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Flashcards in Male Gonad Physiology Deck (71)
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1

What does the extrahypothalamic CNS do?

Physical and emotional stress are mediated through this system and acute physical stress decreases testosterone and LH

2

What parts of the hypothalamus are most important for male fertility?

Preoptic, anterior and ventromedial nuclei

3

What is GnRH?

A peptide neurohormone that is secreted into the hypothyseal portal system. It has a short half life and its serum levels are too low to detect (since it is in the portal system)

4

Where is GnRH produced?

Pre-optic anterior hypothalamus

5

GnRH is released in 2 rhythms, what are they?

1. Circadian/diurnal rhythm

2. Pulsatile (ultradian) rhythm
-Pulses every 60-

6

How is the circadian GnRH rhythm controlled

Controlled by melatonin output with greatest release being in the early morning leading to highest levels of LH and testosterone

7

How often does the pulsatile GnRH rhythm pulse?

Every 60-180minuts

8

Higher frequency pulses of GnRH favors what?

LH secretion

9

Lower frequency pulses of GnRH favors what?

FSH secretion

10

What do non-physiological patterns of pulses do?

Inhibit gonadotropins

11

What controls the pulsatile rhythm of GnRH secretion?

Sex steroid feedback

12

What is self-priming?

GnRH binding sites increase during troughs (lower end) of GnRH pulses

13

What is the flare effect?

Excessively frequent pulsation or continuous GnRH initially increases LH and FSH secretion (flare effect), but leads to GnRH receptor down-regulation w/resulting low LH and FSH levels

14

What is Leuprolide?

GnRH agonist

15

Kallmann Syndrome

A disease of hypothalamic dysfunction in which the GnRH neuron precursors fail to migrate to the hypothalamus. Thus, there is a failure to start puberty and a decreased sense of smell.

Pts require LH and FSH supplements

16

Which hormones have a common alpha subunit?

LH, FSH, hCG, TSH

17

What confers activity if their alpha subunits are the same?

Unique beta subunit

18

Are LH and FSH stored in the same secretory granules?

No

19

What % of the anterior pituitary is gonadotropes?

15%

20

Is there more LH or FSH in the anterior pituitary?

700 IU LH

200 IU FSH

21

Describe the metabolism of LH (half life, residues)

Short half life of about 20min (longer than GnRH)

Rapidly metabolized, liver enzymes recognize sulfate residues

22

What cell type does LH act on and what does it do?

Leydig cells, stimulates the synthesis and release of testosterone

23

What hormone is responsible for the negative feedback of LH?

Testosterone

24

Describe the metabolism of FSH (half life, residues)

-Long half life of 2 hours
-Sialic acid residues inhibit metab
-Serum levels remain steady

25

What cell type does FSH act upon and what does it do?

FSH receptor on Sertoli cells

Stimulates spermatogenesis

26

What hormone is responsible for the negative feedback of FSH?

Inhibin B acts on the pituitary to inhibit FSH and on the hypothalamus to inhibit GnRH

27

Describe the testosterone negative feedback mechanism

Testosterone acts on the hypothalamus to decrease GnRH (with downstream LH/FSH effects) AND acts on the pituitary directly to decrease LH

28

Describe the estradiol negative feedback mechanism

Estradiol acts on the pituitary to decrease LH and FSH (only negative feedback hormone that ONLY acts on pituitary and not the hypothalamus)

29

Where is estradiol produced and how?

Produced in testicle and adrenal gland. Formed from testosterone which undergoes aromatization in adipose tissue to estrodiol. Very potent.

30

What does activin do?

It has a stimulatory effect on pituitary FSH