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Physiology Pt. 3 > GI Physiology: Stomach > Flashcards

GI Physiology: Stomach Flashcards

1
Q

Where does the major portion of digestion happen?

A

The beginning of the small intestine

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2
Q

Digestion in the stomach involves primarily one macronutrient. Which one is it?

A

Protein!

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3
Q

What does the acid do to proteins in the stomach?

A

Denatures them

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4
Q

What are the three major functions of the stomach?

A
  1. Motor
  2. Secrete products
  3. Secrete peptide hormones
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5
Q

What is a function of the stomach that allows you to eat a lot without barfing?

A

It is highly compliant! It can take up ~2L without an increase in pressure.

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6
Q

How does lipase and amylase work in the stomach despite being inactivated at low pH?

A

Since the food bolus that is swallowed is a ball, the enzymes stuck in the middle of the bolus are shielded from the stomach acid and continue to work a little.

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7
Q

Food particles that are >1 mm in diameter are ____ out of the stomach when the stomach is empty.

A

swept

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8
Q

Name six major things that are secreted in the stomach.

A
  1. Pepsinogen
  2. HCl
  3. Mucus
  4. Gastrin
  5. Intrinsic factor
  6. Water
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9
Q

What are the three functions of acid in the stomach?

A
  1. Convert pepsinogen to pepsin
  2. Kills microbes
  3. Denatures protein
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10
Q

Intrinsic factor is necessary for absorption of _____.

A

B12

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11
Q

How much water is secreted into the stomach per day?

A

2.5 L

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12
Q

Where in the GI tract is B12 absorbed?

A

distal ileum

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13
Q

What does gastrin do? What cells secrete it?

A

Stomach G cells secrete gastrin. It stimulates acid secretion by parietal cells, pepsinogen secretion by chief cells, and histamine secretion by ECL cells.

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14
Q

Where are cells located that make somatostatin (3)? What does it do?

A

It is made by cells in the stomach, small intestine, and pancreas (delta cells). It inhibits gastrin release (cells in stomach), decreases endocrine and exocrine secretions (pancreas and liver) and decreases bile flow (liver).

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15
Q

Where are cells located that make CCK? What does it do?

A

Made by cells in the small intestine. It acts on cells in the pancreas and gallbladder to increase muscle contractions and associated enzyme secretion.

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16
Q

Where are cells located that make secretin? What does it do?

A

Made by cells in the duodenum. Acts on the pancreas and bile ducts to increase bicarbonate and fluid secretion.

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17
Q

Where are cells located that make gastrin releasing peptide (GRP)? What does it do?

A

Made by cells in the vagal nerve endings. Acts in the stomach to increase gastrin release.

18
Q

Where are cells located that make gastric inhibitory peptide (GIP)? What does it do?

A

Made by cells in the duodenum and jejunum. Acts on pancreatic cells to decrease fluid absorption.

19
Q

Which GI “hormone” is not a true hormone? Why?

A

GRP is not a true hormone because it is neuroendocrine.

20
Q

Describe the general distribution of GI hormones (gastrin, CCK, secretin, GIP).

A

Gastrin is found in the antrum of the stomach as well as in the small intestine (tapers off distally) and the others are just found in the small intestine primarily.

21
Q

In what structure are chief cells, parietal cells, and ECL cells found primarily? Where are the mucus cells found?

A

Chief cells, parietal cells, and ECL cells are found in the gastric glands (deep).

Mucous cells are found closer to the lumen in the gastric pits.

22
Q

What cells make pepsinogen?

A

Chief cells in the stomach glands

23
Q

What do parietal cells make?

A

H+ and intrinsic factor

24
Q

Where does the majority of protein digestion occur in the GI tract?

A

Small intestine

25
Q

An important component of mucus is _______, a glycoprotein that forms a _____ when it is hydrated.

A

mucin; forms a gel when hydrated

26
Q

Do detergents like bile salts, weak acids like aspirin, alcohol, and NSAIDs disrupt the mucosal barrier of the somach?

A

Yeah

27
Q

30% of stomach ulcers are not caused by H. pylori, but rather by ______-type medications.

A

aspirin

28
Q

If the gastric mucosal barrier is damaged, the underlying epithelium can become denuded, allowing ___ to infiltrate and degranulate ______ cells, releasing ______ that increases vascular permeability resulting in flooding of the GI lumen with Na+, _______, and ______.

A

epithelium denuded –> H+ infiltrates –> mast cell degranulation —> histamine increases vascular permeability –> Na+, blood, and fluid flood the lumen.

29
Q

Parietal cells use a _______ exchanger to pump protons into the stomach, therefore ____ (an ion) must be present in order for this to work.

A

H+/K+ exchanger (PeePee exchanger - proton/potassium), so K+ is needed

30
Q

What is the “alkaline tide?”

A

This refers to the high pH of blood in the venous end of the capillary bed supplying gastric epithelium due to release of bicarbonate as a byproduct of H+ synthesis by parietal cells (CO2 + H2O –> H2CO3 –> HCO3- + H+).

31
Q

Why should you eat a cracker when you get heartburn?

A

Food is a good buffer.

32
Q

Describe the regulation of gastric acid and pepsin secretion.

A

When pH is low (no food so lots of acid), D cells will make somatostatin, which inhibits G cells (they stop making gastrin).

When pH is high (presence of food decreases acid in stomach), D cells stop making somatostatin so G cells can make gastrin. The gastrin gets into the circulation and acts on three cells: ECL cells, Chief cells, and Parietal cells:

ECL cells are stimulated to make histamine, which in turn stimulates both chief and parietal cells.

Chief cells are stimulated by gastrin to make pepsinogen.

Parietal cells are stimulated to make acid.

33
Q

What do H2 blockers do?

A

Inhibit acid secretion in the stomach

34
Q

Can acetylcholine act on ECL, parietal, and chief cells to stimulate them?

A

Yeah

35
Q

Name three receptors present on a parietal cell that can stimulate the cell when the appropriate ligand is bound.

A

muscarinic (Ach), H2 (histamine), gastrin receptor

36
Q

The majority of acid secretion is in response to the _____ phase.

A

gastric

37
Q

What are the four phases of acid secretion?

A
  1. Interdigestive
  2. Cephalic
  3. Gastric
  4. Intestinal
38
Q

Describe how emptying of the stomach contents into the duodenum is regulated.

A

If H+ concentration gets high in the duodenum, it will leak out and loop back to tell the stomach that it needs to slow down (short reflex). H+ can also indirectly act by getting into the blood, stimulating secretin to tell the stomach to slow down.

39
Q

Aside from H+ in the duodenum, what three other things will slow gastric emptying into the duodenum?

A
  1. Fats (FFA)
  2. Proteins (AA)
  3. HypERtonicity
40
Q

By what two mechanisms can the stomach delay emptying into the duodenum?

A
  1. Decrease muscle contractions

2. Pyloric sphincter stays shut

41
Q

_______ neutralizes acid in the duodenum.

A

Bicarbonate

Physiology Pt. 3 (15 decks)

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