w3 - endocrinology: basic princples Flashcards
steroids are derived from
cholesterol
tyrosine and tryptophan derivatives examples 3
epinepgrine
thyroid hormones
melatonin
major determinant of hormone conc
rate of secretion
- feedback loops
raised TSH levels suggest
hypothyroid
hypothalamus sends TRH to ant.pit, who then sends TSH to thyroid. -ve feedback causes reduction in TRH, and so leads to hypothyroiid
assessing pit function 8
9am cortisol FT4,FT3,TSH IGF1 LH,FSH,E2/Testosterone U&E, plasma/urine osmolality dynamic tests imagine \(MRI)
outline the hypothalamic-pit-adrenal (HPA) axis
hypothalamus -> secretes CRH ->ant. pit -> secretes ACTH -> secretes cortisol (-ve feed on hypot and ant.pit) -> physiological effects
9am cotiisol levels are tested at this time due to the lower serum levels t/f
false
high at this time
9am cortisol levels arent enough to determine pit function, what then
dynamic testing
determinants in measuring sex hormone axis
male - circadian rhythm
female - depends on menstrual cycle
prolactin is secreted by lactotroph cells of the ant.pit. it is under tonic inhibition by ___ __
hypothalamic dopamine
prl is mediated by
prolactin receptor (PRLR)
dynamic testing occurs before or after imaging?
usually before
cortisol defiency indicates an ___ insufficiency
adrenal
2 examples of cortisol deficiency
primary adrenal failure - addisons disease
pituitary disease
signs of cushings syndrome
cushingoig facies acne hirsutism abdominal striae and centripetal obesity interscapular + supraclavicular fat pads proximal myopathy osteoporosis hypertension impaired glucose tolerance
4 types of cushings syndrome
pit-cushings
acth-independent cushings
ectopic acth (malignancy)
exogenous steroids
tumour in the cortitroph cells of anterior pituitary lead to
cushings disease (well 70% reported caused by this0
bilateral macronodular adrenal hyperplasia leads tbo
ACTH-independent cushings
low dose dexamethasone suppression test is used to diagnose cushing. what happens? what is tested next, to determine source?
fail to suppress cortisol levels = cushings
measure ACTH
if ATH is high, is adrenal likely to be the origin?
no
ACTH low = adrenal origin
if high, need to distinguish cushings disease and ectopic ACTH
rrise in cortisol and ACTH on CRH test indicates ___ source
pituitary
