Male Reproductive Physiology

Question 1

What do the testis do?

Answer 1

They are the site of germ cell production and are found in the scrotum of humans.

Question 2

What are the main aspects of the testes anatomy and what do they do?

Answer 2

Seminiferous tubules - site of sperm production
Tunica Albuginea - thick layer of connective tissue
Vas deferens
Epididymus
Rete Testis - sperm travels here before entering epididymus

Question 3

What happens in the seminiferous tubule, lumen and the interstitium?

Answer 3

Seminiferous tubule = site of sperm production
Interstitium = steroidogenesis
Lumen = sperm cells collect here before leaving the testis

Question 4

Where does gem cell maturation occur?

Answer 4

From the basal to luminal surface of the seminiferous epithelium

Question 5

What are sertoli cells?

Answer 5

Somatic supporting cells of spermatogenisis

Question 6

What are the functions of the sertoli cells?

Answer 6

Structure - they help germ cells connect with adherens junctions and move germs cells from the basal to the apical membrane

Protective - form blood testis barrier to make an immunological privileged site

Secretory - fluid to form seminiferous tubule lumen, secrete androgen binding protein to transport luminal androgens

Phagocytic - absorb waste organelles

Stimulatory - gap junction allow molecular transfer

Receive and transmit endocrine and paracrine signalling -

Question 7

Do each sertoli cell support a fixed number of germ cells?

Answer 7

Yes - these stop dividing at puberty

Question 8

What does the interstitium consists of?

Answer 8

Blood vessels, leydig cells and supporting cells

Question 9

How do you get dihydrotestosterone (DHT) from Leydig cells?

Answer 9

LH stimulates the production of testosterone which becomes DHT under the influence of 5-alpha reductase

Question 10

Wha are leydig cells the site of?

Answer 10

Testicular steroidogenesis

Question 11

What happens if you remove testosterone from a system?

Answer 11

Destroying leydig cells and therefore removing testosterone results in gradual degeneration of spermatogenesis however, this will bounce back indicating possible stem cells

Question 12

What surrounds the seminiferous tubules and what do they do?

Answer 12

Peritubular myoid cells (PTM) which contract to remove sperm from the cells

Question 13

What is the mechanism behind PTM contraction?

Answer 13

Endothelian1 (ET-1) – ligand released bysertolicells and bind to a dimer on PTM cells causing the PTM cells to contract. Movement of sperms is reliant on paracrinesignallingfromsertolicells

Question 14

Where does contraction of the seminiferous tubules bring sperm to?

Answer 14

The rete testis

Question 15

What does the epididymis do?

Answer 15

They concentrate sperm, help sperm movement, structurally mature the sperm and store it.

Sperm taken straight from the testes is unable to fertilise an oocyte

Question 16

What happens if you take out the C-ros gene in mice?

Answer 16

It changes the pH causing the mice tails to sharply bend and therefore be infertile.

Sperm must have a slightly acidic pH to form correctly

Question 17

What are the epididymal stereocilia and what do they do?

Answer 17

Help concentrate sperm as the liquid from the testes is absorbed into the sperm here. They are tall columnar cells and increase the surface area for absorption of this fluid

Question 18

What happens if you remove androgens from the sperm?

Answer 18

Structures such as the epididymus shrivel up (involutions) and do not work correctly

Question 19

What does the vas deferens do?

Answer 19

This is a long straight tube full of thick muscle which contracts taking the sperm up to the seminal vesicle and the prostate gland and out of the body. They also store some sperm

Question 20

How does a vasectomy work?

Answer 20

The vas deferens are snipped and ligased together which means the sperm that continous to be produced cannot get out of the body, they are instead phagocytosed.

Question 21

What other contraceptions might affect the vas deferens and how does this work?

Answer 21

Vasogel - this gel is injected into the vas deferns and is semi permeable so water can still get through but sperm cannot. This is reversible as when the someone wants to conceive sodium bicarbonate is injected into the vas deferens which dissolves the gel.

Question 22

What is congenital bilateral absence of vas deferens (CBAV) and how is this caused?

Answer 22

In people with cystic fibrosis the vas deferns might not be there. This means they are infertile and is thought to be caused by mutations on the CFTR gene. In some people with cystic fibrosis their only symptom could be CBAV and not things such as pulmonary issues.

Question 23

What percentage of semen is sperm?

Answer 23

4%

Question 24

What does the seminal vesicles do?

Answer 24

They secrete the fluid which surrounds sperm in an ejaculation. This fluid contains lots of fructose which provides the sperm with energy

Question 25

What happens to the fluid from the seminal vesicle at ejaculation and what causes this which is only produced by the seminal vesicles?

Answer 25

Semen coagulates which is promoted by semenogelin 1 and 2

Question 26

What can the seminal vesicle act as in animals (not really humans)?

Answer 26

Sperm plug which blocks the enterance of the vagina and is most commonly seen in animals which are at competition for mates as it stops any other sperm getting in to fertilise.

Question 27

What do seminal vesicles require for normal function?

Answer 27

Androgens

Question 28

What does the prostate do?

Answer 28

Secretes some alkaline fluid to help make up the ejaculate - it contains Zn2+.

Question 29

What is benign prostatic hyperplasia?

Answer 29

The benign growth of the prostate gland which happens in most men as they age

Question 30

What is PSA, what is it produced by and why?

Answer 30

Prostate-specific antigen produced by prostate epithelial cells to cleave the semenogelins liquidifying coagulated semen in the female reproductive tract so they can swim freely.

Question 31

What does the penis do?

Answer 31

Delivers sperm to the female reproductive tract. In humans it is made of the corpus cavemosum which fills with blood to get an erecttion

Question 32

What controls penile erection?

Answer 32

Nitric oxide enters the cell and becomes guanylate cyclase when combined with GTP this becomes cGMP which acts with cGMP specific protien kinase to cause smooth muscle relaxation and contraction through calcium entering and exiting the cell

Question 33

How does viagra work?

Answer 33

PDE-5 converts cGMP to 5’ GMP via PDE-5 which is inhibited in viagra

Question 34

How does semen coagulate after ejaculation and then liquifies?

Answer 34

PSA is inhibited by zinc and this along with sperm and semenogelin form the fluid in an ejaculation.
When ejaculated, this fluid coagulates due to cross linking between semenogelin. This crosslinking is caused by zinc. After 15 - 60 minutes PSA is activated liquidifying the ejaculation and freeing sperm.