hypothalamus/pituitary Flashcards
anterior pituitary
adenohypophysis
- is of epithelial origin
- produce hormones in response to hormones from the hypothalamus delivered via the portal system of veins
- hormones released into the general circulation
- hypothalamus has indirect control through release of regulatory hormones
posterior pituitary
neurohypophysis
- is of neural origin
- contains axons originating from neurons in the hypothalamus
- these axons release hormones (oxytocin and vasopressin) directly into the general circulation
- neurosecretory
where does the thalamus, hypothalamus and epithalamus, embryonically develop from?
forebrain –> diencephalon
boundaries of the hypothalamus
anterior
- anterior commissure
- lamina terminalis
posteriorly
- mammillary bodies
- midbrain
superior
-thalamus
arcuate nucleus of the hypothalamus
- produces hypothalamic releasing factors
- contains DOPA-ergic neurons that inhibit prolactin release
preoptic area of the hypothalamus
- contains sexually dimorphic nucleus
- regulates release of gonadotropic hormones
structures making up the neurohypophysis
- median eminence
- hypothalamohypophyseal tract
- stalk
- posterior lobe
structures making up the adenohypophysis
- pars tuberalis
- anterior lobe
blood supply to the anterior pituitary
neurosecretory neurons release hormones into the superior hypophyseal artery at the median eminence.
The superior hypophyseal artery joins into the primary hypophyseal portal system, these capillaries join to form large vessels (hypophyseal portal veins) which spiral around the infundibulum down to the anterior pituiutary.
These portal veins then join to form a secondary capillary network, branching among endocrine cells
- superior hypophyseal artey
- primary plexus of hypophyseal portal system
- hypophyseal portal veins
- secondary plexus of hypophyseal portal system
- anterior hypophyseal veins
pituitary hormones
- FSH
- LH
- TSH
- adrenocorticotropic hormone
- prolactin
growth hormone
growth hormone
GH-RH released from the arcuate nucleus
GH-IH released from the periventricular nucleus of the hypothalamus
both released into the anterior lobe and cause the production of GH
GH acts on the liver to cause secretion of IGF-1
IGF-1 acts by stimulating growth of skeletal muscles, cartilage and many other tissues
it also feeds back to the stimulate GH-IH and inhibit GH-RH
prolactin and oxytocin
oxytocin = milk letdown
1.
prolactin
prepares mamillary glands for production
- can regulate its own synthesis and release from the anterior pituitary
- prolactin released from the ant pituitary gland acts back on the arcuate nucleus. Causing the release of dopamine in the median eminence
- dopamine has a negative feedback on prolactin
prolactin during lactation
switch from negative to postive feedback
- reduced dopamine secretion
- suckling stimulates
- E2 increases number and responisveness of lactotrophs
HPA axis
E2 feedback on GnRH neuronal network
GnRH location
scattered throughout the hypothalamus so that pathology doesnt effect all of a patients fertility
GnRH
projects down to the median eminence
in females controlled by E2
-surge in mid-cycle
in males controlled by
- regular/ pulsatile release
regulate the release of FSH and LH which act on the ovaries
the process of FSH and LH in male HPG axis
GnRH released in median eminence and travels through the hypophyseal portal capillaries to reach receptors at the gonadotroph
- regulates intracellular pathways for LH and FSH
when these hormones are released from the anterior pituitary they will travel in the bloodstream to the gonads
- LH acts on thecal cells (leydig cells)
- testosterone released acts back negatively on hypothalamus and also ant pituitary - FSH acts on the granulosa cells (sertoli cells)
- produces inhibin which negatively inhibits FSH
LH and FSH in ovarian cycle
LH binds to LH receptors at thecal cells
FSH acts on granulosa cells
feedback pathway in females
GnRh released causing release of FSH and LH
short negative feedback from LH causing E2 release at hypothalamus and pituitary level
P4 also inhibits back to pituitary and hypothalamus
