Spermatogenesis

Question 1

What moves sperm along the vas deferens during ejaculation?

Answer 1

Smooth muscle contractions along the vas deferens

Question 2

What is the route sperm takes from the testes to exit?

Answer 2

Seminiferous tubule lumen
Rete testes
Epididymis
Vas deferens
Seminal vesicle (VD and SV meet)
Prostatic urethra (through prostate gland)
Urethra

Question 3

What tissues of the penis fill during erections?

Answer 3

Spongy tissues of the penis - corpus cavernosum and spongiosum

Increase in hydrostatic pressure

Question 4

What is the function of the testes?

Why do they lie in the scrotum outside the body?

What happens when testes overheat?

Describe their vascularization and innervation

What is their normal volume?

Answer 4

Produce and store and release sperm
Produce hormones to regulate spermatogenesis (especially testosterone)

The optimal temperature for production of sperm is 1.5-2.5 degrees centigrade below body temperature

Overheated testes reduce sperm count

Highly vascularised and highly innervated with nerves

15-25ml volume; measured by orchidometer

Question 5

Describe the structure of the testes and how sperm gets to the epididymis

Answer 5

Lobules
Each lobule has coil of seminiferous tubules
Spermatogenesis in the tubules, they collect in the lumen and all the lobules meet at the rete testes
Then to the epididymis

There is a constant supply of sperm so there is always some in the epididymis

Question 6

How does sperm move from seminiferous tubule to epididymis?

Answer 6

Spermatogonia is produced by mitosis on the edge of the seminiferous tubule.
It moves into the lumen as it develops - this process takes 74 days.
The spermatogonia move down the Sertoli cells towards the centre

Question 7

What is the order of differentiation to form sperm?

Answer 7

Spermatogonia (diploid)
Proportion develop into primary spermatocytes and commit to meiosis
After first meiotic division they form haploid secondary spermatocytes
After second meiotic division they become haploid spermatids – completed meiosis
Then the spermatids are rid of their cytoplasm, grow a tail and grow an acrosome to form mature sperm that goes into the STs lumen

Question 8

Where are spermatogonia found?

What are the wall of the seminiferous tubules made of?

Answer 8

On the basement membrane of STs

Sertoli cells - tall columnar endothelial cells

Question 9

What is between adjacent Sertoli cells and what do they do?

Answer 9

Tight junctions

Form adluminal compartment - i.e. compartment facing lumen, compartment facing BM

Adluminal compartment provides enclosed env. for secretions from Sertoli cells (so they can communicate with sperm cells) + provide protection of sperm cells from immune system/ toxic agents during meiosis/ spermatogenesis

Question 10

What are found on the outside of seminiferous tubules/ between them?

Answer 10

Blood, lymphatic vessels, interstitial fluid, Leydig cells that produce testosterone (which act on Sertoli cells that have testosterone receptors)

Question 11

How often does a new cycle of sperm differentiation (spermatogenesis) occur?

How long does the entire process take?

Answer 11

Every 16 days, a new area of the seminiferous tubules start differentiation again

Entire process takes 74 days

1. Mitotic proliferation of spermatogonia.
2. Meiosis and development of spermatocytes.
3. Spermiogenesis, elongation, loss of cytoplasm, movement of cellular contents.

Question 12

How does each cell from spermatogonium to spermatid remain connected and what is this for?

Answer 12

Cytoplasmic ridges between the cells - form a syncytium

Allows for synchronous development and communication between cells

Question 13

When do sperm forms commit to meiosis?

Answer 13

When the spermatogonia develop into primary spermatocytes

Question 14

When do men stop producing sperm?

Answer 14

Never!

Question 15

What happens to spermatocytes upon completion of meiosis I and II?

Answer 15

They are haploid
They lose their cytoplasm
They grow an acrosome and tail (this is the final stage of spermatogenesis known as spermiogenesis)
Then he spermatids can be released into the ST lumen

Question 16

What are the differences between oogonia and spermatogonia?

Answer 16

Oogonia only have meiosis occur to it
They are of limited number
They are present in the ovary

Spermatogonia can have either meiosis or mitosis occur to it
They are unlimited
They are present in the STs

Question 17

What acts on the testes to produce testosterone? How is this kept in balance?

Answer 17

FSH and LH

-ve feedback

Question 18

What binds the Sertoli and Leydig cells to cause what?

Answer 18

LH binds LHRs on LCs to form testosterone which goes around the body to produce secondary male characteristics/ binds to SCs

Testosterone binds SCs which turns genes on to stimulate spermatogenesis
(SCs provide env. for sperm development)

FSH binds SCs to maintain their health (without FSH SCs die)

Question 19

What are the intra-testicular testosterone levels compared to the plasma?

