Physiology - stomach Flashcards
digestion of protein by x
digestion of carb by x
Starting point for digestion of
proteins (by pepsin and HCl),
continues carbohydrate
digestion (by salivary amylase)
- Distension increases motility due to:
o stretch of smooth muscle
o increased vagus nerve activity and gastrin release
bicarboante secreted from the x neutralizrs tomach acid
pancreas
secretions of gastric glands
functions of gastric secretions
Oxyntic mucosa (fundus and body)
➢ HCl
o activates pepsinogen to pepsin
o denatures protein
o kills most (not all) micro-organisms ingested with food
➢ Pepsinogen
o inactive precursor of the peptidase, pepsin. Note: pepsin once formed
activates pepsinogen (autocatalytic)
➢ Intrinsic factor and Gastroferrin
o bind vitamin B12 and Fe2+ respectively, facilitating subsequent absorption
➢ Histamine
o stimulates HCl secretion
➢ Mucus
o protective
functions of gastric secretions
Pyloric gland area (pylorus and antrum)
➢ Gastrin
o stimulates HCl secretion and motility
➢ Somatostatin
o inhibits HCl secretion
- mucus = protective
HCl secreeted by x cells
parietal cells
Histamine is secreted by the _____ cells in response to stimulation by ______
with activation by ……….. it binds to ………
the increase in ________ increases the number of _______, increasing/decreasing ?? gastric acid secretion from xxx cells
enterochromaffinlike cells
acetylcholine
adenylyl cyclase
H2 receptors
cAMP
proton pumps,
increasing
parietal cells
___ is released by parasympahtetic x neurons
it binds to ……….. receptors
activating ………
increasing intracellular…………..
evoking cell signallig pathways that increase the number of _______
increasing gastric acid secretion from x cells
- ACh
parasympathetic
cholinergic
muscarinic (M3) ACh receptors on
parietal cells
PLC
The increase in
intracellular Ca2+
proton pumps,
parietal cells
Gastrin is released by —- cells
binds to — receptors
activating ——
the increase in intracellular —-
increases the number of ——–
increasing gastric acid secretion from x cells
Gcells
CCK2 receptors
activation of PLC
- The increase in
intracellular Ca2+
parietal cells
somatostatin secreted by —– cells in —
binds to ——- receptors
inhibting/activatnig ???? adenylyl cyclase
decreasing ___________
decreasing/increasing gastric acid secretion from x cells
somatostatin binding to ——— receptors on enterochromaffin cells results in reduced/increased histamine release and decreased/increased gastric acid secretion from x cells
D cells in the gastric glands
SST2R receptors,
inhibiting adenylylncyclase
decreasing cAMP results in
decrease gastric acid secretion
from parietal cells
to SST2R receptors
reduced histamine
decreased gastric acid secretion
fromparietal cells
Stimuli for secretion of H +
act by both
PLC - IP3
cAMP -PKA
signalling
pathways
(gastrin, ACh)
histamine
gastrin + Ach act through the xxx signalling pathway to xxxx H+
PL-IP3
increase secretion of H+
histamine acts through the xx signalling pathway to xxx
cAMP- PKA
increase secretion of H+
prostaglandins + somatostatins act through the …. signalling pathway to…
cAMP-PKA
ihibit secretion of H+
Note the opposing effects
of histamine (stimulation)
and somatostatin and
prostaglandins (inhibition)
upon adenylate cyclase
†pain, nausea and negative emotions decrease / increase vagal nerve activity
(parasympathetic) and increase/decrease sympathetic activity that combined reduce/increase
gastric acid secretion
decrease
increase
reduce
Cephalic hase of gastric acid secretion
– before food reaches the
stomach preparing it stomach to receive food
* driven directly and indirectly by the CNS and vagus nerves
(CN X
gastric phase
when food is in stomach
* involves both physical and chemical mechanisms
intestinal phase
– after food has left stomach
* chyme entering the upper small intestine causes weak
stimulation of gastric section via neuronal and hormonal
mechanisms
dring the cephalic phase
vagus stimulates enteric neurons that
- ACh
- gastrin
- histamine
- somatostatin
during the gastric phase
- D cells + somatostatin
- gastril and parietal cells
- ACh, gastrin, parietal cells
-ECL cells + histamine
