2-hypothalamus And Pituitary 1

Question 1

Posterior pituitary doesn’t synthesize…

Answer 1

Hormones, but stores th3m

Question 2

What are the 5 types of hormone secreting cells?

Answer 2

• gonadotrophs
• somatotrophs
• corticotrophs
• thyrottrophs

-lactotrophs

Question 3

What hormone secreting cells are 1st to be affected by mechanical
lesions?

Answer 3

Gonadotrophs
Somatotrophs

Since they are posterolateral

Next are lactotrophs as they are scattered throughout the gland

Corticotrophs and thyrotrophs are most resilient since they are anteromedial

Question 4

All hormones except for _____ & ______ function by stimulating other end8crine g”ands

Answer 4

GH

PRL

Question 5

What are the 3 classes of anterior pituitary hormones?

Answer 5

POMC- ACTH

Lactogens- GH, PRL, (hPL*) are similar in structure

Glycoproteins-TSH, FSH, LH, (hCG*)

• a chains identical
• B chains differ

Question 6

Describe the structure of growth hormone

Answer 6

GH is a 191 amino acid peptide

• Is similar in structure to PRL & human placentogen (hPL)

Question 7

Where is growth hormone secreted?

Answer 7

By somatotrophs in the anterior pituitary

Question 8

What happens when GH circulates in high concentrations?

Answer 8

High concentrations of GH can have PRL like effects

Question 9

What is the half life of growth hormone?

Answer 9

Circulated unbound

Half life= 20-30 minutes

Question 10

What does somatostatin do?

Answer 10

Inhibits secretion of growth hormone

Also known as GHIH

Question 11

Summarize the mechanism of action of GHRH in the anterior pituitary

Answer 11

GHRH binds to receptor to increase cAMP, and via PKA there is an influx of Ca2+
This causes a release of GH via exocytosis

Question 12

How does the somatotrophs respond to GHRH binding to the receptor?

Answer 12

GHRH receptor binding leads to increased cAMP and increased DNA transcription

This leads to increased GH production

Question 13

What is the response of a somatotrophs to a somatostatin?

Answer 13

Somatostatin binds to receptor, and decreases cAMP and via PKA which is decreased and decreased Ca2+.

Inhibition of release 9f GH via exocytosis

Question 14

What is the structure of the somatostatin?

Answer 14

It is a 14 AA peptide

Question 15

What is the effect of growth hormone in target tissues?

Answer 15

Growth hormone stimulates Tyrosine kinase —> modulation of gene expression —> growth hormone effects

Question 16

Describe the pulsatile secretion of GH

Answer 16

• Occurs in periodic bursts maximal peaks at night.
  
  • Usually in stage 3 & 4 of slow wave of deep sleep

-Mean GH levels are highest at adolescence & level to baseline until senescence & then decline

Question 17

What are the actions of GH?

Answer 17

GH is a major regulator of

• skeletal & soft tissue growth
• carbohydrate, lipid & protein metabolism. It’s overall effect is to increase blood glucose & thus known as diabetogenic

GH hormone exerts it’s actions by both

• direct
• indirect through IGF’s

Question 18

What are the direct actions of GH in liver?

Answer 18

Increased glucose synthesis in liver to raise blood glucose

IGF synthesis in liver to increase IGF

Synth3sis of IGF-binding protein to increase IGF-BP

Question 19

What are the direct actions of GH in adipose tissue?

Answer 19

Increased lipid breakdown to increase free fatty acids & glycerol

Decreased glucose uptake to increase blood glucose

Question 20

What are the direct actions of GH in muscle tissue

Answer 20

Inhibits breakdown of proteins

Increases amino acid up take and protein synthesis

Glucose uptake decreased which increases blood glucose

Question 21

What are the effects of GH on insulin?

Answer 21

GH increases blood glucose, which then increased insulin

Action of insulin is thought to be impaired due to increased FFA, exact mechanism not known

Insulin is required for growth

Question 22

What is the importance of IGFs?

Answer 22

Also known as somatomedins

Structurally related to pro-insulin
• 6 different types of IGF’s, IGF1 is most important one
• IGF1(somatomedin C) is produced mainly in the liver in response to GH
• Bound to IGF-binding proteins – Longer half-life
• Bind to tyrosine kinase receptors of target cell membranes

Question 23

Why are IGFs important?

Answer 23

Important for growth-promoting effects of GH

Question 24

Summarize IGF function

Answer 24

Promote linear bone growth

Increase organ size & function

Insufficient synthesis of IGF’s can result in dwarfism

African pygmies & Levi Loran have this problem

Question 25

What is the function of IGF-1 on Chondrocytes?

Answer 25

• AA uptake
• protein synthesis
• DNA & RNA synthesis
• Chondroitin sulfate
• Collagen
• Cell size & number

Question 26

How is growth hormone regulated?

Answer 26

• It is regulated by 3 different hormones
- Growth hormone releasing hormone
- (GHRH) stimulates the release
- Somatostatin inhibits the release of GH
• 3rd mechanism is through both GH & IGF1(negative feedback to suppress GHRH & increase somatostatin release. This is a positive feedback effect)
• Thyroid hormone has permissive action on growth hormone • In hypothyroid children GH action is impaired

Question 27

Give a general summary of hypersecretion of GH

Answer 27

Usually due to tumor in AP
• It can result in either
- gigantism or acromegaly
• Gigantism occurs if it is before the closure of epiphyseal plates
• The body grows in proportion
• Achieve heights between 7 – 8 feet

Question 28

Explain the clinical significance of acromegaly

Answer 28

If hypersecretion of GH occurs post-puberty results in thickening soft tissues & growth of skull bones resulting in
- growth of orbital ridges causing frontal bossing - prominent chin
- growth of mandible (prognathism)
- widening of teeth
-enlargement of hands, feet, ears & nose - all organ sizes are increased leading to
hypertension & heart failure • Diabetes