Jul 18, 2010

Spermatogenesis and Oogenesis

In humans and other mammals, a complex interplay of hormones regulates gametogenesis

How exactly are gametes produced in the mammalian body? The process, gametogenesis, is based on meiosis, but details differ in females and males. Oogenesis, the development of mature ova (egg cells). Spermatogenesis, the production of mature sperm cells, is a continuous and prolific process in the adult male. Each ejaculation of a human male contains 100 to 650 million sperm cells, and males can ejaculate daily with little loss of fertilising capacity. Spermatogenesis occurs in the seminiferous tubules of the testes.

Oogenesis differs from spermatogenesis in three major ways. First, during the meiotic divisions of oogenesis, cytokinesis is unequal, with almost all the cytoplasm monopolized by a single daughter cell, the secondary oocyte. This large cell can go on to become the ovum; the other products of meiosis, smaller cells called polar bodies, degenerate. By contrast, in spermatogenesis, all four products of meiosis develop into mature sperms. Second, although the cells from which sperm develop continue to divide by mitosis throughout the male′s life, this is thought not to be the case for oogenesis in the human female. Third, oogenesis has long “resting” periods, in contrast to spermatogenesis, which produces mature sperm from precursor cells in an uninterrupted sequence.