Spermatogenesis (repro)

Question 1

Testes background

Answer 1

• produce sperm and store it
• produce hormones which regulate spermatogenesis
• lie in scrotum outside body cavity
• optimum temperature for sperm production 1.5-2.5 degree C below body temp
• overheating of testes reduces sperm count
• well-vascularised and well-innervated
• normal volume of testes is approx 15-25ml measured by an orchidometer

Question 2

Testis

Answer 2

• 90% seminiferous tubules
• site of spermatogenesis
• 600m long in each testis
• tubules tightly coiled
• tubules all lead to epididymis and ultimately vas deferens

Question 3

Sertoli cells, tight junctions and adluminal compartment

Answer 3

• primary germ cells or spermatogonia on the basement membrane
• walls of tubule made up of Sertoli cells (tall columnar endothelial 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

Sperm stages during spermatogenesis

Answer 4

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 spermatocytes:
- move into the adluminal compartment and duplicate their DNA to produce sister chromatids
- they exchange genetic material before entering meiosis l
- they are 46XY diploid
Secondary spermatocytes:
- have undergone meiosis to give 23X and 23Y haploid number of chromosomes arranged as sister chromatids
Spermatids:
- meiosis ll occurs to give 4 haploid spermatids
- round spermatid to elongated spermatid differentiation
Spermatozoa:
- mature sperm extruded into lumen

Question 5

Spermatogensis

Answer 5

• new cycle every 16 days
• entire process takes approx 74 days
  1) Mitotic proliferation of spermatogonia
  2) Meiosis and development of spermatocytes
  3) Spermiogensis, elongation, loss of cytoplasm, movement of cellular contents
• each cell division from a spermatogonium to a spermatid is incomplete
• the cells remains connected to one another by cytoplasmic bridges forming a syncytium allowing synchronous development
• Synctia at various stages of development throughout seminiferous tubule giving continuous supply

Question 6

Steroid production in the testis

Answer 6

• 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 receptor and converts androgens to oestrogen
• FSH establishes a quantitatively normal Sertoli cell population
• androgen initiates and maintains sperm production

Question 7

Anabolic steroids

Answer 7

• interfere with negative feedback

- reduce FSH and LH from pituitary leading to testicular atrophy

Question 8

Oogonia vs Spermatogonia

Answer 8

• Oogonia all laid down in foetus / spermatogonia laid down in foetus
• begin meiosis to make oocyte before birth / begin meiosis to make spermatocyte after puberty
• cannot make more oogonia by mitosis / divide mitotically to make spermatogonia
• limited supply / lifetime supply

Question 9

Glossary

Answer 9

• Spermatogonia – primary male germ cells
• Spermatocytes – male germ cells undergoing meiosis
• Spermatids – immature haploid spermatozoa
• Mitosis – Cell division giving rise to diploid daughter cells
• Meiosis – Cell division giving rise to haploid daughter cells
• Seminiferous tubules – testicular structures that are the site of spermatogenesis
• Spermiogenesis – final phase of sperm maturation
• Adluminal compartment – space between tight junctions of sertoli cells where sperm develop
• Epididymis – duct behind the testis, along which sperm passes to the vas deferens.
• Vas deferens – duct which conveys sperm from the testicle to the urethra