Hypothalamic Pituitary Axis Physiology Flashcards
What are the precursors of cortisol?
CRH in the hypothalamus is changed into ACTH in the pituitary
What are the precursors of thyroxine?
TRH in the hypothalamus is changed into TSH in the pituitary
What are the precursors of testosterone/oestradiol?
GnRH in the hypothalamus changed into LH/FSH in the pituitary
What is the precursor of GH?
GHRH (in the hypothalamus)
What is the precursor of PRL?
DA (in the hypothalamus)
Where are vasopressin and OXT stored?
The posterior pituitary
What causes the clinical presentation of endocrinological diseases?
Size of gland or amount of hormone (may be all three in pituitary)
How are causes of endocrinological diseases investigated?
Size of gland investigated by imaging
Amount of hormone investigated by blood tests
What peripheral hormone is ACTH paired with?
Cortisol
What peripheral hormone is TSH paired with?
Thyroxine
What peripheral hormone is LH/FSH paired with?
Testosterone/oestradiol
What peripheral hormone is GH paired with?
IGF-1
What hormones are included in a usual thyroid function test?
TSH, thyroxine, LH, FSH, testosterone/oestradiol, GH, IGF-1, PRL
When are dynamic tests used?
When baseline tests aren’t sufficient = usually on steroid axis
When are dynamic pituitary stimulation tests used?
If there is too little of a hormone = synacthen stimulation test, insulin stress test/prolonged glucagon test, water deprivation test
What occurs in a synacthen (synthetic ACTH) stimulation test?
Cortisol measured at 0, 30 and 60mins
Normal result is cortisol rises by 150 and reaches 500
What occurs in a inulin stress test/prolonged glucose test?
Cortisol and GH response every 30mins for 2-3hrs
Normal cortisol >500, normal GH >7 micrograms/l
How is a water deprivation test carried out?
Check serum and urine osmolarities for 8hr and then 4h after giving IM DDAVP
What do the results of water deprivation tests mean?
If urine/serum osmol ratio >1.9 then it is normal
Otherwise diabetes insipidus
