Question

1: After a hard day at work, Frank sits down at the table to eat dinner. As he smells the food he can feel his stomach start to growl.

Question 1: Explain the structure of the gastric pits in the stomach and what each different cell secretes, and the action of those secretions.

Question 2: Explain the three phases of gastric secretion control, be sure to explain the how the different hormones affect secretion.

Question 3: Explain how gastric emptying is controlled, be sure to explain how is both promoted and inhibited depending the components of chyme, actions of the stomach and small intestine, and which specific hormones are secreted. After finishing his large meal, Frank sits on the couch and relaxes. As he is sitting there he can hear his digestive tract gurgling.

Question 4: Identify all the different types of motility in the digestive tract and their functions. Be sure to classify those actions that are moving and mixing.

Answer 1

1.

Gastric pits are indentations in the stomach that denote the entrances to gastric glands. They contain several exocrine gastric cells.

Gastric exocrine secretory cells:

Parietal or oxyntic cells- secrete HCl and intrinsic factor.

Chief cells- secrete pepsinogen

Mucous cells- secrete mucus

Endocrine cells known as G-cells found only in pyloric gland area secrete gastrin.

HCl kills bacteria and denatures protein.

The intrinsic factor helps in the absorption of vitamin B12.

Pepsin (activated form of pepsinogen) begins the digestion of proteins. It breaks down complex proteins into peptides.

Gastrin promotes secretion of gastric juice, increases gastric motility, and promotes the growth of gastric mucosa.

2.

Gastric activity is categorized into three phases:

Cephalic phase, gastric phase, and intestinal phase.

During the Cephalic phase, the brain controls the stomach. During the gastric phase, the stomach controls itself. During the intestinal phase, the small intestine controls the stomach.

Cephalic phase:

The stomach responds to senses such as smell, sight, taste, or thinking about food. Approximately 30% of the total secretion of acid occurs before the entry of food into the stomach. Senses are received by the hypothalamus, which sends to the medulla oblongata. The parasympathetic nervous system of the stomach is stimulated by vagus nerves from the medulla, which results in the stimulation of gastric secretion.

H+ secretion from parietal cells is stimulated by acetylcholine, which is released from vagal postganglionic muscarinic nerves into the stomach.

Acetylcholine also triggers the secretion of histamine from enterochromaffin-like cells. this histamine, inturn enhances H+ secretion from parietal cells.

Vagal neurons release Gastrin-releasing peptide (GRP) that stimulates G-cells to secrete gastrin.

Gastric phase:

Approximately 60% of the total acid secretion occurs during the gastric phase.

The secretion of acids is stimulated by swallowed food and protein in food.

The protein in food breaks down into peptides and amino acids, which stimulate G-cells to secrete gastrin.

Inhibitory phase:

Approximately 10% of the acid is secreted during the intestinal phase.

Chyme entering small intestine stimulates duodenum and regulates gastric secretion via nervous reflexes and hormones.

Osmolarity due to the digested products stimulate the secretion of acids.