184 - Intermediary Metabolism

Question 1

Insulin is a _________ hormone that binds to a __________ receptor.

Answer 1

Insulin is a peptide hormone that binds to a tyrosine kinase receptor.

Question 2

What are 4 major effects of insulin signaling?

Answer 2

1) glucose uptake in target tissues (via GLUT-4)
2) stimulation of glycogen synthesis and inhibition of glycogenolysis
3) induction of genes regulating storage of energy carriers (glycogen and triglyceride synthesis)
4) induction of genes for increased protein synthesis

Question 3

What are the major insulin dependent tissues?

Answer 3

muscle, fat, and liver

Question 4

What is c-peptide? How is it used clinically?

Answer 4

c-peptide is a peptide that is cleaved from proinsulin and secreted alongside insulin

it is used as a marker for endogenous insulin

Question 5

What is the mechanism for glucose related insulin release?

Answer 5

plasma glucose is sensed by beta cells (via entry of glucose into cells with GLUT2) –> glucose is used in glycolysis/TCA to produce ATP –> ATP sensitive potassium channels recognize the increased ATP/ADP ratio –> K-ATP channels are inhibited, leading to depolarization –> depolarization activates voltage gated calcium channels (increase in intracellular calcium) –> increased Ca levels trigger release of vesicles with insulin and c-peptide

Question 6

How is glucagon secreted? What does it do?

Answer 6

secreted by alpha cells in the islets of Langerhans

counteracts insulin (with respect to glucose uptake and metabolism)

also stimulates insulin secretion from beta cells, preventing hyperglycemia in response to glucagon

Question 7

How is ghrelin released? What does it do?

Answer 7

Released by cells in the stomach and intestinal wall

levels rise during fasting, inducing hunger and promoting energy conservation

Question 8

How is leptin secreted? What does it do?

Answer 8

secreted by adipose tissue proportional to its mass

induces satiety (decreased sensitivity may lead to obesity)

Question 9

How is glucagon like peptide-1 (GLP-1) secreted? What does it do?

Answer 9

secreted by cells in the intestine in response to food intake

facilitates insulin secretion from beta cells following oral intake

Question 10

What are the levels of insulin and glucagon in the fed state? What happens to glucose uptake and protein/glycogen/triglyceride synthesis?

Answer 10

insulin: high
glucagon: low

glucose uptake, protein/glycogen/triglyceride synthesis: high in liver, muscle, and adipocytes

Question 11

How are glucose levels maintained in the fasting state?

Answer 11

lower insulin levels, higher glucagon levels

glucose released from liver (glycogenolysis and gluconeogenesis)

lipids are mobilized from adipose tissue

lipids are either oxidized (peripheral tissue) or converted to ketones (liver)

amino acids are mobilized from body protein stores (substrate for liver gluconeogenesis)

Question 12

How do ghrelin levels change in the fed vs. fasting state? Leptin levels?

Answer 12

fed: ghrelin low, leptin high (promotes satiety)
fasting: ghrelin high, leptin low (promotes hunger)

Question 13

Levels of which of the following hormones are increased in fasting state:

a) insulin, ghrelin
b) GLP-1, glucagon
c) glucagon, leptin
d) glucagon, ghrelin

Answer 13

d) glucagon, ghrelin

glucagon mobilizes glucose release, ghrelin stimulates hunger

Question 14

In the fed state, which of the following hormones are increased:

a) insulin, ghrelin
b) GLP-1, glucagon
c) insulin and leptin
d) glucagon and ghrelin

Answer 14

c) insulin and leptin

insulin converts glucose to stored form/to energy, leptin triggers satiety

Question 15

What factors stimulate insulin release? Inhibit it?

Answer 15

stimulate: glucose, GLP-1, glucagon, epinephrine (and others)
inhibit: inflammatory cytokines, somatostatin, norepinephrine, leptin, IGF-1