Male Reproductive System Discussion
Male Reproductive System Discussion
Male Reproductive System Discussion Male Reproductive System Discussion For this assignment you will be able to create an infographic or video presentation. Assignment Instructions: 1. Select one of the topics below. The Male Reproductive System, (Chapter 32, p. 793) 2. Explore the topic and gather the information needed to teach your fellow learners. 3. Please create these items using infographics ( Canva.com ) or video ( Powtoon.com ), see instructions below. If you would like to use a different media source, please email your instructor first for permission. ORDER NOW FOR CUSTOMIZED AND ORIGINAL NURSING PAPERS understanding_pathophysiolo Understanding Pathophysiology FIRST CANADIAN EDITION Mohamed Toufic El-Hussein, RN, PhD Associate Professor, School of Nursing Faculty of Health, Community & Education Mount Royal University Calgary, Alberta Kelly Power-Kean, MHS, NP, RN Center for Nursing Studies Memorial University St. Johns, Newfoundland Stephanie Zettel, BN, MN Associate Professor 2 School of Nursing and Midwifery Mount Royal University Calgary, Alberta U.S. AUTHORS Sue E. Huether, MS, PhD Professor Emeritus College of Nursing University of Utah Salt Lake City, Utah Kathryn L. McCance, MS, PhD Professor Emeritus College of Nursing University of Utah Salt Lake City, Utah U.S. Section Editors Valentina L. Brashers, MD Professor of Nursing and Woodard Clinical Scholar Attending Physician in Internal Medicine University of Virginia Health System Charlottesville, Virginia Neal S. Rote, PhD Academic Vice-Chair and Director of Research Department of Obstetrics and Gynecology University Hospitals Case Medical Center William H. Weir, MD, Professor of Reproductive Biology and Pathology Case Western Reserve University School of Medicine 3 Cleveland, Ohio 4 32 Structure and Function of the Reproductive Systems Afsoon Moktar, George W. Rodway, Sue E. Huether, Kelly Power-Kean CHAPTER OUTLINE Development of the Reproductive Systems, 793 Sexual Differentiation in Utero, 793 Puberty and Reproductive Maturation, 795 The Female Reproductive System, 796 External Genitalia, 796 Internal Genitalia, 798 Female Sex Hormones, 801 Menstrual Cycle, 802 Structure and Function of the Breast, 805 Female Breast, 805 Male Breast, 807 2378 The Male Reproductive System, 807 External Genitalia, 807 Internal Genitalia, 809 Spermatogenesis, 810 Male Sex and Reproductive Hormones, 810 Aging and Reproductive Function, 811 Aging and the Female Reproductive System, 811 Aging and the Male Reproductive System, 812 The male and female reproductive systems have several anatomical and physiological features in common. Most obvious is their major functionreproductionthrough which a 23-chromosome female gamete, the ovum, and a 23-chromosome male gamete, the spermatozoon (sperm cell), unite to form a 46-chromosome zygote that is capable of developing into a new individual. The male reproductive system produces sperm that can be transferred to the female reproductive tract. The female reproductive system produces the ovum (pl., ova), and if the ovum is fertilized it is then called the embryo and developing fetus. These functions are determined not only by anatomical structures but also by complex hormonal and neurological factors.1,2 Development of the Reproductive Systems 2379 The structure and function of both male and female reproductive systems depend on steroid hormones called sex hormones and their precursors. Cholesterol is the precursor for steroid hormones, including the sex hormones. Other hormones support reproduction. The actions of both sex and reproductive hormones are summarized in Table 32-1. Sex hormones, like all hormones, act on target tissues by binding with cellular receptors (see Chapter 18). NCSNSMT Male Reproductive System Discussion. Male Reproductive System Discussion Hormonal effects on the reproductive systems begin during embryonic development and continue in varying degrees throughout life. TABLE 32-1 Summary of Female and Male Sex and Reproductive Hormones Hormone (Source) Action in Females Action in Males Dehydroepiandrosterone (DHEA) (adrenal gland, ovary, other tissues) Estrogens (estrone, estradiol, estriol) function through estrogen receptors alpha and beta (ovary and placenta, small amounts in other tissues) Converted to androstenedione and then to estrogens, testosterone, or both Converted to androstenedione and then to estrogens, testosterone, or both Stimulates development of female sexual characteristics: maturation of breast, uterus, and vagina; promotes proliferative development of endometrium during menstrual cycle; during pregnancy promotes mammary gland development, fetal adrenal gland function, and uteroplacental blood flow (see Box 32-1) Contributes to libido, learning, sleep, protein anabolism, growth of muscle and bone; growth of pubic and axillary hair; activation of sebaceous glands, accounting for some cases of acne during puberty Growth at puberty, growth plate fusion in bone, prevention of apoptosis of germ cells Testosterone (adrenal glands from DHEA, ovaries) Gonadotropin-releasing hormone (GnRH) (hypothalamusneuroendocrine cells) Follicle-stimulating hormone (FSH) (anterior