Male Reproductive Endocrinology

Question 1

Axons of GnRH neurons

Answer 1

Extend into pituitary stalk and terminate on hypothalamic-hypophyseal portal system (capillary network) into which they release GnRH

Question 2

Portal system

Answer 2

Blood from capillaries of one organ is transported to capillaries of another organ by a connecting vein or veins (returns to systemic circulation instead of pulmonary)

-allows small quantities of releasing hormones to act on anterior pituitary before dilution through general circulation

Question 3

What pattern do GnRH hormones secrete GnRH?

Answer 3

An episodic pattern

Question 4

How is GnRH captured?

Answer 4

Captured in primary portal plexus (PPP) and transferred to anterior pituitary through portal veins into secondary portal plexus (SPP)

Question 5

Posterior pituitary

Answer 5

Does not have a portal system, axons of paraventricular nucleus (in hypothalamus) extend into posterior pituitary and hormones are captured directly by capillaries

Question 6

Do GnRH hormones have receptors?

Answer 6

GnRH neurons lack receptors for testosterone and estradiol so negative feedback is indirect through presynaptic steroid-sensitive neurons

Question 7

Release of GnRH

Answer 7

Pulsatile and waves of FSH, then LH, then testosterone follow

Question 8

What does FSH act on?

Answer 8

Sertoli cells which release inhibin and provide negative feedback to anterior pituitary to directly suppress FSH release

Question 9

What does LH act on?

Answer 9

Leydig cells which release testosterone that provides negative feedback to GnRH neurons in hypothalamus

Question 10

Testosterone feedback/diffusion

Answer 10

Through blood, or diffuses across basement membrane to sertoli cells where it is converted to dihydrotestosterone (DHT) and/or E2 which feedbacks to hypothalamus reducing GnRH production