Gastric Acid Secretion

Control of Gastric Acid and Secretion

Gastric acid is secreted from the gastric parietal cell by a proton-pump H+/K+ ATPase located at the membrane of the parietal cell

The proton-pump H+/K+ ATPase is a Hydrogen-Potassium Adenosine Triphosphatase Enzyme System, which can be activated by 3 endogenous substances (Neurotransmitters)

1. Acetylcholine (ACh)

2. Histamine [EnteroChromaffin-Like Cell (ECL)]

Gastrin (G Cell)

Pathways in the Control of Gastric Acid and Secretion

Secretion of these substances is controlled centrally by the medulla, and locally by the stomach wall

The taste, smell and distension of food in the stomach stimulate the medulla to release acetylcholine (ACh), which acts on appropriate receptors at:

1. The parietal cell on the stomach wall to secrete gastric acid

2. Histamine storage cells (similar to mast cells) to release histamine, which in turn acts on H2 receptors at the parietal cell to release gastric acid

3. Gastrin cells to release gastrin, which directly stimulates the parietal cell and indirectly induces the histamine storage cells to release histamine and so repeats the process in 2

Peptic Ulcer Diseases

Ulcer that develop in areas of the gastrointestinal (GI) tract exposed to gastric acid are peptic ulcers

Peptic ulcer developed in the stomach are called gastric ulcers

Developed in the duodenum are called duodenal ulcers

Peptic ulcers tend to relapse and most peptic ulcers are duodenal

Gastric ulcers are characterized by epigastric pain precipitated by eating

Duodenal ulcers are characterized by pain relieved by food and often disturbs at night

The most common complication of peptic ulcers is bleeding and another is perforation erosion of the ulcer

Causes of Peptic Ulcer Formation

1. Hyper-secretion of gastric acid (hydrochloric acid) seems to be the immediate cause of duodenal ulcer

2. Hypo-secretion of protective mucus may be the cause of peptic ulcer since the stomach wall is highly adapted to resist gastric acid through the secretion of protective mucus

3. Hyper-secretion of pepsin. Normally, the mucous membrane lining the stomach and duodenal walls can resist acid and pepsin, however, in some people, this resistance breaks down and an ulcer develops

4. Other factors believed to stimulate an increase in acid secretion are emotions, cigarette smoking, certain food medication (e.g. alcohol, coffee, aspirin)

5. Helicobacter pylori (H. pylori)

are microorganism found in the gastric mucosa and have been implicated as a cause of relapse after initial ulcer healer ulcer healing. Eradication of the organism has successfully reduce relapse rate and prevent gastric carcinoma