Pancreas anatomy and pysiology Flashcards
What does the exocrine pancreas do?
Secrete bicarbonate
Describe the exocrine pancreas
- It is the larger component of the pancreas
- Secretes digestive enzymes
- Secretes bicarbonate (base) to neutralise acid produced in the stomach
What stimulates the pancreas to secrete digestive enzymes?
Gastrointestinal hormones e.g. Cholecystokinin
List the digestive enzymes and what they act on
- Trypsin/ carboxypeptidase= proteins
- Ribonuclease= RNA
- Deoxyribonuclease= DNA
- Amylase= starch
- Lipase= triglycerides
Describe the 3 types of islet cell in the endocrine pancreas
- Beta cells= insulin
- Alpha cells= glucagon
- Delta cells = somatostatin
Describe somatostatin
- Produced by the hypothalamus, stomach, intestine and pancreas
- Supresses insulin and glucagon
Describe insulin
- Peptide hormone (so can’t give orally as digestive juices won’t break it down)
- Secreted by B cells
- Prohormone= proinsulin
- Intracytoplasmic pool of proinsulin (vesicles stored in cytoplasm)
Describe C-protein
The c-protein must be removed from the proinsulin before the insulin can be secreted.
C-protein is released at same rate as insulin but it is eliminated a lot slower so is useful to measure to check levels of insulin secretion.
Discuss the structure of insulin
2 polypeptide chains connected by 2 disulphide bonds
-Degraded in liver or kidney via cleavage of the disulphide bonds
Discuss insulin kinetics
- Secreted from pancreas
- Plasma half life=5-8 minutes
- Enters portal system and sent to liver
- ACTS ON LIVER FIRST
Describe the 3 mechanisms used to regulate insulin
1) Nutrients: Glucose and Aa
2) Gastrointestinal hormones: e.g. gastric inhibitory peptide (GIP)
3) ANS (parasympathetic stimulates/ sympathetic inhibits)
State the effect of incretins on insulin
-Incretins increase insulin secretion, we want insulin to be produced whilst eating a meal so the products can be stored and saved for when needed.
How is insulin secreted?
-Via calcium mediated exocytosis
Describe the first and second phases of insulin secretion
- First phase= release of the intracytoplasmic pool of proinsulin
- Second phase= insulin secretion results from new protein synthesis
Describe the release of insulin
- Blood glucose increases
- GLUT2 transporters allow glucose into cell
- Glucose is phosphorylated by glucokinase (traps the glucose in the cell)
- Increase in ATP production
- Inhibits ATP-sensitive potassium channels
- Increased intracellular potassium concentration leads to depolarisation
- Voltage gated calcium channels activated
- Influx of calcium triggers exocytosis of insulin
When insulin binds to a receptor on the plasma membrane, what signalling transduction pathway is triggered?
Tyrosine kinase
What effect does insulin have on GLUT4 transporters?
Insulin stimulates translocation of GLUT4 from the cytoplasmic membrane to the plasma membrane
-GLUT4 proteins are insulin responsive glucose transporters
Where are GLUT4 proteins found?
In skeletal muscle and adipose tissue
What does GLUT2 do?
Senses glucose in the pancreas whereas GLUT4 helps insulin in other tissues by getting glucose into cells.
( also GLUT2 in liver as NO GLUT4)
How does insulin work in the brain?
-No GLUT4- insulin independent GLUT1 transporter
Why does polyphagia occur in cases of diabetes mellitus?
- Insulin is needed for the satiety centre to uptake glucose
- The low insulin in diabetes mellitus means satiety isn’t met and appetite increases.
Discuss insulin and hormone sensitive lipase
-Insulin inhibits HSL-> decreases lipolysis
Stimulates de novo lipogenesis
What is de novo lipogenesis?
Production of fatty acids from glucose
What does HSL do?
Increases delivery of fat to tissues
Where is glucagon metabolised?
Liver and kidney
Is glucagon catabolic or anabolic?
Normally catabolic
Where is glucagon’s main site of action?
The liver
What does glucagon stimulate?
Glycogenolysis
Gluconeogenesis
What stimulates/ inhibits glucagon?
- Inhibited by high blood glucose
- Stimulated by high amino aicd levels
