Vulva is the collective term for the external female genitalia. A pair of slender skin folds, the labia minora, border the openings, A pair of thick, fatty ridges, the labia majora, protect the vaginal opening. A thin piece of tissue called the hymen partly covers the vaginal opening. Several female reproductive structures are important in sexual arousal, and stimulation of them can produce highly pleasurable sensations. The vagina, labia minora, and a small erectile organ called the clitoris all engorge with blood and enlarge during sexual activity. The clitoris consists of a short shaft supporting a rounded glans, or head, covered by a small hood of skin called the prepuce. The clitoris, especially the glans, has an enormous number of nerve endings and sensitive to touch.
1.From each testis, sperm pass into a coiled tube called the epididymis, which stores the sperm while they continue to develop. 2. Sperm leave the epididymis during Ejaculation (the expulsion of sperm-containing ﬂuid from the penis). 3. At that time, muscular contractions propel the sperm from the epididymis through another duct called the vas deferens. 4. The vas deferens joins a short duct from a gland,The seminal vesicle.The two ducts unite to form a short Ejaculatory duct, joins its counterpart conveying sperm from the other testis. 5. Each ejaculatory duct empties into the urethra, which conveys both urine and sperm out through the penis, 6. The human penis consists mainly of erectile tissue essential for insertion of the penis into the vagina. Like the clitoris, the penis consists of a shaft that supports the glans, or head. The glans is richly supplied with nerve endings and is highly sensitive to stimulation. A fold of skin called the prepuce, or foreskin, covers the glans.
Process of Ejaculation occurs in two stages. 1. At the peak of sexual arousal, muscle contractions in multiple glands force secretions into the urethra and propel sperm from the epididymis. At the same time, a sphincter muscle at the base of the bladder contracts, preventing urine from leaking into the urethra from the bladder. Another sphincter also contracts, closing entrance of the urethra into penis. The section of the urethra between the two sphincters ﬁlls with semen and expands. 2. The expulsion stage, the sphincter at base of penis relaxes, admitting semen into the penis. At the same time, a series of strong muscle contractions around the base of the penis and along the urethra expels the semen from the body.
About the time the secondary oocyte forms, the pituitary hormone LH (luteinizing hormone) triggers ovulation, the rupture of the follicle and expulsion of the secondary oocyte. The ruptured follicle then develops into a corpus luteum (“yellow body”). Unless fertilization occurs, the corpus luteum degenerates before another follicle starts to develop.
Hormonal Events Before Ovulation 1.Releasing hormone from the hypothalamus stimulates the anterior pituitary to increase its output of FSH and LH. 2.FSH stimulates the growth of an ovarian follicle, in effect starting the ovarian cycle. In turn, the follicle secretes estrogen. 3.As the follicle grows, secretes more and more estrogen, and the rising but still relatively low estrogen exerts negative feedback on the pituitary keeps blood levels of FSH and LH low. 4.As the time of ovulation approaches, hormone levels change drastically, with estrogen reaching a critical peak (Part D) just before ovulation. This high level of estrogen exerts positive feedback on the hypothalamus makes the pituitary—secrete surges of FSH and LH
Hormonal Events After Ovulation 1.LH stimulates the completion of meiosis I, transforming the primary oocyte in the follicle into a secondary oocyte. 2.It also signals enzymes to rupture the follicle, allowing ovulation to occur, and triggers the development of the corpusluteum from the ruptured follicle (hence its name, luteinizing hormone). 3.LH also promotes the secretion of progesterone and estrogen by the corpus luteum. 4. High levels of estrogen and progesterone in the blood following ovulation have a strong inﬂuence on both the ovary and uterus. The combination of the two hormones exerts negative feedback on the hypothalamus and pituitary, producing falling FSH and LH levels. 5.The drop in FSH and LH prevents follicles from developing and ovulation from occurring during the post-ovulatory phase. Also, the LH drop is followed by the gradual degeneration of the corpusluteum. 6.Near the end of the post-ovulatory phase, the corpus luteum stops secreting estrogen and progesterone---the hypothalamus --stimulate the pituitary to secrete more FSH and LH, and a new cycle begins.
Control of the Menstrual Cycle 1.Hormonal regulation of the menstrual cycle is simpler than that of the ovarian cycle. 2.The menstrual cycle (Part E) is directly controlled by estrogen and progesterone alone. 3.Starting around day 5 of the cycle, the endometrium thickens in response to the rising estrogen and, later, progesterone. When the levels of these hormones drop, the endometrium begins to slough off. 4.Menstrual bleeding begins soon after, on day 1 of a new cycle. What happens in the human ovary and uterus in the absence of fertilization and pregnancy? Early in pregnancy, the developing embryo, implanted in the endometrium, releases a hormone (human chorionic gonadotropin, or hCG). This hormone acts like LH in that it maintains the corpusuteum, which continues to secrete progesterone and estrogen, keeping the endometrium intact.