{"id":1013,"date":"2015-05-19T22:34:14","date_gmt":"2015-05-19T22:34:14","guid":{"rendered":"https:\/\/courses.candelalearning.com\/ap2x2master\/?post_type=chapter&#038;p=1013"},"modified":"2017-08-11T15:55:05","modified_gmt":"2017-08-11T15:55:05","slug":"development-of-the-male-and-female-reproductive-systems","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/nemcc-ap2\/chapter\/development-of-the-male-and-female-reproductive-systems\/","title":{"raw":"Development of the Male and Female Reproductive Systems","rendered":"Development of the Male and Female Reproductive Systems"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\nBy the end of this section, you will be able to:\r\n<ul>\r\n \t<li>Explain how bipotential tissues are directed to develop into male or female sex organs<\/li>\r\n \t<li>Name the rudimentary duct systems in the embryo that are precursors to male or female internal sex organs<\/li>\r\n \t<li>Describe the hormonal changes that bring about puberty, and the secondary sex characteristics of men and women<\/li>\r\n<\/ul>\r\n<\/div>\r\nThe development of the reproductive systems begins soon after fertilization of the egg, with primordial gonads beginning to develop approximately one month after conception. Reproductive development continues in utero, but there is little change in the reproductive system between infancy and puberty.\r\n\r\n&nbsp;\r\n\r\n<strong>FEMALE REPRODUCTIVE SYSTEM<\/strong>\r\n<ul>\r\n \t<li>Ovary \u2013 composed of numerous sac-like ovarian follicles<\/li>\r\n \t<li>Oogenesis <strong>\u2013 <\/strong>process of producing ova\/eggs (female gamete)<\/li>\r\n<\/ul>\r\n&nbsp;\r\n\r\nStages of egg development \u2013 takes about 28 days\r\n\r\n&nbsp;\r\n<ol>\r\n \t<li>Oogonia \u2013 stem cells of the ovaries that will transform into primary oocytes; the oogonia are surrounded by a thin layer of cells called the primordial follicle<\/li>\r\n \t<li>Primary follicle \u2013 contains the primary oocyte that will develop into a mature egg; a lifetime supply of primary oocytes is present from birth (around 2 million); they are inactive until puberty; in response to the monthly secretion of FSH, 1 is stimulated to develop each month<\/li>\r\n \t<li>Secondary follicle \u2013 during development fluid filled space appears between the inner and outer follicle cell<\/li>\r\n \t<li>Mature follicle \u2013 fluid filled follicle that contains the mature egg<\/li>\r\n<\/ol>\r\n<ul>\r\n \t<li>A surge of LH stimulates the completion of Meiosis I of the primary oocyte. It is an uneven division of the cytoplasm. This uneven division result in 1 large ooctye and 1 smaller, nonfunctional structure called a polar body.<\/li>\r\n<\/ul>\r\n<ol start=\"5\">\r\n \t<li>Ovulation \u2013 rupturing of the follicle to release the egg; stimulated by high level of LH<\/li>\r\n<\/ol>\r\n&nbsp;\r\n<ul>\r\n \t<li>When the oocyte is released during ovulation, it is now known as the secondary oocyte. Meiosis II only occurs if the egg is penetrated by a sperm. Meiosis II is the second division of the oocyte and it forms another polar body and the ovum \u2013 egg cell. The fusion of the nuclei of the egg and sperm forms a zygote \u2013 the first cell of an embryo.<\/li>\r\n<\/ul>\r\n<ol start=\"6\">\r\n \t<li>Corpus luteum \u2013 ruptured follicle; it slowly degenerates and the cycle starts over<\/li>\r\n<\/ol>\r\n<strong>\u00a0<\/strong><strong>\u00a0<\/strong>\r\n\r\nUterine Tube (Fallopian Tube) \u2013 receives the secondary oocyte, provides the site for fertilization\r\n\r\n<strong>\u00a0<\/strong>\r\n<ul>\r\n \t<li style=\"list-style-type: none\">\r\n<ul>\r\n \t<li>Infundibulum \u2013 end of each uterine tube that connects to the ovaries<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ul>\r\n&nbsp;\r\n<ul>\r\n \t<li style=\"list-style-type: none\">\r\n<ul>\r\n \t<li>Fimbriae \u2013 fingerlike projections of the infundibulum that surrounds the ovaries to receive the egg<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ul>\r\n&nbsp;\r\n\r\nUterus \u2013 hollow organ that receives the fertilized egg, retains it, and nourishes it\r\n\r\nRegions of the Uterus:\r\n<ol>\r\n \t<li>Body \u2013 main portion<\/li>\r\n \t<li>Fundus \u2013 superior rounded region where uterine tube enters<\/li>\r\n \t<li>Cervix \u2013 narrow outlet which protrudes into the vagina<\/li>\r\n<\/ol>\r\nWalls of the Uterus:\r\n<ol>\r\n \t<li>Endometrium \u2013 inner mucosal layer<\/li>\r\n \t<li>Myometrium \u2013 middle bulky layer of smooth muscle<\/li>\r\n \t<li>Perimetrium\/serous membrane \u2013 the visceral peritoneum<\/li>\r\n<\/ol>\r\n&nbsp;\r\n<ul>\r\n \t<li>Vagina \u2013 opening to exterior from the cervix; serves as birth canal and receives penis during copulation (sexual intercourse)<\/li>\r\n<\/ul>\r\n&nbsp;\r\n\r\nExternal Genitalia\r\n<ul>\r\n \t<li>Mons pubis \u2013 \u201cmountain on the pubis\u201d \u2013 fatty area overlying pubic symphysis<\/li>\r\n \t<li>Labia majora\u2013 outer, elongated hair-covered skin folds<\/li>\r\n \t<li>Labia minora \u2013 delicate, hair free folds that enclose the vestibule<\/li>\r\n \t<li>Vestibule \u2013 region within the labia minora that contains the opening of the urethra and vagina<\/li>\r\n \t<li>Vestibular glands \u2013 pair of glands on both sides of the vagina; secrete mucus for lubrication<\/li>\r\n \t<li>Clitoris \u2013 small protruding structure that contains sensitive erectile tissue (corresponds to the