Reproductive System - Part 2 PDF Fall-2023

Reproductive System- Part 2 Nermin Eissa, Ph.D. College of Health Sciences Abu Dhabi University Fall-2023  Learning Outcomes: List the stages of the ovarian cycle and explain what is occurring in each stage. Describe the process o...

Reproductive System- Part 2 Nermin Eissa, Ph.D. College of Health Sciences Abu Dhabi University Fall-2023  Learning Outcomes: List the stages of the ovarian cycle and explain what is occurring in each stage. Describe the process of oogenesis. Summarize how estrogen and progesterone influence the ovarian cycle. The Effect of Birth Control Pills on the Ovarian Cycle. 2 ©2020 McGraw-Hill Education  Ovarian Cycle: Nonpregnant 1 Oocyte—immature egg; contained within a follicle. Females are born with 2 million follicles, but have only 300,000—400,000 by puberty. Only 400 ever mature; a female produces only one egg per month during her reproductive years. As the follicle matures during the ovarian cycle, it changes from a primary to a secondary to a vesicular (Graafian) follicle. 3 ©2020 McGraw-Hill Education  The Ovarian Cycle Access the text alternative for these images 61 ©2020 McGraw-Hill Education (photo): ©Ed Reschke  Ovarian Cycle: Nonpregnant 2 Oocyte, continued. Primary follicle—epithelial cells surround a primary oocyte. Secondary follicle—follicular fluid surrounds the secondary oocyte. Vesicular follicle—the fluid-filled cavity enlarges to the point that the follicle wall balloons out on the surface of the ovary. 5 ©2020 McGraw-Hill Education  Oogenesis 1 Steps of oogenesis (production of an oocyte): A primary oocyte undergoes meiosis I; the two resulting cells are haploid. One of these cells is called a polar body; its function is simply to hold discarded chromosomes. The secondary oocyte undergoes meiosis II, but only if it is first fertilized by a sperm cell. If it remains unfertilized, it never completes meiosis and dies shortly after being released from the ovary. 6 ©2020 McGraw-Hill Education  Oogenesis Produces Egg Cells Access the text alternative for these images 7 ©2020 McGraw-Hill Education  Oogenesis 2 Steps of oogenesis, continued: Ovulation—the vesicular follicle bursts, releasing the oocyte. The vesicular follicle then develops into a corpus luteum, a glandlike structure. If the egg is not fertilized, the corpus luteum disintegrates. 8 ©2020 McGraw-Hill Education  Oogenesis 3 Steps of oogenesis, concluded: A primary follicle produces estrogen, and a secondary follicle produces estrogen and some progesterone The corpus luteum produces progesterone and some estrogen. 9 ©2020 McGraw-Hill Education  Phases of the Ovarian Cycle 1 Like in males, the hypothalamus secretes GnRH. GnRH stimulates the anterior pituitary to produce FSH and LH; these hormones control the ovarian cycle. 10 ©2020 McGraw-Hill Education  The Hormones that Control the Production of Estrogen and Progesterone by the Ovaries Access the text alternative for these images 11 ©2020 McGraw-Hill Education  Phases of the Ovarian Cycle 2 Follicular phase—the first half of the cycle. FSH promotes the development of primary follicles, which primarily secrete estrogen. As estrogen rises, it exerts negative feedback control over the anterior pituitary secretion of FSH, ending the follicular phase. A surge of LH is released from the anterior pituitary, triggering ovulation on day 14 of a 28-day cycle. 12 ©2020 McGraw-Hill Education  Female Hormone Levels During the Ovarian and Uterine Cycles Access the text alternative for these images 13 ©2020 McGraw-Hill Education  Phases of the Ovarian Cycle 3 Luteal phase—LH promotes the development of the corpus luteum, which secretes high levels of progesterone and some estrogen. If pregnancy does not occur, it regresses and a new cycle begins. 