Spermatogenesis Flashcards
What is the testes?
- produce sperm + store it
- produce hormones which regulate spermatogenesis
- lie in scrotum outside body cavity (optimum temp for sperm prod 1.5-2.5 deg below body)
- overheating of testes reduces sperm count
- well-vascularised, well-innervated
- normal volume of testis approx 15-25ml
What is the structure of the testis like?
- testis is 90% seminiferous tubules - site of spermatogenesis
- 600m long in each testis, tubules are tightly coiled
- tubules lead to an area on one side called rete
- rete leads to epididymis and vas deferens
What kind of cells are the walls of the tubule made up of?
- tall columnar endothelial cells = Sertoli cells
What surrounds the sertoli cells?
- between sertoli cells, lying on basement membrane are primary germ cells or spermatogonia
- spaces between tubules are filled w/ blood + lymph vessels, Leydig cells + interstitial fluid
The sertoli cells form tight junctions between each other. Why is this important?
- tight junctions open to allow passage of spermatogonia to completion of meiosis
- the junctions allow for divisions into luminal and adluminal compartments
- protects spermatogonia from immune attack
- allows specific enclosed enviroment for spermatogenesis which is filled w/ secretions from sertoli cells
What are the comparisons and differences between oognia and spermatogonia?
How long does spermatogenesis take?
- entire process = approx 74 days
- new cycle every 16 days
What are the 3 main stages of spermatogenesis?
- mitotic proliferation of spermatogonia
- meiosis + development of spermatocytes
- spermiogenesis, elongation, loss of cytoplasm, movement of cellular contents -> spermatids (haploid)
Movement into lumen controlled by sertoli cell secretions. Factors produced by sertoli cells are required for development
What is the role of Leydig cells?
- contain LH receptors
- primarily convert cholesterol into androgens
- intra-testicular testosterone levels are 100x those in plasma
What happens to the androgens following production by Leydig cells?
- androgens cross over to + stimulate Sertoli cell function
- thereby control spermatogenesis
- Sertoli cells contain FSH receptors
- convert androgen -> oestrogen
- FSH establishes a quantitavely normal Sertoli cell population
- whereas androgen initiates + maintains sperm production
so sertoli cells need FSH to maintain its population and need testosterone to undergo spermatogenesis
How do anabolic steroids lead to testicular atrophy?
- negative feedback on hypothalamus/pituitary
- reduce FSH/LH secretion
- it’s FSH which maintains sertoli cell population
- so testicular atrophy results due to reduced FSH!
How can anabolic steroids also lead to gynaecomastia in men?
- araomatase present in men (as well as women)
- lots of unbound anabolic steroids
- they are aromatised into oestrogens from androgens
- build up of oestrogen -> gynaecomastia
What structural changes occur to cause and maintain erection?
- vasodilation of corpus cavernosum (+ its arteries)
- engorging corporal tissue with blood
- egorging causes corporal tissue to swell, erecting penis
- engorged corporal tissue compresses penile veins + venules, maintaining erection
- partial constriction of venous return
What part of the nervous system are erection and ejaculation under control of?
- both under autonomic nervous system
- “point + shoot”
What exactly is under each of parasympathetic and sympathetic control in terms of erection and ejaculation?
- parasympathetic: erection + evacuation of urethra
- sympathetic: movement of sperm into epididymis, vas def, penile urethra expulsion of glandular secretions