Pituitary and Fluid Homeostasis Flashcards
The posterior pituitary is an extension of
the anterior hypothalamus (neural connections)
The posterior pituitary secretes what 2 neurohormones
Oxytocin and vasopressin
Proneurohormones of the posterior pituitary
pro neurohormones are cleaved in the axon and released into the synaptic cleft along with the neurophysin
neurophysin
carrier proteins that transport neurohormones down the axon
Action of Oxytocin
myoepithelial surrounding alveoli in breast contraction and contraction of uterine myometrium
Diabetes Insipidus
lack of ADH or response to ADH
Vasopressin V2 receptor Action
bind V2 receptors in distal tubule or collecting duct to promote insertion of aquaporins
Vasopressin V2 receptor mechanism
Adenylyl cyclase and cAMP
Vasopressin V1 receptor Action
vasoconstriction to increase TPR and BP (during hemorrhaging)
V1 receptors
less affinity, require increased [AVP] for activation
Osmoregulators regulate plasma osmolality
cell volume and firing frequency of APs are linked (high plasma Osm = decreased cell V = HIGH firing rate of AP)
High firing rate of osmoregulators causes
increased release of AVP
Plasma osmolality threshold is
280
Is plasma osmolality is <280 then
osmoregulators stop firing APs and vasopressin stops secreting
What monitors blood volume
stretch receptors in venous system and baroreceptors in the arterial system
Stretch receptors and baroreceptors
stretching causes increased AP and release of INHIBITORY NT that decreases vasopressin
An increase in blood volume causes
a decreased sensitivity of the osmoreceptors
A decrease in blood volume causes
an increased sensitivity of the osmoreceptors
If there are conflicting signals from stretch receptors and osmoregulators, which signal overrides the other
stretch receptors indicating the status of BV and BP
What stimulates thirst
osmoreceptors (threshold in 295), osmoreceptors at 280 already increase vasopressin
What other factors stimulate vasopressin release
high body temp, hypoxia, stress, exercise, endorphins, progesterone, nausea, pain
What factors inhibit vasopressin release
etOH, lithium, decreased body temp, glucocorticoids
anterior pituitary is connected to
hypothalamus via portal veins (hypothalamo-hypophyseal veins)
Hypophysiotrophic hormones
hypothalamic hormones stimulate differentiation and proliferation (trophic effects) in the anterior pituitary
6 hypothalamic hormones
thyrotropin-releasing hormone (TRH), corticotropin releasing hormone (CRH), gonadotropin releasing hormone (GnRH), growth-hormone releasing hormone (GHRH), dopamine (DA), and somatostatin (SS)
3 families of hormones released by the anterior pituitary
glycoproteins, somatomammotropins, pro-opiomelanocortin
glycoproteins from the anterior pituitary
follicle stimulating hormone (FSH), luteinizing hormone (LH), thyroid stimulating hormone (TSH)
somatomammotropins from the anterior pituitary
growth hormone (GH), prolactin
pro-opiomelanocortin from the anterior pituitary
ACTH
anterior pituitary hormone release is regulated by
hormones fromt he hypothalamus
if the anterior pituitary is separated from the hypothalamus what would happen to the secretion of the anterior pituitary hormones
they would all decrease except prolactin (normally inhibited by the hypothalamus)
Anterior pituitary hormones are
trophic - regulating growth, development, secretion of adrenal gland, thyroid gland, gonads, and mammary gland
Hypothalamic hormones are secreted by
neurosecretory cells
hypothalamis hormones are all ___________ except dopamine which is _________
peptides; catecholamines
Hypothalamic hormones stimulate anterior pituitary hormone release except for
prolactin; which is inhibited
Long-loop negative feedback
third target endocrine gland may suppress secretions from pituitary and hypothalamus
Short-loop nehative feedback
pituitary suppresses secretion from the hypothalamus
