Endocrinology Flashcards
endocrine system
endocrine cells release hormones that are conveyed by blood stream and act on distant cells
synergistic
2 hormones greater than 1 alone
permissive
presence of one hormone necessary for another to have an effect
antagonistic
2 hormones oppose each others effects
competitive
2 hormones similar in structure compete
3 classes of hormones
steroids - synthesised from cholesterol
peptides - synthesised from amino acids
amino acids - synthesised from tyrosine
steroid hormones
small hydrophobic molecules
released immediately after synthesis
circulate in bound form
slow long lasting effects
peptide hormones
synthesised as preprohormones and stored prior to release
act on cell surface receptors via 2nd messenger systems
amino acids
stored for instant release
pulsatile
hormone released in short bursts
circadian
hormone released in 24 hour schedule e.g. melatonin
posterior pit. gland
neurohypophysis
consists of axons and nerve endings
anterior pit. gland
adenohypophysis
originates from Rathke’s ppouch
consists of endocrine tissue
oxytocin
released from post. pit.
breast contraction
uterine contraction
ADH
post. pit.
water regulation in kidney
hypothalamic hormones
majority stimulate release of other hormone
e.g. GHRH stimulates GH
TRH stimulates TSH
anterior pit. hormones
stimulate release of other hormones
e.g. corticotrophs = ACTH
somatotrophs
stimulate release of growth hormone
acute actions
release fatty acids from adipose tissue
gonadotrophs
stimulate release of sex hormones
T4
thyroxine
main product of thyroid gland
T3
more active than T4 but less abundant
calcitonin
maintains calcium homeostasis
structure of thyroid cells
single layer of follicular cells surrounding pool of colloid
calcitonin cells interspersed
thyroglobulin
glycoprotein synthesised by follicular cells and released into follicular lumen by exocytosis
hypothalamic pituatary axis
hypothalamus released TRH
Anterior pit. releases TSH
TSH reaches the thyroid gland
effects of TSH on thyroid gland
increased: iodine uptake thyroglobulin synthesis iodination of thyroglobulin pinocytosis of colloid lysomal activity size of thyroid cells
1 5’deiodinase
step UP
provides T3 to plasma
2 5’deiodinase
step UP
provides T3 in CNS
3 5’deiodinase
step DOWN
inactivates T4 to rT3
structure of cortex
zona glomerulosa produces aldosterone
zona fasciculata produces cortisol and androgens
zona reticularis produces cortisol and androgens
why does zona glomurulosa produce aldosterone?
it lacks 17 alpha hydroxylase so it has to convert cholesterol to aldosterone
cortisol
mediates stress response
major glucocorticoid
inhibits glucose uptake in muscle and adipose tissue
gonads
testes
ovaries
testes
lots of androgens
less oestrogens
ovaries
lots of oestrogens
less androgens
progesterone
oogenesis
oocytes formed in developing ovary
arrest in prophase of meiosis 1
follicular phase
follicle maturation
several months
ovulation
release of ovum from ovary into fallopian tube
few hours
luteal phase
formation of corpus luteum and its fate
pre antral phase (follicular phase 1)
primordial follicle developed into primary follicle
then becomes mature pre antral follicle
antral phase (follicular phase 2)
appearance of fluid filled atria
increased zona granulosa
growth dependent on pit. FSH
theca cells
catalyse androgen production from cholesterol
granulosa cells
contain aramatose so they can convert androgen to oestrogen
pre ovulatory phase
follicle response to LH surge
arrests in metaphase 2
haploid secondary oocyte
FSH increases
ovulation
oocyte released into peritoneal cavity before being captured by oviduct
remnants of follicle form corpus luteum
luteal phase
corpus luteum develops granulosa cells fill with liquid major product = progesterone oestrogen decreases then rebounds no pregnancy = oestrogen and progesterone decrease, LHand FSH increase pregnancy = placenta releases HcG
FSH
upregulates aramatose gene expression
stimulates growth of immature follicles
prevents apoptosis of antral follicles
LH
acts on theca cells to promote androgen production
acts on granulosa cells to secrete progesterone
oestrogen
prepares reproductive tract for fertilisation
progesterone
promotes uterine secretion to support egg implantation
