Male reproductive endocrinology and spermatogenesis (lec 12) Flashcards
What hormones are produced in males?
GnRH, testosterone and LH
What required are needed for fertile spermatozoa?
- Endocrine regulation of the testis
- Mitotic divisions of spermatogonia
- Meiotic divisions resulting in haploid
spermatids - Morphological transformation of
spermatids into spermatozoa
Spermatozoa have particular endocrine requirements, what are they?
- Adequate secretion of GnRH from the hypothalamus
- FSH and LH secretion from anterior lobe of pituitary
- secretion of gonadal steroids (testosterone and estrogen) High [T] in seminiferous tubule and low [T] in the systemic circculation
- adequate LH receptors in leydigs cells.
Howa are females and males different in their LH secretory pattern?
Female shave high amplitude preovulatory episodes of LH once every several weeks and basal pulsatile episodes between the large preovulatory stages
Men have small LH episodes that occur every 2-6 hours - Testosterone is secreted soon after each episode
Why are the males ready to mate all the time?
No surge centre, only tonic centre in the hypothalamus therefore no cycle
In comparison to females, why is FSH profile lower than that of LH in a male?
GnRH causes a release of the FSH and LH periodically. 4-8 times in 24hrs.
FSH is lower due in to the release of inhibin secretion by sertoli cells. FSH is also has a greater duration compared to LH.
What cells does LH act on in the male?
Leydig cells
What hormone do leydig cells produce?
Testosterone
What do sertoli cells do?
Convert testosterone estrogen
Where and why is high amounts of testosterone required?
in seminiferous tubules for spermatogenesis
Why is pulsatile discharge of LH required for high amount of testosterone?
High amounts of testosterone is needed in the seminiferous tubules for spermatogenesis.
Therefore, Pulsatile discharge of LH prevents sustained concentrations of LH
Thus preventing refractory of leydig cells to Testosterone secretion.
How does testosterone secretion lower/decrease?
- High concentration of LH secretion (high concentration)- this leads to down regulation of LH receptors on leydig cells (reduction of receptors available) - leading to lower Testosterone (pulsatile secretion of T ).
- Dilution of T = Concentrations of Testicular T decrease when they enter the systemic blood,
- Short half life of testosterone
What is the purpose of low peripheral testosterone?
So the T does not down regulate the GnRH in the anterior pituitary and LH receptors.
What effect does pulsatile secretion of Testosterone have on FSH?
Testosterone creates a negative feedback on FSH secretion - needed for spermatogenesis.
How is testosterone stimulated?
LH binds to LH receptors in leydig cells, and FSH binds to sertoli cells. Initiates assembly of enzymes for production of testosterone.
Leydig cells produce Testosterone that is transported to sertoli cells where it is converted to DHT.
Testosterone is produced by the leydig cells is transported into the sertoli cells where it is converted to dihydrotestosterone (DHT) and also estrogen. T and Estrogen of transported by blood to the hypothalamus to exert a negative feedback on GnRH neurons.
ESTROGEN CONVERTED WITH SAME BIOCHEM AS ANTRAL FOLLICLE.
What is product is required in biosynthesis of testosterone and progesterone?
Cholesterol
How is biosynthesis of testosterone?
LH is received by LH receptor - ATP is converted into cAMP, thus produce enzymes such as protein kinase A. de novo synthesis of stAR (steroidogenic acute regulatory protein - regulates cholesterol transfer into the mitochondria)
extra step of conversion from progesterone to testosterone
Testicular endocrine function - can you stimulate artifical testosterone?
yes, you can give the animal an injection of GnRH or HCG similar affect to LH. Force tests to convert what cholesterol in is the leydig cells of testis to testosterone - measure later to maximum level of T
How does sperm production occur in the testis and what steps are required?
spermatogenesis = spermatocytogenesis + meiosis + spermiogenesis
Requires
1. Endocrine regulation of the testis
2. Spermatocytogenesis
3. Meiotic Division (diploid to haploid)
4. Spermiogenesis - formation of spermatozoa from spermatids.
- spermatocytogenesis (proliferation) = occurs in basal compartments of seminiferous tubule against basement membrane. Spermatogonia will divide over mitotic division - proliferate up to 32
- Meiosis - Reduction in chromosomes number, as the spermatogonia (diploid) prepare for meiosis - primary spermatocytes, meiosis 1 = become secondary spermatocytes (haploid).
- Spermatogenesis (differentiation) = then secondary spermatocytes become spermatids = transformed into spermatozoa
What is the comparison between oogenesis and spermatogenesis?
Spermatogenesis - 1 spermatogonia becomes 16 spermatozoa
Oogenesis one remains one
Oogenesis female produce oocytes while in development, releasing oocytes gradually over time. Males produce continuous clones of sperm.
How or what ensures the synchrony of spermatogenesis in males?
Cytoplasmic bridges joining the spermatocytes - developing at same pace
What is it called when the spermatozoa are released from the seminiferous tubule of the sertoli cells?
Spermiation
Spermiogenesis
- The golgi phase - early stage of spermatid - formation of acrosome, proacrosomic, in golgi apparatus gandules form (precursor for proacrosomes) - the centrioles migrate to southern pole of cell below nucleus
- DNA begins to condense, formation of acrosomal granule and vesicle - gives raise to acrosome. Repositioning of proximal and distal centriole (becomes flagellum)
- The cap phase - acrosome moves over surface of the spermatid giving raise to a cap. DC develops the axium (sperm tail flagellum)
- Acrosomal phase - acrosomal extends over majority of sperm nucleus. Nucleus become more condense - lateral plane. Changes in microtubules - arranged into manchette (repositions spermatid)
annulus is defined
extending flagellum
- Maturation phase - full mature acrosome
post nuclear cap region
reorganisation of mitochondria
