Hypothalamic Control of the Pituitary Gland

Question 1

what is The connection between the anterior pituitary and the hypothalamus?

Answer 1

hypothalamo-hypophyseal portal system

Question 2

Describe the hypothalamo-hypophyseal portal system

Answer 2

• Blood enters the median eminence through the superior hypophyseal arteries, which forms a capillary plexus. -Nerve terminals of appropriate hypothalamic neurons terminate here
• hypothalamic 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.

Question 3

Characteristics of the hypothalamo-hypophyseal portal system

Answer 3

• lies outside the blood brain barrier.
• hormones secreted by the involved hypothalamic neurons reach the anterior lobe relatively undiluted and thus at higher concentrations than would be achieved if they had been released into the general circulation.
• Further, hypothalamic hormones act on a local rather than distant target.

Question 4

Type of hormones released by hypothalamus

Answer 4

peptidess, except for dopamine (DA), which is a catecholamine

Question 5

List hormones released by the hypothalamus

Answer 5

• Thyrotropin releasing hormone (TRH) (Thyrotrophs)
• Gonadotropin releasing hormone (GnRH) (gonadotrophs)
• Corticotropin releasing hormone (CRH) (corticotrophs)
• Growth hormone releasing factor (GHRH) (somatotrophs)
• Somatostatin (GH inhibiting hormone; GIH) (somatotrophs)
• Prolactin inhibiting factor (PIH) (aka Dopamine) (mammotrophs)

Question 6

Hypothalamus hormone signaling mechanism

Answer 6

All are G-protein coupled

Question 7

How are hpothalamic hormones secreted?

Answer 7

in a manner similar to neurotransmitter release.

• appropriate stimulation of a hypothalamic neuron will result in generation of action potentials,
• At the nerve terminal, calcium entry through voltage-dependent calcium channels will lead to liberation of hormone (versus neurotransmitter) from secretory vesicles

Question 8

cellular mechanism of hypothalamic hormone action

Answer 8

One point of agreement is that extracellular calcium is required for the release. Involvement of calcium release from intracellular stores is still debatable.

Question 9

CRH and GHRH class of G receptors

Answer 9

Gs and, upon activation, stimulate adenylate cyclase to produce cAMP in corticotrophs and somatotrophs, respectively

Question 10

somatotstatin & DA class of G protein

Answer 10

Gi eventually lead to a decrease in cAMP (DA acts on lactotrophs).

Question 11

CRH mechanism of action

Answer 11

CRH also to an increase in the rate of transcription of POMC and formation of ACTH.

Question 12

GnRH & TRH receptor

Answer 12

Gq, leads to the hydrolysis of membrane phosphatidyl inositol

Question 13

Hormones of the anterior pituitary

Answer 13

HG
PRL
TSH
ACTH
FSH
LH

Question 14

PRL and GH are____________ hormones; TSH, FSH and LH are_________________

Answer 14

polypeptide

glycoproteins

Question 15

Structure of LH, FSH, and TSH

Answer 15

each comprised of an identical α-subunit and a unique β-subunit

Question 16

Cleavage of POMC

Answer 16

give rise to ACTH, an N-terminal fragment and β-lipotropin; subsequent cleavage of β-lipotropin generates γ-lipotropin and β-endorphin. Β-endorphin contains the sequence of metenkephalin, whereas γ-lipotropin contains the sequence of β- MSH.

Question 17

Parts of posterior pituitary

Answer 17

the median eminence, infundibular stem and the infundibular process (pars nervosa).

Question 18

Hormones of posterior pituitary

Answer 18

two nonapeptides, antidiuretic hormone (ADH) and oxytocin

Question 19

Where are Posterior pituitary hormones are synthesized?

Answer 19

in the hypothalamus in two nuclei- the supraoptic nucleus and the paraventricular nucleus.

Question 20

Types of Neurons in SON and PVN

Answer 20

These nuclei have two cell types, both of which produce the hormones-

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

Question 21

T or F: some of the posterior pituitary hormones can reach the anterior lobe where they can have some function

Answer 21

True, as a result of parvocellular neurons. (ex: ADH can act on corticotrophs to increase ACTH production)

Question 22

Stimulation of ADH release

Answer 22

increase in plasma osmolarity or a decrease in blood pressure. It acts on the cells of the renal tubule and collecting ducts to alter water permeability and conserve water.

Question 23

Targets of ADH

Answer 23

ADH receptors:

• V1 coupled to Gq and the Phospholipase C pathway, mediates the vasopressive action of ADH and
• V2 coupled to Gs and the cAMP pathway regulates the effects of ADH on glomerular filtration rates in the kidney.

Question 24

Stimulation of Oxytocin secretion

Answer 24

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

Question 25

Function of oxytocin

Answer 25

• uterus: around the time of birth to cause contraction of the myometrium.
• contraction of myoepithelial cells, producing milk ejection