7.5 Growth Hormones and Gonadotropins

Question 1

What is growth?

Answer 1

Progressive increase in size of an organism.
Net synthesis of proteins.
Includes elongation of bones and size and number of cells in soft tissue.

Question 2

Main influencers on growth

Answer 2

Genetics
Hormones
Nutrition
Freedom from stress and disease

Question 3

Insulin’s impact on growth

Answer 3

Excess stimulates excessive growth
Deficiency may block growth

Question 4

Androgen’s influence on growth

Answer 4

Involved in pubertal growth and stimulation of protein synthesis

Question 5

Thyroid dysfunction’s effect on growth

Answer 5

Hypothyroidism stunts growth
BUT
Hyperthyroidism does not stimulate excess growth

Question 6

What is fetal growth determined by?

Answer 6

• Promoted by placental hormones
  
  • Determined by genetics
  • Neurological growth maximum in late intrauterine and early post-natal life

Question 7

What inhibits growth hormone?

Answer 7

Growth Hormone Inhibiting Hormone (aka somatostatin)

Question 8

What stimulates growth hormone?

Answer 8

Growth Hormone Releasing Hormone

Question 9

Outline the pathway of GH’s action

Answer 9

GHRH -> GH -> Liver -> IGFs -> many tissues

Question 10

GH (type, location, regulators, target tissues)

Answer 10

Peptide hormone, released from the somatotrophs of anterior pituitary gland
Secretion regulated by GHRH and GHIH (somatostatin)
Targets many tissues (skeletal muscle, bone, adipose tissue, liver)

Question 11

Positive stimuli of GH (major and minor)

Answer 11

(Major+)
- Exercise
- Stress
- Hypoglycaemia
- Fasting (IGF-I level low)
- Circadian rhythm (sleep)
(Minor +)
- Increase in amino acids
- Decrease in fatty acids

Question 12

Negative feedback regulators of GH

Answer 12

• GH inhibits GHRH and stimulates GHIH
  
  • IGF inhibits somatotrophs (decreases GH secretion)
  • IGF stimulates GHIH release

Question 13

Insulin-like growth factors (other name, type, location, types, effects)

Answer 13

Seomatomedins
* Peptide hormones with strong mitogenic properties
* Primarily made in liver but also other tissues (exert autocrine/paracrine effect)
* Two types:
○ IGF-1 effects most cells in the body where it stimulates growth, multiplication, and inhibits apoptosis
○IGF-2 is a growth promoting hormone during gestation

Question 14

Growth Hormone receptor

Answer 14

JAK/STAT
Hormone receptor for Growth hormone
Specialised enzyme-linked receptor that is linked to JAK enzymes.
This turns on gene transcription to synthesise a whole new protein.
STAT protein activates gene transcription.

Question 15

METABOLIC effects of GH

Answer 15

Promotes protein synthesis and suppresses protein degradation
Promotes lipolysis (increasing free fatty acids in blood)
Promotes hepatic gluconeogenesis
Decreases insulin sensitivity in muscles, therefore decreasing muscles’ glucose uptake -> muscles use free fatty acids -> increased blood glucose
OVERALL promotes protein synthesis, uses fat stores, but also promotes hyperglycaemia

Question 16

GROWTH effects of growth hormone

Answer 16

Promotes protein synthesis
Suppresses protein degradation
Hyperplasia
Hypertrophy

Question 17

Gonadotropins

Answer 17

• Luteinising Hormone (LH)
  
  • Follicle-stimulating hormone (FSH)
  • Produced in the anterior pituitary
  • Act on gonads by activating cAMP (cyclic adenosine monophosphate)
  • Some circadian rhythm controls gonadotroph release, but mostly pulsating release (higher during sleep).
  • Puberty is initiated by GnRH release