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what connects the hypothalamus with the anterior pituitary

hypothalamo-hypophyseal portal system


describe the hypothalamo-hypophyseal portal system

Blood enters the median eminence through the superior hypophyseal arteries, which forms a capillary plexus. Nerve terminals of hypothalamic neurons terminate here, and their neurohormones are released into this capillary bed and then are transported via the portal system vasculature to a second capillary plexus in the anterior lobe


What classes of hormones does the hypothalamus secrete

peptides and dopamine (catecholamine)


List the hypothalamic hormones

Thyrotropin releasing hormone (TRH), Gonadotropin releasing hormone (GnRH), Corticotropin releasing hormone (CRH), Growth hormone releasing factor (GHRH), Somatostatin (GH inhibiting hormone; GIH), Prolactin inhibiting factor (PIH, aka dopamine)


What effect does TRH have on anterior pituitary

increases release of TSH and PRL


What effect does GnRH have on anterior pituitary

increases release of LH and FSH


What effect does CRH have on anterior pituitary

Increases POMC and ACTH release


What effect does GHRH have on anterior pituitary

release of GH


What effect does somatostatin have on anterior pituitary

decreases release of GH and TSH


What effect does PIH have on anterior pituitary

decreases PRL


describe release of hypothalamic hormones

Stimulation of hypothalamic neurons > action potential > Ca entery at nerve terminal through voltage gated channels > hormone released via secretory vesicles


describe cellular mechanisms of hypothalamic hormones on the anterior pituitary

hypothalamic hormone binds to G-protein receptor on target cells in anterior pituitary > cell signaling mechanisms > hormone release from the receptor is mediated by extracellular Ca


Which hypothalamic hormones bind to Gs and what is the second messenger pathway involved

CRH and GHRH- Bind Gs > stimulate adenylate cyclase to produce cAMP in corticotrophs and somatotrophs respectively.


Which hypothalamic hormones bind to Gi and what is the second messenger pathway involved

somatostatin and DA- Binds Gi > decreased levels of cAMP


GnRH signaling

In gonadotrophs, GnRH receptor activation leads to the hydrolysis of membrane phosphatidyl inositol


TRH signaling

In thyrotrophs and lactotrophs, hydrolysis of phosphatidyl inositol plays role


role of arachidonic acid signaling pathway

may be involved in release mechanism used by pituitary cells


Mechanisms of hormone release at pituitary

1. Second messengers cause Ca flux from outside into cell to mediate release. 2. Production of IP3 (mediated by Gq and PLC) increases cytosolic Ca from intracellular stores mediating release


what is the adenohypophysis and the neurohypophysis

adenohypophysis: anterior pituitary. Neurohypophysis: posterior pituitary


Where are hormones secreted from the anterior pituitary

the pars distalis aka anterior lobe


List the hormones of the anterior pituitary

TSH, LH, FSH, growth hormone, corticotropin (ACTH) and proopiomelanocortin (POMC), prolactin


For each of the anterior pituitary hormones, list the hypothalamic hormone affecting its release and the cell that secretes it

TSH: TRH stimulates release via thyrotrophs. LH and FSH: GnRH stimulates release via gonadrotrophs. GH: GHRH stimulates and somatostatin inhibits release from somatotrophs. ACTH and POMC: CRH stimulates release from corticotrophs. Prolactin: PIH (DA) inhibits release and prolactin releasing factor (TRH) stimulates release from mammotrophs.


Which pituitary hormones are glycoproteins



Which pituitary hormones are polypeptides

growth hormone and prolactin


which pituitary hormones are derived from POMC

ACTH- POMC is cleaved in anterior and intermediate lobes of pituitary giving rise to ACTH, and N terminal fragment and beta-lipotropin.


Describe the pattern of hormone release from adenohypophysis

pulsatile- plasma levels show spikes. Directed by pulsatile secretion of hypothalamic hormones. Strong evidence for LH, FSH, and ACTH. Also, circadian rhythms affect the pattern of release


What controls the pulsatile release of hypothalamic hormones

an endogenous pacemaker



Excess prolactin inhibits pulsatile secretion of GnRH causing gonadal dysfunction


Which hormone is elevated shortly after sleep and which is elevated in the morning

GH secretion is elevated shortly after sleep onset, whereas ACTH is highest during the early morning hours.


Where are neurohypophyseal hormones synthesized

In the supraoptic and paraventricular nucleus of the hypothalamus.


describe the cell types of the supraoptic and paraventricular nuclei

1) the magnocellular neurons, whose processes extend into the posterior pituitary and end in the pars nervosa and 2) the parvocellular neurons, which end at the median eminence and produce the anterior pituitary regulating hormones


Posterior pituitary control of anterior pituitary

some of the posterior pituitary hormones can reach the anterior lobe where they can have some functions e.g. ADH can act on corticotrophs to increase ACTH production. Cortisol, regulated by ACTH, can in turn, inhibit both ADH function in the kidneys and release at the hypothalamus.


List hormones released by neurohypophysis

antidiuretic hormone (ADH) and oxytocin


Synthesis of neurohypophyseal hormones

Synthesized as prohormone > packaged into secretory vesicles and cleaved into hormone and protein neurophysin as vesicles travel down axon of neuron into posterior pituitary > AP activates Ca channels > release of neurohormone


what causes release of ADH

Increased plasma osmolarity or decreased BP


ADH actions

It acts on the cells of the renal tubule and collecting ducts to alter water permeability and conserve water. Also acts as pressor agent, increasing BP


ADH receptors

There are two kinds of ADH receptors: 1. V1 coupled to Gq and the Phospholipase C pathway, mediates the vasopressive action of ADH. 2. V2 coupled to Gs and the cAMP pathway regulates the effects of ADH on glomerular filtration rates in the kidney


When is oxytocin secreted

1. During the passage of the infant through the cervix at childbirth. 2. During sexual intercourse. 3. In response to suckling by the infant during breast-feeding. This neuroendocrine reflex can be conditioned