Objective 2: Discuss the Structure and Function of the Gastric Mucosal Barrier, Including the Histology and Specific Functions of the Cells That Contribute to Gastric Mucosal Protection

Gastric Mucosal Barrier

A protective system that prevents hydrochloric acid and pepsin from damaging the stomach's epithelial lining.

Mucus Layer

A thick protective coating over the gastric mucosa that limits direct contact between gastric acid, pepsin, and epithelial cells.

Bicarbonate (HCO3-)

Ions trapped within the mucus layer that neutralize hydrogen ions and protect the epithelial surface from acid.

pH Gradient

A protective difference in acidity in which the stomach lumen remains highly acidic while the epithelial surface maintains a relatively neutral pH.

Surface Mucous Cells

Cells lining the stomach's internal surface that continuously secrete protective mucus.

Mucous Neck Cells

Cells located in the neck region of gastric glands that contribute to mucus production.

Parietal Cells

Cells in gastric glands that produce hydrochloric acid and intrinsic factor.

Chief Cells

Cells located deeper in gastric glands that secrete inactive pepsinogen and gastric lipase.

Pepsinogen

The inactive precursor of pepsin secreted by chief cells; activated in the acidic stomach environment.

Pepsin

An active digestive enzyme that breaks down proteins into smaller peptides.

Gastric Lipase

An enzyme secreted by chief cells that contributes to dietary fat digestion.

G Cells

Endocrine cells primarily located in the pyloric antrum that secrete gastrin.

Gastrin

A hormone that stimulates gastric acid secretion and promotes gastric activity.

Prostaglandins

Substances that protect the gastric mucosa by increasing blood flow, stimulating mucus and bicarbonate production, and reducing acid secretion.

Mucosal Blood Flow

Blood circulation that supplies oxygen and nutrients to gastric epithelial cells and supports tissue repair.

COX-1

An enzyme involved in prostaglandin synthesis that is inhibited by NSAIDs, weakening gastric mucosal protection.

NSAIDs

Medications that inhibit cyclooxygenase enzymes and reduce protective prostaglandin production, increasing the risk of gastric injury.

Gastric Erosion

Superficial damage to the gastric mucosa that can occur when protective mechanisms are weakened.

What is the primary purpose of the gastric mucosal barrier?

To protect the stomach's epithelial lining from damage caused by hydrochloric acid and pepsin.

What are the two major components of the gastric mucosal barrier?

A thick mucus layer and bicarbonate ions trapped within the mucus.

How does mucus protect the stomach?

It creates a physical coating that prevents gastric acid and pepsin from directly contacting epithelial cells.

How does bicarbonate protect the gastric mucosa?

It neutralizes hydrogen ions near the epithelial surface, maintaining a relatively neutral pH.

How can the stomach lumen remain acidic without damaging its own lining?

The mucus-bicarbonate barrier creates a pH gradient that keeps the epithelial surface relatively neutral.

What is the function of surface mucous cells?

They continuously secrete protective mucus along the stomach's internal surface.

Where are mucous neck cells located, and what do they produce?

They are located in the neck region of gastric glands and contribute to mucus production.

What do parietal cells secrete?

Hydrochloric acid and intrinsic factor.

What do chief cells secrete?

Pepsinogen and gastric lipase.

Why is pepsinogen secreted in an inactive form?

To prevent premature digestion and damage to the cells that produce it.

How is pepsinogen activated?

Hydrochloric acid in the stomach converts inactive pepsinogen into active pepsin.

What is the function of pepsin?

It breaks down proteins into smaller peptides.

What is the function of gastric lipase?

It contributes to the digestion of dietary fats.

What is the function of G cells?

They release gastrin, which stimulates gastric acid secretion.

How do prostaglandins protect the stomach?

They increase mucosal blood flow, stimulate mucus and bicarbonate secretion, and reduce gastric acid secretion.

Why is adequate mucosal blood flow important?

It delivers oxygen and nutrients to epithelial cells and supports tissue repair.

How do NSAIDs weaken the gastric mucosal barrier?

They inhibit COX-1 and decrease prostaglandin production, reducing mucus, bicarbonate, and mucosal blood flow.

How can alcohol damage the stomach?

It directly irritates gastric epithelial cells and weakens the mucosal barrier.

What can happen when the gastric mucosal barrier becomes damaged?

Acid and pepsin can penetrate the lining, causing inflammation, erosion, ulcers, and gastrointestinal bleeding.

Why can excessive gastrin contribute to gastric injury?

It stimulates excessive gastric acid production, increasing exposure of the mucosa to acid.