GI 2: Gastric Function Flashcards
What is the function of the stomach?
➢ Temporary storage of ingested material
➢ Production of Chyme (Mechanical digestion and mixing)
➢ Meter delivery of chyme to duodenum
➢ Partially sterilize meal
➢ Initiates protein digestion
➢ Produce Specialized Secretions
What are the specialized secretions by the stomach?
- HCl acid
- Pepsinogen
- Intrinsic factor
- Mucus
- Hormones/Paracrines
What are the four sections of the stomach?
- cardia
- fundus
- body
- antrum
What are the four types of gastric motility in the stomach?
- receptive relaxation
- peristalsis (trituration/homogenization)
- emptying (pyloric sphincter)
- migrating motility complex (MMC)
What is the function of gastric receptive relaxation?
➢ Accommodate the volume of the meal
➢ Reduce pressure increases preventing gastric reflux and premature gastric emptying
What is the function of gastric peristalsis in the stomach?
➢ Chyme production
➢ Trituration: Mix ingested nutrients with gastric secretions, breakdown large particles and increase SA for digestion
What is the function of emptying the stomach?
➢ ≈ 200 kcal/hr released into small intestine
➢ Important not to overload Small Intestine
What is the function of the migrating motility complex (MMC)?
➢ Sweep ingested solids that cannot be digested out of stomach and through intestinal tract
➢ Occurs during fasting
➢ Takes approximately 90 min to go from stomach to colon
What initiates the gastric receptive relaxation?
- stretch of gastric/duodenal walls
- protein or fat in duodenum (CCK)
Which of these is short and which is long…
ENS
Vago-vagal
ENS - short
Vago-vagal - long
What hormone causes gastric receptive relaxation?
inhibitory signals (NO, VIP) from enteric nervous system
What is gastric peristalsis generated by?
interstitial cells of cajal (pacemaker cells)
What is the frequency of basic electrical rhythm (BER) of the stomach?
3/minute
What influences the rate of gastric emptying?
- solid vs liquid
- nutrient content
- force of gastric contractions
____% of stomach contents emptied 2.5 to 3 hours
50%
Transit through the colon ___________ hours
8 to 15 hours
Total emptying of the stomach ________ hours
4 to 5 hours
Total emptying of the small intestine _______ hours
3 to 5 hours
What increases the force of antral contractions and causes increased gastric emptying?
- gastrin
- distension of stomach
What decreases the force of antral contractions and causes decreased gastric emptying?
contents of duodenum
What are enterogastrones and what are examples?
- hormones secreted by duodenum in response to nutrients and acid in chyme.
1. CCK (Fat, Protein)
2. Secretin (Acid)
3. GIP (Carbohydrate)
What hormone is used during the migrating motility complex (MMC)?
motilin
What is the migrating motility complex (MMC)?
➢ Occurs in between meals (fasting state) approximately every 90 minutes
➢ Intervals of strong propulsive contractions
➢ Sweep stomach and small intestine of indigestible material
➢ Intrinsic to ENS and involves hormone Motilin.
➢ Continue until meal ingested.
What cell makes HCl?
parietal cell (oxyntic)
What cell makes intrinsic factor?
parietal cell (oxyntic)
What cell makes pepsinogen?
chief cell
What cell makes mucus, HCO3-, and trefoil factors?
surface mucous cell
What cell makes histamine?
ECL cells
What cell makes gastrin?
G cells
What cell makes somatostatin?
D cells
What cells make ghrelin?
Gr cells
What cells are part of the oxyntic gland (corpus)?
abundant parietal and chief cells
What cells are part of the pyloric gland (antral)?
mucus-secreting cells
What is the alkaline tide that occurs during parietal cell function?
blood is more basic for a couple of hours due to excess HCO3- in basolateral membrane
What hormones activates the oxyntic cells (acid producing)?
gastrin
histamine
ACh
What hormone inhibits the oxyntic cells (acid producing)?
somatostatin
What side of the membrane are the proton pump inserted into on oxyntic cells?
apical membrane
What is synergism of oxyntic cell function?