penis)<\/li>\r\n<\/ul>\r\n<strong>\u00a0<\/strong>\r\n\r\nHormones produced by the ovaries:\r\n<ol>\r\n \t<li>Estrogens \u2013 cause secondary sex characteristics\r\n<ol>\r\n \t<li>Enlargement of accessory organs (uterine tubes, uterus, vagina, external genitals)<\/li>\r\n \t<li>Development of breasts<\/li>\r\n \t<li>Appearance of axillary and pubic hair<\/li>\r\n \t<li>Increased deposits of fat in hips and breasts<\/li>\r\n \t<li>Widening and lightening of the pelvis<\/li>\r\n \t<li>Menstral cycle<\/li>\r\n \t<li><\/li>\r\n<\/ol>\r\n<\/li>\r\n \t<li>Progesterone \u2013 produced by the corpus luteum; helps establish the menstrual cycle and maintains the uterine lining during pregnancy<\/li>\r\n<\/ol>\r\n&nbsp;\r\n\r\nFemale Reproductive Cycles:\r\n\r\n&nbsp;\r\n<ol>\r\n \t<li>Ovarian cycle \u2013 involve the monthly formation and release of a secondary oocyte and the events that take place in preparation for pregnancy<\/li>\r\n \t<li>Menstrual cycle \u2013 repetitive changes in the uterine lining that lead to monthly menstrual bleeding<\/li>\r\n<\/ol>\r\n<ul>\r\n \t<li>Menopause \u2013 the cessation (stopping) of reproductive cycles, usually occurs between 45 and 55 years<\/li>\r\n<\/ul>\r\n<strong>\u00a0<\/strong>\r\n\r\n<strong>\u00a0<\/strong>\r\n<h2>Development of the Sexual Organs in the Embryo and Fetus<\/h2>\r\nFemales are considered the \u201cfundamental\u201d sex\u2014that is, without much chemical prompting, all fertilized eggs would develop into females. To become a male, an individual must be exposed to the cascade of factors initiated by a single gene on the male Y chromosome. This is called the SRY (<em>S<\/em>ex-determining <em>R<\/em>egion of the <em>Y<\/em> chromosome). Because females do not have a Y chromosome, they do not have the <em>SRY<\/em> gene. Without a functional <em>SRY<\/em> gene, an individual will be female.\r\n\r\nIn both male and female embryos, the same group of cells has the potential to develop into either the male or female gonads; this tissue is considered bipotential. The <em>SRY<\/em> gene actively recruits other genes that begin to develop the testes, and suppresses genes that are important in female development. As part of this <em>SRY<\/em>-prompted cascade, germ cells in the bipotential gonads differentiate into spermatogonia. Without <em>SRY<\/em>, different genes are expressed, oogonia form, and primordial follicles develop in the primitive ovary.\r\n\r\nSoon after the formation of the testis, the Leydig cells begin to secrete testosterone. Testosterone can influence tissues that are bipotential to become male reproductive structures. For example, with exposure to testosterone, cells that could become either the glans penis or the glans clitoris form the glans penis. Without testosterone, these same cells differentiate into the clitoris.\r\n\r\nNot all tissues in the reproductive tract are bipotential. The internal reproductive structures (for example the uterus, uterine tubes, and part of the vagina in females; and the epididymis, ductus deferens, and seminal vesicles in males) form from one of two rudimentary duct systems in the embryo. For proper reproductive function in the adult, one set of these ducts must develop properly, and the other must degrade. In males, secretions from sustentacular cells trigger a degradation of the female duct, called the <strong>M\u00fcllerian duct<\/strong>. At the same time, testosterone secretion stimulates growth of the male tract, the <strong>Wolffian duct<\/strong>. Without such sustentacular cell secretion, the M\u00fcllerian duct will develop; without testosterone, the Wolffian duct will degrade. Thus, the developing offspring will be female. For more information and a figure of differentiation of the gonads, seek additional content on fetal development.\r\n<div class=\"textbox exercises\">\r\n<h3>Practice Questions<\/h3>\r\nA baby\u2019s gender is determined at conception, and the different genitalia of male and female fetuses develop from the same tissues in the embryo. <a href=\"http:\/\/www.babycenter.com\/2_inside-pregnancy-girl-or-boy_10313041.bc#videoplaylist\" target=\"_blank\" rel=\"noopener\">View this animation to see a comparison of the development of structures of the female and male reproductive systems in a growing fetus.<\/a> Where are the testes located for most of gestational time?\r\n[reveal-answer q=\"110685\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"110685\"]The testes are located in the abdomen.[\/hidden-answer]\r\n\r\n<\/div>\r\n<h2>Further Sexual Development Occurs at Puberty<\/h2>\r\n<strong>Puberty<\/strong> is the stage of development at which individuals become sexually mature. Though the outcomes of puberty for boys and girls are very different, the hormonal control of the process is very similar. In addition, though the timing of these events varies between individuals, the sequence of changes that occur is predictable for male and female adolescents. As shown in the image below, a concerted release of hormones from the hypothalamus (GnRH), the anterior pituitary (LH and FSH), and the gonads (either testosterone or estrogen) is responsible for the maturation of the reproductive systems and the development of <strong>secondary sex characteristics<\/strong>, which are physical changes that serve auxiliary roles in reproduction.