GI Physiology - Stomach (Dr. Olgun)

where protein digestion begins by the secretion of a protease

stomach

t/f: stomach's role is for the storage and processing of ingested food

true

What protects the epithelial cell layer of the stomach from its low pH environment?

Mucin

What phase of digestion is the following:

Begins with the arrival of food in the stomach

Gastric phase

What is the purpose of the gastric phase?

To sterilize, mix food with gastric juice, reduce particle size, begin digestion of protein and store food for timely delivery to duodenum

What stimulates the gastric phase?

- Distension of the stomach

- Presence of food in the lumen

Which of the following are results/processes for the gastric phase?

A. Secretion: Gastric Juice

B. Motility: Storage, Mixing and Propulsion

C. Digestion: Minimal (initiation of protein digestion)

D. Absorption: Minimal (drugs, EtOH)

E. Endocrine function (Gastrin, Ghrelin)

F. All of the above

F. All of the above

Which of the following is not considered a physical function of the stomach?

a. compliance of wall allows increase volume with little increase in pressure

b. storage allows digestion by enzymes

c. mixing of food, fluid, gastric enzymes

d. Kneading of food particles to <1mm diameter

e. Metered emptying in response to duodenal feedback

f. Emptying the "wrong" way (vomit), a defense against ingested substances that may be harmful

g. none of the above

g. none of the above (all are functions!)

sphincter that separates esophagus from stomach:

lower esophageal sphincter

sphincter that separates stomach from duodenum:

pyloic sphincter

What secreted product of the stomach does the following?

- Converts pepsinogen into pepsin

- Kills microbes and denatures protein

hydrogen ion

What secreted product of the stomach does the following?

Begins protein digestion

Pepsinogens/Pepsin

What secreted product of the stomach does the following?

Lubricates and protects mucosa

mucus

What secreted product of the stomach does the following?

Necessary for normal absorption of vitamin B12

intrinsic factor

What secreted product of the stomach does the following?

Dissolves and dilutes ingested material secreted from stomach (2-2.5L/day)

water

what 3 cells found in gastric glands secrete digestion products & what do they secrete?

- Parietal cells: acid

- Enterochromaffin cells: histamine

- Chief cells: pepsinogen

these cells secrete acid and intrinsic factor:

parietal cells

these cells secrete histamine:

enterochromaffin cells

these cells secrete pepsinogen:

chief cells

What cells decreases GI activity and secretion (mostly in ANTRUM)?

Somatostatin (D cells)

________ increases appetite (mostly in fundus)

Ghrelin

How does Cl- compare in gastric juice vs plasma levels?

Cl- higher than plasma levels

How does H+ compare in gastric juice vs plasma levels?

H+ is 1 million times greater than plasma levels

How does K+ compare in gastric juice vs plasma levels?

K+ is higher than plasma levels

How does Na+ compare in gastric juice vs plasma levels?

Na+ is lower than plasma levels, very low at high flow rates

____-____ L of gastric juice is secreted per day

2-3

The surface of the stomach is protected by the ___________

gastric mucosal barrier

What are the 5 agents discussed in lecture known to disrupt the Gastric Mucosal barrier?

- Weak acids (aspirin)

- Alcohol

- NSAIDs

- Detergents (bile salts/acids)

- Inflammation (H.Pylori)

t/f: H Pylori interferes with the stomach's mucosal barrier by directly causing peptic ulcers

false

t/f: H Pylori interferes with the stomach's mucosal barrier by causing a inflammatory response that results in the interference of the mucosal barrier, resulting in peptic ulcers

true

What is the most common cause of gastritis and peptic ulcers?

infection with H. Pylori

the mucus layer allows the pH at the cell surface to remain near __

7

the pH in the gastric juice in the lumen is __

1-2

What is the parietal cell mechanism for HCl secretion?

H+/K+ ATPase ("Proton pump")

The following steps are the mechanism for what?

1. H+ and HCO3- generated in cell

2. H+/K+ ATPase "proton pump" secretes H+ against gradient (1 million-fold!)

3. HCO3- exchanged for Cl- at basolateral membrane to maintain intracellular pH

4. Cl- diffuses down gradient, secreted into lumen through Cl channel

5. K+ is recycled at the apical membrane

Parietal cell mechanism for HCl secretion

________ used to be commonly performed to reduce acid secretion in peptic ulcer disease

Vagotomy (severing vagus nerves near stomach)

__________ strongly increases vascular permeability

histamine

breakage of gastric mucosal allows back-diffusion of ____ which damages tissue

H+

3 mechanisms of communication that regulate the GI tract:

Endocrine (Gastrin)

Neurocrine (Ach)

Paracrine (Histamine)

An example of an endocrine in the GI system is

Gastrin

An example of a neurocrine in the GI system is

gastrin-releasing peptide (GRP)

An example of a paracrine in the GI system is

Histamine

G cells secrete _____

gastrin

these cells secrete somatostatin:

D cells

D cells secrete ______

somatostatin

What inhibits gastrin release, therefore inhibiting acid?

somatostatin from D cells

What stimulates acid and pepsinogen secretion?

gastrin from G cells

Everything short of having food entering the stomach is considered the _________

cephalic phase

The _______ is the sole neural link between the brain's higher functions and gastric secretion

vagus nerve

The vagus nerve is the sole neural link between the brain's higher functions and gastric secretion. It exerts its effects through two separate pathways: direct stimulation by _______ and indirect through _______

acetylcholine, gastrin

What cells are the following:

Release H+ and intrinsic factor. Low pH conditions helps to kill bacteria in food and to denature protein.

