Endocrinology (pit/panc/thy) (SUGER) Flashcards
what is the main purpose of the endocrine system
to release hormones directly into the blood
allows rapid adaptive changes
what is the pituitary gland aka
hypophysis
where is the pituitary gland located
depression in the SPHENOID bone at the base of the brain, just below the hypothalamus (sella turcica)
how is the pituitary gland connected to the hypothalamus
by the infundibulum (pituitary stalk), containing axons from hypothalamus neurones and small blood vessels
what is the pituitary gland composed of
2 adjacent lobes: anterior and posterior
what is sig about the embryology of the pituitary gland’s lobes
both develop from diff tissues before joining together
which hormone(s) has a positive feedback loop (pituitary gland)
oxytocin
which hormone(s) has a negative feedback loop (pituitary gland)
all but oxytocin
what is the role of the hypothalamus
homeostasis (thirst, sleep, temp)
- controls endocrine function via pituitary
what are the 5 hormones released by the hypothalamus
- CRH (corticotropin-releasing hormone)
- GHRH (growth hormone-releasing hormone)
- SST (somatostatin)
- TRH (thyrotrophin-releasing hormone)
- GnRH (gonadrotropin-releasing hormone)
- DA (dopamine)
what does CRH do
stimulates release of ACTH (adrenocorticotropic hormone)
what des GHRH do
stimulates GH release
what does SST do
inhibits release of GHRH
what does TRH do
stimulates release of TSH (thyroid-stimulating hormone)
what does GnRH do
stimulates release of LH/FSH
what does DA do
inhibits prolactin release (negative control by dopamine)
are there neural connections btwn hypothalamus and ant pit?
no
does the anterior pituitary gland have a blood supply
no
how does the ant pit gland receive blood?
- through a portal venous circulation from hypothalamus (superior hyphoseal)
- offers a local route for blood to be delivered directly
does the posterior pituitary gland have a blood supply
yes
what is a hypophysiotropic hormone
collective term for a hypothalamic hormone that regulates ant pituitary gland function
how many hormones does the anterior pituitary gland secrete
6
list the 6 peptide hormones the ant pit secretes
- FSH
- LH
- ACTH
- TSH
- Prolactin
- GH
(FLATP(I)G)
where is FSH prod
gonadotrophs
what does FSH do
stimulates ovarian follicle growth
what is the mnemonic for hormones of the anterior pituitary
FLATPIG
where is LH prod
gonadrotrophs
what does LH do
stimulates ovulation
where is ACTH prod
corticotrophs
what does ACTH do
stimulates adrenal cortex to secrete cortisol
where is TSH prod
thyrotrophs
what does TSH do
stimulates thyroid to release thyroxine (T3/T4) thus increasing metabolism
where is prolactin prod
lactotrophs
what does prolactin do
stimulates lactation, helps breast development
where is GH prod
somatotrophs
what does GH do
stimulates growth and protein synthesis
give an overview of what TRH does
TRH –> TSH –> incr release of T3/4 from thyroid –> increased metabolism
give an overview of what GnRH does
GnRH –> LH/FSH –> targets gonads to increase oestrogen, progesterone & testosterone
give an overview of what GHRH does
GHRH –> GH –> stimulates growth and protein synthesis
give an overview of what SST does
SST –> inhibits GH –> inhibits growth and protein synthesis
give an overview of what CRH does
CRH –> ACTH –> increases cortisol prod in adrenal cortex
give an overview of what DA does
DA –> inhibits prolactin –> inhibits growth and milk prod
why is long-loop neg feedback important in eg cortisol
- stressful stimulation = increased CRH thus increased ACTH and then cortisol
- elevation of plasma cortisol –> inhibits CRH-secreting neurones and also ACTH-secreting cells of ant pit
- so, cortisol doesn’t increase that much –> important bc of damaging effects of excess cortisol on immune function & metabolic reactions
name an example of short-loop negative feedback
prolactin: acts on hypothalamus to stimulate DA secretion which then inhibits prolactin secretion
what are the 2 main ways in which ant pit tumours can present
pressure on local structures (optic nerves, bitemporal hemianopia)
pressure on normal pituitary (excess/inadequate release of pituitary hormones)
does the post pit prod hormones
no
what does the post pit do
stores and releases 2 peptide hormones that are prod by hypothalamus (ADH and oxytocin)
where is ADH synthesised
hypothalamus: in the cell body of the SUPRAOPTIC NUCLEUS
where is oxytocin synthesised
hypothalamus: in the cell body of the PARAVENTRICULAR NUCLEUS
where do the axons of the supraoptic/paraventricular nuclei pass
down the pituitary stalk and terminate in the post pti
what does ADH do
- increases renal fluid reabsorption (aquaporins)
- acts on blood vessels to cause vasoconstriction thus incr BP
what does oxytocin do
provides positive feedback system during labour (stimulates lactation)
what is ADH released in response to
- decreased blood vol
- trauma, stress
