Anterior Pituitary Flashcards
what does hypophysectomy cause
stops growth and lactation
atrophy (thyroid/adrenal cortex/gonads)
disruption to (salt and water balance, carb and protein metabolism)
anatomy of the pituitary
adenohypophysis/anterior - glandular
neurohypophysis/posterior - neuronal processes in SON/PVN
intermediate lobe - forms MSH, not in adults (in animals/babies)
posterior lobe formation
forebrain (diencephalon) invagination
anterior lobe formation
buccal cavity outgrowth (rathke’s pouch)
formation steps
1) outgrowth of tissue forms at diencephalon (FB becomes thalamus and hypothalamus)
2) outgrowths combine
3) anterior and posterior lobes begin to form (Rathke’s pouch removal)
4) posterior lobe (neural tissue) anterior lobe (non-neural tissue) sella turcica (skull) protects pituitary gland
posterior vs anterior pituitary connections
posterior pituitary has neural connections
anterior pituitary has no neural connections - connected to median eminence via pituitary portal system
blood supply
blood passes capillary loops through long/short hypophyseal portal vessels (specific to anterior pituitary)
superior hypophyseal artery supplies ME and stalk
inferior hypophyseal artery supplies posterior lobe directly / indirectly to the anterior lobe via short portal veins
inferior and superior artery connected via trabecular artery
A and P lobes drain into venous sinuses
2 features of the anterior pituitary
hypothalamic hypophysiotropic hormones (very diluted released into wider circulation)
feedback by target gland hormones
where are hypothalamic hypophysiotropic hormones synthesised
in the cell body and transported to axon terminal to be stored until release in adjacent capillary
control of hypothalamic hypophysiotropic hormone release
1) 1 or more neurons in neural pathway converge on 1 neurosecretory hormone
2) direct synapse on soma/dendrite of neurosecretory hormone
3) axo-axonic synapse on nerve ending of neurosecretory hormone
4) neuron releases NT into portal vessels which modifies action of neurohormone
5 cells in the anterior pituitary
gonadotroph cells
corticotroph cells
somatotroph cells
lactotroph cells
thyrotroph cells
tropic vs trophic
tropic = hormone release
trophic = stimulates growth of downstream tissue
hormone release
TSH/LH/FSH/ACTH - tropic
GH - stimulates growth of liver hormones/somatomedians - trophic
PRL - not trophic/tropic
episodic hormone secretion
not secreted at a constant rate
secreted in a pulsatile pattern
GH secretion
spontaneous surges throughout the day
occurs 3-4hrs (undetectable inbetween)
GHRH and somatostatin determine GH rhythm (peak during sleep)