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