pituitary, gonadotroph cells) Luteinizing hormone (LH) (anterior pituitary, gonadotroph cells) Stimulates secretion of gonadotropins (FSH and LH) from anterior pituitary Gonadotropin; promotes development of ovarian follicle; stimulates estrogen secretion Gonadotropin; triggers ovulation; promotes development of corpus luteum 2380 Stimulates spermatogenesis, stimulates development of primary and secondary sexual characteristics, promotes growth of muscle and bone (anabolic effect); growth of pubic and axillary hair; activates sebaceous glands, accounting for some cases of acne during puberty; maintains libido Stimulates secretion of gonadotropins (FSH and LH) from anterior pituitary Gonadotropin; promotes development of testes and stimulates spermatogenesis by Sertoli cells Gonadotropin; stimulates testosterone production by Leydig cells of testis Inhibin (ovary and testes) Inhibits FSH production in anterior Inhibits FSH production in pituitary (perhaps by limiting anterior pituitary GnRH) Human chorionic Supports corpus luteum, which gonadotropin (hCG) secretes estrogen and progesterone (placenta) during first 7 weeks of pregnancy Activin (ovary) Stimulates secretion of FSH and pituitary response to GnRH and FSH binding in dominant granulosa cells Progesterone (ovary Promotes secretory changes in and placenta) endometrium during luteal phase of menstrual cycle; quiets uterine myometrium (muscle) activity and prevents lactogenesis during pregnancy Relaxin (corpus Inhibits uterine contractions during luteum, myometrium pregnancy and softens pelvic joints and placenta) and cervix to facilitate childbirth Sexual Differentiation in Utero Initially, in embryonic development, the reproductive structures of male and female embryos are homologous (the same) or undifferentiated. They consist of one pair of primary sex organs, or gonads, and two pairs of ductsthe mesonephric ducts (wolffian ducts) and the paramesonephric ducts (müllerian ducts) (Figure 321). The müllerian ducts are the precursor of the internal female sex organs (oviducts, uterus, cervix, and upper vagina). Müllerian ducts are initially formed regardless of genotypic sex and require no SRY signalling for development. SRY signalling is required in males to cause regression of the müllerian ducts, which in turn prevents the development of the female reproductive tract. The wolffian ducts are the precursor of male internal sex organs (secrete testosterone and promote development of the male sex organs). 2381 FIGURE 32-1 Internal Genitalia Development. Embryonic and fetal development of the internal genitalia. MIF, Müllerian inhibitory factor; SRY, sex-determining region on the Y chromosome (it produces TDF); TDF, testes-determining factor; see text for additional details. NCSNSMT Male Reproductive System Discussion The first sign of development of reproductive organs (male or female) occurs during the fifth week of gestation. Between 6 to 8 weeks of gestation, the male embryo will differentiate under the influence of testes-determining factor (TDF), a protein expressed by a gene in the sex-determining region on the Y chromosome (SRY). When the SRY gene is expressed, male gonadal development prevails. TDF stimulates the male gonads to develop into the two testes, and between 8 to 9 weeks gestation testosterone secretion begins. Müllerian inhibitory hormone (MIF), secreted by Sertoli cells in the testes, promotes degeneration of the müllerian ducts. Without MIF, the müllerian ducts would develop and the wolffian ducts would degenerate with loss of male sex organ development. By 9 months gestation, the male gonads (testes) have descended into the scrotum. The testes produce sperm after puberty. 2382 Female gonadal development occurs in the absence of SRY expression and with the expression of other genes.3 The presence of estrogen and the absence of testosterone and MIF cause a loss in the wolffian system, and at 6 to 8 weeks gestation the two female gonads develop into ovaries, which will produce ova. In females, the mesonephric ducts deteriorate and the upper ends of paramesonephric ducts become the fallopian tubules, whereas the lower ends join to become the uterus, cervix, and upper two-thirds of the vagina (see Figure 32-1). The fallopian tubes will carry ova from the ovaries to the uterus during a womans reproductive years. Lack of testosterone and the presence of estrogen promote the development of external genitalia (lower end of vagina, labia, and clitoris). Like the internal reproductive structures, the external structures develop from homologous embryonic tissues. During the first 7 to 8 weeks gestation, both male and female embryos develop an elevated structure called the genital tubercle (Figure 32-2). Testosterone is necessary for the genital tubercle to differentiate into external male genitalia; otherwise, female genitalia develop, which may occur even in the absence of ovaries, possibly because of the presence of placental estrogens. 