Endocrine Physio of GH

Question 1

2 major determinants of normal post-uterine growth

Answer 1

GH

IGF-1

Question 2

2 major functions of GH

Answer 2

Growth (mostly mediated by IGF-1)

Metabolic actions

Question 3

Metabolic actions of GH on

1. Liver
2. Muscle
3. Adipose

Answer 3

Counterregulatory hormone that opposes insulin action

1. Increased blood glucose production
2. Decrease glucose uptake
3. Increase lipolysis

Question 4

4 counter regulatory hormones to insulin

Answer 4

Glucagon
Epinephrine
GH
Cortisol

Question 5

GH secretion rhythm

Answer 5

Pulsatile release (ultradian)
Peaks during deep sleep which is important for growth promotion (circadian rhythm)

Question 6

Secretion of GH during sleep

Answer 6

Serotonergic and cholinergic fibers stimulate GHRH neurons in the arcuate nucleus
Cause the release of GH in the AP
Inhibitory neurons that release SS from the hypothalamus are stimulated in the periventricular nucleus

Question 7

Ghrelin

Answer 7

Released from the stomach during fasting

Turns GH on to prevent hypoglycemia

Question 8

Long feedback loop

Answer 8

Target hormone feeds back on the pituitary, hypothalamus, and/or CNS to regulate the axis

Question 9

Short feedback loop

Answer 9

AP hormone feeds back on the hypothalamus to regulate the axis

Question 10

Very short feedback loop

Answer 10

AP hormone feeds back on the pituitary to regulate the axis

Question 11

Function of GH binding protein

Answer 11

Reduces rate of GH degradation (extends the half life)

Acts as a reservoir of GH

Question 12

GH Receptor

Answer 12

Extracellular receptor
Tyrosine kinase associated receptor
Activation initiates a cascade of phosphorylation reactions

Question 13

2 IGF-1 effects

Answer 13

Growth (one of the primary ones is at the growth plate)
Insulin-like actions (anabolic) - these are weak
You need a lower concentration of IGF1 to stimulate growth than you do to stimulate the insulin like effects

Question 14

Gigantism

Answer 14

GH hypersecretion prior to pubertal epiphyseal fusion
Because the growth plate is still open you get elongated long bones
From pituitary hyperplasia
Somatotroph hyperplasia due to hypersecretion of GHRH

Question 15

Acromegaly

Answer 15

Excess GH after puberty
Long bones do not lengthen because GH excess started after closure of the epiphyseal growth plate
Progressive thickening of bones and soft tissue of head, hands, and feet
From primary GH excess (pituitary adenoma usually), extra pituitary GH excess, etc