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© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor,

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Presentation on theme: "© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor,"— Presentation transcript:

1 © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey Chapter 27 Human Reproduction

2 27.3 Reproductive anatomy of the human female  There are anatomical differences between the human male and female reproductive systems, but have some important similarities. 1.A pair of gonads, the organs that produce gametes. 2.Ducts that store and deliver gametes 3.Structures that facilitate copulation.  A woman’s gonads, ovaries, are each about an inch long, with a bumpy surface (Figure 27.3 A).  The bumps are follicles, each consisting of one or more layers of cells that surround, nourish, and protect a single developing egg cell.  The ovaries produce hormones specifically, the follicle cells produce the female sex hormone estrogen.  A female is born with 1–2 million follicles, but only several hundred will release egg cell during her reproductive years. Starting at puberty, one follicle (or, rarely, more than one) matures and releases an immature egg after every 28 days until menopause, usually around age 50.  An immature egg cell is ejected from the follicle in a process called ovulation. © 2012 Pearson Education, Inc.

3  After ovulation, the follicular tissue grows within the ovary form a solid mass called the corpus luteum; It will secrete additional estrogen and Progesterone (maintain the uterine lining during pregnancy)  If the released egg is not fertilized, the corpus luteum degenerates, and a new follicle matures during the next cycle.  Each ovary lies next to the opening of an oviduct, also called a fallopian tube. © 2012 Pearson Education, Inc.

4  After ovulation, the follicular tissue grows within the ovary form a solid mass called the corpus luteum; It will secrete additional estrogen and Progesterone (maintain the uterine lining during pregnancy)  If the released egg is not fertilized, the corpus luteum degenerates, and a new follicle matures during the next cycle.  Each ovary lies next to the opening of an oviduct, also called a fallopian tube.  The surface of the ovary is separated from the opening of the oviduct by a tiny space. © 2012 Pearson Education, Inc.  When ovulation occurs, the egg cell passes across the space and into the oviduct, where cilia sweep it toward the uterus.  If sperm are present, fertilization may occur in the upper part of the oviduct.  The resulting zygote starts to divide, thus becoming an embryo, as it moves along within the oviduct.

5 Uterus, the actual site of pregnancy © 2012 Pearson Education, Inc.  The uterus, also known as the womb, is the actual site of pregnancy. The uterus is about 3 inches long, but during pregnancy it expands considerably as the baby develops.  The uterus has a thick muscular wall, and its inner lining, the endometrium, is richly supplied with blood vessels. An embryo implants in the endometrium, and development is completed there.  The term embryo is used for the stage in development from the first division of the zygote until body structures begin to appear, about the 9th week in humans.  From the 9th week until birth, a developing human is called a fetus. In about 1% of pregnancies, the embryo implants somewhere else, resulting in an ectopic pregnancy. Most ectopic pregnancies occur in the oviduct and are called tubal pregnancies. It is a serious medical emergency. That requires surgical intervention; otherwise, it can rupture surrounding tissues, causing severe bleeding and even death of the mother.

6 Cervix and Vagina © 2012 Pearson Education, Inc. It is recommended that women have a yearly Pap test in which cells are removed from around the cervix and examined under a microscope for signs of cervical cancer.  The narrow neck at the bottom of the uterus is the cervix, which opens into the vagina.  Vagina is a thin-walled, but strong, muscular chamber that serves as the birth canal through which the baby is born.  The vagina is also the repository for sperm during sexual intercourse.  Glands near the vaginal opening secrete mucus during sexual arousal, lubricating the vagina and facilitating intercourse.  The vagina opens to the outside just behind the opening of the urethra, the tube through which urine is excreted.

7 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.

8 27.4 Reproductive anatomy of the human male © 2012 Pearson Education, Inc.  The male gonads, or testes (singular, testis), are each housed outside the abdominal cavity in a sac called the scrotum.  A testis and scrotum together are called a testicle.  Sperm cannot develop at human body temperature; the scrotum keeps the sperm- forming cells about 2°C cooler, which allows them to function normally.  In cold conditions, muscles around the scrotum contract, pulling the testes toward the body, thereby maintaining the proper temperature.

9 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.

