Spermatogenesis Flashcards
What moves sperm along the vas deferens during ejaculation?
Smooth muscle contractions along the vas deferens
What is the route sperm takes from the testes to exit?
Seminiferous tubule lumen Rete testes Epididymis Vas deferens Seminal vesicle (VD and SV meet) Prostatic urethra (through prostate gland) Urethra
What tissues of the penis fill during erections?
Spongy tissues of the penis - corpus cavernosum and spongiosum
Increase in hydrostatic pressure
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?
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
Describe the structure of the testes and how sperm gets to the epididymis
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
How does sperm move from seminiferous tubule to epididymis?
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
What is the order of differentiation to form sperm?
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
Where are spermatogonia found?
What are the wall of the seminiferous tubules made of?
On the basement membrane of STs
Sertoli cells - tall columnar endothelial cells
What is between adjacent Sertoli cells and what do they do?
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
What are found on the outside of seminiferous tubules/ between them?
Blood, lymphatic vessels, interstitial fluid, Leydig cells that produce testosterone (which act on Sertoli cells that have testosterone receptors)
How often does a new cycle of sperm differentiation (spermatogenesis) occur?
How long does the entire process take?
Every 16 days, a new area of the seminiferous tubules start differentiation again
Entire process takes 74 days
- Mitotic proliferation of spermatogonia.
- Meiosis and development of spermatocytes.
- Spermiogenesis, elongation, loss of cytoplasm, movement of cellular contents.
How does each cell from spermatogonium to spermatid remain connected and what is this for?
Cytoplasmic ridges between the cells - form a syncytium
Allows for synchronous development and communication between cells
When do sperm forms commit to meiosis?
When the spermatogonia develop into primary spermatocytes
When do men stop producing sperm?
Never!
What happens to spermatocytes upon completion of meiosis I and II?
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
What are the differences between oogonia and spermatogonia?
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
What acts on the testes to produce testosterone? How is this kept in balance?
FSH and LH
-ve feedback
What binds the Sertoli and Leydig cells to cause what?
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)
What are the intra-testicular testosterone levels compared to the plasma?
100x more
How do anabolic steroids cause testicular atrophy?
They cause decrease in LH/ FSH Testosterone decrease from LCs Decrease in SC population Decrease in sperm Testicular atrophy
What happens to the arteries leading to the penis and veins leading away from the penis in an erection?
Arteries dilate (of corpus cavernosum and corpus spongiosum), veins constrict So increased pressure and erection
Which nervous systems control erection and ejaculation?
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.
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?
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
Which gland produces pre-ejaculate? What is it’s function and what is in that?
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
What happens after sperm has moved up the vas deferens by SNS smooth muscle contractions and reaches the seminal vesicles?
The SV contracts to mix seminal vesicle fluid in with the sperm.
What makes up the seminal vesicle secretions?
How much of the ejaculate is made up of seminal secretions?
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.
What makes up the prostate secretions?
How much of the ejaculate is made up of prostate secretions?
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.
What is the consistency of sperm when it is ejaculated? Why? What happens after 10 minutes?
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
What are the normal parameters in sperm analysis?
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
What is infertility?
1 years unprotected intercourse without pregnancy
Structure of a spermatozoon?
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.
What happens in the acrosome and capacitation reactions?
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)
What increases the chance of sperm fertilizing an egg?
Capacitation gives a lot of sperm developing to fertilize at different time points, increasing the chances of the sperm fertilizing the egg