- increased blood carbon dioxide
- decreased blood oxygen
- increased osmotic pressure of blood
which receptors do all pituitary/hypothalamic hormones act on
G-protein coupled receptors
where does the pancreas lie
retroperitoneal, lies post to greater curvature of stomach (head lies near c-portion of duodenum)
what are acini
small clusters of glandular epithelial cells
what is the exocrine function of the pancreas performed by
acinar cells
what % of pancreatic cells are acini & islet of langerhan cells
98-99% = acini 1-2% = islet of langerhans cells
what are the 3 cells of the islets of langerhans
alpha
beta
delta
what do alpha cells secrete
glucagon
what do beta cells secrete
insulin
what do delta cells secrete
somatostatin
what kind of actions do insulin and glucagon have
reciprocal
what is glycogenolysis
breakdown of glycogen to glucose
what is gluconeogenesis
formation of glucose from non-carb substrates
what does insulin do
- suppresses hepatic glucose output (decreased glycogenolysis/gluconeogenesis)
- increases glucose uptake into insulin sensitive tissues
- suppresses lipolysis
- suppresses muscle breakdown (decreased ketogenesis)
what does glucagon do
- increases hepatic glucose output (increases glycogenolysis/gluconeogenesis)
- reduces peripheral glucose uptake
- stimulates peripheral release of gluconeogenic precursors ie glycerol and amino acids
- stimulates lipolysis
- stimulates muscle glycogenolysis and breakdown (increased ketogenesis)
what is the precursor of insulin
proinsulin
what are the 4 steps in insulin secretion
- glucose enters beta cells via GLUT2 transporter
- glucokinase metabolises glucose –> glycolysis & Krebs prod ATP
- ATP closes K+ channel –> no K+ efflux –> cell depolarises (ie becomes more positive)
- depolarisation –> Ca2+ influx (voltage gated channels that open when depolarisation occurs) –> exocytosis of insulin
describe the 3 steps in insulin action
- insulin binds to insulin receptor on target cell
- increased exocytosis of GLUT4 vesicles to cell membrane –> more GLUT4 vesicles in cell membrane
- increased glucose uptake through GLUT4 receptors (thus decreasing blood glucose levels)
what is the liver’s ST response to high blood glucose
glycogenesis (glucose –> glycogen)
what is the liver’s LT response to high blood glucose
lipogenesis (formation of triglycerides)
what is the liver’s ST response to low blood glucose
glycogenolysis (glycogen – glucose)
what is the liver’s LT response to low blood glucose
gluconeogenesis (amino acids/lactate –> glucose)
where are there glucose sensors
primary in islets of langerhans, then also medulla, hypothalamus and carotid bodies
what happens in the fasting state?
ALL glucose comes from liver
- gluconeogenesis (pyruvate from glucose-alanine cycle)
- hepatic glycogen stores utilised - glucagon
low insulin levels - glucose supplied to brain/rbc (insulin dependant tissues)
what happens in the fed state?
- rising glucose levels increases insulin synthesis and decreases glucagon synthesis
- glucose travels to liver (40%) /muscle (60%) –> replenishes glycogen stores
- excess glucose –> fat in adipocytes
what is hypoglycaemia
low blood glucose
what is high blood glucose
hyperglycaemia
where is the thyroid gland located
C5-T1, inferior to thyroid cartilage
behind sternohyoid/sternothyroid muscles
wraps around cricoid cartilage/sup tracheal rings
what is the structure of the thyroid
divided into 2 lobes, connected by an isthmus
what is the blood supply of the thyroid gland
sup & inf thyroid arteries (paired)
what is the superior thyroid artery a branch of
external carotid artery
what is the inferior thyroid artery a branch of
subclavian artery
what is the venous drainage of the thyroid gland
jugular vein
what are the 2 cell types of the thyroid gland
follicular cells and c cells
what do follicular cells produce
t3 and t4
what do c cells secrete
calcitonin
what is t3
triiodothyronine (biologically active)
what is t4
thyroxine (de-iodinisedin peripheral tissues to form t3
how are t3 and t4 carried in the bloodstream
bound to albumin and thyroxine binding protein
what is the function of thyroid
absorption of iodine
what is the function of thyroxine
conversion to t3
what is the major thyroid hormone
t3
does t3 have a higher blood conc or t4
t4
what can t4 be thought of as
a reservoir for additional t3
list the 4 steps in thyroid hormone synthesis
- TSH released from ant pit
- Na/I symporter increases iodine uptake
- thyroglobulin iodinised - catalyses by thyroperoxidae
- thyroglobulin + tyrosine –> thyroxine (T3/T4)
what does t3 do
- incr metabolic rate
- important in brain maturation
what do the parathyroid glands do
regulate calcium and phosphate levels
when does the parathyroid gland secrete PTH
- low calcium levels
- high phosphate levels
whats the difference btwn endogenous and exogenous insulin
endogenous insulin has C peptide attached - exogenous is free insulin
