The Female Reproductive System, Lecture notes of Biology

Download The Female Reproductive System and more Lecture notes Biology in PDF only on Docsity! reproductive system 541 Reproductive motility also results in infertility. A major cause of reduced sperm cell motility is the presence of antisperm antibodies, which are produced by the immune system and bind to sperm cells. In cases of infertility due to low sperm cell count or reduced motility, fertility can sometimes be achieved by collecting several ejaculations, concentrating the sperm cells, and inserting them into the female’s reproductive tract, a process called artificial insemination (in-sem-i-nā ′ shŭ n). 19.5 Female reproDuctive system Learning Outcomes After reading this section, you should be able to A. name the organs of the female reproductive system, and describe their structure. B. Describe the anatomy and histology of the ovaries. C. Discuss the development of the oocyte and the follicle, and describe ovulation and fertilization. D. Describe the structure of the uterine tubes, uterus, vagina, external genitalia, and mammary glands. The female reproductive organs consist of the ovaries, the uter- ine tubes (or fallopian tubes), the uterus, the vagina, the external genitalia, and the mammary glands (see figure 19.1b). The internal reproductive organs of the female are located within the pelvis, between the urinary bladder and the rectum (figure 19.8). The uterus and the vagina are in the midline, with an ovary to each side of the uterus (figure 19.9). The internal reproductive organs are held in place within the pelvis by a group of ligaments. The most conspicuous is the broad ligament, which spreads out on both sides of the uterus and attaches to the ovaries and uterine tubes. ovaries The two ovaries (ō ′ vă -rē z; ovum, egg) are small organs suspended in the pelvic cavity by ligaments. The suspensory ligament extends from each ovary to the lateral body wall, and the ovarian ligament attaches the ovary to the superior margin of the uterus (figure 19.9). In addition, the ovaries are attached to the poste- rior surface of the broad ligament by folds of peritoneum called the mesovarium (mez′ ō -vā ′ rē -ŭ m). The ovarian arteries, veins, and nerves traverse the suspensory ligament and enter the ovary through the mesovarium. A layer of visceral peritoneum covers the surface of the ovary. The outer part of the ovary is composed of dense connective tissue and contains ovarian follicles (figure 19.10). Each of the ovarian complications. In other cases, ED can be due to defective stimula- tion of the erectile tissue by nerve fibers or reduced response of the blood vessels to neural stimulation. Some men can achieve erections by taking oral medications, such as sildenafil (Viagra), tadalafil (Cialis), or verdenafil (Livitra), or by having specific drugs injected into the base of the penis. These drugs increase blood flow into the erectile tissue of the penis, resulting in erection for many minutes. Before ejaculation, the ductus deferens begins to contract rhythmically, propelling sperm cells and testicular fluid from the epididymis through the ductus deferens. Contractions of the ductus deferens, seminal vesicles, and ejaculatory ducts cause the sperm cells, testicular secretions, and seminal fluid to move into the urethra, where they mix with prostatic secretions released by contraction of the prostate. Emission is stimulated by sympathetic action potentials that originate in the lumbar region of the spinal cord. Action potentials cause the reproductive ducts to contract and stimulate the seminal vesicles and the prostate gland to release secretions. Consequently, semen accumulates in the urethra. Ejaculation results from the contraction of smooth muscle in the wall of the urethra and skeletal muscles surrounding the base of the penis. Just before ejaculation, action potentials are sent to the skeletal muscles that surround the base of the penis. Rhythmic contractions are produced that force the semen out of the urethra, resulting in ejaculation. In addition, muscle tension increases throughout the body. infertility in males Infertility (in-fer-til′ i-tē ) is reduced or diminished fertility. The most common cause of infertility in males is a low sperm cell count. If the sperm cell count drops to below 20 million sperm cells per milliliter, the male is usually sterile. The sperm cell count can decrease because of damage to the testes as a result of trauma, radiation, cryptorchidism (See Clinical Impact “Descent of the Testes”), or infections, such as mumps, which block the ducts in the epididymis. Reduced sperm cell counts can also result from inadequate secretion of luteinizing hormone and follicle-stimulating hormone, which can be caused by hypothyroidism, trauma to the hypothalamus, infarctions of the hypothalamus or anterior pituitary gland, or tumors. Decreased testosterone secretion reduces the sperm cell count as well. Even when the sperm cell count is normal, fertility can be reduced if sperm cell structure is abnormal, as occurs due to chromo- somal abnormalities caused by genetic factors. Reduced sperm cell CLINICAL IMPACT Male Pattern Baldness some men have a genetic ten- dency called male pattern baldness, which develops in response to testosterone and other androgens. When testosterone levels increase at puberty, the density of hair on top of the head begins to decrease. Baldness usually reaches its maximum rate of development when the individual is in the third or fourth decade of life. minoxidil (mi-noks′si-dil; rogaine) is a drug that effec- tively prevents a decrease in hair growth in many men who exhibit male pattern bald- ness. it is most effective in those who are young and just starting to show evidence of baldness. minoxidil causes blood vessels to dilate, including those close to hair follicles, which may explain how it works. However, the mechanism has not been confirmed. 