\r\n\r\nThe first changes begin around the age of eight or nine when the production of LH becomes detectable. The release of LH occurs primarily at night during sleep and precedes the physical changes of puberty by several years. In pre-pubertal children, the sensitivity of the negative feedback system in the hypothalamus and pituitary is very high. This means that very low concentrations of androgens or estrogens will negatively feed back onto the hypothalamus and pituitary, keeping the production of GnRH, LH, and FSH low.\r\n\r\nAs an individual approaches puberty, two changes in sensitivity occur. The first is a decrease of sensitivity in the hypothalamus and pituitary to negative feedback, meaning that it takes increasingly larger concentrations of sex steroid hormones to stop the production of LH and FSH. The second change in sensitivity is an increase in sensitivity of the gonads to the FSH and LH signals, meaning the gonads of adults are more responsive to gonadotropins than are the gonads of children. As a result of these two changes, the levels of LH and FSH slowly increase and lead to the enlargement and maturation of the gonads, which in turn leads to secretion of higher levels of sex hormones and the initiation of spermatogenesis and folliculogenesis.\r\n\r\nIn addition to age, multiple factors can affect the age of onset of puberty, including genetics, environment, and psychological stress. One of the more important influences may be nutrition; historical data demonstrate the effect of better and more consistent nutrition on the age of menarche in girls in the United States, which decreased from an average age of approximately 17 years of age in 1860 to the current age of approximately 12.75 years in 1960, as it remains today. Some studies indicate a link between puberty onset and the amount of stored fat in an individual. This effect is more pronounced in girls, but has been documented in both sexes. Body fat, corresponding with secretion of the hormone leptin by adipose cells, appears to have a strong role in determining menarche. This may reflect to some extent the high metabolic costs of gestation and lactation. In girls who are lean and highly active, such as gymnasts, there is often a delay in the onset of puberty.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"550\"]<a href=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/403\/2015\/04\/21031941\/Figure_28_03_01.jpg\" target=\"_blank\" rel=\"noopener\"><img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/403\/2015\/04\/21031941\/Figure_28_03_01.jpg\" alt=\"This flow chart shows the different hormones and the organs they act on at the onset of puberty. The hypothalamus is shown on top. The right half of the flowchart shows the hormones in females and the left half shows the hormones in males.\" width=\"550\" height=\"764\" \/><\/a> Figure 1. Click to view a larger image. During puberty, the release of LH and FSH from the anterior pituitary stimulates the gonads to produce sex hormones in both male and female adolescents.[\/caption]\r\n<h3>Signs of Puberty<\/h3>\r\nDifferent sex steroid hormone concentrations between the sexes also contribute to the development and function of secondary sexual characteristics. Examples of secondary sexual characteristics are listed in Table 1.\r\n<table id=\"development_of_the_secondary_sexual_characteristics\" summary=\"The first column lists Male Development of the Secondary Sexual Characteristics and the second column lists Female Development of the Secondary Sexual Characteristics.\">\r\n<thead>\r\n<tr>\r\n<th colspan=\"2\">Table 1. Development of the Secondary Sexual Characteristics<\/th>\r\n<\/tr>\r\n<tr>\r\n<th>Male<\/th>\r\n<th>Female<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr>\r\n<td>Increased larynx size and deepening of the voice<\/td>\r\n<td>Deposition of fat, predominantly in breasts and hips<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Increased muscular development<\/td>\r\n<td>Breast development<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Growth of facial, axillary, and pubic hair, and increased growth of body hair<\/td>\r\n<td>Broadening of the pelvis and growth of axillary and pubic hair<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\nAs a girl reaches puberty, typically the first change that is visible is the development of the breast tissue. This is followed by the growth of axillary and pubic hair. A growth spurt normally starts at approximately age 9 to 11, and may last two years or more. During this time, a girl\u2019s height can increase 3 inches a year. The next step in puberty is menarche, the start of menstruation.\r\n\r\nIn boys, the growth of the testes is typically the first physical sign of the beginning of puberty, which is followed by growth and pigmentation of the scrotum and growth of the penis. The next step is the growth of hair, including armpit, pubic, chest, and facial hair. Testosterone stimulates the growth of the larynx and thickening and lengthening of the vocal folds, which causes the voice to drop in pitch. The first fertile ejaculations typically appear at approximately 15 years of age, but this age can vary widely across individual boys. Unlike the early growth spurt observed in females, the male growth spurt occurs toward the end of puberty, at approximately age 11 to 13, and a boy\u2019s height can increase as much as 4 inches a year. In some males, pubertal development can continue through the early 20s.