1.2 Flashcards
Where do male germ cells colonise?
Sex cords in the medulla of the primordial gonad.
What do sex cords connect with?
Rete testis, epididymis and vas deferens
What do germ cells do after colonisation of the gonad?
Proliferation by mitosis to form spermatogonia stem cell (self regerating).
Reshuffle genetically and reduce to haploid by meiosis.
Cytodifferentiate into mature gametes
What happens to the sex cords at puberty?
They hollow out to form seminiferous tubules where sperm are produced.
Describe spermatogonia.
Maintained by mitosis, have not begun meiosis.
Raw material for spermatogenesis available up to and beyond 70 years.
Sit in periphery of seminiferous tubules.
Describe A1 Spermatogonia
These undergo differentiation to produce either more type A (stem) cells or type B cells, which differentiate into spermatozoa.
How do type B spermatognium divide?
Fixed number of mitotic divisions to produce 64 diploid primary spermatocytes, linked together by cytoplasm bridges.
How do primary spermatocytes divide?
The chain of primary spermatocytes, linked by the cytoplasm bridge, push their way to the lumen of the seminiferous tubule and begin meiosis to form 4 haploid spermatids each.
How many spermatids does each A1 spermatognium yield?
up to 256 spermatids
What are the functions of meiosis?
Reduce the chromosome number to 23 (haploid).
Ensures every gamete is genetically unique.
In females how many of the daughter cells of meiosis matures? What happens to the others?
One –> oocyte
Others –> Polar bodies
How does genetic variation arise form meiosis?
Crossing over - exchange of regions of DNA between two homologous chromosomes. (Recombination -Prophase I)
Random segregation - distribution of chromosomes among four gametes.
Independent assortment - two homolog chromosomes of a pair must go into separate gametes.
What is the process of spermoiogenesis
Spermatids released into lumen of tubules
Remodelling spermatids to form spermatozoa, breaking of cytoplasmic bridges as they pass through the tete testis, ductuli efferent and epididymis.
Non motile until they reach epididymis
Describe sertoli cell function
Testicular origin
Help spermatogonia by feeding and stimulating
Site of action for hormones controlling spermatogenesis.
Secrete fluid to wash non motile spermatids to rete testis (assisted by peristaltic contration)
What is spermiation?
Spermatids released into lumen of seminiferous tubules.
How long does spermatogenesis take?
70 days
How often do new groups of A1 Spermatogonia arise?
16 days
How many spermatogenic processes occur simultaneously?
4
Describe the spermatogenic wave.
Production of sperm is continuous because different sections along the length of the tubule begin the process at different times so some part is always releasing sperm. A wave of production sweeps along the length of the tubule.
The distance on the tube between parts that are in the same stage is the spermatogenic wave.
What is the spermatogenic cycle?
The development of A1 spermatogonia to 256 sperms.
The amount of time it takes for reappearance of the same stage of the cycle within a given segment of the tubule.
Describe emission and what it is dependent on.
Contractions of the vas deferens sweep sperm to be mxdd with other components of semen form the seminal vesicles (60%) and prostate (20%).
Dependent on the sympathetic NS
Describe the constituents of semen.
2ml per ejaculate.
Seminal vesicle secretions (70%) - amino acids, citrate, fructose, prostaglandins.
Prostatic secretions (25%) - proteolytic enzymes, zinc.
Sperm (via vas deferens - 2-5%) - 200-500 million per ejaculate
Bulbourethral (Cowper) gland secretions - mucoproteins help lubricate and neutralise acidic urine in distal urethra.
What is the path of sperm and where do secretions join?
Seminiferous tubules
Rete testis
Ductuli efferentes
Epididymis Vas deferens (Seminal vesicle secretion)
Urethra (Prostate and bulbourethral gland)
Describe the maturation of sperm.
Conditions in female genital tract stimulate:
Removal of glycoproteins and cholesterol from sperm membrane.
Activation of sperm signalling pathways
Allow sperm to bind to zona pellucid of oocyte and initiate acrosome reaction.
