Gastric Motility and Pancreatic Function

Question 1

How is the Enteric Nervous system organised?

Answer 1

• Intrinsic neurons of the 2 nerve plexuses (myenteric and submucosal) of the digestive tract are the neurons that lie completely within the wall of the gut.
• Autonomic neurons that bring signals from the CNS to the digestive tract are called extrinsic neurons.
• ENS neurons release more than 30 neurotransmitters and neuromodulators.
• Neurotransmitters in the enteric nervous system include serotonin, vasoactive intestinal peptide and nitric oxide.

Question 2

What mechanisms are involved in the neutralisation of gastric acid in the duodenum? E.g. control of bicarbonate secretion in the duodenum?

Answer 2

• Bicarbonate production from Brunner’s gland duct cells (submucosa)
• The production of bicarbonate is controlled by the presence of acid in the stomach which triggers:

A - Vagal and ENS reflexes which trigger bicarb secretion from Brunner’s gland duct cells (submucosa)

B - Release of secretin from S cells which stimulates the secretion of bicarb from Brunners gland duct cells and inhibits gastric acid secretion from paritel cells

Question 3

What is the role of gastric motility in digestion and what are the mechanisms controlling gastric emptying?

Answer 3

Gastric motility ensures that food is mixed & digested thoroughly by the stomach before food enters the small intestine for absorption

Mechanisms controlling Gastric emptying:

• Gastric emptying is controlled by hormones such as secretin (reduces gastric motility), CCK (cholecystokinin, decreases gastric motility), GIP and GLP-1(reduce motility)
• Gastric emptying is also controlled by the osmoreceptors in the intestine wall, which detect the hyperosmotic solution of acid, enzymes and digested food to inhibit gastric emptying.

Question 4

What are the functions of the Pancreas?

Answer 4

1) Secretes digestive pancreatic enzymes by acinar cells
2) Secretes bicarbonate by Brunner’s glands duct cells

Question 5

What are the actions of secretin and CCK on pancreatic and bile secretion?

Answer 5

Secretin - stimulates the release of bicarbonate and pancreatic enzymes and bile

CCK - stimulates release of pancreatic enzymes and release of bile

Question 6

What are the stimuli that cause the release of secretin and CCK?

Answer 6

Secretin - release in response to low gastric pH, i.e. production of gastric acid

CCK - released in response to presence of FA’s and AA’s in stomach

Question 7

What controls pancreatic enzyme secretion?

Answer 7

1) Increased CCK secretion

2) Distension of small intestine and presence of food in intestine

3) Vagal stimulation

Question 8

What is the role of zymogens?

Answer 8

Zymogens are inactive forms of digestive enzymes

Zymogens must first be activated by enterokinase

Enterokinase converts Trypsinogen to Trypsin

Trypsin converts all other zymogens into their active forms

Question 9

What is the anatomy and histology of the pancreas?

Answer 9

Anatomy:

Tail

Body

Neck

Head

Uncinate process

Endocrine Histology:

Islets of Langerhans (produce Insulin, Glucagon and Somatostatin)

Exocrine Histology:

Acinar cells - Ducts - Pancreatic Duct

Duct cells - secrete bicarbonate

Acinar cells - secrete digestive enzymes

Question 10

What is the structure of the exocrine pancreas?

Answer 10

1) Acinar cells
2) Lobules
3) Intercalated ducts
4) Intralobular ducts
5) Interlobular ducts
6) Main pancreatic duct
7) Common bile duct
8) Sphincter of Oddi
9) Duodenum (Major duodenal papilla)