6- Spermatogenesis

Question 1

What are the functions of the testes?

Answer 1

• Produce sperm and store it
• Produce hormones which regulate Spermatogenesis
• the normal volume in the testes is approximately 15-25 ml (measured by an orchidometer)

Question 2

Describe the anatomy of the testes?

Answer 2

Lie in scrotum outside the body cavity
It’s well- vascularised and well innervated
Testis is 90% seminiferous tubules, site of Spermatogenesis
600m long in each testis, tubules are tightly coiled
Tubules all lead up epididymis and ultimately bad deferens

Question 3

What is the optimum temperature for sperm production?

Answer 3

1.5-2.5 degree Celsius
Overheating of the testes reduces sperm count

Question 4

Describe the structure of a seminiferous tubule cross-section

Answer 4

There are primary germ cells, or spermatogonia on the basement membrane.

The walls of the tubule are made up of tall, columnar endothelial cells called Sertoli cells.
The tight junctions between them form abluminal compartments.
This allows for a specific enclosed environment for spermatogenesis which is filled with secretions from Sertoli cells.

The spaces between the tubules are filled with blood and lymphatic vessels, Leydig cells and interstitial fluid.

Question 5

Describe the stages of sperm during Spermatogenesis

Answer 5

Spermatogonia
- Germ cell on basement membrane, capable of mitotic or meiotic division to produce primary spermatocytes or more spermatogonia by mitosis. They are diploid

Primary spermatocyte
- 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 spermatocyte
- Secondary spermatocytes have undergone meiosis I to give 23X + 23Y haploid number of chromosomes arranged as sister chromatids.

Spermatids
- Meiosis II occurs to give 4 haploid spermatids. Round spermatid to elongated spermatid differentiation.

Spermatozoa
- Mature sperm extruded into the lumen.

Question 6

What are the events that occur in spermatogenesis?

Answer 6

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

Each cell division from a spermatogonium to a spermatid is incomplete - the cells remain connected to one another by cytoplasmic bridges forming a syncytium allowing synchronous development.

Syncytia at various stages of development throughout seminiferous tubule giving continuous supply.

Question 7

How long does a spermatogenesis cycle last?

Answer 7

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

Question 8

Describe the process of steroid production on the testis?

Answer 8

Leydig cells contain LH receptors and primarily convert cholesterol into androgens.

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.

Question 9

What are the effects of anabolic steroids on the male HPG axis?

Answer 9

• testosterone based therefore increase negative feedback
• Reduce FSH/LH from pituitary leading to testicular atrophy (decrease in size and loose their function)
• Reduce Sertoli cell production

Question 10

Compare the similarities and differences between oogonia v spermatogonia

Answer 10

Oogonia:

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

Spermatogonia:

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

Question 11

Describe the neural control of ejaculation.

Answer 11

The autonomic nervous system causes coordinated smooth muscle contractions of the vas deferens, glands and urethra.

Under parasympathetic control:
- erection

Under sympathetic control:
- movement of sperm into epididymis, vas deferens, penile urethra (emission)

Under somatic control (perineal branch of the pudendal nerve from nerve roots S2-S4):
- expulsion of the glandular secretions and evacuation of the urethra

Question 12

Describe the cardiovascular and neural control of an erection.

Answer 12

There is vasodilation of the corpus cavernosum, and partial constriction of the venous return to the penis. This causes blood to rush in, causing the erection.

Erections are under parasympathetic control.

Question 13

What is ejaculate?

Answer 13

• Normal ejaculate volume: 1.5-6ml
• Initial portion of the ejaculate is most sperm rich.
  99.9% lost before reaching ampulla of the uterine tube.
• 300 million sperm is produced each day on average and approximately 120 million is in ejaculate

Question 14

What does seminal fluid contain?

Answer 14

Seminal fluid consists of secretions from:
- seminal vesicles
- prostate
- bulbo-urethral gland combined with epididymal fluid

Question 15

Describe the role bulbo-urethral gland in the production of ejaculate

Answer 15

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 16

Describe the role of the seminal vesicles in the production of ejaculate

Answer 16

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

Question 17

Describe the role of the prostate in the production of ejaculate

Answer 17

Secretes milky or white fluid roughly 30% of the seminal fluid.
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.