\r\n<h2>Chapter Review<\/h2>\r\nThe reproductive systems of males and females begin to develop soon after conception. A gene on the male\u2019s Y chromosome called <em>SRY<\/em> is critical in stimulating a cascade of events that simultaneously stimulate testis development and repress the development of female structures. Testosterone produced by Leydig cells in the embryonic testis stimulates the development of male sexual organs. If testosterone is not present, female sexual organs will develop.\r\n\r\nWhereas the gonads and some other reproductive tissues are considered bipotential, the tissue that forms the internal reproductive structures stems from ducts that will develop into only male (Wolffian) or female (M\u00fcllerian) structures. To be able to reproduce as an adult, one of these systems must develop properly and the other must degrade.\r\n\r\nFurther development of the reproductive systems occurs at puberty. The initiation of the changes that occur in puberty is the result of a decrease in sensitivity to negative feedback in the hypothalamus and pituitary gland, and an increase in sensitivity of the gonads to FSH and LH stimulation. These changes lead to increases in either estrogen or testosterone, in female and male adolescents, respectively. The increase in sex steroid hormones leads to maturation of the gonads and other reproductive organs. The initiation of spermatogenesis begins in boys, and girls begin ovulating and menstruating. Increases in sex steroid hormones also lead to the development of secondary sex characteristics such as breast development in girls and facial hair and larynx growth in boys.\r\n<h2>Self Check<\/h2>\r\nAnswer the question(s) below to see how well you understand the topics covered in the previous section.\r\n\r\nhttps:\/\/www.openassessments.org\/assessments\/301\r\n<div class=\"textbox exercises\">\r\n<h3>Critical Thinking Questions<\/h3>\r\n<ol>\r\n \t<li>Identify the changes in sensitivity that occur in the hypothalamus, pituitary, and gonads as a boy or girl approaches puberty. Explain how these changes lead to the increases of sex steroid hormone secretions that drive many pubertal changes.<\/li>\r\n \t<li>Explain how the internal female and male reproductive structures develop from two different duct systems.<\/li>\r\n \t<li>Explain what would occur during fetal development to an XY individual with a mutation causing a nonfunctional <em>SRY<\/em> gene.<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"564917\"]Show Answers[\/reveal-answer]\r\n[hidden-answer a=\"564917\"]\r\n<ol>\r\n \t<li>As an individual approaches puberty, two changes in sensitivity occur. The first is a decrease of sensitivity in the hypothalamus and pituitary to negative feedback, meaning that it takes increasingly larger concentrations of sex steroid hormones to stop the production of LH and FSH. The second change in sensitivity is an increase in the sensitivity of the gonads to the FSH and LH signals, meaning that the gonads of adults are more responsive to gonadotropins than are the gonads of children. As a result of these two changes, the levels of LH and FSH slowly increase and lead to the enlargement and maturation of the gonads, which in turn leads to secretion of higher levels of sex hormones and the initiation of spermatogenesis and folliculogenesis.<\/li>\r\n \t<li>The internal reproductive structures form from one of two rudimentary duct systems in the embryo. Testosterone secretion stimulates growth of the male tract, the Wolffian duct. Secretions of sustentacular cells trigger a degradation of the female tract, the M\u00fcllerian duct. Without these stimuli, the M\u00fcllerian duct will develop and the Wolffian duct will degrade, resulting in a female embryo.<\/li>\r\n \t<li>If the <em>SRY<\/em> gene were not functional, the XY individual would be genetically a male, but would develop female reproductive structures.<\/li>\r\n<\/ol>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<h2>Glossary<\/h2>\r\n<strong>M\u00fcllerian duct: <\/strong>duct system present in the embryo that will eventually form the internal female reproductive structures\r\n\r\n<strong>puberty: <\/strong>life stage during which a male or female adolescent becomes anatomically and physiologically capable of reproduction\r\n\r\n<strong>secondary sex characteristics: <\/strong>physical characteristics that are influenced by sex steroid hormones and have supporting roles in reproductive function\r\n\r\n<strong>Wolffian duct: <\/strong>duct system present in the embryo that will eventually form the internal male reproductive structures","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<p>By the end of this section, you will be able to:<\/p>\n<ul>\n<li>Explain how bipotential tissues are directed to develop into male or female sex organs<\/li>\n<li>Name the rudimentary duct systems in the embryo that are precursors to male or female internal sex organs<\/li>\n<li>Describe the hormonal changes that bring about puberty, and the secondary sex characteristics of men and women<\/li>\n<\/ul>\n<\/div>\n<p>The development of the reproductive systems begins soon after fertilization of the egg, with primordial gonads beginning to develop approximately one month after conception. Reproductive development continues in utero, but there is little change in the reproductive system between infancy and puberty.