GI 2: Gastric Function Flashcards by Cucumber inBrine

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

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What are the specialized secretions by the stomach?

HCl acid
Pepsinogen
Intrinsic factor
Mucus
Hormones/Paracrines

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What are the four sections of the stomach?

cardia
fundus
body
antrum

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What are the four types of gastric motility in the stomach?

receptive relaxation
peristalsis (trituration/homogenization)
emptying (pyloric sphincter)
migrating motility complex (MMC)

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What is the function of gastric receptive relaxation?

➢ Accommodate the volume of the meal
➢ Reduce pressure increases preventing gastric reflux and premature gastric emptying

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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

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What is the function of emptying the stomach?

➢ ≈ 200 kcal/hr released into small intestine
➢ Important not to overload Small Intestine

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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

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What initiates the gastric receptive relaxation?

stretch of gastric/duodenal walls
protein or fat in duodenum (CCK)

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Which of these is short and which is long…

ENS
Vago-vagal

ENS - short
Vago-vagal - long

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What hormone causes gastric receptive relaxation?

inhibitory signals (NO, VIP) from enteric nervous system

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What is gastric peristalsis generated by?

interstitial cells of cajal (pacemaker cells)

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What is the frequency of basic electrical rhythm (BER) of the stomach?

3/minute

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What influences the rate of gastric emptying?

solid vs liquid
nutrient content
force of gastric contractions

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____% of stomach contents emptied 2.5 to 3 hours

50%

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Transit through the colon ___________ hours

8 to 15 hours

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Total emptying of the stomach ________ hours

4 to 5 hours

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Total emptying of the small intestine _______ hours

3 to 5 hours

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What increases the force of antral contractions and causes increased gastric emptying?

gastrin
distension of stomach

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What decreases the force of antral contractions and causes decreased gastric emptying?

contents of duodenum

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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)

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What hormone is used during the migrating motility complex (MMC)?

motilin

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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.

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What cell makes HCl?

parietal cell (oxyntic)

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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