Parietal cells

Freed ________ binds to Intrinsic factor. B12-IF complex moves through the length of the small intestine. B12-IF complex is broken apart in the distal ileum and B12 is absorbed.

B12

Pepsinogen is secreted by _______

chief cells

_________ release pepsinogen which is cleaved to the active protease pepsin.

Chief cells

________ release gastrin. Gastrin stimulates Chief and Parietal cells to secrete more pepsinogen, H+ and Intrinsic factor.

G cells

What is the target of gastrin?

Parietal cell in the stomach

What is the cell source and target of gastrin releasing peptide (GRP)?

- Vagal nerve endings

- Antrum of the stomach

What is the target of somatostatin?

- Stomach

- Pancreas

- Liver

Cholecystokinin and secretin both target the pancreas, but how do they differ?

CCK: Increases enzyme secretion

Secretin: Increases HCO3

In the gastric phase, distension of the stomach excites ___________

stretch receptors

in Gastric phase, elevated pH activates

chemoreceptors in mucosa

T/F: Pepsin cleaves proteins to peptide fragments

True

the BULK of protein digestion occurs in the ________

small intestine

the only digestion that occurs in the stomach is of ______

protein

in a resting stage, the stomach is _____ for gastrin release

negative

in a stimulated stage, the stomach is _____ for gastrin release

positive

what causes the D cells to release somatostatin?

low pH

high pH will affect G cells by ______ gastrin release

stimulating

low pH will affect G cells by ______ gastrin release

inhibiting

somatostatin will inhibit:

G cell release of gastrin

gastrin acts on what cells?

parietal cells

chief cells

enterochromaffin-like cells (ECLs)

enterochromaffin cells will stimulate parietal cells using _______

histamine

What 3 things stimulate parietal cell?

- Ach

- Gastrin

- Histamine

peptides and amino acids (from food) as well as stomach stretching acts on what cell to initiate gastric reflexes?

G cells

what true hormone is released into circulation and initiates digestive mechanisms?

gastrin

H+ and pepsinogen secretion is increased by _________

gastrin

H+ and pepsinogen secretion is inhibited by _________

somatostatin

at a pH of 1-2, the stomach is _________

resting

at a pH of ≥3, the stomach is _________

stimulated

list 3 positive regulators of digestion:

- Acetylcholine

- Gastrin

- Histamine

Most H+/K+ ATPases are sequestered within ________ in the parietal cell cytoplasm

tubulovesicles

t/f: Upon hormonal stimulation (rising pH) the Tubulovesicles fuse with the cell membrane which significantly increases H+/K+ ATPase in the cell membrane. This increase of H+/K+ ATPases in the membrane allows large numbers of hydrogen ions to be pumped into the stomach.

true

The majority of chyme entering the small intestine is ____in size

<1mm

t/f: Only small amounts of partially digested food (chyme) passes through the pyloric sphincter and enters the small intestine at a time

true

During periods when the stomach is empty and no digestion is occurring the material that was not digestible is...

Cleared from the stomach

___________ is the barium swallow that shows esophageal dilatation with uniform tapering of the distal esophagus, and this is known as the "Bird's beak appearance"

Achalasia

Narrowing of the lower esophageal sphincter (LES) is known as..

Achalasia

What are the 3 different treatment methods for GERD/Heart Burn?

- Antacids

- H2 receptor blockers

- Proton Pump inhibitors

What are the functions of gastric motility?

- Receive food bolus

- Storage of food

- Mix with digestive juices

- Grind to smaller pieces

- Propulsion (gastric emptying)

- Clear food during interdigestive period (migrating motor complex)

Where are the thickest muscle layers of the stomach?

Antrum and pylorus

What are the three components to gastric motlity?

- Proximal stomach motility

- Distal stomach motility

- Gastric emptying

What is the function of segmentation in small intestine motility?

Mixes chyme in a back-and-forth manner

What is the function of peristalsis in small intestine motility?

Propels chyme distally

when digestive products move into the small intestine and it is already filled/overactive, what products are released to slow passage of chyme?

- CCK

- GIP

- Secretin

products moving into the small intestine (CCK, GIP, Secretin) is a ______ regulator of digestion

negative

_________ is important in which as food is ingested there is no increase in pressure within the stomach, therefore stomach contents remain in stomach

Stomach Compliance

Pepsinogen is cleaved to _________ by HCl and begins protein digestion.

Pepsin

H+ and pepsinogen secretion is increased by gastrin and inhibited by ____________

Somatostatin

What phase is the following?

The pH of the stomach is low and this stimulates D cells to secrete somatostatin that in turn inhibits gastrin release from G cells.

interdigestive phase

What phase is the following?

Mediated through the vagus nerve/submucosal plexus and is a positive regulator for all stomach functions.

cephalic phase