<\/p>\n<p>&nbsp;<\/p>\n<p><strong>FEMALE REPRODUCTIVE SYSTEM<\/strong><\/p>\n<ul>\n<li>Ovary \u2013 composed of numerous sac-like ovarian follicles<\/li>\n<li>Oogenesis <strong>\u2013 <\/strong>process of producing ova\/eggs (female gamete)<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p>Stages of egg development \u2013 takes about 28 days<\/p>\n<p>&nbsp;<\/p>\n<ol>\n<li>Oogonia \u2013 stem cells of the ovaries that will transform into primary oocytes; the oogonia are surrounded by a thin layer of cells called the primordial follicle<\/li>\n<li>Primary follicle \u2013 contains the primary oocyte that will develop into a mature egg; a lifetime supply of primary oocytes is present from birth (around 2 million); they are inactive until puberty; in response to the monthly secretion of FSH, 1 is stimulated to develop each month<\/li>\n<li>Secondary follicle \u2013 during development fluid filled space appears between the inner and outer follicle cell<\/li>\n<li>Mature follicle \u2013 fluid filled follicle that contains the mature egg<\/li>\n<\/ol>\n<ul>\n<li>A surge of LH stimulates the completion of Meiosis I of the primary oocyte. It is an uneven division of the cytoplasm. This uneven division result in 1 large ooctye and 1 smaller, nonfunctional structure called a polar body.<\/li>\n<\/ul>\n<ol start=\"5\">\n<li>Ovulation \u2013 rupturing of the follicle to release the egg; stimulated by high level of LH<\/li>\n<\/ol>\n<p>&nbsp;<\/p>\n<ul>\n<li>When the oocyte is released during ovulation, it is now known as the secondary oocyte. Meiosis II only occurs if the egg is penetrated by a sperm. Meiosis II is the second division of the oocyte and it forms another polar body and the ovum \u2013 egg cell. The fusion of the nuclei of the egg and sperm forms a zygote \u2013 the first cell of an embryo.<\/li>\n<\/ul>\n<ol start=\"6\">\n<li>Corpus luteum \u2013 ruptured follicle; it slowly degenerates and the cycle starts over<\/li>\n<\/ol>\n<p><strong>\u00a0<\/strong><strong>\u00a0<\/strong><\/p>\n<p>Uterine Tube (Fallopian Tube) \u2013 receives the secondary oocyte, provides the site for fertilization<\/p>\n<p><strong>\u00a0<\/strong><\/p>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li>Infundibulum \u2013 end of each uterine tube that connects to the ovaries<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li>Fimbriae \u2013 fingerlike projections of the infundibulum that surrounds the ovaries to receive the egg<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p>Uterus \u2013 hollow organ that receives the fertilized egg, retains it, and nourishes it<\/p>\n<p>Regions of the Uterus:<\/p>\n<ol>\n<li>Body \u2013 main portion<\/li>\n<li>Fundus \u2013 superior rounded region where uterine tube enters<\/li>\n<li>Cervix \u2013 narrow outlet which protrudes into the vagina<\/li>\n<\/ol>\n<p>Walls of the Uterus:<\/p>\n<ol>\n<li>Endometrium \u2013 inner mucosal layer<\/li>\n<li>Myometrium \u2013 middle bulky layer of smooth muscle<\/li>\n<li>Perimetrium\/serous membrane \u2013 the visceral peritoneum<\/li>\n<\/ol>\n<p>&nbsp;<\/p>\n<ul>\n<li>Vagina \u2013 opening to exterior from the cervix; serves as birth canal and receives penis during copulation (sexual intercourse)<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p>External Genitalia<\/p>\n<ul>\n<li>Mons pubis \u2013 \u201cmountain on the pubis\u201d \u2013 fatty area overlying pubic symphysis<\/li>\n<li>Labia majora\u2013 outer, elongated hair-covered skin folds<\/li>\n<li>Labia minora \u2013 delicate, hair free folds that enclose the vestibule<\/li>\n<li>Vestibule \u2013 region within the labia minora that contains the opening of the urethra and vagina<\/li>\n<li>Vestibular glands \u2013 pair of glands on both sides of the vagina; secrete mucus for lubrication<\/li>\n<li>Clitoris \u2013 small protruding structure that contains sensitive erectile tissue (corresponds to the penis)<\/li>\n<\/ul>\n<p><strong>\u00a0<\/strong><\/p>\n<p>Hormones produced by the ovaries:<\/p>\n<ol>\n<li>Estrogens \u2013 cause secondary sex characteristics\n<ol>\n<li>Enlargement of accessory organs (uterine tubes, uterus, vagina, external genitals)<\/li>\n<li>Development of breasts<\/li>\n<li>Appearance of axillary and pubic hair<\/li>\n<li>Increased deposits of fat in hips and breasts<\/li>\n<li>Widening and lightening of the pelvis<\/li>\n<li>Menstral cycle<\/li>\n<li><\/li>\n<\/ol>\n<\/li>\n<li>Progesterone \u2013 produced by the corpus luteum; helps establish the menstrual cycle and maintains the uterine lining during pregnancy<\/li>\n<\/ol>\n<p>&nbsp;<\/p>\n<p>Female Reproductive Cycles:<\/p>\n<p>&nbsp;<\/p>\n<ol>\n<li>Ovarian cycle \u2013 involve the monthly formation and release of a secondary oocyte and the events that take place in preparation for pregnancy<\/li>\n<li>Menstrual cycle \u2013 repetitive changes in the uterine lining that lead to monthly menstrual bleeding<\/li>\n<\/ol>\n<ul>\n<li>Menopause \u2013 the cessation (stopping) of reproductive cycles, usually occurs between 45 and 55 years<\/li>\n<\/ul>\n<p><strong>\u00a0<\/strong><\/p>\n<p><strong>\u00a0<\/strong><\/p>\n<h2>Development of the Sexual Organs in the Embryo and Fetus<\/h2>\n<p>Females are considered the \u201cfundamental\u201d sex\u2014that is, without much chemical prompting, all fertilized eggs would develop into females. To become a male, an individual must be exposed to the cascade of factors initiated by a single gene on the male Y chromosome. This is called the SRY (<em>S<\/em>ex-determining <em>R<\/em>egion of the <em>Y<\/em> chromosome). Because females do not have a Y chromosome, they do not have the <em>SRY<\/em> gene. Without a functional <em>SRY<\/em> gene, an individual will be female.