Stomach Flashcards
three regions of the stomach
cardia, body/corpus, antrum
covers the entire surface of the stomach
viscid mucous
characteristic of the cardia, body, and antrum of stomach
cardia - no acid secreting cells but responsible for mucous and HCO3-
body - gastric gland, parietal and chief cells, mucous secreting neck cells, ECL cells which release histamine
antrum - pyloric glands contain endocrine cells (gastrin G cell and somatostatin D cells) and chief cells (secrete pepsinogen)
what is the motor and protection function of the stomach
motor - reservoir, mixing, kneading, regulated emptying
protection - destroys pathogens
what is the exocrine and endocrine secretion function of the stomach
exocrine - H+, intrinsic factor, pepsinogen, mucus, HCO3, H2O, gastric lipase
endocrine - gastrin and somatostatin
some other motor functions of the stomach
- Relaxation and dilation to receive and store food
- Contracts to mix food with water and gastric secretions
- Churning: grind food to decrease particle size
- Moves the resultant chyme through the pyloric sphincter into the duodenum- at an appropriate rate
stomach motility in fasting state
in fasting state: stimulation of the migration motor complex which cleans the gut every 1-2 hours (or 90 mins)
stomach motility in fed state
- when meal enter stomach: vago-vagal reflex (receptive relaxation & accomodation)
- peristalsis begins: increased gastric pressure, slow sustained propulsive contraction that pushes food towards the closed pyloric sphincter in the antrum (retropulsion - no food leaves the stomach in the immediate post prandial phase)
- antral systole: contractions of distal stomach grinds food and mixes it with gastric juices –> powerful contractions “antral systole” force food back for more mixing
amount of chyme that goes through the pyloric sphincter and the size of particles
1mL
particles less than 2mm
what is pyloric stenosis
hypertrophy of pyloric sphincter which causes project vomiting from force exerted on pylorus
characteristics seen in patients with pyloric stenosis
- occurs mainly in children and it makes them always hungry
- dehydrated
- olive shaped mass felt in right upper quadrant
- string sign (where pylorus is constricted) on CT scan
- mushroom sign (aka kirklin sign) on CT
emptying of stomach is regulated by what
ANS and gut hormones
types of contractions in motility
tonic contraction - low amplitude and in orad region
phasic contraction - caudad region
rates of emptying of different fluids and materials in descending order
water or isotonic saline > acid and caloric fluids > fatty material
what initiates the peristaltic wave that leads to circumferential constrictor waves»_space; mixing, grinding, and propeling
pacemaker
what is dumping syndrome
rapid gastric emptying that leads to distension of proximal small intestine
what causes diarrhea in dumping syndrome
hypertonic fluid pulling fluid into the lumen
symptoms of dumping syndrome
tachycardia, diarrhea, sweating, hypertension, flushing, palpitation, abdominal discomfort, autonomic reflexes –> release of GIT hormones
cell type in pit or neck of the oxyntic gland and what do they secrete
mucus surface cells and mucus neck cells
they secrete mucus, bicarbonate, and water
what does HCl and intrinsic factor do
HCl - activates pepsin, kills bacteria, denatures protein
intrinsic factor - activates vit b12 to enable absorption in lumen
what increases secretion of parietal cells
gastrin, acetylcholine, histamine
function of pepsinogen and gastric lipase
pepsinogen - digest proteins once cleaved to pepsin
gastric lipase - starts fat digestion
what stimulates secretion of chief cells
acetylcholine and secretin
what increases secretion in the neck/pit of the oxyntic gland
acetylcholine
cell types after the neck of the oxyntic gland and what they secrete
parietal cells (oxyntic) –> secrete HCl, intrinsic factor, water
cells active in base of oxyntic gland and what they secrete
peptic chief cells –> secrete pepsinogen, gastric lipase, water
area of stomach that is oxyntic gland and that is pyloric area
oxyntic gland - 80%
pyloric - 20%
explain the mechanism for the secretion of gastric acid/HCl
- H+ is pumped out of the cell via the H+/K+ ATPase on the apical surface
- the K+ leaks back out into the lumen via a channel to provide the K+ needed for the exchange for H+
- the H+ is provided by CO2 coming into cell and with H20 and CA forming H2CO3 which dissociates to H+ and HCO3-
- the HCO3- is pumped back into the plasma (alkaline tide) in exchange for Cl- (using HCO3-/Cl- exchanger)
- the Cl then exits the cell into the lumen to provide the Cl- to use to make HCl with the already secreted H+
what protects the mucosa
mucous gel barrier
oxyntic fluid vs. non oxyntic fluid
oxyntic fluid - high H+, Cl-, and K+ with low Na and no HCO3
non oxyntic fluid - high HCO3, Na, Cl with low K+ and H+
what is happening when you vomit
you are getting rid of acid (HCl) so you have an increase in bicarb making person alkalotic –> metabolic alkalosis
also because of decrease in H+, K+ will replace H+ on the transporter to be secreted hence person become hypokalemic
time spent in cephalic and gastric phase in stimulation of acid secretion
cephalic - 30%
gastric - 50%
what is happening in the cephalic phase
vagus nerve is stimulated due to sight or smell of food –> stimulation of acetylcholine which triggers –> parietal cells, gastrin releasing peptide (act on G cells to produce gastrin which acts on parietal cells to produce HCl)
negative feedback for HCl - how do you stop its production
increased H+ –> inhibits G cells
increased H+ –> increases D cells (somatostatin) which inhibits G cells
if G cells are inhibited then they can’t act on parietal cells to release HCl
more ways to inhibit parietal cells
somatostatin can directly inhibit it
somatostatin can inhibit ECl which releases histamine
PGE2 can directly inhibit it
what happens if fats, acids, proteins, or hyperosmolar fluid gets into the small intestine
stimulation of enteric hormones like CCK, secretin, GIP, neurotensin, peptide YY, VIP, somatostatin
what digestive enzymes are present in the stomach and what they digest
gastric amylase - starch
gastric lipase - butter fat
intrinsic factor - facilitate b12 absorption
pepsin - protein
what does chief cell secrete
pepsinogen which in presence of pH less than 5 is activated to pepsin
importance of bicarb rich zone in protection of the mucosa
- if any of the H+ is able to cross the mucus gel barrier into the bicarb rich zone, the bicarb can neutralize the ion
- also inactivates pepsinogen so that there is no protein degradation of the epithelium
what does the integrity of the defense barrier depend on
balance of defensive and aggressive factors so you want to have more bicarb, mucus, blood flow, growth factors, cell renewal, prostaglandins
treatment for pyloric
antibiotics