10 © 2012 Pearson Education, Inc. The reproductive system of human males contains three sets of glands: 1. The seminal vesicles (two seminal vesicles secrete a thick fluid that contains fructose, provides most of the energy to sperm as they propel themselves through the female reproductive tract.), 2. The prostate gland (secretes a thin fluid that further nourishes the sperm), 3. The bulbourethral glands (two bulbourethral glands secrete a clear, alkaline mucus. Together, the sperm and the glandular secretions make up semen, ejaculated from the penis during orgasm and is about 2–5 mL semen/during a typical ejaculation. About 95% of the fluid consists of glandular secretions and 5% is made up of sperm (typically 200–500 million of them), only one of which may eventually fertilize an egg. The alkalinity of the semen balances the acidity of urine in the urethra and neutralizes the acidic environment of the vagina, protecting the sperm and increasing their motility.

11 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.

12 How hormones control sperm production by the testes © 2012 Pearson Education, Inc.  The hypothalamus secretes a releasing hormone that regulates release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) by the anterior pituitary  FSH increases sperm production by the testes, while LH promotes the secretion of androgens, mainly testosterone.  Androgens stimulate sperm production.  In addition, androgens carried in the blood help maintain homeostasis by a negative-feedback mechanism (red arrows), inhibiting secretion of both the releasing hormone and LH  Under the control of this chemical regulating system, the testes produce hundreds of millions of sperm every day, from puberty well into old age.

13 27.5 The formation of sperm and egg cells requires meiosis © 2012 Pearson Education, Inc. Both sperm and egg are haploid (n) cells that develop by meiosis from diploid (2n) cells in the gonads. The diploid chromosome number in humans is 46; that is, 2n = 46. The formation of gametes is called gametogenesis There are significant differences in gametogenesis between human males (spermatogenesis) and females (oogenesis)

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15 Sperm develop in the testes in coiled tubes called the seminiferous tubules  Diploid cells that begin the process are located near the outer wall of the tubules  These cells multiply continuously by mitosis, and each day about 3 million of them differentiate into primary spermatocytes, the cells that undergo meiosis  Meiosis I of a primary spermatocyte produces two secondary spermatocytes, each with the haploid number of chromosomes (n = 23)  Meiosis II then forms four cells, each with the haploid number of chromosomes  A sperm cell develops by differentiation of each of these haploid cells and is gradually pushed toward the center of the seminiferous tubule  From there it passes into the epididymis, where it matures, becomes motile, and is stored until ejaculation  In human males, spermatogenesis takes about 10 weeks © 2012 Pearson Education, Inc.

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17 Oogenesis, the development of a mature egg © 2012 Pearson Education, Inc.  Oogenesis actually begins prior to birth, when a diploid cell in each developing follicle begins meiosis.  At birth, each follicle contains a dormant primary oocyte, a diploid cell that is resting in prophase of meiosis I  A primary oocyte can be hormonally triggered to develop further. Between puberty and menopause, about every 28 days.  FSH (follicle-stimulating hormone) from the pituitary stimulates one of the dormant follicles to develop. The follicle enlarges, and the primary oocyte completes meiosis I and begins meiosis II. Meiosis then halts again at metaphase II  In the female, the division of the cytoplasm in meiosis I is unequal, with a single secondary oocyte receiving almost all of it. The smaller of the two daughter cells, called the first polar body, receives almost no cytoplasm.  The secondary oocyte is released by the ovary during ovulation. it enters the oviduct, and if a sperm cell penetrates it, the secondary oocyte completes meiosis II.  Meiosis II is also unequal, yielding a second polar body and the mature egg (ovum). The haploid nucleus of the mature egg can then fuse with the haploid nucleus of the sperm cell, producing a zygote.

18  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.

19 27.6 Hormones synchronize cyclic changes in the ovary and uterus © 2012 Pearson Education, Inc. For simplicity, ovarian cycle is divided into two phases, separated by ovulation Hormonal messages links these two cycles—synchronizing follicle development in the ovaries and establishment of uterine lining for supporting growing embryo Actually one integrated cycle involving two organs Reproductiv e cycle Ovarian cycle in ovaries of 28 days Pre- ovulatory phase Post- ovulatory phase Menstrual cycle in the uterus –3-5 days The first day of period is day 1 of menstrual cycle The endometrium ruptures and leave the body through vagina After menstruation, regrows and max thicken on days

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21 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

22 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.

23 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.


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