Gastric Motility and Pancreatic Function

Question 1

1. Where do peristaltic waves start & end in the stomach?
2. T/F mixing occurs in the body of the stomach.
3. Compare body & antrum muscle thickness & the consequence of that.

Answer 1

1. Body to antrum
2. False. Body has a thin muscle that produces weak contraction (no mixing).
3. Antrum has a thick muscle therefore powerful contraction so mixing happens there. Pyloric sphincter also contracts.
   Only small quantity of gastric content (chime) entering duodenum. Further mixing as antral contents forced back towards the body.

Question 2

1. What produces gastric peristaltic waves?
2. What is found in longitudinal muscle layer?
3. What causes slow waves?
4. What is basic electrical rhythm (BER)?
5. How do slow waves produce contraction of the muscle?
6. What determines strength of contraction?

Answer 2

1. Peristaltic rhythm (3/min) generated by pacemaker cells.
2. Pacemaker cells
3. Spontaneous depolarisation/repolarisation.
4. slow wave rhythm
5. slow waves conducted through gap junctions along longitudinal muscle layer. Slow wave depolarisation sub-threshold - require further depolarisation to induce APs which will lead to contraction.
6. number of APs

Question 3

How is acid neutralised in duodenum?

Answer 3

Bicarbonate secretion from Brunner’s gland duct cells (submucosal glands).

Question 4

How is HCO3 secretion controlled in duodenum?

Answer 4

Acid in duodenum triggers:

• Long (vagal) & short (ENS) reflexes which stimulate HCO3 secretion
• release of secretin from S cells stimulate HCO3 secretion from pancreas & liver. Acid neutralisation inhibits secretin release (-ve feedback control)

Question 5

1. What are the 3/4 parts of pancreas?

2. Where does accessory pancreatic duct drain into?

Answer 5

1. Head (located within curvature of duodenum), neck, body, tail (extends to spleen).
2. Duodenum

Question 6

Describe the endocrine portion of pancreas.

Answer 6

Pancreatic islets (islets of Langerhans): islet beta cells produce insulin, & alpha cells produces glucagon (control [glucose]blood.
Islet cells secrete somatostatin (controls secretion of insulin & glucagon).

Question 7

Describe exocrine portion.

Answer 7

Acinar cells make up lobules. Lobules connected by intercalated ducts drain into intralobular ducts which drain > interlobular ducts > main pancreatic duct > common bile duct which via hepatopancreatic ampulla (sphincter of Oddi), drain into duodenum.

Question 8

What is the function of exocrine pancreas?

Answer 8

Responsible for digestive function of pancreas.
Duct cells secrete bicarbonate.
Acinar cells secrete digestive enzymes.

Question 9

How does acinar cells store digestive enzymes & why?

Answer 9

As inactive zymogen granules to prevent autodigestion of pancreas.

Question 10

Where is enterokinase found & what is its function?

Answer 10

Bound to brush border of duodenal enterocytes. Function is to convert trypsinogen (released by pancreas) to trypsin.

Question 11

What is the function of trypsin?

Answer 11

Converts all other zymogens to active forms.

Question 12

Name categories of pancreatic enzymes & state their function.

Answer 12

Proteases: cleave peptide bonds
Nucleases: hydrolyse DNA/RNA
Elastases: digest collagen
Phospholipases: convert phospholipids to fatty acids
Lipases: convert triglycerides to fatty acids & glycerol
A-amylase: convert starch to maltose + glucose.

Question 13

What stimulates zymogen secretion?

Answer 13

Cholecystokinin (CCK)

Question 14

CCK is released in response to what?

Answer 14

Fat/amino acids in duodenum

Question 15

What else controls the pancreatic function?

Answer 15

Neural control (vagal/local reflexes) - triggered by arrival of organic nutrients in duodenum.