Gastric Secretion Flashcards
Fundus
(top part)
Storage
Body
(middle)
Storage, HCL, mucus, pepsinogen, intrinsic factor
Antrum
(bottom)
Mixing & grinding food
Gastrin (hormone for HCL release by g cells)
3 Gastric gland cells:
- Mucous neck cells (mucous)
- Chief cells (pepsinogen)
- Parietal cells (HCL & intrinsic factor)
Pepsin is stored in an inactive form as pepsinogen to prevent
degradation of proteins in stomach wall
CO2 waste product in blood enters stomach cell, combines with H2O to give
carbonic acid, which dissociates into bicarbonate & hydrogen ions
H ion then actively transported into stomach lumen using
hydrogen potassium ATPase (Stomach lumen pH<2)
Bicarbonate (HCO3) ion is released back into blood in exchange for
CL in (blood pH>7.4)
CL diffuses into
stomach lumen
Stomach lumen pH:
pH<2
3 types of control of gastric acid secretion:
- Neurocrine (vagus/local reflexes)
- Endocrine (gastrin)
- Paracrine (histamine)
3 types of control of gastric acid secretion:
- Neurocrine (vagus/local reflexes)
- Endocrine (gastrin)
- Paracrine (histamine)
Cephalic phase stimulation (in head):
- Sight, smell, taste
- Increase vagus nerve activity
- Ach release, gastrin release by G cells (increase HCL release by parietal cells)
- Release of ach and gastrin also stimulate enterochromaffin-like cells to release histamine (increase HCL release by parietal cells)
Gastric phase stimulation:
- Stomach stretching -> stimulate vagus/enteric reflex -> Ach released
- Peptide in lumen -> stimulate G cells -> gastrin released
- Gastrin/Ach release -> enterochromaffin-like cells -> histamine released
Mechanisms Stimulating
Gastric Acid Secretion involves:
Cephalic phase & Gastric phase
Mechanisms Inhibiting
Gastric Acid Secretion involves:
Cephalic phase, Gastric phase, Intestinal phase
For gastric acid secretion inhibition, in the Cephalic phase what happens?
stop eating –> vagal activity reduced
For gastric acid secretion inhibition, in the Gastric phase what happens?
decrease in pH by overproduction of HCL that is not used –> reduced gastrin release
Intestinal phase
- Acid in duodenum from stomach activates enterogastric reflex & released secretin
- This reduces gastrin stimulation & release)
- When fat and carbs enter duodenum, gastric inhibitory peptide released, gastrin & HCL secretion reduced
What are Enterogastrones?
Hormones released from gland cells in duodenal mucosa - secretin, cholecystokinin (CCK), GIP
When are Enterogastrones released?
- Released in response to acid, hypertonic solutions, fatty acids or monoglycerides in duodenum
- Act collectively to prevent further acid build up in duodenum
Enterogastrones have 2 strategies:
- Inhibit gastric acid secretion
2. Contract pyloric sphincter to prevent acid moving down
What is Pepsinogen?
A substance which is secreted by the stomach wall & converted into the enzyme pepsin by gastric acid
Pepsinogen is stored as an
inactive precursor (secreted by Chief cells)
Pepsins inactivated at what pH?
neutral pH (to prevent cellular damage)
Pepsinogen cleaved into pepsin at what pH?
pH<3 (low pH)
Inactive precursor =
Zymogen
What is gastric mucus produced by?
surface epithelial cells & mucus beck cells
What does gastric mucus do?
- Protects mucosal surface from mechanical injury
- Protects against gastric acid corrosion & pepsin digestion
Intrinsic factor produced by
Parietal cells
Intrinsic factor required for
vitamin B12 absorption
Intrinsic factor/B12 complex absorbed from
ileum
Defect in intrinsic factor causes
Pernicious Anaemia (failure of erythrocyte maturation)
