Male reproductive endocrinology and spermatogenesis (lec 12)

Question 1

What hormones are produced in males?

Answer 1

GnRH, testosterone and LH

Question 2

What required are needed for fertile spermatozoa?

Answer 2

• Endocrine regulation of the testis
• Mitotic divisions of spermatogonia
• Meiotic divisions resulting in haploid
  spermatids
• Morphological transformation of
  spermatids into spermatozoa

Question 3

Spermatozoa have particular endocrine requirements, what are they?

Answer 3

1. Adequate secretion of GnRH from the hypothalamus
2. FSH and LH secretion from anterior lobe of pituitary
3. secretion of gonadal steroids (testosterone and estrogen) High [T] in seminiferous tubule and low [T] in the systemic circculation
4. adequate LH receptors in leydigs cells.

Question 4

Howa are females and males different in their LH secretory pattern?

Answer 4

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

Question 5

Why are the males ready to mate all the time?

Answer 5

No surge centre, only tonic centre in the hypothalamus therefore no cycle

Question 6

In comparison to females, why is FSH profile lower than that of LH in a male?

Answer 6

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.

Question 7

What cells does LH act on in the male?

Answer 7

Leydig cells

Question 8

What hormone do leydig cells produce?

Answer 8

Testosterone

Question 9

What do sertoli cells do?

Answer 9

Convert testosterone estrogen

Question 10

Where and why is high amounts of testosterone required?

Answer 10

in seminiferous tubules for spermatogenesis

Question 11

Why is pulsatile discharge of LH required for high amount of testosterone?

Answer 11

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.

Question 12

How does testosterone secretion lower/decrease?

Answer 12

1. 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 ).
2. Dilution of T = Concentrations of Testicular T decrease when they enter the systemic blood,
3. Short half life of testosterone

Question 13

What is the purpose of low peripheral testosterone?

Answer 13

So the T does not down regulate the GnRH in the anterior pituitary and LH receptors.

Question 14

What effect does pulsatile secretion of Testosterone have on FSH?

Answer 14

Testosterone creates a negative feedback on FSH secretion - needed for spermatogenesis.

Question 15

How is testosterone stimulated?

Answer 15

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.

Question 16

What is product is required in biosynthesis of testosterone and progesterone?

Answer 16

Cholesterol

Question 17

How is biosynthesis of testosterone?

Answer 17

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

Question 18

Testicular endocrine function - can you stimulate artifical testosterone?

Answer 18

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

Question 19

How does sperm production occur in the testis and what steps are required?

Answer 19

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.

Answer 20

1. spermatocytogenesis (proliferation) = occurs in basal compartments of seminiferous tubule against basement membrane. Spermatogonia will divide over mitotic division - proliferate up to 32
2. Meiosis - Reduction in chromosomes number, as the spermatogonia (diploid) prepare for meiosis - primary spermatocytes, meiosis 1 = become secondary spermatocytes (haploid).
3. Spermatogenesis (differentiation) = then secondary spermatocytes become spermatids = transformed into spermatozoa

Question 21

What is the comparison between oogenesis and spermatogenesis?

Answer 21

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.

Question 22

How or what ensures the synchrony of spermatogenesis in males?

Answer 22

Cytoplasmic bridges joining the spermatocytes - developing at same pace

Question 23

What is it called when the spermatozoa are released from the seminiferous tubule of the sertoli cells?

Answer 23

Spermiation

Question 24

Spermiogenesis

Answer 24

1. 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
2. DNA begins to condense, formation of acrosomal granule and vesicle - gives raise to acrosome. Repositioning of proximal and distal centriole (becomes flagellum)
3. The cap phase - acrosome moves over surface of the spermatid giving raise to a cap. DC develops the axium (sperm tail flagellum)
4. 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

5. Maturation phase - full mature acrosome

post nuclear cap region

reorganisation of mitochondria

Question 25

Compare eutherian mammals and marsupial mammals

Answer 25

eutherian mammals - when the nucleus condenses down to come the sperm head typically does the nuclear flattening pattern where as marsupials do this in dorsal ventral plane - nucleus become T shape to flagellum (resistance) - has to become hydrodynamic therefore needs to spin in tests or when leaves the tests - rotation causes hydrodynamic plane.

mechanical structural changes are still going on with T-shape when travelling through the epididymus

Question 26

What is the variations between american and australian sperm?

Answer 26

american - sperm forms pairs as they make their way along the epididymis. majority of american families - form sperm pairs where australia - single sperm