184b - Intermediary metabolism

Question 1

Which cells secrete GLP-1 and GIP?

What is the stimulus?

Answer 1

L cells in the jejunum

Secreted in response to feeding

Question 2

How does glucose affect the secretion of glucagon?

Answer 2

Glucose inhibits glucagon secretion

Question 3

How does the beta cell sense glucose?

Answer 3

Glucose enters islet cells via insulin-independent GLUT2 tranpsorter

• -> Glycolysis
• -> ATP generated
• -> Closes ATP-dependent K+ channel
• -> Depolarization
• -> Voltage-gated Ca2+ channels open
• -> Insulin release

Question 4

Which cells secrete ghrelin?

What is the stimulus?

Answer 4

Gastric wall cells

Secreted during a fasting state; hunger signal

When your stomach GRRRrowls you secrete GhRRRelin

Question 5

Describe the signaling pathway that is activated when glucagon binds to its receptor

Answer 5

Glucagon receptor is a GPCR

Gs -> cAMP -> PKA -> energy mobilization, glucogneogenesis

Question 6

How does glucagon affect insulin release?

Answer 6

Glucagon stimulates insulin release

Kind of counter-intuitive: Glucagon’s main job is to mobilize energy

BUT, will also stimulate insulin release to prevet hyperglycemia when energy is mobilized

Question 7

What kind of receptor is the leptin receptor?

What is the end result of receptor activation?

Answer 7

JAK-STAT

• Satiety signals to the hypothalamus (ventromedial nucleus)

Question 8

Describe the signaling pathway that is activated when insulin binds to its receptor

Answer 8

Insulin receptor = tyrosine kinase

• Insulin binds
• Dimerization
• Phosphorylates downstream proteins
  
  • PKC/PI3 kinase pathway = energy storage
• > Glycogen and FA storage, GLUT4 activation
  
  • RAS/MAP kinase pathway = use energy to grow
• > Gene expression, cell growth/differentiation

Question 9

What kind of receptor is the ghrelin receptor?

What is the end result of receptor activation?

Answer 9

GPCR

• Induces hunger (signals to lateral nucleus of the hypothalamus)
• Decreases energy expenditure

Question 10

Levels of the following hormones are increased in fasting state

1. Insulin, ghrelin
2. GLP-1, glucagon
3. Glucagon, leptin
4. Glucagon, ghrelin

Answer 10

d. Glucagon, ghrelin

Question 11

List 3 mechanisms that insulin uses to lower blood glucose

Answer 11

• Glucose uptake into myocytes and adipocytes
• Decreaed glycogen breakdown, increased glycogen formation
• Decreased glucagon production

Question 12

In a fed state, the following hormones are increased:

1. Insulin, ghrelin
2. GLP-1, glucagon
3. Insulin and leptin
4. Glucagon and ghrelin

Answer 12

c. Insulin and leptin

Question 13

How does growth hormone affect insulin secretion?

Answer 13

Growth hormone stimulates insulin secretion

(but also causes insulin resistance?)

Question 14

Which hormones make beta cells more sensitive to rising glucose, therefore potentiating insulin release? (2)

Answer 14

GLP-1, GIP

• Still need rising glucose as a stimulus for insulin release, but threshold is lower

Question 15

Which cells secrete glucagon?

Answer 15

Alpha-cells in the Islets of Langerhans