Flashcards in Male Gonad Physiology Deck (71)
What does the extrahypothalamic CNS do?
Physical and emotional stress are mediated through this system and acute physical stress decreases testosterone and LH
What parts of the hypothalamus are most important for male fertility?
Preoptic, anterior and ventromedial nuclei
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)
Where is GnRH produced?
Pre-optic anterior hypothalamus
GnRH is released in 2 rhythms, what are they?
1. Circadian/diurnal rhythm
2. Pulsatile (ultradian) rhythm
-Pulses every 60-
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
How often does the pulsatile GnRH rhythm pulse?
Higher frequency pulses of GnRH favors what?
Lower frequency pulses of GnRH favors what?
What do non-physiological patterns of pulses do?
What controls the pulsatile rhythm of GnRH secretion?
Sex steroid feedback
What is self-priming?
GnRH binding sites increase during troughs (lower end) of GnRH pulses
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
What is Leuprolide?
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
Which hormones have a common alpha subunit?
LH, FSH, hCG, TSH
What confers activity if their alpha subunits are the same?
Unique beta subunit
Are LH and FSH stored in the same secretory granules?
What % of the anterior pituitary is gonadotropes?
Is there more LH or FSH in the anterior pituitary?
700 IU LH
200 IU FSH
Describe the metabolism of LH (half life, residues)
Short half life of about 20min (longer than GnRH)
Rapidly metabolized, liver enzymes recognize sulfate residues
What cell type does LH act on and what does it do?
Leydig cells, stimulates the synthesis and release of testosterone
What hormone is responsible for the negative feedback of LH?
Describe the metabolism of FSH (half life, residues)
-Long half life of 2 hours
-Sialic acid residues inhibit metab
-Serum levels remain steady
What cell type does FSH act upon and what does it do?
FSH receptor on Sertoli cells
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
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
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)
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.