spermatogenesis

Question 1

Testes

Answer 1

Testes
• Produce sperm and store it. Produce hormones which regulate spermatogenesis.
• Lie in scrotum outside body cavity….optimum temperature for sperm production 1.5-2.5oC below body.
• Overheating of testes reduces sperm count.
• Well-vascularised, well-innervated.
• Normal volume of testes approximately 15-25ml
• measured by orchidometer

Question 2

Testis

Answer 2

• Testis is 90% seminiferous tubules, site of spermatogenesis.
• 600m long in each testis! Tubules are tightly coiled.
• Tubules all lead to epididymis and ultimately vas deferens.

Question 3

Sertoli cells, tight junctions & adluminal compartment

Answer 3

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 and interstitial fluid.

Question 4

Spermatogonia

Answer 4

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

Question 5

Primary Spermatocytes

Answer 5

The move into the adluminal compartment and duplicate their DNA to produce sister chromatids which exchange genetic material before entering meiosis 1. They are 46 XY diploid

Question 6

Secondary spermatocytes

Answer 6

Secondary spermatocytes have undergone meiosis 1 to give 23X + 23Y haploid number of chromosomes arranged as sister

Question 7

Spermatids

Answer 7

Meiosis 2 occurs to give 4 haploid spermatids. Roun spermatid to elongated spermatid differentiation

Question 8

Spermatoza

Answer 8

Mature sperm extruded into the lumen

Question 9

Spermatogenesis steps

Answer 9

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

Question 10

Steroid production in the testis

Answer 10

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.

Question 11

Oogina

Answer 11

Oogonia all laid down in foetus.

Begin meiosis to make oocyte before birth
Cannot make more oogonia by mitosis.

Limited supply

Question 12

Spermatogonia

Answer 12

Spermatogonia laid down in foetus.

Begin meiosis to make spermatocyte after puberty OR…

Divide mitotically to make more spermatogonia.

Lifetime supply.

Question 13

Parasympathetic control

Answer 13

Erection

Question 14

Sympathetic nervous system control

Answer 14

• movement of sperm into epididymis, vas deferens, penile urethra (emission)

Question 15

Somatic nervous system (perineal branch of the pudendal nerve from nerve roots S2–S4)

Answer 15

• Expulsion of the glandular secretions & evacuation of urethra.

Question 16

Bulbo-urethral gland

Answer 16

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 17

Seminal vesicle

Answer 17

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 18

Sperm tail

Answer 18

Midpiece - mitochondrial sheath, plasma membrane, Axoneme, mitochondria (Outer dense fibre
Principal piece - axoneme, plasma membrane, longitudinal, Outer dense fibre,
End piece - plasma membrane, central pair, double of the axoneme