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REGUB3: Hypothalamus-pituitary target organ axes - Feedback control 1…
REGUB3: Hypothalamus-pituitary target organ axes - Feedback control 1
Hypothalamus
below thal + above pit, pn either side of 3rd ventricle
connected to limbic system + autonomic brainstem
interface between int + ext signals
Pit/hypophysis
in sella turcica (bony cavity in base of brain)
physiologically divisible...
ant/adenohypophysis
arises from Rathke's such on pharynx epithelium
hence epithelial cells
connected to hypothal via vasc link
makes GH,ACH,TSH,FSH,LH,Prolactin
contains somatotropes(30-40%),corticotropes(20%), thyrotropes,gonadotropes,lactotropes
blood supply: almost all through hypothal
(anatomical link = hypothal-hypophyseal portal system)
post/neurohypophysis
arises from neural tissue outgrowth from hypothal
hence glial type cells
connected to hypothal via neural pathway
forms a system of neurosecretory neurons producing oxytocin + ADH
cell bodies lie in 2 well-defined clusters in hypothal...
supraoptic nuclei
paraventricular nuclei
hormones bind to neurophysins (carrier proteins)
secreted by exocytosis + separate immediately
require a few days to travel
they embryologically arise from different sources
hormonal release controlled by hypothal
Factors regulating ant pit hormone secretion
1) hypothal hypophysiotropic hormones
small peptide hormones
tropic hormones control secretion of another hormone
TRH stims TSH + prolactin
CRH releases adrenocorticotropin
GHRG stims GH
GHIH inhibits GH + TSH
PIH (identical to dopamine)
PRH
2) feedback by target gland hormones
long loop, short loop, ultrashort loop
+ve e.g. oestrogen with GRH+LH
-ve e.g. progesterone with GRH+LH
Control of hypothal hypophysiotropic hormones
unclear
environmental (stress)
emotions (irregular menstruation)
chemical inputs
hypothal not guarded by BBB