542 Chapter 19 Re pr od uc tiv e Medial view PosteriorAnterior Uterus Uterine tube Ovary Urinary bladder Urethra Clitoris Vaginal orifice Urethral orifice Labia minora Labia majora Vertebral column Cervix of uterus Rectum Vagina Pubic symphysis Mons pubis Figure 19.8 Female Pelvis the female reproductive tract, including the uterus, the vagina, and the surrounding pelvic structures, is shown in a medial view of the female pelvis. note that the female reproductive and urinary tracts open separately to the exterior. Figure 19.9 Female Reproductive Organs anterior view of the uterus, uterine tubes, and associated ligaments. the uterus and uterine tubes are cut in section (on the left side), and the vagina is cut to show the internal anatomy. the inset shows the relationships among the ovary, the uterine tube, and the ligaments that suspend them in the pelvic cavity. Fundus Uterine tube Mesovarium Ovary Broad ligament Broad ligament Fimbria Uterine cavity Ovary Ovarian ligament Round ligament Endometrium Myometrium (muscular layer) Broad ligament (cut) Perimetrium (serous layer) Cervical canal Opening of cervix Body Cervix Vagina (cut) Uterus Suspensory ligament Ampulla of uterine tube Uterine tube Anterior view reproductive system 545 Reproductive uterine tubes A uterine tube, also called a fallopian (fa-lō ′ pē -an) tube or oviduct (ō ′ vi-dŭ ct), is associated with each ovary. The uterine tubes extend from the area of the ovaries to the uterus. They open directly into the peritoneal cavity near each ovary and receive the secondary oocyte. The opening of each uterine tube is surrounded by long, thin processes called fimbriae (fim′ brē -ē ; fringes) (see figure 19.9). The fimbriae nearly surround the surface of the ovary. As a result, as soon as the secondary oocyte is ovulated, it comes into contact with the surface of the fimbriae. Cilia on the fimbriae surface sweep the oocyte into the uterine tube. Fertilization usu- ally occurs in the part of the uterine tube near the ovary, called the ampulla (am-pul′ lă ). The fertilized oocyte then travels to the uterus, where it embeds in the uterine wall in a process called implantation. uterus The uterus (ū ′ ter-ŭ s; womb) is as big as a medium-sized pear (see figures 19.8 and 19.9). It is oriented in the pelvic cavity with the larger, rounded part directed superiorly. The part of the uterus superior to the entrance of the uterine tubes is called the fundus (fŭ n′ dŭ s). The main part of the uterus is called the body, and the narrower part, the cervix (ser′ viks; neck), is directed inferiorly. Internally, the uterine cavity in the fundus and uterine body continues through the cervix as the cervical canal, which opens into the vagina. The cervical canal is lined by mucous glands. The uterine wall is composed of three layers: a serous layer, a muscular layer, and a layer of endometrium (see figure 19.9). The outer layer, called the perimetrium (per-i-mē ′ trē -ŭ m), or serous layer, of the uterus is formed from visceral peritoneum. The mid- dle layer, called the myometrium (mı̄ ′ ō -mē ′ trē -ŭ m), or muscular layer, consists of smooth muscle, is quite thick, and accounts for the bulk of the uterine wall. The innermost layer of the uterus is the endometrium (en′ dō -mē ′ trē -ŭ m), which consists of simple columnar epithelial cells with an underlying connective tissue layer. Simple tubular glands, called spiral glands, are formed by folds of the endometrium. The superficial part of the endometrium is sloughed off during menstruation. The uterus is supported by the broad ligament and the round ligament. In addition to these ligaments, much support is provided inferiorly to the uterus by skeletal muscles of the pelvic floor. If form a zygote (zı̄ ′ gō t) and complete fertilization. The zygote has 23 pairs of chromosomes (a total of 46 chromosomes). All cells of the human body contain 23 pairs of chromosomes, except for the male and female gametes. The zygote divides by mitosis to form 2 cells, which divide to form 4 cells, and so on. The mass of cells formed may eventually implant in, or attach to, the uterine wall and develop into a new individual (see chapter 20). Follicle Development As we discussed, when a female is in her mother’s uterus, her ovaries have already begun oocyte formation. The primary oocytes present at birth are surrounded by a primordial follicle. A primordial follicle is a primary oocyte surrounded by a single layer of flat cells, called granulosa cells (figure 19.11). Once puberty begins, some of the pri- mordial follicles are converted to primary follicles when the oocyte enlarges and the single layer of granulosa