Spermatogenesis

Question 1

Where does spermatogenesis occur?

Where is it stored and where does it then travel?

Answer 1

Spermatogenesis occurs in the testes

The sperm is then temporarily stored in the epididymis for a few days

Sperm then enters the vas deferens were it meets the urethra. The prostate also contributes some fluid to the ejaculate

Question 2

What are the 2 functions of the testes?

Answer 2

• Produce sperm and store it.

* Produce hormones which regulate spermatogenesis.

Question 3

Where do the testes lie and at what temperature?

Answer 3

• Lie in scrotum outside body cavity….optimum temperature for sperm production 1.5-2.5oC below body.

Question 4

What is the normal volume of the testes?

Answer 4

15-25ml

Question 5

What do the testes mainly consist of?

Answer 5

Testis is 90% seminiferous tubules, site of spermatogenesis

Question 6

Describe the structure of the testes

Answer 6

Lobules are also found separated between septa which is a huge site for spermatogenesis
600m long in each testis! Tubules are tightly coiled.
Tubules all lead to epididymis and ultimately vas deferens

On image

Question 7

Describe how and where the sperm is produced

What is this process mediated by?

Answer 7

• Sperm enters the recess of the testes and then through the vas deferens
• Here is a section of a seminiferous tubule. The sperm start on the outer edges of the tubule and move inwards towards the lumen
• Within the tubule, on the outer edges is the spermatogonia which are diploid cells, that reproduce themselves by mitosis. A portion of them at any given time will commit to meiosis, here they become primary spermatocytes. They produce haploid cells and develop into sperm.
• This process is mediated by the Sertoli cells, they form a compartment where they secrete scrofactors, adhesion molecules and other adhesion molecules to help move the sperm onlong as they develop
Sertoli cells, tight junctions & adluminal compartment

On image

Question 8

What are the primary germ cells (spermatogonia) attached to?

What are the walls of the tubule made up of?
What are the tight junctions called? What do these allow?

What are spaces between the tubule filled with?

Answer 8

• Primary germ cells or spermatogonia on the basement membrane
• Walls of tubule made up of tall columnar endothelial cells Sertoli cells. Tight junctions between these form Adluminal compartment.
• Allows specific enclosed environment for spermatogenesis which is filled with secretions from Sertoli cells.
• Spaces between the tubules are filled with blood and lymphatic vessels, Leydig cells (secrete androgens and testosterone) and interstitial fluid.
• Spermatids are released into the lumen as sperm (they develop a tail ect)

Question 9

Look at a cross-section of the seminiferous tubule

Answer 9

On image

Question 10

Describe the genetic content throughout spermatogenesis

Answer 10

• Germ cell on basement membrane, capable of mitotic or meiotic division to produce primary spermatocytes or more spermatogonia by mitosis. They are diploid.
• They move into the adluminal compartment and duplicate their DNA to produce sister chromatids which exchange genetic material before entering meiosis I. They are 46XY diploid.
• Secondary spermatocyctes have undergone meiosis I to give 23X + 23Y haploid number of chromosomes arranged as sister chromatids.
• Meiosis II occurs to give 4 haploid spermatids. Round spermatid to elongated spermatid differentiation.
• Mature sperm extruded into the lumen.

Question 11

When does a new cycle start and how long does the process take?

Answer 11

New cycle every 16 days, the entire process takes approximately 74 days.

Question 12

What are the 3 stages of sperm production?

Answer 12

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

Question 13

Why is each cell division from a spermatogonium to a spermatid is incomplete?

Answer 13

the cells remain connected to one another by cytoplasmic bridges forming a syncytium allowing synchronous development.

Question 14

Remind yourself of the HPG axis for males and females?

Answer 14

On image

Question 15

Describe how steroids are produced in the testes

Answer 15

• Leydig cells contain LH receptors and primarily convert cholesterol into androgens. Intra-testicular testosterone levels are 100x those in plasma.
• Androgens cross over to and stimulate Sertoli cell function and thereby control spermatogenesis.
• Sertoli cells contain FSH receptors and converts androgens to oestrogen.
• FSH establishes a quantitatively normal Sertoli cell population.
• Androgen initiates and maintains sperm production.
1. LH binds to the leidig cells which produce testosterone, which controls spermatogenesis via the Sertoli cells.
2. The pituitary also produces FSH which binds to Sertoli cells which maintains a normal Sertoli cell population

Question 16

What do anabolic steroids do?

Answer 16

• Anabolic steroids reduce FSH and LH from the pituitary which results in testicular atrophy

Question 17

Compare Oogonia v Spermatogonia

Answer 17

Oogonia all laid down in foetus.
Begin meiosis to make oocyte before birth.
Cannot make more oogonia by mitosis.
Limited supply.

Spermatogonia laid down in foetus.
Begin meiosis to make spermatocyte after puberty OR…
Divide mitotically to make more spermatogonia.
Lifetime supply.

Question 18

What causes an erection?

Answer 18

Vasodilation of the corpus cavernosum. Partial constriction of the venous return.

Question 19

What does the parasympathetic, sympathetic and somatic nervous system control

Answer 19

Parasympathetic control
• Erection – dilation of arteries and constriction of veins

Sympathetic nervous system control
• movement of sperm into epididymis, vas deferens, penile urethra (emission)

Somatic nervous system (perineal branch of the pudendal nerve from nerve roots S2–S4)
• Expulsion of the glandular secretions
• & evacuation of urethra.

Question 20

How many sperm are produced on average?

Answer 20

• 300 million sperm produced per day on average.
o 3,500 per second so 9 million during this lecture
o approximately 120 million in average ejaculate

Question 21

What is the normal ejaculate volume?

What is the most sperm rich portion?

Answer 21

• Normal ejaculate volume is 1.5ml - 6ml.
o around one third to just over a teaspoon full

• Initial portion of the ejaculate is most sperm rich.

Question 22

How much sperm makes it?

Answer 22

• 99.9% lost before reaching ampulla of the uterine tube.

o around 120,000 sperm get near to egg, only one enters

Question 23

What does seminal fluid consist of?

Answer 23

• Seminal fluid consists of secretions from:

o seminal vesicles, prostate, bulbo-urethral gland combined with epididymal fluid

Question 24

What fluid is added to the sperm?

Answer 24

When the sperm are in the epididymis they are in a small amount of fluid and not really swimming, very dormant. During ejaculation they pass by the seminal vesicle and prostate to form a fluid.

Question 25

What is the function of Bulbo-Urethral Gland?

Answer 25

Produces a clear viscous secretion high in salt, known as pre-ejaculate. This fluid helps to lubricate the urethra for spermatozoa to pass through, neutralizing traces of acidic urine

Question 26

What is the function of seminal vesicles? What does it contain?

Answer 26

Secretions comprise 50-70% of the ejaculate. Contains proteins, enzymes, fructose, mucus, vitamin C, and prostaglandins. High fructose concentration provides energy source High pH protects against acidic environment in vagina

Question 27

What is the function of the prostate?

Answer 27

Secretes milky white fluid roughly 30% of seminal fluid. The protein content is less than 1% and includes proteolytic enzymes, prostatic acid phosphatase and prostate-specific anitgen which are involved in liquefaction. High zinc concentration 500-1000x times more thna blood for antibacterial purposes

Question 28

Describe the structure of the sperm

Answer 28

On image