<\/p>\n<p>In both male and female embryos, the same group of cells has the potential to develop into either the male or female gonads; this tissue is considered bipotential. The <em>SRY<\/em> gene actively recruits other genes that begin to develop the testes, and suppresses genes that are important in female development. As part of this <em>SRY<\/em>-prompted cascade, germ cells in the bipotential gonads differentiate into spermatogonia. Without <em>SRY<\/em>, different genes are expressed, oogonia form, and primordial follicles develop in the primitive ovary.<\/p>\n<p>Soon after the formation of the testis, the Leydig cells begin to secrete testosterone. Testosterone can influence tissues that are bipotential to become male reproductive structures. For example, with exposure to testosterone, cells that could become either the glans penis or the glans clitoris form the glans penis. Without testosterone, these same cells differentiate into the clitoris.<\/p>\n<p>Not all tissues in the reproductive tract are bipotential. The internal reproductive structures (for example the uterus, uterine tubes, and part of the vagina in females; and the epididymis, ductus deferens, and seminal vesicles in males) form from one of two rudimentary duct systems in the embryo. For proper reproductive function in the adult, one set of these ducts must develop properly, and the other must degrade. In males, secretions from sustentacular cells trigger a degradation of the female duct, called the <strong>M\u00fcllerian duct<\/strong>. At the same time, testosterone secretion stimulates growth of the male tract, the <strong>Wolffian duct<\/strong>. Without such sustentacular cell secretion, the M\u00fcllerian duct will develop; without testosterone, the Wolffian duct will degrade. Thus, the developing offspring will be female. For more information and a figure of differentiation of the gonads, seek additional content on fetal development.<\/p>\n<div class=\"textbox exercises\">\n<h3>Practice Questions<\/h3>\n<p>A baby\u2019s gender is determined at conception, and the different genitalia of male and female fetuses develop from the same tissues in the embryo. <a href=\"http:\/\/www.babycenter.com\/2_inside-pregnancy-girl-or-boy_10313041.bc#videoplaylist\" target=\"_blank\" rel=\"noopener\">View this animation to see a comparison of the development of structures of the female and male reproductive systems in a growing fetus.<\/a> Where are the testes located for most of gestational time?<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q110685\">Show Answer<\/span><\/p>\n<div id=\"q110685\" class=\"hidden-answer\" style=\"display: none\">The testes are located in the abdomen.<\/div>\n<\/div>\n<\/div>\n<h2>Further Sexual Development Occurs at Puberty<\/h2>\n<p><strong>Puberty<\/strong> is the stage of development at which individuals become sexually mature. Though the outcomes of puberty for boys and girls are very different, the hormonal control of the process is very similar. In addition, though the timing of these events varies between individuals, the sequence of changes that occur is predictable for male and female adolescents. As shown in the image below, a concerted release of hormones from the hypothalamus (GnRH), the anterior pituitary (LH and FSH), and the gonads (either testosterone or estrogen) is responsible for the maturation of the reproductive systems and the development of <strong>secondary sex characteristics<\/strong>, which are physical changes that serve auxiliary roles in reproduction.<\/p>\n<p>The first changes begin around the age of eight or nine when the production of LH becomes detectable. The release of LH occurs primarily at night during sleep and precedes the physical changes of puberty by several years. In pre-pubertal children, the sensitivity of the negative feedback system in the hypothalamus and pituitary is very high. This means that very low concentrations of androgens or estrogens will negatively feed back onto the hypothalamus and pituitary, keeping the production of GnRH, LH, and FSH low.<\/p>\n<p>As an individual approaches puberty, two changes in sensitivity occur. The first is a decrease of sensitivity in the hypothalamus and pituitary to negative feedback, meaning that it takes increasingly larger concentrations of sex steroid hormones to stop the production of LH and FSH. The second change in sensitivity is an increase in sensitivity of the gonads to the FSH and LH signals, meaning the gonads of adults are more responsive to gonadotropins than are the gonads of children. As a result of these two changes, the levels of LH and FSH slowly increase and lead to the enlargement and maturation of the gonads, which in turn leads to secretion of higher levels of sex hormones and the initiation of spermatogenesis and folliculogenesis.<\/p>\n<p>In addition to age, multiple factors can affect the age of onset of puberty, including genetics, environment, and psychological stress. One of the more important influences may be nutrition; historical data demonstrate the effect of better and more consistent nutrition on the age of menarche in girls in the United States, which decreased from an average age of approximately 17 years of age in 1860 to the current age of approximately 12.75 years in 1960, as it remains today. Some studies indicate a link between puberty onset and the amount of stored fat in an individual. This effect is more pronounced in girls, but has been documented in both sexes. Body fat, corresponding with secretion of the hormone leptin by adipose cells, appears to have a strong role in determining menarche. This may reflect to some extent the high metabolic costs of gestation and lactation. In girls who are lean and highly active, such as gymnasts, there is often a delay in the onset of puberty.