endocrinology: pituitary Flashcards
what is main site of hormone release
pituitary gland
what kind of molecules can hormones be
amines, peptides or steroids
where are peptide hormones secreted
pituitary gland, parathyroid, heart, stomach, liver and kidney
where are amines secreted
amines derived from tyrosine are secreted from thyroid and adrenal medulla
what are steroid hormones, where are they secreted and how do they act
steroids are lipids derived from cholesterol, secreted by gonads, adrenal cortex and placenta, including testosterone and estradiol
steroid hormones bind to nuclear membrane receptors producing acitvated hormone receptor complex, which binds to DNA activating specific genes
steroid hormones use transport proteins called globins which carry them in the intracellular aqueous environment.
how does developmental origin of organs effect hormone secretion
glands of ectodermal and endodermal origin during development produce peptide and amine hormones, mesodermal glands produce steroid hormones.
how do hormones produced in brain reach circulation
hormones are produced in brain, transported down axons to the posterior pituitary, anterior pituitary has vascular supply which convey signals causing release in hormone
where does synthesis of posterior pituitary hormones occur
synthesis of posterior pituitary hormones occurs in cell bodies of magnocellular neurones (PVN (paraventricular nucleus) and SON(supraoptic nucleus)), axonal transport from hypothalamus to posterior pituitary
what are cells types in the pituitary that can be differentiated by dye, what hormones do they secrete
when anterior pituitary tissue is stained with dyes such as hematoxylin and eosin, 3 distinct types of epithelial cells; acidophils whose cytoplasm stain red/pink, basophils whose cytoplasm stain blue/purple and chromophobes cytoplasm stains poorly
acidophils contain polypeptide hormones: somatotropes and lactotropes
basophils contain glycoprotein hormones: thyrotropes and gonadotropes as well as corticotropes which produce ACTH which is polypeptide
chromophobes have minimal or no hormonal content, may be acidophils or basophils which are depleted of hormone or stem cells which have not yet differentiated
where is thyroid stimulating hormone produced, what is its effect
thyrotrophs, stimulates synthesis and secretion of thyroid hormones, these cells are in anterior pituitary
where are LH and FSH produced, what is their function
gonadotrophs in anterior pituitary, stimulate steroid biosynthesis and germ cell maturation in gonads, stimulat ovaries,
where is ACTH produced, what is its function
corticotrophs in anterior pituiary, stimulates steroid in adrenal cortex
where is growth hormone produced, what are its effects
somatotrophs in anterior pituitary, stimulates growth via IGF-1
where is prolactin produced, what are its effects
lactotrophs in anterior pituitary, lactation
which anterior hormones are glycoproteins
TSH, LH and FSH are heterodimeric glycoproteins, they have common alpha subunit and different specific beta subunits
what is structure of peptide hormones of anterior pituitary
ACTH it is a 39AA long fragment of POMC
growth hormone and prolactin are 190 AA peptides
where is melanocyte stimulating hormone secreted
in the intermediate lobe which is between posterior and anterior pituitary
what role does hypothalamus have in pituitary endocrinology
synthesis and secretion of anterior hormones can be under control of hypothalamic releasing hormones and hypothalamic inhibitory factors
what hormones are produced by the hypothalamus, what are their effects on other hormones
TRH released from hypothalamus stimulates TSH
GnRH stimulates LH and FSH
CRH stimulates ACTH
GHRH stimulates growth hormone
somatostatin inhibits growth
hormone
stimulatory hormones from hypothalamus increase stimulation of either adenylate cyclase or phospholipase C
describe the axis involved in growth hormone
GHRH released from hypothalamus, causes stimulation of growth hormone from anterior pituitary
growth hormone stimulates IGF-1 release, which produces negative feedback to growth hormone and GHRH
IGF-1 is produced in the liver, somatostatin produced in hypothalamus inhibits growth hormone
stress also inhibits GHRH
how is prolactin release controlled
negative control by dopamine
describe the HPT axis
THR from hypothalamus stimulates TSH which stimulates thyroid hormones T3 and T4, all hormones provide negative feedback to previous hormones
describe the HPG axis
GnRH stimulates LH and FSH which stimulate progesterone, oestradiol and testosterone
all hormones inhibit previous hormones that stimulate them
what is HPA axis
CRH from hypothalamus stimulates ACTH from anterior pituitary which stimulates cortisol production in adrenal medulla
usual axis negative feedback
what are the different levels of feedback in hormone axes
short loop negative feedback from anterior pituitary to hypothalamus
long loop is from outside hypothalamo-pituitary complex, effects of gonadal steroids and corticosteroids
higher brain centres can over ride negative feedback, example; chronic stress overrides negative feedback on CRH and ACTH and increases negative feedback on GnRH and GHRH
what may cause lack/ too much of pituitary hormones, what are effects of this
functional disconnection of pituitary gland may happen due to cranial trauma, pressure on pituitary stalk (due to a tumour) or inflammation/infection, defects in migration of hypothalamic neurones
hyposecretion of anterior pituitary hormones; due to rare mutation in genes, can cause dwarfism, may be due to radiation harming somatotrophs which are sensitive
hypersecretion of anterior pituitary hormones; most common functional pituitary tumors; prolactinomas; cause lactation (galactorrhea) and infertility (suppression of HPG axis)
GH hypersecretion causes giantism in infancy or acromegaly in adults
what are hormones secreted by posterior pituitary
2 posterior hormones; oxytocin and vasopressin, both 9AAs long, only differ in 2 AAs, both packed in grandules and secreted with carrier proteins called neurophysins
how does vasopressin regulate body water
vasopressin increases water permeability of water duct via aquaporins, increases urea permeability and salt reabsorption
cells in hypothalamus measure osmolality of the blood plasma
Vasopressin produced in supraoptic and paraventricular nuclei transported to and released from posterior pituitary
vasopressin also regulates blood pressure via urine volume
standard osmolality of blood plasma is 290 mOsm/kg
what is oxytocin, how is it produced
oxytocin stimulates milk ejection, smooth muscle contraction in uterus at birth, establishes maternal behaviour
oxytocin secretion is stimulated by positive feedback mediated by neural reflexes, causing suckling reflex and fergusson reflex