– combination of factors creates a greater level of acid secretion than just additive
The short and long neural control of oxyntic cells result in what being secreted when the stimulus is stretch?
Acid
pepsin
intrinsic factor
gastrin
What neurotransmitters cause the short and long neural control mechanisms to stimulate oxyntic cells?
ACh
GRP (gastrin releasing peptide)
Stretch on the gastric walls causes what to be secreted?
ACh
GRP (gastrin releasing peptide)
gastrin
What does somatostatin do to parietal cells?
inhibits parietal cells directly and by inhibiting gastrin and histamine
What stimulates D cells to secrete somatostatin?
HCl
What does somatostatin inhibit?
G cells = gastrin
ECL cells = histamine
Parietal cells = HCl (acid)
What are the three phases of GI activation?
- cephalic phase (via vagus)
- gastric phase (local, vagal, and gastrin-histamine stimulation)
- intestinal phase (nervous and hormones)
What is the stimulus for cephalic phase of acid secretion?
Sight of food
Smell of food
Taste of food
Thoughts of food
What is the cephalic phase of acid secretion?
- acid secretion goes up
- somatostatin levels go up
- acid levels are kept low because of somatostatin
What is the gastric phase of acid secretion?
- food in stomach buffers the acid and prevents somatostatin secretion (= more acid)
- distension of stomach causes acid secretion
- peptides stimulate G cells which produce gastrin (= more acid)
What is the intestinal phase of acid secretion?
increased H+
distension
osmolarity
fats in duodenum
What is the intestinal phase of acid secretion?
- intestinal stimuli cause release of enterogastrones (CCK, secretin, GLP1, GIP)
- enterogastrones inhibit G cells, ECL cells, and parietal cells (= less acid in stomach)
- increase parasympathetics
What do enterogastrones (CCK, secretin, GLP1, GIP) do to acid secretion?
inhibit acid secretion
How do you regulate acid during the interdigestive period (fasting)?
➢ Acid is secreted at low levels
➢ Lack of buffer (no food) causes low pH in stomach (3)
➢ Basal secretions stimulated by Histamine and Ach
➢ Gastrin low due to low pH in gastric lumen
➢ Function: Possibly to sterilize gastric lumen
What do PPIs (proton pump inhibitor) do?
➢ Binds to and inhibits H+/K+ pump
➢ Produces nearly 100% inhibition.
➢ May have side effects related to functions of acid.
What is the funciton of acid?
➢ Facilitates digestion of proteins.
➢ Protects against some pathogens.
➢ Increases absorption of B12, iron, calcium.
What is required for Vitamin B12 absorption?
intrisic factor
What can deficiency of vitamin B12 via low intrinsic factor cause?
pernicious anemia
What is the function of a chief cell?
Secretes pepsinogen to initiate digestion of protein
How is pepsinogen activated into pepsin?
- low pH (less than 5)
- HCl
What is the main activation of chief cells?
local and vagal reflexes that release Ach
How do chief and parietal cells work together to create pepsin for protein breakdown?
What is the only known appetite stimulant?
ghrelin
What hormone may partly account for the anorexia and weight loss seen in some patients following gastric resection?
ghrelin
What ghrelin level increase following decrease in body fat what happens?
- increase in hunger/eating
- decrease in metabolism
What is the gastric mucosal barrier?
➢ Two hydrophilic layers separated by hydrophobic barrier
➢ Mucus is secreted by mucous cells onto surface of epithelium
➢ Contains long chains of oligosaccharides that expand and retain water
➢ Viscoelastic substance that coats surface of gastric epithelial cells
➢ Limit diffusion of acid through the plane of the gel via a mechanism known as viscous fingering
➢ Micro-climate with high pH produced by surface cell secretion of HCO3
What is mucus secretion stimulated by in the gastric mucosal barrier?
prostaglandins
(NSAIDS decrease prostaglandins)
What protein helps stabilize the gastric mucosal barrier?
trefoil
What are the causes of ulcers?
– “No acid, no ulcer”
* Helicobacter pylori-bacterial infection destroys the
gastric diffusion barrier
* Zollinger-Ellison Syndrome-G Cell tumor
