Pituitary Hormones Flashcards
body functions dictated by the posterior pituitary gland
water balance
blood volume
intake - thirst
output - urine volume
body functions dictated by the anterior pituitary gland
metabolic rate
stress response
growth
reproduction
lactation
2 types of neurosecretory cells in hypothalamus
magnocellular
parvocellular
median eminence
neurovascular region of hypothalamus
where neurohormones are transported to once made in the neuronal bodies
corticotroph
15-20% of anterior pit
products:
- ACTH –> adrenal gland
- beta-lipotropin –> adipose and melanocytes
thyrotroph
3-5% of anterior
TSH –> thyroid gland
gonadotroph
10-15% of anterior
LH –> gonads
FSH –> gonads
somatotroph
40-50% of anterior
GH –> all tissues
mammotroph
10-25% of anterior
prolactin –> breasts, gonads
how are anterior pituitary hormones secreted
pulsatile fashion
for efficient and effective signaling of target tissues for the ability to change the signal strength and regulating ongoing metabolic clearance of the hormone
regulation mechanisms of anterior pituitary hormones
- releasing and inhibiting hormones from hypothalamus
2. negative feedback mechanism
corticotropin
39 amino acids
precursor molecule = POMC
first 18 amino acids have full biological activity…first 24 are identical across species
modification of POMC
cleaved into beta-lipotropin, ACTH, and NH2-terminal peptide
modification of corticotropin during fetal life and at end of pregnancy
cleaved into melanocyte stimulating hormone and cotricotropin like peptide (cotricotropin)
modification of beta-lipotropin during fetal life and at end of pregnancy
split into lipotropin and beta-endorphin
effect of stress and sleep-wake on ACTH secretion
- hypothalamus to secrete corticotropin releasing hormone (CRH)
- anterior pit to release ACTH
- which negatively regulates CRH secretion from hypothalamus
- anterior pit to release ACTH
ACTH effect on adrenal gland
(+) cortisol release from adrenal gland
cortisol negatively regulates
- CRH release from hypothalamus
- ACTH release from anterior pituitary
2 molecules released from hypothalamus that (+) ACTH release from anterior pituitary
CRH and ADH
molecule released from hypothalamus that (-) ACTH release from anterior pituitary
BNP
NE, ACh, and serotonin on hypothalamus
(+) release of ANP and CRH –> (+) ACTH
gamma-aminobutyric acid
endorphins
ACTH itself
cortisol
EFFECTS on hypothalamus
(-) release of ANP and CRH –> (-) ACTH
prolactin-GH hormone family
GH, hPL, hCS
share amino acid sequence homologies
can be divided into GH and prolactin sub-families
glycoprotein hormone family
FSH, LH, and Thyrotropin
each consists of 2 noncovalently linked subunits alpha and beta
- alpha is common to all 3
- beta is unique to each and confers specificity
alpha subunit is considered to be more abundant than the unique beta
FSH and LH levels after menopause
increase
general regulation of FSH and LH
integration of LHRH (GnRH) signal
feedback effects of gonadal steroids
peptide hormones (inhibin)
effects on gonadal steroids and peptide hormones on FSH and LH release without LHRH
ineffective…need LHRH to for those to have any effect at all
rate of LHRH pulse per hour for maintaining LH and FSH secretion
1 pulse per hour
when LHRH pulse frequency is decrease to 1 every 3 hours…
FSH secretion is preferentially stimulated
more frequent LHRH pulses…
initially increase frequency of LH pulse and mean LH concentrations
estradiol (ovaries) and dihydrotestosterone (testes)
negative feedback on LHRH (GnRH) release and thus reduce release of LH
also inhibits FSH and LH release directly by (-) pituitary release
endorphin and Dopamine effect on hypothalamus in gonadotropin regulation
inhibits hypothalamic release of GnRH
NE effect on hypothalamus in gonadotropin regulation
stimualtes hypothalamic release of GnRH
Follistatin, Inhibin, and Activin
released from gonads (peptide hormones) upon FSH and LH stimulation
follistatin –> (-) pituitary FSH
inhibin –> (-) pituitary FSH and hypothalamus GnRH
activin –> (+) pituitary for FSH
neurohormones secreted by posterior pituitary
ADH (AVP)
oxytocin
very close in structure (only 2 of the 9 amino acids are different..and same disulfide bond is present)
amino acid difference between ADH and oxytocin
ADH: X-X-Phe-X-X-X-X-Arg-X
Oxytocin: X-X-lle-X-X-X-X-Leu-X
closeness causes overlap in hormone effects
neurophysins
I = for OTC
II = for ADH
packaged and secreted with these…without them, the hormones remain in the secretary vesicles
four factors that regulate ADH secretion
osmolarity
body fluid volume
CSF concentration of Na+
changes in body temperature
osmoreceptors for ADH secretion
located in anterior hypothalamus…mainly on neurons of the OVLT
as little as 1% rise in osmolarity will increase their firing and stimulate ADH producing neurons in the supraoptic nucleus and the paraventricular nucleus of the hypothalamus
thereby increase plasma ADH
hypovolemia and ADH
increase ADH release with blood volume decreases by ~10%
located in the right atrium
increase of Na+ in CSF
increases ADH via Na-sensors
ADH through V1 and V2 receptors
ADH acts on V1a receptors –> causes vasoconstriction
V2 receptors (kidney) tend to counterbalance this effect
do this to conserve water and regulate plasma tonicity
ADH effect on ACTH secretion
increases ACTH secretion –> (+) cortisol levels
ADH activation of V2 receptors in kidney tubule and cortical collecting duct cells
causes antidiuresis in 3 ways
- stimulate Na/K-2Cl co transport in the thick ascending limb
- increase the permeability of the collecting duct to urea
- increase permeability of the collecting ducts to water
body temperature on ADH secretion
increase = (+) ADH