cells becomes enlarged and cuboidal. Subsequently, several layers of granulosa cells form, and a layer of clear material called the zona pellucida (zō ′ nă pel- lū ′ sid-dă ) is deposited around the primary oocyte. Approximately every 28 days, hormonal changes stimulate some of the primary follicles to continue to develop (figure 19.11). The primary follicle becomes a secondary follicle as fluid-filled spaces called vesicles form among the granulosa cells, and a cap- sule called the theca (thē ′ kă ; a box) forms around the follicle. The secondary follicle continues to enlarge, and when the fluid- filled vesicles fuse to form a single, fluid-filled chamber called the antrum (an′ trŭ m), the follicle is called the mature follicle, or graaf- ian (graf′ ē -ă n) follicle. The primary oocyte is pushed off to one side and lies in a mass of granulosa cells called the cumulus cells. The mature follicle forms a lump on the surface of the ovary. During ovulation, the mature follicle ruptures, forcing a small amount of blood, follicular fluid, and the secondary oocyte, surround- ed by the cumulus cells, into the peritoneal cavity. In most cases, only one of the follicles that begin to develop forms a mature follicle and undergoes ovulation. The other follicles degenerate. After ovu- lation, the remaining cells of the ruptured follicle are transformed into a glandular structure called the corpus luteum (kō r′ pŭ s, body; loo′ tē -ŭ m, yellow). If pregnancy occurs, the corpus luteum enlarges in response to a hormone secreted by the placenta called human chorionic gonadotropin hormone (hCG) (kō -rē -on′ ik gō ′ nad-o- trō ′ pin) (see table 19.1). If pregnancy does not occur, the corpus luteum lasts for 10–12 days and then begins to degenerate. CLINICAL IMPACT Cancer of the Cervix Cancer of the cervix is rela- tively common in women. in the united states, approximately 11,000 women are diagnosed with cervical cancer annually, and about 3700 women die from it each year. it has been estimated that 70% of all cases of cervical cancer can be linked to infection with 2 of the over 100 types of the human papillomavirus (Hpv, types 16 and 18). an immunization (Gardisil) has been developed that targets types 16 and 18, as well as 2 types (6 and 11) that are linked to 90% of genital warts cases. Fortunately, cervical cancer can be detected and treat- ed. a Pap smear is a diagnostic test to determine if a woman has cancer of the cervix. By inserting a swab through the vagina, a physician obtains a sample of epithelial cells from the area of the cervix and the wall of the vagina. these cells are smeared on a glass slide and later stained and examined microscopically for signs of cancer. early in the development of cervical cancer, the cells of the cervix change in a characteristic way. cells that are cancerous appear less mature than the characteristic epithelial cells of the cervix or vaginal wall. 546 Chapter 19 Re pr od uc tiv e ing structures (figure 19.12). The vestibule (ves′ ti-bool) is the space into which the vagina and urethra open. The urethra opens just anterior to the vagina. The vestibule is bordered by a pair of thin, longitudinal skin folds called the labia minora (lā′ bē-ă, lips; mı̄-nō′ ră, small). A small, erectile structure called the clitoris (klit′ ŏ-ris, klı̄′ tŏ-ris) is located in the anterior margin of the vesti- bule. The two labia minora unite over the clitoris to form a fold of skin called the prepuce. The clitoris (see figure 19.8) consists of a shaft and a dis- tal glans. Like the glans penis, the clitoris is well supplied with sensory receptors, and it is made up of erectile tissue. Additional erectile tissue is located on each side of the vaginal opening. On each side of the vestibule, between the vaginal opening and the labia minora, are openings of the greater vestibular glands. These glands produce a lubricating fluid that helps main- tain the moistness of the vestibule. Lateral to the labia minora are two prominent, rounded folds of skin called the labia majora (mă-jō′ ră; large). The two labia majora unite anteriorly at an elevation of tissue over the pubic symphysis called the mons pubis (monz pū′ bis) (figure 19.12). The lateral surfaces of the labia majora and the surface of the mons pubis are covered with coarse hair. The medial surfaces of the labia majora are covered with numerous sebaceous and sweat glands. The space between the labia majora is called the pudendal cleft. Most of the time, the labia majora are in contact with each other across the midline, closing the pudendal cleft and covering the deeper structures within the vestibule. The region between the vagina and the anus is the clinical perineum (per′ i-nē′ um; area between the thighs). The skin and muscle of this region can tear during childbirth. To prevent such tearing, an incision called an episiotomy (e-piz-ē-ot′ ō-mē) is sometimes made in the clinical perineum. Traditionally, this clean, straight incision has been thought to result in less injury, less trouble in healing, and less pain. However, many studies report less injury and pain when no episiotomy is performed. mammary Glands The mammary (mam′ ă-rē; relating to breasts) glands are the organs of milk production and are located in the breasts (fig- ure 19.13). The mammary glands are