Introduction to the HPA axis Flashcards
What are the six anterior pituitary hormones?
GH, TSH,ACTH, FSH,LH, prolactin
What controls the secretion of GH?
by the hypothalamus via:
GHRH and somatotropin
GHRIH and somatostatin
How does GH act and what is its primary effect?
In some tissues GH acts via second messengers which are produced in the liver (IGF 1 and IGF 2).
Involved in tissue turnover and repair, promotes growth in adolescence by increasing protein synthesis and collagen deposition. foetal growth is independent of GH.
What is the action and functions of oxytocin?
acts via IP3 to cause contraction of smooth muscle of the uterus and breast. most important during parturition and lactation.
What controls and stimulates the secretion of prolactin?
secretion is controlled by prolactin release inhibiting factor - dopamine.
secretion isstimulated by: mild stress, nipple stimulation, coitus.
TRHstimulates prolactinsynthesis.
What are the actions of prolactin?
controls milk production in women.
proliferation and differentiation of mammary tissue during pregnancy
inhibits gonadotrophin release and/or the response of ovaries to these trophic hormones (so ovulation doesn’t occur during breastfeeding).
Which structures synthesise and stores ADH and oxytocin?
synthesised as inactive precursors and converted to the active hormone in posterior pituitary. inactive hormones are transported from supraoptic and paraventricular nuclei along hypothalamico-neurohypophyseal tract and stored in posterior pituitary.
What is the function of ADH?
controls water content through its action on cells of distal part of nephron and collecting tubules of the kidney
What causes ADH to be released?
increase in plasma osmolarity (thirst)
stimuli from stretch receptors in cardiovascular system or angiotensin release detects hypovolaemia.
What are the disorders of ADH secretion?
disorders of fluid balance e.g. diabetes insipidus - excess dilute urine produced due to low/absent ADH secretion, or reduced sensitivity of the kidney to the hormone
Which drugs increase the effects of ADH?
NSAIDs and carbamazepine, aldosterone (Na+ retention)
Which drugs reduce the effects of ADH?
lithium, colchicine, vinca alkaloids (Na+ excretion)
Which biochemical tests are carried out to investigate ADH secretion?
TSH and T4, cortisol, LH and FSH, PRL test, testosterone/periods. 9am
Which clinical investigations are taken for ADH?
presentation - primary or secondary?
stimulate secretion? - ACTH or suppress secretion? - dexamethasone
biochemical tests
imaging - MRI
visual field tests
bilateral hemianopsia? - due to compression of optic chiasm
What are the clinical manifestations of sellar masses?
approx. 90% are pituitary adenomas.
neurological symptoms associated with under or over secretion of pituitary hormones e.g. hypogonadism, hormone deficiencies.
visual impairment e.g. bitemporal hemianopsia, due to compression of optic chiasma, diplopia, headache.
