Gastric Secretion

Question 1

What is the anatomy of the stomach and what are the functions of the different components?

Answer 1

Fundus - storage

Body:

Storage

Mucus production

HCl production

Pepsinogen

Intrinsic factor

Pyloric Antrum:

Mixing/grinding

Gastrim

Question 2

What is the importance of gastric acid and pepsin secretion and describe the hormonal and neural mechanisms responsible for their control?

Answer 2

Gastric acid and pepsin secretion are critical to the digestion process that occurs in the stomach

Gastric acid releases the digestive enzymes and breaks down proteins

Pepsin is a digestive enzyme which breaks down proteins

Neuronal control of Acid secretion:

1) Sight, smell, taste of food
2) Vagus nerve activated
3) Vagus nerves stimulates Gastrin release from G cells and ACh release, both of which act on parietal cells
4) Gastrin and ACh also stimulate ECL cells to produce Histmaine, which also acts on Parietal cells
5) Once you stop eating, Vagal activity decreases and so does the production of ACh and Gastrin from G cells

Gastric control of Acid secretion:

1) Distension of stomach, peptides in lumen of stomach both stimulate further ACh and Gastrin secretion
2) ACh and Gastrin secretion stimulates parietal cells to produce gastric acid
3) Eventually when the pH drops too low, Gastrin secretion stops

Question 3

What is the role of intrinsic factor in vitamin B12 absorption?

Answer 3

Intrinsic factor is produced by parietal cells and is required for vitamin B12 absorption.

Without intrinsic factor, B12 cannot be absorbed

The intrinsic factor/B12 complex gets absorbed from the Ileum

A lack of vitamin B12 is called Pernicious Anaemia

Question 4

What are the functions of the gastric mucus?

Answer 4

• Protects the lining of the stomach from gastric acid and pepsinogen digestion

Question 5

What are the steps involved in Gastric acid secretion?

Answer 5

1) Cephalic phase:

• Anticipation of food stimulates Vagus nerve
• Vagus nerve releases ACh which acts on Parietal cells to produce Gastric acid
• Vagal stimulation also produces gastrin releasing peptides, which act on G cells to secrete Gastrin which activates Parietal cells to produce Gastric acid
• Vagus nerve also activates ECL (Enterochromaffin like cell) cells to release Histamine

2) Gastric phase:

• Distension of the stomach and presence of peptides in the stomach lumen stimulate Parietal cells to produce Gastric acid

3) Intestinal phase:

• Further Gastric acid is secreted when the chyme enters the small intestine and stimulated by small intestien distension and presence of amino acids