Hypersecretion of anterior pituitary hormones Flashcards
What are the causes of hyperpituitarism?
1) Most commonly due to a pituitary tumour
2) can be caused by a tumour elsewhere i.e. Cushings - too much ACTH- too much cortisol- produced by tumour in the gut.
What is the one main presentation of hyperpituitarism?
tumour of the pituitary can squash the optic chiasm which is located above the pituitary gland. compression of optic chiasm can cause visual field defects i.e. bitemporal hemianopia.
Bitemporal hemianopia- compression of the optic chiasm where nasal retinae fibres cross over it can cross loss of visual field at outer parts. the nasal retinae fibres supply the outer visual fields.
Excess of anterior pituitary hormones can cause?
1) too much ACTH- causes too much cortisol from adrenal cortex which causes Cushings syndrome
2) too much TSH- thyrotoxicosis
3) too much gonadotrophins- precocious (early) puberty in children and ovarian hyperstimulation and large ovaries in women.
4) too much prolactin- hyperprolactinaemia (too much prolactin)
5) GH- acromegaly (growth of soft connective tissue and cartilage in adults) , gigantism (children grow very tall, not seen in adults because they have already finished growing)
what is hyperprolactinaemia?
Hyperprolactinaemia- when too much prolactin is produced.
this is physiologically normal during pregnancy and breastfeeding so cannot be used as a diagnostic.
Pathologically most commonly it occurs when there is a tumour in pituitary. Commonly microadenomas in the pituitary- less than 1cm
too much prolactin can switch of GnRH pulsatility. it switches off the hypothalamo-gonadal axis. GnRH is not produced by hypothalamus so no LH/FSH produced in anterior pituitary so no oestrogen or testosterone made in gonads. GnRH pulsatility is more frequent during puberty but can be switched off if there is too much prolactin- it is a cause of secondary hypogonadism.
What are some of the presentations of hyperprolactinaemia due to pituitary adenoma?
women:
1) galactorrohea- milk production outside of lactation.
2) secondary amenorrohea or oligomenorrhoea - because of this women tend to present hyperprolactinaemia earlier than men.
3) loss libido
4) infertility
men:
1) galactorrohoea- uncommon because oestrogen is needed to prime the breast, men do not have oestrogen
2) loss of libido
3) erectile dysfunction
4) infertility
how is prolactin secretion normally regulated?
lactrotrophs in anterior pituitary have D2 receptors which dopamine from hypothalamic doapminergic neurones binds to. Dopamine inhibits prolactin release.