2383 FIGURE 32-2 External Genitalia Development. NCSNSMT Male Reproductive System Discussion. Male Reproductive System Discussion Embryonic and fetal development of the external genitalia. Anterior pituitary development begins between the fourth and 2384 fifth weeks of fetal life, and the vascular connection between the hypothalamus and the pituitary is established by the twelfth week. Gonadotropin-releasing hormone (GnRH) is produced in the hypothalamus by 10 weeks gestation and controls the production of two gonadotropins, luteinizing hormone (LH) and folliclestimulating hormone (FSH), by the anterior pituitary gland. In the female fetus, high levels of FSH and LH are excreted. FSH and LH stimulate the production of estrogen and progesterone by the ovary. The production of FSH and LH increases until about 28 weeks gestation, when the production of estrogen and progesterone by the ovaries and placenta is high enough to result in the decline of gonadotropin production.4 Production of primitive female gametes (ova) occurs solely during fetal life. From puberty to menopause, one female gamete matures per menstrual cycle. Production of the male gametes (sperm) begins at puberty; after that, millions are produced daily, usually for life. By the end of pregnancy, a sensitive negative feedback system, which includes the gonadostat (also known as the gonadotropinreleasing hormone pulse generator), is operative in the human fetus. The gonadostat responds to high levels of placental estrogens by releasing low levels of GnRH. Soon after birth, steroid hormone levels drop because of the loss of maternal placental hormones. Hypothalamic pulsatile GnRH is secreted and gonadotropins LH and FSH are released; their levels peak at 3 to 6 months for boys and at 12 to 18 months for girls and then fall steadily. The gonadotropins will be suppressed until the onset of puberty. Puberty and Reproductive Maturation Puberty is the onset of sexual maturation and differs from adolescence. Adolescence is the stage of human development between childhood and adulthood and includes social, psychological, and biological changes. In girls, puberty begins at about age 8 to 9 years with thelarche (breast development). In boys, puberty begins laterat about age 11 years and occurs earlier with increased weight and body mass index.5 Genetics, environment, ethnicity, general health, and nutrition can influence the timing of puberty. There is an association between obesity and earlier puberty in girls perhaps from higher estrogen levels related to 2385 leptin, gonadotropin, and estrogen secretion.6 Girls who have low body fat and reduced body weight and perform intense exercise may experience delayed maturation.7 Reproductive maturation involves the hypothalamic-pituitarygonadal axis, the central nervous system, and the endocrine system (Figure 32-3). There is a sequential series of hormonal events that promote sexual maturation as puberty approaches. About 1 year before puberty in girls, nocturnal pulses of gonadotropin secretion (i.e., LH and FSH) and an increased response in the pituitary to GnRH occur. This gonadotropin secretion and increased pituitary response, in turn, stimulates gonadal maturation (gonadarche) with estradiol secretion in girls and testosterone secretion in boys. Estradiol causes development of the breasts (thelarche), maturation of the reproductive organs (vagina, uterus, ovaries), and deposition of fat in the females hips. Estrogen and increased production of growth factors cause rapid skeletal growth in both boys and girls.NCSNSMT Male Reproductive System Discussion Testosterone causes growth of the testes, scrotum, and penis. A positive feedback loop is created with gonadotropins stimulating the gonads to produce more sex hormones. The most important hormonal effects occur in the gonads. In males, the testes begin to produce mature sperm that are capable of fertilizing an ovum. Male puberty is complete with the first ejaculation that contains mature sperm. In females, the ovaries begin to release mature ova. Female puberty is complete at the time of the first ovulatory menstrual period; however, puberty can take up to 1 to 2 years to complete after menarche. Adrenarche is the increased production of adrenal androgens (dehydroepiandrosterone [DHEA] and androstenedione, which are converted to testosterone and estrogen) before puberty, which occurs in both sexes and is manifested by growth of axillary and pubic hair and activation of sweat and sebaceous glands. Puberty is complete when an individual is capable of reproduction. 2386 FIGURE 32-3 Hormonal Stimulation of the Gonads. The hypothalamicpituitary-gonadal axis. Quick Check 32-1 1. When do sex hormones first exhibit an effect on sexual development? 