primary function of tests
- hormone production (testosterone)
- sperm production
Seminiferous tubules
- Key cell types for testicular function:
–> LEYDIG CELL = lie between the tubules and produce TESTOSTERONE
–> close proximity to capillaries where testosterone is secreted (testosterone also acts on sertoli cells)
–> SERTOLI CELLS = part of the wall of the tubules and divide the tubules into two compartments
Sertoli cells
- tight junction helps form a blood-testis barrier
- below tight junctions spermatogonia develop into primary spermatocytes
- tight junctions open and allow spermatocytes to access adluminal compartment
- KEY FUNCTIONS
–> support germ cells
–> signal spermatogenesis
–> regulat pituitary function
- PRODUCE ANDROGEN BINDING PROTEIN (ABP) (attracts testosterone for spermatogenesis)
Describe male regulation
- Gonadotropins regulate testicular functions
–> LH is a key regulator of testosterone production in Leydig cells
–> PSH is a key regulator of SERTOLI CELLS proliferation and seminiferous tube growth
describe the regulation of gonadotropin release
- GnRH = regulates pusatile release which is impacted by multiple factors
- Testosterone = from leydig cells inhibits release through negative feedback loop
- Inhibin B = produced by sertoli cells in response to FSH inhibits release through negative feedback
- Activin = from multiple tissues, BLOCKS effects of inhibin B (negative effect on negative regulator = positive regulator)
Describe the synthesis of Testosterone
- LH promotes
–> CHOLESTEROL movement from outer to inner mitochondrial membrane by steroidogenic acute regulatory protein (StAR)
–> conversion of choelsterol to pregnolone
- 17Beta-hydroxysteroid dehydrongenase to form testosterone
- Aromatase also expressed by Ledig cells converts testosterone to 17beta-estradiol (some estrogen in testes)
- Secreted testosterone is primarily bound to porteins (albumin, SHBG, Androgen-binding protein from sertoli cells)
describe the effects of testosterone
- Testosterone mediates its effects by:
–> binding and activating androgen receptors
–> conversion to DHT and binding to androgen receptors (prolonged adrogen action) (DHT is a long acting testosterone)
- long acting testosterone effects
–> conversion to estradiol and binding to estrogen receptors
Make a note card about spermatogenesis
- recognize 4 haploid mature sperm
- compare this to female phsyiology
- time for maturation takes 70 days (continuos germ cell production where in females you stop and get a decline)
what occurs in follicular phase
- follicle production of estradiol and inhibins
–> estradiol production is under control of LH and FSH
- follicular phase is followed by ovulation
–> rise in estradiol produces a low-amplitude, high frequency LH secretion need for follicle development
- estradiol positive feebad produces LH and FSH surge at mid-cycle which induces ovulation
- Inhibins A and B regulate LH and FSH secretion
- Estrogen promotes proliferation of the endometrial lining
**ESTRADIOL**
what occurs in luteal phase (afer ovulation)
- corpus luteum forms
- followed by menes
- Endocrine function
**ESTRADIOL and PROGESTERONE**
describe the production of estradiol
- theca cells synthesize androstenedione in repsonse to LH
- Androstenedione is convereted to estradiol in granulosa cells which controlled by FSH
describe ovulation
- Day 14, ovulation is stimulated by surge in LH
- LH stimualted rupture of the follicle by promoting a remodeling of the follicle through changes in gene expression patterns and cell signaling events
- COrpus luteum forms
–> temporary endocrine gland
–> estradiol and progesterone (Progesterone is thermogenic –> produces an increase in body temp) (signifies luteal phase)
describe the process of implantation and formation of the placenta
1) Hatching = breakdown of the zona pellucida
2) apposition = trophoblastic cells of the blastocyst makes contact with endometrium
3) Adhesion = integrin mediated attachment between the trophoblast and stromal cells (decidual cells) of the endometrium
4) invasion = trophoblasts differentiates into cytotrophoblast and syncytiotrophoblasts (syncytiotrophoblasts send out protrusions and invade endometrium
5) invading syncytiotrophoblast breaks through maternal veins and arteries
–> allows for pools of maternal blood to inerface with syncytiotrophoblasts
6) primary chorionic villi form and within villi, capillaris form
what occurs to corpus leuteum after implantantion
- corpus luteum does not regress
- instead placental derived human chorionic gonadotropin (hCG) stimualtes ovarian steroidogenesis
- Corpus luteum secretes relaxin to inhibit myometrial contractions
- After week 8, maintenance of pregnancy is not dependent on corpus luteum since the placent can synthesize steroids
