MT

gametogenesis 

  • Gametogenesis is the process by which gametes are produced

  • Spermatogenesis - formation of spermatozoa

  • Oogenesis - formation of eggs or ovaries

  • Cell division and gamete production

    • Mitosis - produces diploid cells (genetically identical cells)
    • Diploid - will have full set of chromosomes 46 in 23 pairs
    • Haploid - half of the number of chromosomes 23 one of each pair
    • Meiosis - produces cells that are genetically different

  • Oogenesis

  • spermatogenesis

  • Spermatogenesis occurs in the testis

    • These are large cells in the walls of seminiferous tubules that nourish the developing spermatids and protect them from the immune system
    • These cells are stimulated by the secretion of testosterone from leading cells in the testis

  • oogenesis

    • Follicle stimulating hormone(FSH) secreted by the pituitary promotes the growth of primary oocytes into follicles the oocyte is surrounded by epithelial cells usually only 1 follicle will develop into a graafian follicle which grows and moves to the surface if the ovary
    • The follicle eventually bursts releasing the egg (ovulation)
    • The empty follicle devolves into a corpus lutes
    • This secretes the hormone progesterone for a while before starting to degenerate

  • Fertilization

    • Less than 1% of sperm will reach the oocyte
    • Sperm reach the oocyte by a mixture of peristaltic contractions and the swimming actions of the tails
    • The oocyte also secretes chemical attractants

  • Capacitation

    • Sperm undergo further maturation whilst in the female tract
    • The membrane around the acrosome become fragile enabling the release of digestive enzymes
    • The release of enzymes help the sperm penetrate the layer of follicular cells and the zona pellucida
    • Sperm bind to receptors in zona pellucida and normally only 1 enters the oocyte syngamy
    • Syngamy causes depolarisation of the membrane triggering the release of calcium ions
    • Release of calcium triggers the vertical reaction preventing polyspermy
    • Once the sperm has entered the oocyte this triggers the final meiotic division and this forms the female pronucleus
    • The 2 nuclei fuse complementing fertilization
    • After fertilization
    • About 36 hours after the first division or cleavage takes place
    • Division continues for the next few days to form a morula a solid ball of cells by the end of the 4th day
    • By the 5th day morula has developed into a hollow ball of cells called a blastocyst

  • Implantation

    • By day 6 the blastocyst has entered the uterus and after a short time it attaches to the endometrium with the inner cell mass next to the endometrium
    • The trophoblast cells will go on to form the embryonic membranes and the placenta
    • Embryonic development lasts for the first 2 months