2. Why are sex hormones necessary for reproduction? The Female Reproductive System 2387 The function of the female reproductive system is to produce mature ova; if fertilization occurs, the female reproductive system provides protection and nourishment of the fetus until it is expelled at birth. The most important internal reproductive organs in females are the ovaries, fallopian tubes, uterus, and vagina. The external genitalia protect body openings and play an important role in sexual functioning. External Genitalia Figure 32-4 shows the external female genitalia, known collectively as the vulva, or pudendum. The major structures are as follows: FIGURE 32-4 External Female Genitalia. Mons pubis: Fatty layer of tissue over pubic symphysis (joint formed by union of the pubic bones). During puberty it becomes covered with pubic hair, and sebaceous and sweat glands become more active. Estrogen causes fat to be deposited under the skin, gives the mons pubis a moundlike shape, and protects the pubic symphysis during sexual 2388 intercourse. Labia majora (sing., labium majus): Two folds of skin arising at the mons pubis and extending back to the fourchette, forming a cleft. During puberty the amount of fatty tissue increases, pubic hair grows on lateral surfaces, and sebaceous glands on hairless medial surfaces secrete lubricants. This structure is highly sensitive to temperature, touch, pressure, and pain; it is homologous to the male scrotum; and it protects the inner structures of the vulva. Labia minora (sing., labium minus): Two smaller, thinner, asymmetrical folds of skin within the labia majora that form the clitoral hood (prepuce) and frenulum, then split to enclose the vestibule, and converge near the anus to form the fourchette. The labia minora are hairless, pink, and moist; they are well supplied by nerves, blood vessels, and sebaceous glands that secrete bactericidal fluid with a distinctive odour that lubricates and waterproofs vulvar skin. The labia swell with blood during sexual arousal. Clitoris: Richly innervated erectile organ between the labia minora.NCSNSMT Male Reproductive System Discussion. Male Reproductive System Discussion It is a small, cylindrical structure having a visible glans and a shaft that lies beneath the skin; the clitoris is homologous to the penis. It secretes smegma, which has a unique odour that may be sexually arousing to the male. Like the penis, the clitoris is a major site of sexual stimulation and orgasm. With sexual arousal, erectile tissue fills with blood, causing the clitoris to enlarge slightly. Vestibule: An area protected by the labia minora that contains the external opening of the vagina, called the introitus or vaginal orifice. A thin, perforated membrane, the hymen, may cover the introitus. The vestibule also contains the opening of the urethra, or urinary meatus (orifice). These structures are lubricated by two pairs of glands: Skene glands and Bartholin glands. The ducts of the Skene glands (also called the lesser vestibular or paraurethral glands) open on both sides of the urinary meatus. The ducts of the Bartholin glands (greater vestibular or vulvovaginal glands) open on either side of the introitus. In response to sexual stimulation, Bartholin glands secrete mucus that lubricates the inner labial surfaces, as well as enhances the viability and motility of sperm. Skene 2389 glands help lubricate the urinary meatus and the vestibule. Secretions from both sets of glands facilitate coitus. In response to sexual excitement, the highly vascular tissue just beneath the vestibule also fills with blood and becomes engorged. Perineum: An area with less hair, skin, and subcutaneous tissue lying between the vaginal orifice and anus. Unlike the rest of the vulva, this area has little subcutaneous fat so the skin is close to the underlying muscles. The perineum covers the muscular perineal body, a fibrous structure that consists of elastic fibres and connective tissue and serves as the common attachment for the bulbocavernosus, external anal sphincter, and levator ani muscles. The perineum varies in length from 2 to 5 cm or more and has elastic properties. The length of the perineum and the elasticity of the perineal body influence tissue resistance and injury during childbirth. Internal Genitalia Vagina The vagina is an elastic, fibromuscular canal that is 9 to 10 cm long in a reproductive-age female. It extends up and back from the introitus to the lower portion of the uterus. As Figure 32-5 shows, the vagina lies between the urethra (and part of the bladder) and the rectum. Mucosal secretions from the upper genital organs, menstrual fluids, and products of conception leave the body through the vagina, which also receives the penis during coitus. During sexual excitement, the vagina lengthens and widens and the anterior third becomes congested with blood. 2390 FIGURE 32-5 Internal Female Genitalia and Other Pelvic Organs. (From Ball, J.W., Dains, J.E., Flynn, J.A., et al. [2015]. Seidels guide to physical examination [8th ed.]. St. Louis: Mosby.) The vaginal wall is composed of four layers: 1. Mucous membrane lining of squamous epithelial cells that thickens and thins in response to hormones, particularly estrogen. The squamous epithelial membrane is continuous with the membrane that covers the lower part of the uterus. In women of reproductive age, the mucosal layer is arranged in transverse wrinkles, or folds, called rugae (sing., ruga) that permit stretching during coitus and childbirth 2. Fibrous connective tissue containing numerous blood and lymphatic vessels 3. Smooth muscle 4. Connective tissue and a rich network of blood vessels The upper part of the vagina surrounds the cervix, the lower end 2391 of the uterus (see Figure 32-5). The recessed space around the cervix is called the fornix of the vagina. The posterior fornix is deep Male Reproductive System Discussion Get a 10 % discount on an order above $ 100 Use the following coupon code : NURSING10
