Spermatogenesis Flashcards
What is the function of the testes?
- Produce sperm and store it
- Produce hormones which regulate spermatogenesis
- Testosterone, inhibin, growth factors
Why is the scrotum containing the testes outside the body cavity?
For optimum temperature for sperm production is 1.5-2.5 degrees below body temp
What can overheating do to the testes?
Reduce the sperm count
What is the normal volume of the testes and how can this be measured?
- Normal volume 15-25ml
- Measured via an ORCHIDOMETER
What percentage of the testes are seminiferous tubules?
What is the funciton of these?
What do the seminiferous tubules lead to?
- Testes is 90% seminiferous tubules
- site of spermatogenesis
- Tubules lead to epididymis and ultimately the vas deferens
What are the walls of the seminiferous tubule made of? What do the junctions between these form?
- Tall columnar endothelial cells called Sertoli Cells
- Tight junctions between these form the Adluminal compartment
What is the function of the adluminal compartment?
Compartment for a specific enclosed environment for spermatogenesis - filled with secretions from Sertoli cells
Why do sperm have a lifetime supply?
Spermatogonia (are diploid primary germ cells) present on the basement membrane. These can either undergo meiotic divisions to become sperm or undergo mitosis to replenish themselves.
What is the male analogue of theca cells? What do they produce?
Male analogue are Leydig cells - these produce testosterone
What are spermatogonia?
- Germ cell on basement membrane
- Capable of mitotic division (to replenish themselves) or meiotic division to produce primary spermatocytes
- DIPLOID
What are primary spermatocytes?
- Move to the adluminal compartment and duplicate their DNA to produce sister chromatids which exchange genetic material before they enter meiosis I
- They are 46XY diploid
What are secondary spermatocytes?
Have undergone meiosis I to give 23X and 23Y haploid number of chromosomes arranged as sister chromatids
What are spermatids?
- Meiosis II occurs to give 4 haploid spermatids
- Round spermatid to elongated spermatid differentiation
What are spermatozoa?
Mature sperm extruded into the lumen
How often does a new spermatogenesis cycle occur?
Every 16 days
Summarise the steps that occur in spermatogenesis?
- Mitotic proliferation of spermatogonia.
- Meiosis and development of spermatocytes.
- Spermiogenesis, elongation, loss of cytoplasm, movement of cellular contents.
What allows for the synchronous development of sperm?
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.
What is the difference between oogonia and spermatogonia?
- Spermatogonia and oogonia is laid down in foetus
- Spermatogonia begin to make spermatocyte after puberty and can divide by mitosis for a lifetime supply vs oogonia begin meiosis before birth and cannot make more
- Lifetime supply of spermatogonia, limited supply of oogonia
Describe the HPG axis and how it controls spermatogenesis
In folliculogenesis mainly oestrogen released in first stage and progesterone is released later from corpus luteum in a cyclical process
In MALES = GnRH released stimulates LH/FSH release to the testis - produces testosterone/DHT acting in a negative feedback manner
What is the primary role of the leydig cells?
- Contain LH receptors converting cholesterol to androgens
What causes erection and ejaculation?
- Vasodilation of corpus cavernosum tissue
- Partial constriction of venous return
- ANS causes co-ordinated Smooth muscle contractions of vas-deferens, glands and urethra
What is the function of the bulbo-urethral gland?
- Produces a clear viscous secretion high in salt called pre-ejaculate
- Fluid helps lubricate urethra for spermatozoa to pass through neutralising traces of acidic urine