modified sweat glands. Externally, each of the breasts of both males and females has a raised nipple surrounded by a circular, pigmented area called the areola (ă-rē′ ō-lă). In prepubescent children, the general structure of the male and female breasts is similar, and both males and females possess a rudimentary duct system. The female breasts begin to enlarge during puberty, under the influence of estrogen and progesterone. Some males also experience a minor and temporary enlargement of the breasts at puberty. Occasionally, the breasts of a male can become permanently enlarged, a condition called gynecomastia (gı̄′ nĕ-kō-mas′ tē-ă). Causes of gynecomastia include hormonal imbalances and the abuse of anabolic steroids. Each adult female breast contains mammary glands con- sisting of usually 15–20 glandular lobes covered by adipose tissue (figure 19.13a,b). It is primarily this superficial adipose tissue that gives the breast its form. Each lobe possesses a single lactiferous duct that opens independently to the surface of the ligaments that support the uterus or muscles of the pelvic floor are weakened, as may occur due to childbirth, the uterus can extend inferiorly into the vagina, a condition called a prolapsed uterus. Severe cases require surgical correction. vagina The vagina (vă-jı̄′ nă) is the female organ of copulation; it receives the penis during intercourse. It also allows menstrual flow and childbirth. The vagina extends from the uterus to the outside of the body (see figures 19.8 and 19.9). The superior portion of the vagina is attached to the sides of the cervix, so that a part of the cervix extends into the vagina. The wall of the vagina consists of an outer muscular layer and an inner mucous membrane. The muscular layer is smooth muscle and contains many elastic fibers. Thus, the vagina can increase in size to accommodate the penis during intercourse, and it can stretch greatly during childbirth. The mucous membrane is moist stratified squamous epithelium that forms a protective surface layer. Lubricating fluid passes through the vaginal epithelium into the vagina. In young females, the vaginal opening is covered by a thin mucous membrane called the hymen (hı̄′ men; membrane). In rare cases, the hymen may completely close the vaginal orifice and it must be removed to allow menstrual flow. More commonly, the hymen is perforated by one or several holes. The openings in the hymen are usually greatly enlarged during the first sexual intercourse. The hymen can also be perforated or torn earlier in a young female’s life during a variety of activities, including strenu- ous exercise. The condition of the hymen is therefore an unreliable indicator of virginity. external Genitalia The external female genitalia, also called the vulva (vŭl′ vă) or pudendum (pū-den′ dŭm), consist of the vestibule and its surround- Prepuce Labia minora Vagina Vestibule Anus Pudendal cleft Mons pubis Clitoris Urethra Labia majora Clinical perineum Figure 19.12 Female External Genitalia reproductive system 547 Reproductive nipple. The duct of each lobe is formed as several smaller ducts, which originate from lobules, converge. Within a lobule, the ducts branch and become even smaller. In the milk-producing, or lactating, mammary gland, the ends of these small ducts expand to form secretory sacs called alveoli. Myoepithelial cells sur- round the alveoli and contract to expel milk from the alveoli (figure 19.13c). The breasts are supported by suspensory ligaments that extend from the fascia over the pectoralis major muscles to the skin over the breasts (figure 19.13b). The nipples are very sensitive to tactile stimulation and contain smooth muscle. When the smooth muscle contracts in response to stimuli, such as touch, cold, and sexual arousal, the nipple becomes erect. CLINICAL IMPACT Cancer of the Breast Cancer of the breast is a seri- ous, often fatal disease that most often occurs in women. regular self-examination of the breast can lead to early detection of breast cancer and effective treatment. in addition, mammography (ma-mog′ră fe) often allows tumors to be identified even before they can be detected by palpation. mammography uses low-intensity x-rays to detect tumors in the soft tissue of the breast. once a tumor is identified, a biopsy is nor- mally performed to determine whether the tumor is benign or malignant. most tumors of the mammary glands are benign, but those that are malignant can spread to other areas of the body and ultimately lead to death. Nipple (b) Nonlactating breast (c) Lactating breast Areola Lobule Lobe Adipose tissue Suspensory ligaments Rib Pectoralis major Fascia Lactiferous ducts Lactating Epithelium Epithelium Lobule Alveoli Alveoli Lobe Lactiferous duct Myoepithelial cell Nonlactating Figure 19.13 Anatomy of the Breast (a) each lactiferous duct of the mammary gland branches. at the end of each branch is one or more alveoli. (b) the nonlactating breast has a duct system that is not extensively developed. the branches of the lactiferous ducts end as small, tubelike structures. (c) the lactating breast has a well-developed duct system with many branches. the branches of the lactiferous duct end with well-developed alveoli. adipose tissue is abundant in both the nonlactating and the lactating breast. (a)