Male Reproductive System Discussion
Male Reproductive System Discussion Male Reproductive System Discussion For this assignment you will be able to create an infographic or video presentation. Assignment Instructions: 1. Select one of the topics below. The Male Reproductive System, (Chapter 32, p. 793) 2. Explore the topic and gather the information needed to teach your fellow learners. 3. Please create these items using infographics ( Canva.com ) or video ( Powtoon.com ), see instructions below. If you would like to use a different media source, please email your instructor first for permission. ORDER NOW FOR CUSTOMIZED AND ORIGINAL NURSING PAPERS understanding_pathophysiolo Understanding Pathophysiology FIRST CANADIAN EDITION Mohamed Toufic El-Hussein, RN, PhD Associate Professor, School of Nursing Faculty of Health, Community & Education Mount Royal University Calgary, Alberta Kelly Power-Kean, MHS, NP, RN Center for Nursing Studies Memorial University St. Johns, Newfoundland Stephanie Zettel, BN, MN Associate Professor 2 School of Nursing and Midwifery Mount Royal University Calgary, Alberta U.S. AUTHORS Sue E. Huether, MS, PhD Professor Emeritus College of Nursing University of Utah Salt Lake City, Utah Kathryn L. McCance, MS, PhD Professor Emeritus College of Nursing University of Utah Salt Lake City, Utah U.S. Section Editors Valentina L. Brashers, MD Professor of Nursing and Woodard Clinical Scholar Attending Physician in Internal Medicine University of Virginia Health System Charlottesville, Virginia Neal S. Rote, PhD Academic Vice-Chair and Director of Research Department of Obstetrics and Gynecology University Hospitals Case Medical Center William H. Weir, MD, Professor of Reproductive Biology and Pathology Case Western Reserve University School of Medicine 3 Cleveland, Ohio 4 32 Structure and Function of the Reproductive Systems Afsoon Moktar, George W. Rodway, Sue E. Huether, Kelly Power-Kean CHAPTER OUTLINE Development of the Reproductive Systems, 793 Sexual Differentiation in Utero, 793 Puberty and Reproductive Maturation, 795 The Female Reproductive System, 796 External Genitalia, 796 Internal Genitalia, 798 Female Sex Hormones, 801 Menstrual Cycle, 802 Structure and Function of the Breast, 805 Female Breast, 805 Male Breast, 807 2378 The Male Reproductive System, 807 External Genitalia, 807 Internal Genitalia, 809 Spermatogenesis, 810 Male Sex and Reproductive Hormones, 810 Aging and Reproductive Function, 811 Aging and the Female Reproductive System, 811 Aging and the Male Reproductive System, 812 The male and female reproductive systems have several anatomical and physiological features in common. Most obvious is their major functionreproductionthrough which a 23-chromosome female gamete, the ovum, and a 23-chromosome male gamete, the spermatozoon (sperm cell), unite to form a 46-chromosome zygote that is capable of developing into a new individual. The male reproductive system produces sperm that can be transferred to the female reproductive tract. The female reproductive system produces the ovum (pl., ova), and if the ovum is fertilized it is then called the embryo and developing fetus. These functions are determined not only by anatomical structures but also by complex hormonal and neurological factors.1,2 Development of the Reproductive Systems 2379 The structure and function of both male and female reproductive systems depend on steroid hormones called sex hormones and their precursors. Cholesterol is the precursor for steroid hormones, including the sex hormones. Other hormones support reproduction. The actions of both sex and reproductive hormones are summarized in Table 32-1. Sex hormones, like all hormones, act on target tissues by binding with cellular receptors (see Chapter 18). NCSNSMT Male Reproductive System Discussion. Male Reproductive System Discussion Hormonal effects on the reproductive systems begin during embryonic development and continue in varying degrees throughout life. TABLE 32-1 Summary of Female and Male Sex and Reproductive Hormones Hormone (Source) Action in Females Action in Males Dehydroepiandrosterone (DHEA) (adrenal gland, ovary, other tissues) Estrogens (estrone, estradiol, estriol) function through estrogen receptors alpha and beta (ovary and placenta, small amounts in other tissues) Converted to androstenedione and then to estrogens, testosterone, or both Converted to androstenedione and then to estrogens, testosterone, or both Stimulates development of female sexual characteristics: maturation of breast, uterus, and vagina; promotes proliferative development of endometrium during menstrual cycle; during pregnancy promotes mammary gland development, fetal adrenal gland function, and uteroplacental blood flow (see Box 32-1) Contributes to libido, learning, sleep, protein anabolism, growth of muscle and bone; growth of pubic and axillary hair; activation of sebaceous glands, accounting for some cases of acne during puberty Growth at puberty, growth plate fusion in bone, prevention of apoptosis of germ cells Testosterone (adrenal glands from DHEA, ovaries) Gonadotropin-releasing hormone (GnRH) (hypothalamusneuroendocrine cells) Follicle-stimulating hormone (FSH) (anterior pituitary, gonadotroph cells) Luteinizing hormone (LH) (anterior pituitary, gonadotroph cells) Stimulates secretion of gonadotropins (FSH and LH) from anterior pituitary Gonadotropin; promotes development of ovarian follicle; stimulates estrogen secretion Gonadotropin; triggers ovulation; promotes development of corpus luteum 2380 Stimulates spermatogenesis, stimulates development of primary and secondary sexual characteristics, promotes growth of muscle and bone (anabolic effect); growth of pubic and axillary hair; activates sebaceous glands, accounting for some cases of acne during puberty; maintains libido Stimulates secretion of gonadotropins (FSH and LH) from anterior pituitary Gonadotropin; promotes development of testes and stimulates spermatogenesis by Sertoli cells Gonadotropin; stimulates testosterone production by Leydig cells of testis Inhibin (ovary and testes) Inhibits FSH production in anterior Inhibits FSH production in pituitary (perhaps by limiting anterior pituitary GnRH) Human chorionic Supports corpus luteum, which gonadotropin (hCG) secretes estrogen and progesterone (placenta) during first 7 weeks of pregnancy Activin (ovary) Stimulates secretion of FSH and pituitary response to GnRH and FSH binding in dominant granulosa cells Progesterone (ovary Promotes secretory changes in and placenta) endometrium during luteal phase of menstrual cycle; quiets uterine myometrium (muscle) activity and prevents lactogenesis during pregnancy Relaxin (corpus Inhibits uterine contractions during luteum, myometrium pregnancy and softens pelvic joints and placenta) and cervix to facilitate childbirth Sexual Differentiation in Utero Initially, in embryonic development, the reproductive structures of male and female embryos are homologous (the same) or undifferentiated. They consist of one pair of primary sex organs, or gonads, and two pairs of ductsthe mesonephric ducts (wolffian ducts) and the paramesonephric ducts (müllerian ducts) (Figure 321). The müllerian ducts are the precursor of the internal female sex organs (oviducts, uterus, cervix, and upper vagina). Müllerian ducts are initially formed regardless of genotypic sex and require no SRY signalling for development. SRY signalling is required in males to cause regression of the müllerian ducts, which in turn prevents the development of the female reproductive tract. The wolffian ducts are the precursor of male internal sex organs (secrete testosterone and promote development of the male sex organs). 2381 FIGURE 32-1 Internal Genitalia Development. Embryonic and fetal development of the internal genitalia. MIF, Müllerian inhibitory factor; SRY, sex-determining region on the Y chromosome (it produces TDF); TDF, testes-determining factor; see text for additional details. NCSNSMT Male Reproductive System Discussion The first sign of development of reproductive organs (male or female) occurs during the fifth week of gestation. Between 6 to 8 weeks of gestation, the male embryo will differentiate under the influence of testes-determining factor (TDF), a protein expressed by a gene in the sex-determining region on the Y chromosome (SRY). When the SRY gene is expressed, male gonadal development prevails. TDF stimulates the male gonads to develop into the two testes, and between 8 to 9 weeks gestation testosterone secretion begins. Müllerian inhibitory hormone (MIF), secreted by Sertoli cells in the testes, promotes degeneration of the müllerian ducts. Without MIF, the müllerian ducts would develop and the wolffian ducts would degenerate with loss of male sex organ development. By 9 months gestation, the male gonads (testes) have descended into the scrotum. The testes produce sperm after puberty. 2382 Female gonadal development occurs in the absence of SRY expression and with the expression of other genes.3 The presence of estrogen and the absence of testosterone and MIF cause a loss in the wolffian system, and at 6 to 8 weeks gestation the two female gonads develop into ovaries, which will produce ova. In females, the mesonephric ducts deteriorate and the upper ends of paramesonephric ducts become the fallopian tubules, whereas the lower ends join to become the uterus, cervix, and upper two-thirds of the vagina (see Figure 32-1). The fallopian tubes will carry ova from the ovaries to the uterus during a womans reproductive years. Lack of testosterone and the presence of estrogen promote the development of external genitalia (lower end of vagina, labia, and clitoris). Like the internal reproductive structures, the external structures develop from homologous embryonic tissues. During the first 7 to 8 weeks gestation, both male and female embryos develop an elevated structure called the genital tubercle (Figure 32-2). Testosterone is necessary for the genital tubercle to differentiate into external male genitalia; otherwise, female genitalia develop, which may occur even in the absence of ovaries, possibly because of the presence of placental estrogens. 