14 ©2020 McGraw-Hill Education  Estrogen and Progesterone 1 Estrogen and progesterone. Responsible for the secondary sex characteristics: Terminal hair after puberty. Greater fat accumulation under the skin. Both estrogen and progesterone are also required for breast development. Prolactin is involved in milk production after pregnancy. CHECK POINT 15 ©2020 McGraw-Hill Education  Estrogen and Progesterone 3 Menopause—when the ovarian cycle ceases. Usually between ages 45 and 55. The ovaries no longer respond to gonadotropic hormones, and they no longer secrete estrogen or progesterone. At the onset of menopause, menstruation becomes irregular, but it is not complete until menstruation is absent for 1 year. 16 ©2020 McGraw-Hill Education  Uterine Cycle: Nonpregnant 1 Uterine cycle—a cyclical series of events caused by estrogen and progesterone. Twenty-eight-day cycles are divided as follows: Days 1 to 5: menstruation—low levels of estrogen and progesterone cause the endometrium to disintegrate and its blood vessels to rupture. Menses—the flow of blood and tissues out of the vagina. 17 ©2020 McGraw-Hill Education  Uterine Cycle: Nonpregnant 2 Uterine cycle, continued. Days 6 to 13: proliferative phase—increased production of estrogen by a new follicle causes the endometrium to thicken and become glandular. On day 14—ovulation. 18 ©2020 McGraw-Hill Education  Uterine Cycle: Nonpregnant 3 Uterine cycle, concluded. Days 15 to 28: secretory phase—increased production of progesterone by the corpus luteum causes the endometrium thicken. Also causes the uterine glands to mature and produce a thick secretion. The endometrium is now prepared to receive the developing embryo; if this does not occur, the corpus luteum regresses. The resulting low level of progesterone causes menstruation. 19 ©2020 McGraw-Hill Education  Ovarian and Uterine Cycles: Nonpregnant Ovarian and Uterine Cycles: Nonpregnant. Ovarian Cycle Events Uterine Cycle Events Follicular phase—days FSH secretion Menstruation—days Endometrium 1 to 13 begins. 1 to 5 breaks down. Follicle maturation Proliferative Endometrium occurs. phase—days 6 to 13 rebuilds. Estrogen secretion is prominent. Ovulation-day 141 LH spike occurs. Luteal phase-days 15 to LH secretion Secretory phase— Endometrium 28 continues. days 15 to 28 thickens, and glands Corpus luteum are secretory. forms. Progesterone secretion is prominent. 1 assuming a 28-day cycle. 20 ©2020 McGraw-Hill Education  Fertilization and Pregnancy 1 Only one sperm is needed to fertilize the egg, which is then called a zygote. As the zygote travels down the uterine tube to the uterus, it begins mitosis. Once it is made of many cells, it is called an embryo. The endometrium is now prepared to receive the developing embryo. 21 ©2020 McGraw-Hill Education  Fertilization and Pregnancy 2 The embryo implants in the endometrial lining several days following fertilization. Implantation signals the beginning of a pregnancy. An abortion may be spontaneous (referred to as a miscarriage) or induced. Both end with loss of the embryo or fetus. 22 ©2020 McGraw-Hill Education  Placenta 1 Placenta—sustains the developing embryo. Originates from both maternal and fetal tissues. Where exchange between fetal and maternal blood occurs. Produces human chorionic gonadotropin (HCG)— maintains the corpus luteum. A pregnancy test detects HCG in the blood or urine. 23 ©2020 McGraw-Hill Education  Placenta 2 Placenta, continued. Rising amounts of HCG stimulate the corpus luteum to produce increasing amounts of progesterone. This progesterone shuts down the hypothalamus and anterior pituitary, so no new follicles begin to develop. The progesterone maintains the uterine lining where the embryo now resides, preventing menstruation. 24 ©2020 McGraw-Hill Education  The Effect of Pregnancy on the Corpus Luteum and Endometrium 25 ©2020 McGraw-Hill Education  Placenta 3 Placenta, concluded. Eventually, the placenta produces progesterone and some estrogen. So the corpus luteum is no longer needed and it regresses. CHECK POINT 26 ©2020 McGraw-Hill Education  Birth Control Pills Birth control pills to prevent pregnancy usually involve taking active pills (contain estrogen and progesterone) for 21 days, then inactive pills (do not contain them) for 7 days. The uterine lining builds up while the active pills are being taken. Progesterone decreases after the last active pills are taken, causing menstruation. 27 ©2020 McGraw-Hill Education  The Effect of Birth Control Pills on the Ovarian Cycle 28 ©2020 McGraw-Hill Education  Check Your Progress Summarize the roles of estrogen and progesterone in the ovarian and uterine cycles. CHECK POINT 29 ©2020 McGraw-Hill Education