Spermatogenesis (repro) Flashcards
Testes background
- 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
Testis
- 90% seminiferous tubules
- site of spermatogenesis
- 600m long in each testis
- tubules tightly coiled
- tubules all lead to epididymis and ultimately vas deferens
Sertoli cells, tight junctions and adluminal compartment
- 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
Sperm stages during spermatogenesis
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
Spermatogensis
- 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
Steroid production in the testis
- 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
Anabolic steroids
- interfere with negative feedback
- reduce FSH and LH from pituitary leading to testicular atrophy
Oogonia vs Spermatogonia
- 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
Glossary
- 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
