Hypothalamo-pituitary axis Flashcards
How does the pituitary develop?
Anterior pituitary develops from the ectoderm on the roof of the mouth and moves upwards
Posterior pituitary develops from the diencephalon
What is the Rathke’s pouch?
The roof of the mouth from which the anterior pituitary develops from
What is the role of the posterior pituitary hormones?
ADH increases absorption of water
Oxytocin stimulates synthesis of milk
What produces GH and what is it’s role?
GnRH and somatostatin -> GH
GH produces IFG-1
What is IGF-1?
Insulin like growth factor which acts like insulin
What produces TSH and what is it’s role?
Thyrotropin releasing hormone (TRH)
TSH produces T4 and T3
What produces prolactin and what is it’s role?
Dopamine and TRH produce prolactin
Prolactin produces milk glands and has a role in the immune system
What produces ACTH and what is it’s role?
Corticotrophin releasing hormone and ADH
Produces cortisol
What produces FSH and LH and what are their roles?
Kisspeptin and GnRH
FSH and LH produce sex steroids, inhibin, ovulation and spermatogenesis
What are the steps of the thyroid axis?
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)
What inhibition is there in the thyroid axis?
T4 inhibits TRH and TSH
Somatostatin inhibits TSH
How does primary and secondary underactivity of the thyroid occur?
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)
How does primary and secondary overactivity of the thyroid occur?
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
What are the steps of the GH axis?
GHRH and Ghrelin release GH which then produces IGF which goes on to produce somatostatin
What is the inhibition of the GH axis?
GH is inhibited by somatostatin (negative feedback)
IGF inhibits GF and GFRH
What are the functions of GHRH?
- promotes cell clusters so that hormones can be released in co-ordination
- increase in GH cell number
- increase in GH synthesis
- stimulates GH release
What is the receptor for GH?
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
What is McCune Albright syndrome?
- 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
What are the steps of the adrenal axis?
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
What inhibition is there in the adrenal axis?
Cortisol inhibits CRH, ADH and ACTH due to negative feedback
What are the 2 types of Cushing’s syndrome?
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
What is Addison’s disease?
Decreased cortisol levels due to lack of adrenal gland steroid production
What are the steps of the gonadal axis?
Kisseptin produces GnRH which produces LH and FSH and these go on to produce oestrogen and progesterone
What is the inhibition of the gonadal axis?
Oestrogen and progesterone inhibit LH and FSH as well as Kisspeptin
Why is the gonadal axis different in puberty?
Oestrogen does not inhibit kisspeptin but instead stimulates its production
