Hypothalamic Control Pituitary Gland

Question 1

What hormones are released by the hypothalamus?

Answer 1

Thyrotropin Releasing Hormone
Gonadotropin Releasing Hormone
Corticotropin Releasing Hormone
Growth Hormone Releasing Factor
Somatostatin (Gonadotropin Inhibiting Factor GIF)
Prolactin Inhibiting Factor

Question 2

What hormones do Thyrotropin Releasing Factor and Prolactin Inhibiting Factor affect?

Answer 2

TRH increases Thyroid Stimulating Hormone (TSH) and Prolactin (PRL) release. PIF inhibits Prolactin (PRL) release.

Question 3

What hormones do Growth Hormone Releasing Factor and Somatostatin affect?

Answer 3

GHRF increases Growth Hormone release. Somatostatin (GH inhibiting factor, GIH)

Question 4

What hormones do Gonadotropin Releasing Hormone and Corticotropin Releasing Hormone affect?

Answer 4

Gonadotropin Releasing Hormone (GnRH) increases Leutinizing Hormone (LH) and Follicle Stimulating Hormone (FSH) release. Corticotropin Releasing Hormone (CRH) increases POMC and ACTH release.

Question 5

How do hypothalamic neurons release their hormones?

Answer 5

Stimulus-dependent secretion of hypothalamic hormones occurs in a manner similar to neurotransmitter release. In brief, 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. Thus, just as for neurotransmitter release, hormone secretion from hypothalamic neurons is calcium-dependent.

Question 6

What type of receptors do CRH and GHRH bind to?

Answer 6

CRH and GHRH receptors are coupled to Gs and, upon activation, stimulate adenylate cyclase to produce cAMP in corticotrophs and somatotrophs, respectively.

Question 7

What type of receptor do Somatostatin and Dopamine (PIF) bind to?

Answer 7

The interaction of somatostatin with Gi on somatotrophs eventually leads to a decrease in cAMP (inhibiting the release of Growth Hormone in somatotrophs and TSH in thyroptrophs). Similarly, DA (PIF) binding to Gi receptors leads to a reduction in cAMP levels in lactotrophs (inhibits lactation via inhibition of PRL secretion).

Question 8

What additional effect does CRH exert at its target cells?

Answer 8

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

Question 9

What type of receptor does Gonadotropin Releasing Hormone bind to?

Answer 9

In gonadotrophs, GnRH receptor activation leads to the hydrolysis of membrane phosphatidyl inositol (PI3) via Gq receptor activation and Phospholipase C.

Question 10

What factor to all releasing hormone need in order to trigger release of their target hormones?

Answer 10

Extracellular Calcium is required for all vesicle releases from the anterior pituitary. Intracellular calcium is not known to play a role.

Question 11

What cells produce PRL and what hormones act upon these cells?

Answer 11

Mammotrophs
Prolactin Inhibiting Factor/Dopamine
Prolactin Releasing Factor/TRH

Question 12

What cells produce Growth Hormone and what hormones act upon these cells?

Answer 12

Somatotrophs
GHRH
Somatostatin

Question 13

What cells produce TSH and what hormones act on these cells?

Answer 13

Thyrotrophs

TRH

Question 14

What cells produce LH and FSH and what hormones act on these cells?

Answer 14

Gonadotrophs

GnRH

Question 15

What cells produce POMC and ACTH and what hormones act on these cells?

Answer 15

Corticotrophs

CRH

Question 16

Which anterior pituitary hormones are polypeptides and which are glycoproteins?

Answer 16

Polypeptides:
PRL
GH

Glycoproteins:
TSH
FSH
LH

Question 17

What is the relationship between ACTH and POMC, and what other molecules are related to them?

Answer 17

ACTH is a derivative of a prohormone called POMC, which is cleaved in both the anterior and intermediate lobes of the pituitary to 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. The post-translational processing of POMC is different in the intermediate lobe where α-MSH is predominantly generated after ACTH is further cleaved.

Question 18

Where are the hormones from the posterior pituitary produced and where are they secreted?

Answer 18

Posterior pituitary hormones are synthesized in the hypothalamus in two nuclei- the supraoptic nucleus, which and the paraventricular nucleus. 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 and 2) the parvocellular neurons, which end at the median eminence close to the endings of hypothalamic neurons that produce the anterior pituitary regulating hormones. Thus, some of the posterior pituitary hormones can reach the anterior lobe where they can have some functions

Question 19

What is one action of a posterior pituitary hormone on the anterior pituitary?

Answer 19

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.

Question 20

What actions does ADH have and when is it expressed?

Answer 20

ADH is secreted in response to an 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. At high concentrations it is a powerful pressor agent, acting to increase blood pressure; for this reason, it was originally called vasopressin.

Question 21

What receptors does ADH act on?

Answer 21

There are two kinds of 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 22

What are the three situations in which Oxytocin is released?

Answer 22

Oxytocin is secreted in three interpersonal situations:

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.

Question 23

What structures does the hypothalamus receive input from?

Answer 23

The hypothalamus receives inputs from the thalamus, limbic system including olfactory bulb, hippocampus, habenula and amygdala, the retina, reticular activating substance and the neocortex, information regarding pain, sleep versus wakefulness, emotions, fright, rage, olfactory sensations, light reaches the hypothalamus and can affect the activity of the neurosecretory neurons.