Bio notes April 8

Bio notes April 8 - Bio notes April 8 2008...

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Bio notes April 8, 2008 Reproduction -gamete production -hormonal regulation -compartivie reproduction oogensis -t he process, gametogenesis , is based on meiosis, but details differ in females and males. Oogenesis , the development of mature ova (egg cells), is described in Figure 46.11 , on the next page. 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 fertilizing capacity. Spermatogenesis occurs in the seminiferous tubules of the testes. Figure 46.12 describes the process in some detail. Oogenesis differs from spermatogenesis in three major ways. 1. 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 sperm (compare Figures 46.11 and 46.12). 2. 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 (but see the text in Figure 46.11). 3. Third, oogenesis has long “resting” periods, in contrast to spermatogenesis, which produces mature sperm from precursor cells in an uninterrupted sequence.
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Speratogenies
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Unequal cell membrane division in oogenesis Control with hormones -general scheme ^ see pictures Hormone control - Hypo GnRH production that stimulates FSH And LH production o Fhs stims sterloi cells (linig of tubes for the support of developing spermatids) o Lh stims ledug cells (production of testosterone wihich stimulates sperm proctuciot o Both stim. Sperm production fhs and la indirectly through test production o Test neg keeos test levels constant In females The Ovarian Cycle. 1 The cycle begins with the release from the hypothalamus of GnRH, which 2 stimulates the pituitary to secrete small amounts of FSH and LH. 3 The FSH (true to its name) stimulates follicle growth, aided by LH, and 4 the cells of the growing follicles start to make estrogen. Notice in Figure 46.13d that there is a slow rise in the amount of estrogen secreted during most of the follicular phase , the part of the ovarian cycle during which follicles are growing and oocytes maturing. (Several follicles begin to grow with each cycle, but usually only one
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Bio notes April 8 - Bio notes April 8 2008...

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