Answer 19

100x more

Question 20

How do anabolic steroids cause testicular atrophy?

Answer 20

They cause decrease in LH/ FSH
Testosterone decrease from LCs
Decrease in SC population
Decrease in sperm
Testicular atrophy

Question 21

What happens to the arteries leading to the penis and veins leading away from the penis in an erection?

Answer 21

Arteries dilate (of corpus cavernosum and corpus spongiosum), veins constrict 
So increased pressure and erection

Question 22

Which nervous systems control erection and ejaculation?

Answer 22

Autonomic (involuntary)
PNS - erection

SympNS - ejaculation (movement of sperm into epididymis, vas deferens, penile urethra (emission)

SomNS - expulsion of the glandular secretions
+ evacuation of urethra.

Question 23

How much sperm is produced per day?

What is the normal ejaculate volume? Does that mean x ml of sperm is lost per ejaculate?

Which part of ejaculate is sperm rich?

How much of sperm is lost before reaching ampulla of uterine tube?

From where do secretions come from to make up the seminal fluid?

Answer 23

300 million
5-6 ml
No - ejaculate also has other secretions (semen)
Initial part
99.9%
Seminal vesicle, prostate gland, bulbo-urethral gland + you have epididymal fluid

Question 24

Which gland produces pre-ejaculate? What is it’s function and what is in that?

Answer 24

Bulbo-urethral gland

It is a clear viscous secretion that lubricates the urethra for spermatozoa and neutralises a low pH env. (due to urine/ bacteria)

It is high in salt

Question 25

What happens after sperm has moved up the vas deferens by SNS smooth muscle contractions and reaches the seminal vesicles?

Answer 25

The SV contracts to mix seminal vesicle fluid in with the sperm.

Question 26

What makes up the seminal vesicle secretions?

How much of the ejaculate is made up of seminal secretions?

Answer 26

Contains proteins, enzymes, fructose, mucus, vitamin C and prostaglandins. High fructose concentrations provide energy source. High pH protects against acidic environment in vagina.

Secretions comprise 50-70% of the ejaculate.

Question 27

What makes up the prostate secretions?

How much of the ejaculate is made up of prostate secretions?

Answer 27

Protein content is less than 1% and includes proteolytic enzymes, prostatic acid phosphatase and prostate-specific antigen which are involved in liquefaction. High zinc concentration 500–1,000 times that in the blood is antibacterial.

Milky or white fluid roughly 30% of the seminal fluid; responsible of the colour of the semen.

Question 28

What is the consistency of sperm when it is ejaculated? Why? What happens after 10 minutes?

Answer 28

Sperm is jelly like, viscous and lumpy when ejaculated; if it was runny it may just fall out of the vagina.

Due to it’s initial consistency it stays in the vagina and cervix, then after 10 minutes the sperm becomes liquid (liquefaction) and runny

Question 29

What are the normal parameters in sperm analysis?

Answer 29

Volume
1.5 – 6.0 ml

Sperm concentration
>15million/ml

Liquefaction
<30 minutes

Motility (if sperm is swimming)
>40%

Progressive motility (if sperm is getting anywhere)		
>32%

Vitality (live)
>58%

Morphology (normal/ abnormal shapes)
>4%; 80% abnormal sperm is still normal.

pH
>7.2

Leucocytes
<1 million/ml

Question 30

What is infertility?

Answer 30

1 years unprotected intercourse without pregnancy

Question 31

Structure of a spermatozoon?

Answer 31

Acrosome – invaginates the membrane + is full of enzymes

Behind the acrosome is the nucleus with DNA; little cytoplasm

The mitochondrial sheath has a lot of mitochondria producing ATP for energy

The tail has an axoneme; 9 pairs of tubules with a pair of tubules in the centre. They run all the way to the end of the tail. It is the same structure you find in the villi in the lungs, bacterial flagella

The middle 2 tubules are like the plumber sticks for toilets. They produce a rhythmical longitudinal sliding motion ||||||||||| to cause the tail to move.

Question 32

What happens in the acrosome and capacitation reactions?

Answer 32

In the acrosome reaction, the enzymes are released from the acrosome (by the head exploding) and they cut through the outer cells/ burrow their way through the zona pellucida of the oocyte and find the oocyte. All of this only happens if in close proximity to the egg.

A freshly ejaculated sperm cannot fertilize an egg. The sperm has to go through ‘capacitation’ (changes in the membrane of the head of the sperm which takes 4-18 hours and then they can fertilize)

Question 33

What increases the chance of sperm fertilizing an egg?

Answer 33

Capacitation gives a lot of sperm developing to fertilize at different time points, increasing the chances of the sperm fertilizing the egg