10. Pancreas Flashcards
What is the embryological origin of the pancreas?
Outgrowth of the foregut
What proportion of the pancreas is responsible for exocrine secretions?
99%
What is the exocrine function of the pancreas?
Secretion of digestive enzymes and alkaline secretions into the duodenum.
What 2 hormones are released by the endocrine pancreas?
Insulin
Glucagon
Which cells are responsible for insulin secretion?
Beta cells (75%)
Which cells are responsible for glucagon secretion?
Alpha cells (25%)
What name is given to the regions of the pancreas that contain endocrine cells?
Islets of langerhans
What signals insulin release?
Feeding - glucose
What signals glucagon release?
Fasting
What are the target tissues for insulin?
Liver, adipose, skeletal muscle
How do the target tissues of glucagon differ to those of insulin?
Glucagon doesn’t have an effect on skeletal muscle
Which pancreatic hormone is considered anabolic?
Insulin
What is the normal plasma glucose range?
3.3-6 mmol/L
After a meal 7-8 mmol/L
What is the renal threshold for glucose?
10mmol
What happens if glucose levels rise above the renal threshold?
Glucosuria
How does the renal threshold alter in pregnant patients and elderly patients?
Pregnancy - decreases
Elderly - increases
Why is it so important to tightly regulate plasma glucose levels?
Energy supply - brain uses glucose at a fast rate and is sensitive to depletion
Osmolarity of plasma
What type of hormones are insulin and glucagon, how does this determine their transport in the blood?
Peptide hormones
Water soluble - no transport needed
Which pancreatic hormone is anabolic?
Insulin
Outline the structure of insulin.
2 peptide chains connected by 3 disulphide bonds
What structural feature of insulin confers stability?
Disulphide bonds
What occurs in insulin storage vesicles prior to release, how is this clinically useful?
Proteolysis to produce insulin + C-peptide in equal amounts. Plasma C-peptide can be used to measure levels of endogenous insulin secretion.
How much of it’s insulin stores does the pancreas secrete each day?
Only 15% - rest is stored
Which ion channel is present on the beta-cell membrane which controls insulin secretion?
ATP sensitive - K+ channel
How does the ATP K+ channel regulate insulin secretion?
When glucose levels are high, it enters the beta cell and enters glycolysis to produce ATP.
ATP binds to the K+ channel, inactivating it.
Hyper polarisation of the cell opens volatage-gated calcium channels.
Calcium influx triggers exocytosis of vesicles.
What type of receptor is the insulin receptor?
Tyrosine kinase - alpha and beta chain
How does insulin alter glucose uptake in target cells?
Inserts GLUT4 transporter to cell membranes to increase glucose uptake.
Increases glycogen synthesis
What effect does insulin have on muscle tissue?
Increased uptake of amino acids, increased protein synthesis.
What effect does insulin have on adipose tissue?
Increases lipogenesis and TAG storage.
How does the structure of glucagon compare to that of insulin?
Peptide hormone but a single chain with no disulphide bonds.
What are the main actions of glucagon?
Increase glycogenolysis, gluconeogenesis, ketogenesis and lipolysis.
What receptor type does glucagon bind to?
GPCR - alpha s
The half-life of insulin in plasma is approximately?
5 minutes - relatively short half life to respond rapidly to changes in glucose concentration.
How many disulphide bonds are there in insulin?
3 in total: 2 link the A and B chains
1 bond within A chain
What properties of C-peptide make it such a useful clinical marker?
it has a longer half life and so is more stable than insulin in plasma
Which glucose transporter is the primary transporter of glucose in pancreatic β cells?
GLUT2
Where else is GLUT2 important?
Liver - bi-directional so allows glucose release from gluconeogenesis as well as absorption
What is the medical term used to describe excessive thirst?
Polydipsia
