Lecture 4: Male reproductive system

Question 1

Why do we need testicles?

Answer 1

They produce two important things

1. Hormones: androgen, oestrogen, inhibin/activin and relaxin-like factors
2. Sperm!

Question 2

When does testicle development begin?

Answer 2

around 6 weeks gestation

Question 3

Why does it appear before the pituitary gland?

Answer 3

Pituitary gland (anterior) makes LH and FSH, which are water soluble hormones made in adults. But hGF is produced by the placenta, which acts on the same receptor as LH. Therefore, the testes growth is driven by the placenta.

Question 4

What is the phases of spermatogenesis? (there are three)

Answer 4

• Mitotic divisionA diploid spermatogonium goes through its first mitotic division to make two daughter cells. The fate of one of the daughter cells will be a stem cell and will remain attached to the basement membrane. The other spermatogonium will now be the primary spermatocyte that will move towards the lumen of the seminiferous tubule. This process takes 16 days.
• Meiotic divisionDNA replication occurs within the primary spermatocyte and this cell will undergo meiosis I, producing two daughter cells that are now called secondary spermatocytes. Bought secondary spermatocyte will undergo meiosis II, whihc will produce haploid cells called spermatids. This phase takes ~24 days.
• CytodifferentiationThis last step is where the spermatids will physically mature from a round cell into a sperm. This process takes 24 days.

Question 5

What is the length of the spermatogenic cycle?

Answer 5

16 days. This is how long it takes to make a primary spermatocyte from a spermatogonia.

Question 6

Cycle of the seminiferous epithelium (What is happening spatially in the SE)

Answer 6

Each cross section of the tubule will display the synchronization of sperm development at a given time

Question 7

What is the spermatogenic wave?

Answer 7

What is the spermatogenic wave?

Question 8

What cell controls the temporal and spatial organisation of spermatogenesis?

Answer 8

• Sertoli cell (nurse cells)- They are able to provide the right micro-envrioement for spermatogenesis to occur. One reason is that it is involved in creating a blood testis barrier. They are connected by tight junctions, which creates this barrier, separating the area that creates spermatogonia (basal compartment) and the area for meiosis and cyto-differentiation to occur (luminal compartment)

Question 9

Sperm has been made but it needs to grow up! Where does it go now?

Answer 9

• When the sperm has been made in the lumen of the seminiferous tubule, it will then be transported to the retes testis → epididymis. They move via fluid pressure from both scretions from the testis and cilia in the efferent duct of the rectus testis.
• This migration takes 6 days.
• At this point the sperm can’t fertilise an egg and can’t swim
• Sertoli cells, along with the epithelium of epididymis produce a fluid rich in nutrients and hormones that the sperm can bathe in. This fluid is important for the immature sperm to undergo a maturation process called capacitation.
• after 10-14 days, sperm in the epididymis is matured and is able to fertilise an egg, but it still wont swim (because there are inhibitory proteins in the epididymis fluid that prevents them from swimming)

Question 10

Vans deferens

Answer 10

• The main hub for mature sperm STORAGE (120 million)! The ampulla of the vans deferens can store sperm for months.
• Its a muscular tube that contracts during ejaculation to move spermatozoa out of the epididymis and into ejaculatory duct.
• Ejaculatory duct → urethra as it passes the prostate gland

Question 11

Prostate gland

Answer 11

• Round, donut shaped organ.
• 70% glandular tissue and 30% muscle
• is superior to bladder
• Sperm passes through the prostate and MIXES in with the seminal vesicle (60% of semen) and prostatic fluid (20-30% of semen). When this happens, sperm enable their swimming capabilities. The glandular secretions also contain proteins that allow the sperm to survive in the female reproductive tract.

Question 12

Endocrinology of the male reproductive tract

Answer 12

GnRH from hypothalamus travels down axon terminal into anterior pituitary. It produces LH, which acts on Leydig cells that sit outside the seminiferous tubules. when stimulated it causes the synthesis of testosterone, which can get converted into DHT and act on sexual characteristics. Testosterone also acts on androgen receptors on Sertoli cells inside the seminiferous tubules and promote the synthesis of sperm. There is a negative feedback loop where increase testosterone and inhibin act on anterior pituitary and hypothalamus, respectively, to decrease release of LH and GnRH, respectively.

Question 13

What happens to male reproductive system if you remove the pituitary gland?

Answer 13

No hypothalamus= No FSH, no LH and therefore regression of male accessory glands and gonads (testes shrivel up)

We cant just give a continuous infusion of GnRH so that FSH and LH can be made because GnRH is released in a pulsatile fashion. Continuous would desensitise and down regulate receptors.

If there is any sort of delay in LH administration after the pituitary is removed, LH by it self can NOT restore spermatogenesis. You would also need FSH because they act on the sertoli cells to stimulate androgen receptors (i.e. androgen receptor for testosterone). Once sertoli cells are sensitive to testosterone, then testosterone can upregulate the expression of FSH receptors by a positive feedback system.