Hypothalamo-pituitary axis

Question 1

How does the pituitary develop?

Answer 1

Anterior pituitary develops from the ectoderm on the roof of the mouth and moves upwards
Posterior pituitary develops from the diencephalon

Question 2

What is the Rathke’s pouch?

Answer 2

The roof of the mouth from which the anterior pituitary develops from

Question 3

What is the role of the posterior pituitary hormones?

Answer 3

ADH increases absorption of water

Oxytocin stimulates synthesis of milk

Question 4

What produces GH and what is it’s role?

Answer 4

GnRH and somatostatin -> GH

GH produces IFG-1

Question 5

What is IGF-1?

Answer 5

Insulin like growth factor which acts like insulin

Question 6

What produces TSH and what is it’s role?

Answer 6

Thyrotropin releasing hormone (TRH)

TSH produces T4 and T3

Question 7

What produces prolactin and what is it’s role?

Answer 7

Dopamine and TRH produce prolactin

Prolactin produces milk glands and has a role in the immune system

Question 8

What produces ACTH and what is it’s role?

Answer 8

Corticotrophin releasing hormone and ADH

Produces cortisol

Question 9

What produces FSH and LH and what are their roles?

Answer 9

Kisspeptin and GnRH

FSH and LH produce sex steroids, inhibin, ovulation and spermatogenesis

Question 10

What are the steps of the thyroid axis?

Answer 10

TRH in the hypothalamus produces TSH in the pituitary gland which then produces T4 in the adrenal gland which goes on to produce T3 (liothyronine)

Question 11

What inhibition is there in the thyroid axis?

Answer 11

T4 inhibits TRH and TSH

Somatostatin inhibits TSH

Question 12

How does primary and secondary underactivity of the thyroid occur?

Answer 12

Primary - defect of the target organ so not enough hormone produced there (e.g. T4/T3 in the thyroid axis)
Secondary - pituitary gland defect (low TSH for example in the thyroid axis)

Question 13

How does primary and secondary overactivity of the thyroid occur?

Answer 13

Primary - high target organ hormone levels but there is suppressed pituitary hormone
Secondary - high pituitary hormone release so lots act on target organ causing enlargement as too much stimulus

Question 14

What are the steps of the GH axis?

Answer 14

GHRH and Ghrelin release GH which then produces IGF which goes on to produce somatostatin

Question 15

What is the inhibition of the GH axis?

Answer 15

GH is inhibited by somatostatin (negative feedback)

IGF inhibits GF and GFRH

Question 16

What are the functions of GHRH?

Answer 16

• promotes cell clusters so that hormones can be released in co-ordination
• increase in GH cell number
• increase in GH synthesis
• stimulates GH release

Question 17

What is the receptor for GH?

Answer 17

GPCR
- ligand binds to GPCR -> phosphorylation -> activates G protein -> alpha unit detaches from the G protein to bind to adenylate cyclase -> increases cAMP activity -> increases PKA levels -> produces a cellular response

Question 18

What is McCune Albright syndrome?

Answer 18

• spontaneous mutation in the embryo prevents downregulation of cAMP
• This means PKA levels remain high and there is a constant increased cellular response
• Hyper-functioning of endocrine organs (may result in goitre)
• leads to bone deformities, skin deformations
• more common in females

Question 19

What are the steps of the adrenal axis?

Answer 19

CRH and ADH forms ADH in the hypothalamus which goes on to produce ACTH in the pituitary gland and this produces cortisol in the adrenal gland

Question 20

What inhibition is there in the adrenal axis?

Answer 20

Cortisol inhibits CRH, ADH and ACTH due to negative feedback

Question 21

What are the 2 types of Cushing’s syndrome?

Answer 21

ACTH independent -> increased cortisol independent of ACTH but instead may be due to an adrenal tumour

ACTH dependent -> raised levels of ACTH due to a pituitary defect such as adenoma which leads to increased cortisol levels

Question 22

What is Addison’s disease?

Answer 22

Decreased cortisol levels due to lack of adrenal gland steroid production

Question 23

What are the steps of the gonadal axis?

Answer 23

Kisseptin produces GnRH which produces LH and FSH and these go on to produce oestrogen and progesterone

Question 24

What is the inhibition of the gonadal axis?

Answer 24

Oestrogen and progesterone inhibit LH and FSH as well as Kisspeptin

Question 25

Why is the gonadal axis different in puberty?

Answer 25

Oestrogen does not inhibit kisspeptin but instead stimulates its production