Bio Lecture 24 Insulin/Glucagon

Question 1

What are normal blood glucose levels?

Answer 1

70-100 mg/dl

Question 2

In general terms, how do insulin and glucagon act to influence blood sugar levels?

Answer 2

Insulin is used to lower blood sugar levels

Glucagon is used to raise blood sugar levels

Question 3

What is the pancreas responsible for?

Answer 3

Pancreas controls digestion and regulates glucose homeostasis.

Question 4

What are the different types of cells that make up the pancreas?

Answer 4

Exocrine portion is the main make-up of the pancreas. It is made of acinar cells that secrete digestive enzymes into the duodenum.
Ductal cells make the ducts for the exocrine cells.
Endocrine cells (islet of Langerhans) make up only 1-2% of the cells and they produce insulin and glucagon

Question 5

What four cells make up the islet of Langerhans?

Answer 5

Alpha cells: make glucagon
Beta cells: make insulin (most abundant and located in the middle)
Delta cells: make somatostatin
PP cells: make pancreatic polypeptides

Question 6

Summarize the production of insulin.

Answer 6

N-terminal tail of the protein directs it to bind with SRP protein and a protein translocator so the polypeptide will form in the lumen of the RER. This forms the preproinsulin.
In the RER, the preproinsulin is cleaved to remove the signal sequence and proinsulin is formed.
PDI protein and a chaperone protein align the disulfide bridges between A and B chains.
Transferred to cis-golgi where it is cleaved into C-peptide and insulin.
Stored in vesicles and ready for secretion.

Question 7

What are incretins?

Answer 7

Incretins are insulin secretion stimulating agents which are hormones released by the gut in response to glucose.
Causes increase in Insulin and decrease in glucagon. GLP-1 is an example. It has a short half-life because it is cleaved by DPP-4.

Question 8

Explain insulin secretion.

Answer 8

Can be secreted in regulated and constitutive fashion.
Regulated is stimulated by secretagogues.
1) Glut-2 allows glucose into Beta cells
2) Glucose phosphorylated
3) Glucose->ATP
4) Increased ATP closes K+ channel
5) Increased K+ depolarizes membrane
6) Voltage Ca2+ channel opens and calcium enters cell
7) Ca2+ mobilizes the secretory vesicles

Question 9

How does the drug sulfonylurea treat diabetes?

Answer 9

It inhibits the K+ channel in Beta cells which ultimately causes Ca2+ in the cell and causes insulin vesicles to be released.

Question 10

How are insulin and glucagon metabolized in the body?

Answer 10

At least half of insulin and glucagon are metabolized in the liver. The kidney largely takes care of the rest.
Both have half-lives of no longer than 5 minutes

Question 11

Why is C-peptide a better way to measure insulin levels in the blood?

Answer 11

C-peptide has a longer half-life than insulin (30 mins) and is therefore around longer to be measured.

Question 12

How do epinephrine, dietary amino acids, blood glucose, incretins, and neural input affect insulin levels?

Answer 12

All increase except for epinephrine and Neural can do both.

Question 13

How do epinephrine, dietary amino acids, blood glucose, incretins, cortisol, and neural input affect glucagon levels?

Answer 13

All increase except for blood glucose and incretins. Insulin also decreases the amount of glucagon in the blood.

Question 14

What receptor is used for insulin and what tissues are insulin-sensitive?

Answer 14

RTK receptor in liver, muscle, adipose tissues

Question 15

What receptor is used for glucagon and in what tissues?

Answer 15

G-coupled receptor only in the liver.

Question 16

What is the main source for energy in the fasting state?

Answer 16

Fatty acids and ketone bodies except for the cells that can only use glucose.