Human Reproduction

Gametogenesis

Gametogenesis Spermatogenesis refers to the process by which spermatozoa are produced from the germinal epithelium of the testis Oogenesis is the process where ova is produced from germinal epithelium of the ovaries

Summary of the steps of spermatogenesis Spermatogonia (2n) in germinal epithelium of seminiferous tubules Mitosis Primary spermatocytes (2n) Meiosis (first division) Secondary spermatocytes (n) Meiosis (second division) Spermatids (n) sperm cells/spermatozoa

Spermatogenesis At puberty, the germinal epithelial cells lining the seminiferous tubules start to produce sperms/spermatozoa by meiosis Each germinal epithelium is diploid and in humans the diploid number is 46 Since the sperm is produced by meiosis, each one will be haploid with 22 single chromosome and X or Y chromosome

Spermatogenesis The process is as follows: Cells of germinal epithelium become actively dividing cells called spermatogonia Each spermatogonium, which is diploid (2n), enlarges to become a primary spermatocyte (also 2n)

Spermatogenesis Primary spermatocyte undergoes the first meiotic division forming 2 haploid secondary spermatocytes Each secondary spermatocyte undergoes the second meiotic division to produce 2 spermatids Each spermatid matures to form a spermatozoan Each spermatozoan is made up of a head, a middle-piece and a tail

Sperm Microscopic cells produced by the male's testicles which can fertilize the female's ovum. They are tiny, living cells 100 times smaller than a pencil dot. (the smallest cell in a man’s body Enough sperm would fit on the head of a pin to re-populate the earth if each sperm fertilized an egg. It is destroyed by warm body temperature, acidic environment. It can survive in a women’s body for 5-8 days. Any sperm not ejaculated are passed in the urine.

Oogenesis

Summary of the steps of oogenesis Oogonia (2n) in germinal epithelium of seminiferous tubules Mitosis Primary oocytes (2n) Meiosis (first division) Secondary oocyte (n) Meiosis (second division) ootid (n) ovum

Ova The female reproductive cell. They are the largest cells in the female body. (about the size of a grain of sand.) The female baby is born with all the ova she will ever have (about 200,000 in each ovary). About 400-500 ova mature and are released over a lifetime