Gastric Physiology Flashcards

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Questions and Answers

What do parietal cells secrete?

Hydrochloric acid and intrinsic factor

Where is gastric acid produced?

It is produced by the parietal cells in the fundus of the stomach

What stimulates the increased production of HCl?

An increase in gastrin and histamine

How do histamine and gastrin stimulate HCl production?

By binding to their respective receptors on parietal cells, activating the proton pump. Signup and view all the answers

What is the second messenger for gastrin and acetylcholine?

Calcium Signup and view all the answers

What is the second messenger for histamine?

cAMP Signup and view all the answers

How do calcium and cAMP activate the proton pump?

They act through protein kinases to activate the enzyme H+/K+ ATPase. Signup and view all the answers

What substances suppress parietal cell activity?

Prostaglandins, secretin, gastric inhibitory peptide, somatostatin. Signup and view all the answers

How does an acute H. Pylori infection affect acid production?

Induces a short period of hypochlorhydria. Signup and view all the answers

How does a chronic H. Pylori infection affect HCl?

Leads to increases in the basal and stimulated acid output. Signup and view all the answers

What is Zollinger Ellison syndrome?

A condition characterized by gastric acid hypersecretion and severe peptic ulceration. Signup and view all the answers

What is the role of intrinsic factor?

Facilitates cobalamin (Vitamin B12) absorption. Signup and view all the answers

Where is gastrin secreted?

G cells in the gastric antrum. Signup and view all the answers

Where is somatostatin secreted?

From D cells. Signup and view all the answers

What are the two mechanisms that gastrin enhances gastric acid secretion?

It stimulates parietal cells and histamine-secreting enterochromaffin-like cells. Signup and view all the answers

What does it mean that histamine is a major 'paracrine stimulator' of acid secretion?

Effects of histamine are localized to adjacent or nearby cells. Signup and view all the answers

Where is histamine localized?

In mucosal mast cells and enterchromaffin cells. Signup and view all the answers

What is the primary stimulus to histamine release?

Gastrin. Signup and view all the answers

The effects of histamine are mediated by which receptor?

The H2 receptor. Signup and view all the answers

What cells secrete pepsinogen II?

Mucous cells throughout the stomach. Signup and view all the answers

What cells is mucous secreted by?

Superficial epithelial cells and mucous cells. Signup and view all the answers

Why is the mucous barrier important?

It provides a barrier to H+ to protect against luminal acid and pepsin injury. Signup and view all the answers

Where is bicarbonate secreted in the GIT?

By the epithelial cells of the stomach and the duodenum. Signup and view all the answers

How do prostaglandin E2 and I2 affect acid secretion?

They inhibit it by having a paracrine inhibitory effect. Signup and view all the answers

Study Notes

Acid Production and Regulation

Parietal cells secrete hydrochloric acid (HCl) and intrinsic factor.
Gastric acid is produced by parietal cells located in the fundus of the stomach.
Increased production of HCl is stimulated by gastrin and histamine.

Mechanisms of HCl Production

Histamine binds to histamine-2 receptors and gastrin binds to gastrin receptors on the basolateral surface of parietal cells.
Binding of these ligands triggers the generation of second messengers: calcium for gastrin and acetylcholine; cAMP for histamine.
Calcium and cAMP activate the proton pump (H+/K+ ATPase) through protein kinases, leading to H+ release.

Inhibition of Acid Production

Prostaglandins and peptides like secretin, gastric inhibitory peptide, and somatostatin suppress parietal cell activity by inhibiting cAMP production through inhibitory G proteins.
Acute H. pylori infections cause a short period of hypochlorhydria (reduced stomach acid).
Chronic H. pylori infections increase basal and stimulated acid output due to heightened gastrin stimulation and decreased somatostatin.

Zollinger-Ellison Syndrome

Characterized by gastric acid hypersecretion, severe peptic ulceration, and gastrinoma (non-beta cell islet tumor of the pancreas).
Results in elevated gastrin levels, stimulating excess HCl production.

Intrinsic Factor and Gastrin

Intrinsic factor is essential for vitamin B12 absorption and is secreted alongside HCl.
G cells in the gastric antrum secrete gastrin in response to food presence or gastric releasing peptide release.

Somatostatin and its Role

Secreted from D cells; inhibits gastrin and thus HCl production, affected by vagal stimulation.
Gastrin enhances gastric acid secretion through trophic actions on parietal and histamine-secreting enterochromaffin-like cells.

Histamine in Acid Secretion

Acts as a paracrine stimulator, affecting adjacent cells; localizes primarily in mucosal mast cells and enterchromaffin cells.
Gastrin is the primary trigger for histamine release from CL cells, responsible for mediating acid secretion via the H2 receptor on parietal cells.

Pepsinogen and Mucus Production

Pepsinogen II is secreted by mucous cells throughout the stomach and activated by gastric acid into pepsin, which functions as a proteolytic enzyme.
Mucous, secreted by superficial epithelial and mucous cells, is vital for protecting the stomach lining from acid and pepsin injury.

Importance of Mucous Barrier

Provides a critical barrier against H+ and safeguards the gastric mucosa from corrosive effects of luminal acid and pepsin.

Bicarbonate Secretion

Bicarbonate is secreted by epithelial cells in the stomach and duodenum, particularly enhanced at pH levels below 3.

Prostaglandin Effects

Prostaglandins E2 and I2 inhibit acid secretion through paracrine mechanisms, contributing to the regulation of gastric acid production.

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Description

Test your knowledge on gastric physiology with these flashcards focusing on parietal cells and hydrochloric acid production. Learn about the secretion processes, stimulation by gastrin and histamine, and the location of gastric acid production in the stomach. Perfect for anyone studying biology or medicine.