<\/p>\n<div style=\"width: 560px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/403\/2015\/04\/21031941\/Figure_28_03_01.jpg\" target=\"_blank\" rel=\"noopener\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/403\/2015\/04\/21031941\/Figure_28_03_01.jpg\" alt=\"This flow chart shows the different hormones and the organs they act on at the onset of puberty. The hypothalamus is shown on top. The right half of the flowchart shows the hormones in females and the left half shows the hormones in males.\" width=\"550\" height=\"764\" \/><\/a><\/p>\n<p class=\"wp-caption-text\">Figure 1. Click to view a larger image. During puberty, the release of LH and FSH from the anterior pituitary stimulates the gonads to produce sex hormones in both male and female adolescents.<\/p>\n<\/div>\n<h3>Signs of Puberty<\/h3>\n<p>Different sex steroid hormone concentrations between the sexes also contribute to the development and function of secondary sexual characteristics. Examples of secondary sexual characteristics are listed in Table 1.<\/p>\n<table id=\"development_of_the_secondary_sexual_characteristics\" summary=\"The first column lists Male Development of the Secondary Sexual Characteristics and the second column lists Female Development of the Secondary Sexual Characteristics.\">\n<thead>\n<tr>\n<th colspan=\"2\">Table 1. Development of the Secondary Sexual Characteristics<\/th>\n<\/tr>\n<tr>\n<th>Male<\/th>\n<th>Female<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Increased larynx size and deepening of the voice<\/td>\n<td>Deposition of fat, predominantly in breasts and hips<\/td>\n<\/tr>\n<tr>\n<td>Increased muscular development<\/td>\n<td>Breast development<\/td>\n<\/tr>\n<tr>\n<td>Growth of facial, axillary, and pubic hair, and increased growth of body hair<\/td>\n<td>Broadening of the pelvis and growth of axillary and pubic hair<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>As a girl reaches puberty, typically the first change that is visible is the development of the breast tissue. This is followed by the growth of axillary and pubic hair. A growth spurt normally starts at approximately age 9 to 11, and may last two years or more. During this time, a girl\u2019s height can increase 3 inches a year. The next step in puberty is menarche, the start of menstruation.<\/p>\n<p>In boys, the growth of the testes is typically the first physical sign of the beginning of puberty, which is followed by growth and pigmentation of the scrotum and growth of the penis. The next step is the growth of hair, including armpit, pubic, chest, and facial hair. Testosterone stimulates the growth of the larynx and thickening and lengthening of the vocal folds, which causes the voice to drop in pitch. The first fertile ejaculations typically appear at approximately 15 years of age, but this age can vary widely across individual boys. Unlike the early growth spurt observed in females, the male growth spurt occurs toward the end of puberty, at approximately age 11 to 13, and a boy\u2019s height can increase as much as 4 inches a year. In some males, pubertal development can continue through the early 20s.<\/p>\n<h2>Chapter Review<\/h2>\n<p>The reproductive systems of males and females begin to develop soon after conception. A gene on the male\u2019s Y chromosome called <em>SRY<\/em> is critical in stimulating a cascade of events that simultaneously stimulate testis development and repress the development of female structures. Testosterone produced by Leydig cells in the embryonic testis stimulates the development of male sexual organs. If testosterone is not present, female sexual organs will develop.<\/p>\n<p>Whereas the gonads and some other reproductive tissues are considered bipotential, the tissue that forms the internal reproductive structures stems from ducts that will develop into only male (Wolffian) or female (M\u00fcllerian) structures. To be able to reproduce as an adult, one of these systems must develop properly and the other must degrade.<\/p>\n<p>Further development of the reproductive systems occurs at puberty. The initiation of the changes that occur in puberty is the result of a decrease in sensitivity to negative feedback in the hypothalamus and pituitary gland, and an increase in sensitivity of the gonads to FSH and LH stimulation. These changes lead to increases in either estrogen or testosterone, in female and male adolescents, respectively. The increase in sex steroid hormones leads to maturation of the gonads and other reproductive organs. The initiation of spermatogenesis begins in boys, and girls begin ovulating and menstruating. Increases in sex steroid hormones also lead to the development of secondary sex characteristics such as breast development in girls and facial hair and larynx growth in boys.<\/p>\n<h2>Self Check<\/h2>\n<p>Answer the question(s) below to see how well you understand the topics covered in the previous section.