Pancreas Anatomy and Physiology

Question 1

• What is the function of the exocrine pancreas?

Answer 1

Secretes digestive enzymes in response to gastrointestinal hormones & bicarbonate in response to secretin

Question 2

• What are the three cell types of the endocrine pancreas?

Answer 2

Beta cells -> insulin – 60-70%
Alpha cells -> glucagon – 20-25%
Delta cells -> somatostatin – 10%

Question 3

• Where is somatostatin produced?

Answer 3

Hypothalamus, stomach, intestine, pancreas (delta cells)

Question 4

• What are the actions of somatostatin?

Answer 4

Negative feedback system for GH, inhibits release of TSH, inhibits gastrointestinal hormones, inhibits release of pancreatic enzymes, inhibits release of insulin and glucagon

Question 5

• What is involved in the secretion of insulin?

Answer 5

Removal of C-peptide from proinsulin

Question 6

• Where does degradation of insulin take place?

Answer 6

In the liver of kidneys via cleavage of the two disulphide bonds & within target cells after receptor binding

Question 7

• What three mechanisms regulation insulin secretion?

Answer 7

Nutrients, gastrointestinal hormones (gastric inhibitory peptide (GIP) stimulates) & autonomic NS (PSNS stimulates, SNS inhibits)

Question 8

• What process releases insulin?

Answer 8

Calcium-mediated exocytosis

Question 9

• What are the first and second phases of insulin secretion?

Answer 9

First phase represents release of the intracytoplasmic pool of proinsulin
Second phase insulin secretion results from new protein synthesis

Question 10

• Describe the beta cell events that result in insulin release

Answer 10

GLUT2 transporters allow glucose to enter, phosphorylation of glucose to glucokinase, increase in ATP production, inhibits ATP-sensitive potassium channels, increased intracellular potassium concentration leads to depolarization, voltage-gated calcium channels activated, influx of calcium triggers exocytosis of insulin

Question 11

• What pathway is activated by insulin binding to receptors on the plasma membrane?

Answer 11

Activates the tyrosine kinase signal transduction pathway

Question 12

• What is the role of glucose transporter 4 in insulin-mediated glucose uptake?

Answer 12

Insulin stimulates translocation of GLUT4 proteins from cytoplasmic vesicles to plasma membrane, GLUT4 proteins are the insulin-responsive glucose transporters in skeletal muscle and adipose tissue (GLUT2 in the liver, GLUT1 in the brain)

Question 13

• What is the primary site of action of glucagon?

Answer 13

Liver

Question 14

• What does glucagon stimulate in the liver?

Answer 14

Glycogenolysis & gluconeogenesis

Question 15

• What factors affect glucagon secretion?

Answer 15

Inhibited by high blood glucose levels, stimulated by high amino acid levels

Question 16

• What are the actions of insulin on energy metabolism?

Answer 16

Muscle – promotes muscle glucose uptake, stimulates glycogenesis
Liver – inhibits glycogenolysis, stimulates glycogenesis, promotes de novo lipogenesis, inhibits gluconeogenesis
Brain – taken up by satiety and appetite centres
Fat metabolism – inhibits HSL (decreases lipolysis), stimulates de novo lipogenesis, increases delivery of fat to tissues
Protein metabolism – increases amino acid uptake by tissues, decreases rate of gluconeogenesis within the liver (less amino acids supplied)