Pancreas anatomy and physiology

Question 1

Label the canine pancreas and associated structures

Answer 1

Question 2

what digestive enzymes are secreted from the pancreas?

Answer 2

Trypsin and carboxypeptidase - acts on peptides/proteins
Lipase - acts on triglycerides
Amylasae - acts on starch
Phospholipase - acts on phospholipids
Ribonuclease - acts on RNA
Deoxyribonuclease - acts on DNA

Question 3

What cells are found in the Islets of Langerhans and what do they secrete?

Answer 3

Beta cells - insulin
Alpha cells - glucagon
Delta cells - somatostatin

Question 4

What is the function of somatostatin?

Answer 4

Produced by hypothalamus, stomach, intestine and pancreas
Suppressed insulin and glucagon secretion
Also inhibits growth hormone

Question 5

How is insulin produced?

Answer 5

First synthesised as preprohormone
Then converted to prohormone = proinsulin
Intracytoplasmic pool of proinsulin ready for quick release
Removal of C-peptide from proinsulin => insulin

Question 6

Describe the structure and degradation of insulin

Answer 6

2 polypeptide chains connected by 2 disulfide bonds
Degradation by liver or kidney via cleavage of disulfide bonds within target cells

Question 7

Describe the role of C-peptide in insulin secretion

Answer 7

Connecting peptide - removed from pro-insulin upon secretion
Released in equal amounts to insulin
Biologically inactive and removed at slower rate
Can be used to measure pancreatic function

Question 8

Describe the flow of insulin

Answer 8

Secreted by pancreas
Enters portal vein => liver
Acts upon liver
Enters general circulation

Question 9

How is insulin secretion regulated?

Answer 9

3 mechanisms:
- nutrients: glucose and AAs
- GI hormones (incretins) e.g., gastric inhibitory peptide (GIP and glucagon like peptide (GLP-1)
- ANS (PNS stimulates, SNS inhibits)

Question 10

What is the effect of nutrients on insulin?

Answer 10

Increased secretion when nutrients are abundant (after feeding)
Moves energy substrates into storage
Insulin = anabolic hormone

Question 11

What is the process that causes release of insulin from B-cells?

Answer 11

calcium-mediated exocytosis

Question 12

How is insulin secretion controlled by the intestinal tract?

Answer 12

Increased GIP (gastric inhibitory peptide) and GLP-1 (glucagon-like-peptide) when food reaches intestine
=> insulin release from pancreas

Question 13

Describe the parasympathetic control of insulin secretion

Answer 13

Increase in parasympathetic activity via vagus nerve => stimulates insulin secretion after feeding

Question 14

Describe the sympathetic control of insulin secretion

Answer 14

Direct innervation (sympathetic neurones)
Indirect response via adrenaline
Stress response: hyperglycaemia
Insulin secretion and action are inhibited

Question 15

What are the 2 phases of insulin secretion?

Answer 15

First phase: release of intracytoplasmic pool of proinsulin via calcium mediated exocytosis
Second phase: insulin secretion from new protein synthesis

Question 16

Describe the process of calcium mediated exocytosis in beta cells

Answer 16

Question 17

How do GLUT4 glucose transporters work?

Answer 17

Insulin stimulates translocation of GLUT4 proteins from cytoplasmic vesicles to plasma membrane in skeletal muscle and adipose tissues
Insulin-responsive glucose transporters

Question 18

Fill in this table of the function and location of glucose transporter types

Answer 18

Question 19

Describe the impact of insulin on the brain

Answer 19

Insulin-independent GLUT1 transporter takes glucose into cells based on conc gradient
No GLUT4 in brain except for in satiety and appetite centres so insulin required for glucose uptake here (this is how hypothalamus detects glucose levels)
Without insulin => increased appetite

Question 20

Describe the effect of insulin on fat metabolism

Answer 20

Inhibits hormone-sensitive lipase (HSL) => decreases lipolysis
Stimulates lipogenesis (production of fatty acids from glucose)
Promotes lipoprotein lipase (LPL) => increases delivery of fatty acids in tissues

Question 21

How does insulin stimulate lipogenesis?

Answer 21

Excess glucose increases TCA cycle intermediates (citrate)
Activates acetyl CoA carboxylase (ACC)
Forms malonyl CoA (Fat precursor)

Question 22

What is the impact of insulin on protein metabolism?

Answer 22

Increases AA uptake by tissues
Increases rate of transcription and translation
Inhibits catabolism of proteins
Depresses rate of gluconeogenesis within liver (inhibits enzymes and lower AA supply from tissues)

Question 23

What is the impact of insulin on the liver?

Answer 23

No GLUT4 - glucose uptake by GLUT2
Inactivates liver glycogen phosphorylase (inhibits glycogenolysis)
Increases glycogen synthase activity (stimulates glycogenesis)
Promotes conversion of glucose into fats (lipogenesis)
Inhibits gluconeogenesis

Question 24

Describe the formation and metabolism of glucagon

Answer 24

Secreted by alpha cells of pancreas
Synthesised as preproglucagon
Rapidly converted to glucagon
Matbolised in liver and kidneys

Question 25

What is the action of glucagon?

Answer 25

Catabolic hormone
Respond to hypoglycaemia
Active between meals to maintain glucose levels (inter-prandial period)
Activated during negative energy balance (starvation)
Stimulates glycogenolysis and gluconeogensis in the liver

Question 26

Why is glucagon secreted after a protein-rich meal?

Answer 26

high amino acid levels - promotes gluconeogenesis
Post-prandial hypoglycaemia protection:
- increased insulin stimulated by AAs would cause low blood glucose levels

Question 27

Why are both insulin and glucagon stimulated by amino acids in circulation?

Answer 27

Insulin => decreased amino acids and glucose levels
Glucagon => protection from hypoglycaemia due to decreased glucose

Question 28

Fill in this table showing the effect of hormones on metabolism

Answer 28