<\/p>\n<p><iframe src=\"https:\/\/lumenoea.herokuapp.com\/assessments\/load?src_url=https:\/\/lumenoea.herokuapp.com\/api\/assessments\/301.xml&#38;results_end_point=https:\/\/lumenoea.herokuapp.com\/api&#38;assessment_id=301&#38;confidence_levels=true&#38;enable_start=true&#38;eid=https:\/\/courses.lumenlearning.com\/nemcc-ap2\/chapter\/development-of-the-male-and-female-reproductive-systems\/\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><\/iframe><\/p>\n<div class=\"textbox exercises\">\n<h3>Critical Thinking Questions<\/h3>\n<ol>\n<li>Identify the changes in sensitivity that occur in the hypothalamus, pituitary, and gonads as a boy or girl approaches puberty. Explain how these changes lead to the increases of sex steroid hormone secretions that drive many pubertal changes.<\/li>\n<li>Explain how the internal female and male reproductive structures develop from two different duct systems.<\/li>\n<li>Explain what would occur during fetal development to an XY individual with a mutation causing a nonfunctional <em>SRY<\/em> gene.<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q564917\">Show Answers<\/span><\/p>\n<div id=\"q564917\" class=\"hidden-answer\" style=\"display: none\">\n<ol>\n<li>As an individual approaches puberty, two changes in sensitivity occur. The first is a decrease of sensitivity in the hypothalamus and pituitary to negative feedback, meaning that it takes increasingly larger concentrations of sex steroid hormones to stop the production of LH and FSH. The second change in sensitivity is an increase in the sensitivity of the gonads to the FSH and LH signals, meaning that the gonads of adults are more responsive to gonadotropins than are the gonads of children. As a result of these two changes, the levels of LH and FSH slowly increase and lead to the enlargement and maturation of the gonads, which in turn leads to secretion of higher levels of sex hormones and the initiation of spermatogenesis and folliculogenesis.<\/li>\n<li>The internal reproductive structures form from one of two rudimentary duct systems in the embryo. Testosterone secretion stimulates growth of the male tract, the Wolffian duct. Secretions of sustentacular cells trigger a degradation of the female tract, the M\u00fcllerian duct. Without these stimuli, the M\u00fcllerian duct will develop and the Wolffian duct will degrade, resulting in a female embryo.<\/li>\n<li>If the <em>SRY<\/em> gene were not functional, the XY individual would be genetically a male, but would develop female reproductive structures.<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<h2>Glossary<\/h2>\n<p><strong>M\u00fcllerian duct: <\/strong>duct system present in the embryo that will eventually form the internal female reproductive structures<\/p>\n<p><strong>puberty: <\/strong>life stage during which a male or female adolescent becomes anatomically and physiologically capable of reproduction<\/p>\n<p><strong>secondary sex characteristics: <\/strong>physical characteristics that are influenced by sex steroid hormones and have supporting roles in reproductive function<\/p>\n<p><strong>Wolffian duct: <\/strong>duct system present in the embryo that will eventually form the internal male reproductive structures<\/p>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-1013\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Anatomy &amp; Physiology. <strong>Provided by<\/strong>: OpenStax CNX. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@8.25\">http:\/\/cnx.org\/contents\/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@8.25<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Download for free at http:\/\/cnx.org\/contents\/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@8.25<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":20,"menu_order":9,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Anatomy & Physiology\",\"author\":\"\",\"organization\":\"OpenStax CNX\",\"url\":\"http:\/\/cnx.org\/contents\/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@8.25\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@8.25\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-1013","chapter","type-chapter","status-publish","hentry"],"part":1078,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/nemcc-ap2\/wp-json\/pressbooks\/v2\/chapters\/1013","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/nemcc-ap2\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/nemcc-ap2\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/nemcc-ap2\/wp-json\/wp\/v2\/users\/20"}],"version-history":[{"count":13,"href":"https:\/\/courses.lumenlearning.com\/nemcc-ap2\/wp-json\/pressbooks\/v2\/chapters\/1013\/revisions"}],"predecessor-version":[{"id":2345,"href":"https:\/\/courses.lumenlearning.com\/nemcc-ap2\/wp-json\/pressbooks\/v2\/chapters\/1013\/revisions\/2345"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/nemcc-ap2\/wp-json\/pressbooks\/v2\/parts\/1078"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/nemcc-ap2\/wp-json\/pressbooks\/v2\/chapters\/1013\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/nemcc-ap2\/wp-json\/wp\/v2\/media?parent=1013"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/nemcc-ap2\/wp-json\/pressbooks\/v2\/chapter-type?post=1013"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/nemcc-ap2\/wp-json\/wp\/v2\/contributor?post=1013"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/nemcc-ap2\/wp-json\/wp\/v2\/license?post=1013"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}