GIT Physiology 2: Gastric Secretion & Mucosal cell barrier

Flashcards based on the Gastric Secretion & Mucosal lecture notes to help students review and prepare for their exam.

What are the two major anatomic regions of the stomach?

Oxyntic area and Pyloric gland area

What is the function of pepsin in the stomach?

Initiates protein digestion

What is the significance of intrinsic factor secreted by the stomach?

Essential for Vitamin B12 uptake in the terminal ileum.

What cells secrete a thick, viscous, alkaline mucus in the gastric mucosa?

Surface epithelial cells (surface mucous cells)

Where is the oxyntic mucosa located?

Fundus and body of the stomach

What do mucous neck cells secrete?

Thin, watery mucus

What do parietal cells secrete?

HCl and intrinsic factor

What is secreted by chief cells?

Pepsinogen

What cells secrete histamine?

Enterochromaffin-like (ECL) cells

What cells secrete gastrin?

G cells

What cells secrete somatostatin?

D cells

What is the average volume of gastric secretion per day?

2 Liters

What is the average pH of gastric secretion?

2

What is the primary mechanism for H+ secretion into the stomach lumen?

Primary active transport in exchange with K+

What enzyme is present in parietal cells and is essential for HCl secretion?

Carbonic anhydrase

What is the alkaline tide?

The blood leaving the stomach is alkaline because HCO3- has been added to it.

What is pepsinogen and where is it released from?

Inactive enzyme released from chief (peptic) cells

What is the optimum pH for pepsin activity?

Less than 2

What is the result when parietal cells are damaged?

Absence of intrinsic factor leading to failure of vitamin B12 absorption and pernicious anemia.

What hormone is the most potent stimulant of parietal cells?

Gastrin

How does gastrin promote secretion of gastric juice?

Directly stimulates parietal cells and indirectly stimulates ECL cells

What are the effects of increased parasympathetic nerve activity on the stomach?

Increased HCl production, pepsinogen release, gastrin release, mucous release, and gastric smooth muscle contraction

Which neurotransmitter is released from ENS in response to both short local reflexes and vagal stimulation?

Acetylcholine

What is the effect of Somatostatin on parietal cells, chief cells, G cells, and ECL cells?

Inhibition of secretion

Regulation of acid secretion by the parietal cell is increased by what substances?

Acetylcholine, gastrin, and histamine

Regulation of acid secretion by the parietal cell is decreased by what substances?

Prostaglandin (PGE2)

What are the three phases of gastric secretion?

Cephalic, Gastric, and Intestinal phases

Which phase of gastric secretion is stimulated before food ever reaches the stomach?

Cephalic phase

What percentage of gastric secretion is the Cephalic Phase responsible for?

25-30%

What stimuli can trigger the cephalic phase?

Chewing, tasting, swallowing, sight, smell, or thinking of food

What percentage of gastric secretion is the Gastric Phase responsible for?

60-70%

What factors arising from food presence in the stomach can stimulate the gastric phase?

Protein, distention of the stomach, caffeine, and alcohol

Which phase of gastric secretion is largely hormonal?

Intestinal Phase

What inhibits gastric secretion in the Inhibitory Intestinal Phase?

Fat, Acid, Hypertonic Fluid and distension stimulate the enterogastric reflex

What protects the Gastric Mucosa?

Gastric Mucosal Barrier

How is the effectiveness of mucosal barrier reduced?

Aspirin and Helicobacter pylori

How do Mucus and HCO3- protect the epithelial cells?

Creates a neutral pH along the epithelial plasma membrane

How do gastric and duodenal epithelial cells protect themselves from the low pH?

Secrete bicarbonate on their apical faces to maintain a neutral pH

Why isn't protein digestion affected in gastric atrophy?

Pancreatic and small intestinal enzymes can completely digest protein.

What is a peptic ulcer?

A breakdown of the barrier which prevents irritation and autodigestion of the mucosa by gastric juice.