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IV) Female Reproductive System B) Oogenesis. IV) Female Reproductive System B) Oogenesis. where as the sperm is small the ovum is much larger because it is packed full of nutrients so it can divide rapidly after fertilization.
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IV) Female Reproductive System B) Oogenesis • where as the sperm is small the ovum is much larger because it is packed full of nutrients so it can divide rapidly after fertilization. • like a sperm cell an ovum oocyte undergoes a type of cell division that halves the number of chromosomes (called meiosis).
IV) Female Reproductive System B) Oogenesis • like a sperm cell an ovum oocyte undergoes a type of cell division that halves the number of chromosomes (called meiosis). • Oogenesis • is the formation of an ovum • occurs in specialized cells in the ovaries called follicles. • a follicle contains two types of cells • a primary oocyte • cells of the granulosa ~ the granulosa is the layer of cells that form the follicle wall. They provide nutrients for the developing oocytes.
IV) Female Reproductive System B) Oogenesis • a primary oocyte • cells of the granulosa ~ the granulosa is the layer of cells that form the follicle wall. They provide nutrients for the developing oocytes. • begins when the nutrient follicle cells which ARE surrounding the primary oocyte begin to divide. • the primary oocyte undergoes cell division and while this occurs the majority of cytoplasmic nutrients move to one of the poles and form a secondary oocyte. • the secondary oocyte contains 23 chromosomes. • the remaining cell, called the first polar body, receives little cytoplasm and dies.
IV) Female Reproductive System B) Oogenesis • as the follicle cells surrounding the secondary oocyte start to proliferate a fluid filled cavity forms. • the dominant follicle begins to push outwards trying to escape the ovary. • constriction of blood vessels weaken the ovarian wall. • enzymes weaken the follicle wall from the inside. • the seconday oocyte (with the first polar body) is released, this is called ovulation.
IV) Female Reproductive System B) Oogenesis • enzymes weaken the follicle wall from the inside. • the seconday oocyte (with the first polar body) is released, this is called ovulation. • the follicle cells that were surrounding the secondary oocyte stay in the ovary and transform into the corpus luteum. • the corpus luteum secretes hormones essential for pregnancy. • if no pregnancy occurs, the corpus luteum degenerates. • after its release from the ovary the secondary oocyte is swept into the end of the Fallopian tube by the fimbriae. • the secondary ooctye is moved along the Fallopian tube by cilia • if healthy sperm is present fertilization will occur.
IV) Female Reproductive System B) Oogenesis • after its release from the ovary the secondary oocyte is swept into the end of the Fallopian tube by the fimbriae. • the secondary ooctye is moved along the Fallopian tube by cilia • if healthy sperm is present fertilization will occur. • after fertilization in the Fallopian tube • the secondary oocyte undergoes an uneven division again. • the cells that retain most of the cytoplasm (nutrients) becomes the ovum. • the other cell becomes the second polar body, which deteriorates. • if no fertilization occurs, the secondary oocyte will deteriorate within 24 hours and die. • the women will then undergo a menstrual cycle.
IV) Female Reproductive System • if no fertilization occurs, the secondary oocyte will deteriorate with 24 hours and die. • the women will then undergo a menstrual cycle. • along with the development of the secondary sexual characteristics puberty also initiates the menstrual cycle. • secondary sexual characteristics in females include: • enlarged breasts • hair growth in armpits and pubic area • wider hips • fat deposits around buttocks and hips • angle from thigh to ankle is slightly bent
IV) Female Reproductive System C) Menstrual Cycle • the menstrual cycle includes: • oogenesis, ovulation, thickening and shedding of the endometrium • it can be divided into four distinct phases • Flow phase • Follicular phase • Ovulatory phase • Luteal phase
IV) Female Reproductive System C) Menstrual Cycle • Flow phase • Follicular phase • Ovulatory phase • Luteal phase • Flow phase • marked by shedding of the endometrium, or menstruation. • the only phase of female reproductive cycle that can be determined externally. • this is why the flow phase is used to mark the beginning of the cycle. • on average five days are required for the uterus to completely shed the endometrium.
IV) Female Reproductive System C) Menstrual Cycle • this is why the flow phase is used to mark the beginning of the cycle. • on average five days are required for the uterus to completely shed the endometrium. • Follicular Phase • characterized by the development of the follicles within the ovary. • as the follicle develops the hormone estrogen is secreted. • estrogen activates the development of secondary sexual characteristics and causes thickening of the endometrium. • takes place between days 6 and 13 of the female menstrual cycle.
IV) Female Reproductive System C) Menstrual Cycle • estrogen activates the development of secondary sexual characteristics and causes thickening of the endometrium. • takes place between days 6 and 13 of the female menstrual cycle. • Ovulatory Phase • the secondary oocyte bursts from the ovary and follicular cells differentiate into the corpus luteum. • Day 14 of the menstrual cycle (on average)
IV) Female Reproductive System C) Menstrual Cycle • the secondary oocyte bursts from the ovary and follicular cells differentiate into the corpus luteum. • Day 14 of the menstrual cycle. • Luteal Phase • begins when the corpus luteum starts to develop. • occurs between days 15 and 28 • estrogen levels begin to decline when the oocyte leaves but are restored when the corpus luteum forms. • corpus luteum secretes both estrogen and progesterone. • progesterone hormone: • stimulates the endometrium and prepares the uterus for an embryo • inhibits further ovulation • inhibits uterine contraction • firms the cervix to prevent expulsion of the fetus
IV) Female Reproductive System C) Menstrual Cycle • progesterone hormone: • stimulates the endometrium and prepares the uterus for an embryo • inhibits further ovulation • inhibits uterine contraction • firms the cervix to prevent expulsion of the fetus • if fertilization does not occur the concentrations of estrogen and progesterone will decrease. • the uterus will start to contract (cramps) • contraction makes the endometrium pull away from the uterus wall. • shedding of the endometrium marks the next flow phase.
