mucosa from acid
 Also secretes gastrin (hormone)
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10. Pyloric glands
 Composed of three types of cells
1. Mucous neck cells – similar with mucous neck
cells of oxyntic glands. Secretes mucus
2. Peptic or chief cells – secrete pepsinogen
3. G cells – secretes gastrin (key role in regulation
of gastric secretion)
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11. Surface mucous cells
 Location: entire surface of stomach mucosa
 Secretes large amounts of viscid mucous
 Mucus is alkaline
 Coats the stomach mucosa with a gel layer of mucus
 More than 1 mm thick
 Major protection to stomach wall from acid
 Also helps for lubrication of food
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12. Composition of gastric juice
 Amount: 1.5 – 2 L (adult human)
 Consumption of meal
 Stimulates gastric glands
 Secretion of gastric juice
 Gastric juice mainly composed of water and solutes
 Inorganic- Hcl, sodium, potassium and bi carbonates
 Organic – enzymes - Pepsin, gastric lipase, Gelatinase
and Intrinsic factor DR Sai Sailesh Kumar G 12

13. Mechanism of HCL secretion
 When stimulated, parietal cells secrete acid solution
that contains about 160mmol/L of HCL
 pH of this acid is 0.8
 Extremely acidic
 Hydrogen ions concentration is 3 million times that
of arterial blood
 To concentrate this much hydrogen ions it requires
1500 cal of energy per liter of gastric juice
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14. Mechanism of HCL secretion
 Parietal cell contain large branching intracellular
canaliculi
 Hydrochloric acid is formed at the villus like
projections inside these canaliculi
 It is then conducted through the canaliculi to the
secretory end of the cell
 The main driving force for HCL secretion is
hydrogen-potassium pump
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15. Parietal cell
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16. Parietal cell
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17. DR Sai Sailesh Kumar G 17

18. Step One
 Water inside the parietal cell dissociates into H+
and OH- in the cell cytoplasm
 H+ is actively secreted into the canaliculus in
exchange for potassium
 Active exchange process
 Catalyzed by H+- K+ ATPase
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19. Step Two
 At the basolateral side ( extra cellular fluid side)
 K+ ions are transported into the cell by sodium
potassium pump
 K+ ions tends to leak into the lumen
 Recycled back into the cell by H+- K+ ATPase
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20. Step Three
 At the basolateral side ( extra cellular fluid side)
 Sodium potassium pump creates low intra
cellular sodium concentration
 Sodium in the canaliculus is reabsorbed in the
cell cytoplasm
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21. Step Four
 Pumping of H+ out of the cell by H+ - K+ ATP ase
 Accumulation of OH- in the cell
 OH- combines with carbon dioxide
 Forms HCO3- (bicorbonate)
 Reaction is catalyzed by carbonic anhydrase
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22. Step Five
 HCO3- (bicorbonate) transported across basolateral
membrane into ECF
 In exchange for chloride ions which enter the cells
and secreted into the canaliculus
 Makes a strong solution of HCL in the canaliculus
 HCL is then secreted outwards through the open
end of canaliculus into the lumen of the gland
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23. Step Six
 Water passes into the canaliculus through osmosis
 Because of extra ions secreted into canaliculi
 Final secretion in the canaliculus
1. Water
2. HCL (150-160 mEq/L)
3. KCL (15 mEq/L)
4. Small amounts of Nacl
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24. Regulation
 Stimulation of acid secretion by acetyl choline
 Acetyl choline released by parasympathetic stimulation
 Excites secretion of pepsinogen by peptic cells
 HCL by parietal cells
 Mucus by mucus cells
 In comparison, gastrin and histamine of acid by parietal
cells but have little effect on the other cells
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25. Regulation
 Stimulation of acid secretion by histamine
 Enterochromaffin like cells (ECL cells) secrete
histamine
 The rate of formation and secretion of HCL is
directly related with amount of histamine
released by ECL cells
 ECL cells are stimulated by hormone gastrin
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26. Regulation
 Stimulation of acid secretion by gastrin
 Gastrin is secreted by G cells ( gastrin cells)
 These cells located in the pyloric glands in the distal end of
the stomach
 Gastrin is polypeptide hormone
 Two forms-
 Larger form - G-34 ( 34 amino acids)
 smaller form - G-17 – ( 17 amino acids)
 Smaller form is more abundant
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27. Regulation
 Meat or food containing protein reach to antral end of
stomach
 Some of the proteins in the food has stimulatory effect
on G cells
 Secretion of gastrin into blood
 Transport of gastrin to ECL cells of stomach
 Release of histamine into deep oxyntic glands
 Stimulation of gastric hydrochloric acid secretion
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28. Regulation
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29. DR Sai Sailesh Kumar G 29

30. THANK YOU
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