Lecture 6 Chapter 46.4, 47.1 Book notes

Lecture 6 Chapter 46.4, 47.1 Book notes - Biology 110b...

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Biology 110b Chapter 46.4, 47.1 Book notes (Page 973) In humans and other mammals, a complex interplay of hormones regulates gametogenesis. The process, gametogenesis , is based on meiosis, but details differ in females and males. Oogenesis is the development of mature ova (egg cells), and spermatogenesis , is the production of mature sperm cells, and it occurs in the seminiferous tubules of the testes. Oogenesis differs from spermatogenesis in three major ways: 1. 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 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. 2. 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. 3. Oogenesis has long “resting” periods, in contrast to spermatogenesis, which produces mature sperm from precursor cells in an uninterrupted sequence. Two different types of cycles occur in female mammals: 1. Humans and certain other primates have menstrual cycles . 2. Other mammals have estrous cycles . Ovulation occurs at a time the both cycles after the endometrium has started to thicken and develop a rich blood supply, preparing the uterus for the possible implantation of an embryo. In menstrual cycles, the endometrium is shed from the uterus through the cervix and vagina in a bleeding called menstruation . In estrous cycles, the endometrium is reabsorbed by the uterus and no extensive bleeding occurs. In some mammals, the only time the vagina permits mating is called estrus . The term menstrual cycle refers to changes that occur in the uterus; therefore it is also called the uterine cycle . It is caused by cyclic events that occur in the ovaries called the ovarian cycle . (Page 974) Oogenesis begins in the female embryo with differentiation of primordial germ into oogonia , ovary- specific stem cells. At prophase I, primary oocytes , remain quiescent within small follicles (cavities lined with protective coverings) until puberty, when hormones reactivate them. Follicale stimulating hormone (FSH) periodically stimulates a follicle to grow and induces its primary oocyte to complete meiosis I and start meiosis II. Meiosis then stops again. Arrested at metaphase II, the secondary oocyte is released at ovulation, when its follicle breaks open.
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Biology 110b Chapter 46.4, 47.1 Book notes The meiotic divisions in oogenesis involve unequal cytokinesis, with the smaller cells becoming polar bodies (the first polar body may or may not divide again). The ruptured follicle left behind after ovulation develops into the corpus luteum. If the released oocyte is
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Lecture 6 Chapter 46.4, 47.1 Book notes - Biology 110b...

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