2383 FIGURE 32-2 External Genitalia Development. NCSNSMT Male Reproductive System Discussion. Male Reproductive System Discussion Embryonic and fetal development of the external genitalia. Anterior pituitary development begins between the fourth and 2384 fifth weeks of fetal life, and the vascular connection between the hypothalamus and the pituitary is established by the twelfth week. Gonadotropin-releasing hormone (GnRH) is produced in the hypothalamus by 10 weeks gestation and controls the production of two gonadotropins, luteinizing hormone (LH) and folliclestimulating hormone (FSH), by the anterior pituitary gland. In the female fetus, high levels of FSH and LH are excreted. FSH and LH stimulate the production of estrogen and progesterone by the ovary. The production of FSH and LH increases until about 28 weeks gestation, when the production of estrogen and progesterone by the ovaries and placenta is high enough to result in the decline of gonadotropin production.4 Production of primitive female gametes (ova) occurs solely during fetal life. From puberty to menopause, one female gamete matures per menstrual cycle. Production of the male gametes (sperm) begins at puberty; after that, millions are produced daily, usually for life. By the end of pregnancy, a sensitive negative feedback system, which includes the gonadostat (also known as the gonadotropinreleasing hormone pulse generator), is operative in the human fetus. The gonadostat responds to high levels of placental estrogens by releasing low levels of GnRH. Soon after birth, steroid hormone levels drop because of the loss of maternal placental hormones. Hypothalamic pulsatile GnRH is secreted and gonadotropins LH and FSH are released; their levels peak at 3 to 6 months for boys and at 12 to 18 months for girls and then fall steadily. The gonadotropins will be suppressed until the onset of puberty. Puberty and Reproductive Maturation Puberty is the onset of sexual maturation and differs from adolescence. Adolescence is the stage of human development between childhood and adulthood and includes social, psychological, and biological changes. In girls, puberty begins at about age 8 to 9 years with thelarche (breast development). In boys, puberty begins laterat about age 11 years and occurs earlier with increased weight and body mass index.5 Genetics, environment, ethnicity, general health, and nutrition can influence the timing of puberty. There is an association between obesity and earlier puberty in girls perhaps from higher estrogen levels related to 2385 leptin, gonadotropin, and estrogen secretion.6 Girls who have low body fat and reduced body weight and perform intense exercise may experience delayed maturation.7 Reproductive maturation involves the hypothalamic-pituitarygonadal axis, the central nervous system, and the endocrine system (Figure 32-3). There is a sequential series of hormonal events that promote sexual maturation as puberty approaches. About 1 year before puberty in girls, nocturnal pulses of gonadotropin secretion (i.e., LH and FSH) and an increased response in the pituitary to GnRH occur. This gonadotropin secretion and increased pituitary response, in turn, stimulates gonadal maturation (gonadarche) with estradiol secretion in girls and testosterone secretion in boys. Estradiol causes development of the breasts (thelarche), maturation of the reproductive organs (vagina, uterus, ovaries), and deposition of fat in the females hips. Estrogen and increased production of growth factors cause rapid skeletal growth in both boys and girls.NCSNSMT Male Reproductive System Discussion Testosterone causes growth of the testes, scrotum, and penis. A positive feedback loop is created with gonadotropins stimulating the gonads to produce more sex hormones. The most important hormonal effects occur in the gonads. In males, the testes begin to produce mature sperm that are capable of fertilizing an ovum. Male puberty is complete with the first ejaculation that contains mature sperm. In females, the ovaries begin to release mature ova. Female puberty is complete at the time of the first ovulatory menstrual period; however, puberty can take up to 1 to 2 years to complete after menarche. Adrenarche is the increased production of adrenal androgens (dehydroepiandrosterone [DHEA] and androstenedione, which are converted to testosterone and estrogen) before puberty, which occurs in both sexes and is manifested by growth of axillary and pubic hair and activation of sweat and sebaceous glands. Puberty is complete when an individual is capable of reproduction. 2386 FIGURE 32-3 Hormonal Stimulation of the Gonads. The hypothalamicpituitary-gonadal axis. Quick Check 32-1 1. When do sex hormones first exhibit an effect on sexual development? 2. Why are sex hormones necessary for reproduction? The Female Reproductive System 2387 The function of the female reproductive system is to produce mature ova; if fertilization occurs, the female reproductive system provides protection and nourishment of the fetus until it is expelled at birth. The most important internal reproductive organs in females are the ovaries, fallopian tubes, uterus, and vagina. The external genitalia protect body openings and play an important role in sexual functioning. External Genitalia Figure 32-4 shows the external female genitalia, known collectively as the vulva, or pudendum. The major structures are as follows: FIGURE 32-4 External Female Genitalia. Mons pubis: Fatty layer of tissue over pubic symphysis (joint formed by union of the pubic bones). During puberty