lec 6 Flashcards
Hydrochloric acid (HCl) function
- Activates the enzyme precursor pepsinogen
- Aids in the breakdown of connective tissue and muscle fibers
- Denatures protein بفك الflods
- Along with salivary lysozyme, kills most of the microorganisms ingested with food
Aids in the breakdown of connective tissue and muscle fibers how
reducing large food particles into smaller particles
Parietal cells secrete
HCL + IF
The pH of HCL
is about 0.8,
hydrogen ion concentration at 0.8 PH
about 3 million times that of the arterial blood
the pH of the cytoplasm of the parietal cell is
7.2 to 7.4
the parietal cells secrete an acid solution that contains
0.17 N HCl,
160 mmol/L) of HCl
HCL in other cells
4 X 10-5meq/L
that gastric venous blood has a higher pH than arterial blood when the stomach is secreting acid
To concentrate the hydrogen ions this tremendous amount requires more than 1500 calories of energy per liter of
gastric juice. While hydrogen ions are secreted, bicarbonate ions diffuse into the blood
alkaline tide”
HCO3-
is added to the venous blood, the pH of the blood increases
fate of HCO3-
will be secreted in pancreatic secretions to neutralize H+ in the small intestine.)
If vomiting occurs
gastric H+ never arrives in the small intestine, there is
▼
no stimulus for pancreatic HCO3
-secretion, and
▼
the arterial blood becomes alkaline (metabolic alkalosis).
The agents that stimulate H+ secretion
- Acetylcholine
- Gastrin
- Histamine
Acetylcholine and Gastrin will stimulate H+ secretion
Gq and the second messenger is IP3 and
increased intracellular [Ca+)
Acetylcholine and Gastrin will stimulate H+ secretion
Gq and the second messenger is IP3 and
increased intracellular [Ca+)
Histamine will stimulate H+ secretion
H2 receptor is coupled to adenylyl cyclase via a Gs protein. The second messenger for histamine is cAMP.
The second messenger for
histamine is
cAMP.
the second messenger for Acetylcholine and Gastrin
IP3 and
increased intracellular [Ca+].
Vagal stimulation (In the direct path)
vagus nerve →Acetylcholine → M3 r on parietal cell → HCL
Vagal stimulation in the indirect path
- vagus n → Gastrin Releasing Peptide (GRP) →M3 r on G cells → Gastrin (carried from antrum to body by blood to stimulate H+ secretion
- vagus n→ Gastrin Releasing Peptide (GRP → M1 →entero-chromaffin-like(ECL) cells → Histamine →H2 receptor on P.C > H+
The direct pathway is blocked by
Atropine
atropine does not block HCl secretion completely
because it does not inhibit the indirect pathway, which uses GRP as a neurotransmitter.
Vagotomy
eliminates both direct and indirect
pathways.
Gastrin secretion increased by
- Stomach contents
2. Vagal stimulation
Gastrin secretion increased by Stomach contents ?
Small peptides and stomach distension→ vago-vagal reflex →stimulate G cell → gastrin
gastrin stimulate H+ secretion by Directly effect on parietal cell
Gastrin will bind Chole-cysto-kinin type B
(CCK-B) receptor in parietal cell
Gastrin will stimulate parietal cells to secretHCl
gastrin stimulate H+ secretion Indirectly effect on ECL cell
Gastrin will bind Chole-cysto-kinin type B
(CCK-B) receptor in entro-chromaffin cell
(ECL); which stimulates Histamine secretion
Histamine will diffuse from Enterochromaffin-like (ECL) cells to the nearby parietal cells
in paracrine Fashion
H2 receptor-blocking drugs
cimetidine (the direct action of histamine
b. the histamine-potentiated effect of both acetylcholine and gastrin)
The rate of hydrochloric is regulated
by independent actions of histamine, acetylcholine, and gastrin
by interactions among the three agents
(potentiation)
result
ow concentration of stimulus given together can produce maximal effects
explanation of potentiation in parietal cell
1.Each agent stimulates HCl secretion via a different receptor
2.both acetylcholine and gastrin stimulate
histamine release from enterochromaffin like cell
Mechanism decrease release of
Hydrochloric acid by parietal cell
- Low pH (< 3.0) in the stomach
- Somatostatine
- prostaglandin
Low pH (< 3.0) in the stomach
- Negative feedback
2. inhibits gastrin
When the pH of the stomach contents is
< 3.0
- .(After a meal is ingested
2. When the stomach emptied
Somatostatin is a
14-amino-acid peptide
the gastrointestinal tract D cells located
the antrum and enteric nerves
Somatostatin in
the gastrointestinal tract D cells (located in the antrum), and enteric nerves and
pancreas from D cell in island of Langerhans
the hypothalamus
Somatostatin physiologic effects
- inhibits the secretion of numerous hormones and transmitters (GI hormones
Pancreases and hypothalamus
2.reduces intestinal fluid and pancreatic secretion
3.slows GIT motility and inhibits gallbladder contraction
4.direct contraction of vascular smooth muscle→ Lading to a reduction of portal and splanchnic blood flow
5.inhibits secretion of some anterior pituitary hormones.
Prostaglandins and Somatostatine inhibit gastric H+ secretion by
activating a Gi protein,
inhibiting adenylyl cyclase and
decreasing cAMP levels
D cell in the antrum is stimulated by directly by
vagaus → calcitonin gene releasing peptide (CGRP) on M2
2.H+ is sensed by the D cells in the antrum Somatostatin transfer from D cell to parital cell by blood to inhibit HCl through Somatostatin type 2 (SST2)
receptor