it becomes covered with pubic hair, and sebaceous and sweat glands become more active. Estrogen causes fat to be deposited under the skin, gives the mons pubis a moundlike shape, and protects the pubic symphysis during sexual 2388 intercourse. Labia majora (sing., labium majus): Two folds of skin arising at the mons pubis and extending back to the fourchette, forming a cleft. During puberty the amount of fatty tissue increases, pubic hair grows on lateral surfaces, and sebaceous glands on hairless medial surfaces secrete lubricants. This structure is highly sensitive to temperature, touch, pressure, and pain; it is homologous to the male scrotum; and it protects the inner structures of the vulva. Labia minora (sing., labium minus): Two smaller, thinner, asymmetrical folds of skin within the labia majora that form the clitoral hood (prepuce) and frenulum, then split to enclose the vestibule, and converge near the anus to form the fourchette. The labia minora are hairless, pink, and moist; they are well supplied by nerves, blood vessels, and sebaceous glands that secrete bactericidal fluid with a distinctive odour that lubricates and waterproofs vulvar skin. The labia swell with blood during sexual arousal. Clitoris: Richly innervated erectile organ between the labia minora.NCSNSMT Male Reproductive System Discussion. Male Reproductive System Discussion It is a small, cylindrical structure having a visible glans and a shaft that lies beneath the skin; the clitoris is homologous to the penis. It secretes smegma, which has a unique odour that may be sexually arousing to the male. Like the penis, the clitoris is a major site of sexual stimulation and orgasm. With sexual arousal, erectile tissue fills with blood, causing the clitoris to enlarge slightly. Vestibule: An area protected by the labia minora that contains the external opening of the vagina, called the introitus or vaginal orifice. A thin, perforated membrane, the hymen, may cover the introitus. The vestibule also contains the opening of the urethra, or urinary meatus (orifice). These structures are lubricated by two pairs of glands: Skene glands and Bartholin glands. The ducts of the Skene glands (also called the lesser vestibular or paraurethral glands) open on both sides of the urinary meatus. The ducts of the Bartholin glands (greater vestibular or vulvovaginal glands) open on either side of the introitus. In response to sexual stimulation, Bartholin glands secrete mucus that lubricates the inner labial surfaces, as well as enhances the viability and motility of sperm. Skene 2389 glands help lubricate the urinary meatus and the vestibule. Secretions from both sets of glands facilitate coitus. In response to sexual excitement, the highly vascular tissue just beneath the vestibule also fills with blood and becomes engorged. Perineum: An area with less hair, skin, and subcutaneous tissue lying between the vaginal orifice and anus. Unlike the rest of the vulva, this area has little subcutaneous fat so the skin is close to the underlying muscles. The perineum covers the muscular perineal body, a fibrous structure that consists of elastic fibres and connective tissue and serves as the common attachment for the bulbocavernosus, external anal sphincter, and levator ani muscles. The perineum varies in length from 2 to 5 cm or more and has elastic properties. The length of the perineum and the elasticity of the perineal body influence tissue resistance and injury during childbirth. Internal Genitalia Vagina The vagina is an elastic, fibromuscular canal that is 9 to 10 cm long in a reproductive-age female. It extends up and back from the introitus to the lower portion of the uterus. As Figure 32-5 shows, the vagina lies between the urethra (and part of the bladder) and the rectum. Mucosal secretions from the upper genital organs, menstrual fluids, and products of conception leave the body through the vagina, which also receives the penis during coitus. During sexual excitement, the vagina lengthens and widens and the anterior third becomes congested with blood. 2390 FIGURE 32-5 Internal Female Genitalia and Other Pelvic Organs. (From Ball, J.W., Dains, J.E., Flynn, J.A., et al. [2015]. Seidels guide to physical examination [8th ed.]. St. Louis: Mosby.) The vaginal wall is composed of four layers: 1. Mucous membrane lining of squamous epithelial cells that thickens and thins in response to hormones, particularly estrogen. The squamous epithelial membrane is continuous with the membrane that covers the lower part of the uterus. In women of reproductive age, the mucosal layer is arranged in transverse wrinkles, or folds, called rugae (sing., ruga) that permit stretching during coitus and childbirth 2. Fibrous connective tissue containing numerous blood and lymphatic vessels 3. Smooth muscle 4. Connective tissue and a rich network of blood vessels The upper part of the vagina surrounds the cervix, the lower end 2391 of the uterus (see Figure 32-5). The recessed space around the cervix is called the fornix of the vagina. The posterior fornix is deep Male Reproductive System Discussion Get a 10 % discount on an order above $ 100 Use the following coupon code : NURSING10
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