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13.2: Sexual Development, Anatomy and Physiology

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    110546
  • This page is a draft and under active development. Please forward any questions, comments, and/or feedback to the ASCCC OERI (oeri@asccc.org).

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    Learning Objectives
    1. Describe the process of prenatal sexual differentiation in humans.
    2. Identify male and female reproductive structures that originate from homologous embryonic tissues versus those that are formed from separate (Wolffian and Müllerian) duct systems.
    3. Identify the functions of the main reproductive structures for both males and females.
    4. Understand the basic events occurring in the ovaries and uterus during the human menstrual cycle.
    5. Explain the four phases in the human sexual response cycle (Masters and Johnson).

    Overview

    This section covers development of the male and female reproductive systems (including prenatal sex differentiation, homologous structures and reproductive ducts, and sexual maturation during puberty), and adult sexual anatomy and physiology (including the male reproductive system, the female reproductive system, the menstrual cycle, and the sexual response cycle.

    Development of the Reproductive Systems

    The reproductive system is the human organ system responsible for the production of gametes (sperm or eggs), the meeting of gametes during fertilization, and the carrying of an embryo/fetus. The reproductive system is the only body system that differs substantially between individuals, typically divided into male and female forms (Figure \(\PageIndex{1}\)), although there is actually a range of biological sex (see the differences of sexual development section). Many embryonic structures that will develop into the reproductive system start out the same in males and females, but by birth, the reproductive systems have differentiated. This section will describe how male and female reproductive structures typically form during development and the role of several hormones.

    Male and female outlines with some reproductive structures labeled; the caption lists those indicated
    Figure \(\PageIndex{1}\): Reproductive Systems in the Human Male and Female. Both systems produce sex hormones and gametes. The male reproductive system additionally delivers gametes to the female; the epididymis and testes are labeled. The female reproductive system additionally supports an embryo/fetus until birth and produces milk for the infant; the mammary glands, ovaries, and uterus are labeled.

    The gonads (the testes in males and the ovaries in females) produce gametes (sperm in males and eggs in females). A gamete is a haploid cell- a cell that contains one full set of chromosomes, or half the number needed to create a new individual. When two haploid gametes combine during fertilization, they form a single diploid cell, which now contains two full sets of chromosomes (the necessary number to create a new individual) and is called a zygote (fertilized egg). In mammals, the ovum always contains an X chromosome, which can be fertilized by a sperm bearing either an X or a Y chromosome; this process is called sex determination. XX is the chromosomal sex of a female mammal and XY is the chromosomal sex of a male mammal.

    Besides producing gametes, the gonads also produce sex hormones. Sex hormones, such as androgens and estrogens, are endocrine hormones that control the development of sex organs before birth, sexual maturation at puberty, and reproduction once sexual maturation has occurred. Other reproductive system organs have various functions, such as maturing gametes, delivering gametes to the site of fertilization, and providing an environment for the development and growth of offspring.

    Prenatal Sex Differentiation

    The process of becoming female or male is called sexual differentiation. Although both the X and the Y chromosomes are called sex chromosomes, only the Y chromosome contains genes that determine sex. A single gene on the Y chromosome, called SRY (for "sex-determining region Y gene"; Figure \(\PageIndex{2}\)), triggers male development in the embryo. Without a Y chromosome, the embryo develops a female body plan, so you can think of a female as the default sex of the human species (as is the case for all mammals).

    Drawing of the Y chromosome with the SRY Testes-determining factor gene labeled
    Figure \(\PageIndex{2}\): The SRY gene on the short arm of the Y chromosome causes the undifferentiated gonads of an embryo to develop into testes. Otherwise, the gonads develop into ovaries.

    The gonads of the embryo are initially undifferentiated, meaning that they are indeterminate- identical in XX and XY embryos- and able to become either testes or ovaries. Starting around the sixth week after conception in genetically male (XY) embryos, the SRY gene initiates the production of a protein called testes determining factor. Testes determining factor causes the undifferentiated gonads to develop into testes. The testes secrete hormones — including testosterone — that trigger other changes in the developing offspring (now called a fetus), causing it to develop a complete male reproductive system. Without a Y chromosome, an embryo will develop ovaries that will then produce estrogens. Estrogens, in turn, enable the formation of the other organs of a female reproductive system.

    Homologous Structures and Reproductive Ducts

    Undifferentiated embryonic tissues develop into different structures in male and female fetuses. Structures that arise from the same tissues in males and females are called homologous structures. The testes and ovaries, for example, are homologous structures that develop from the undifferentiated gonads of the embryo. Likewise, the penis and clitoris are homologous structures that develop from the same embryonic tissues, as are the scrotum and the skin folds of the labia majora. The formation of typical male external anatomy (the penis and scrotum) requires the conversion of testosterone into a more potent androgen called dihydrotestosterone, whereas the formation of typical female external anatomy (the clitoris and the labia) does not require hormones. In this manner, the same embryonic tissue develops into one structure or another in a given individual, or occasionally forms a structure that is intermediate between the typical male or female form.

    Not all tissues in the prenatal reproductive tract have the potential to develop into either male or female forms. The internal reproductive structures (for example the uterus, uterine tubes, and part of the vagina in females; and the epididymis, vas deferens, and seminal vesicles in males) form from one of two rudimentary duct systems in the embryo. For full reproductive function in the adult, one set of these ducts must develop properly, and the other must degrade. In males, cells in the testes secrete Müllerian inhibiting substance, which causes the Müllerian duct (the female duct) to degenerate. At the same time, testosterone secretion stimulates growth of the male tract, the Wolffian duct. Without Müllerian inhibiting substance, the Müllerian duct will develop; without testosterone, the Wolffian duct will degrade. Thus, the developing offspring will be female (Figure \(\PageIndex{3}\)), following the default female body form.

    Diagram of two embryonic duct systems that form male and female internal reproductive structures; described in caption
    Figure \(\PageIndex{3}\): Differentiation of the male and female reproductive systems occurs during the fetal period of development. Initially, the cloaca, bipotential gonads, and both Wolffian and Mullerian ducts are present. In both sexes, the cloaca becomes the urinary bladder and urethra.With masculinization (shown on the left), the Mullerian ducts degrade and the Wolffian ducts become the epididymis and the ductus (vas) deferens. The bipotential gonads become testes. With feminization (shown on the right), the Wolffian ducts degrade and the Mullerian ducts become the uterine tubes and the uterus. The bipotential gonads become ovaries.

    Sexual Maturation during Puberty

    Puberty is a period of rapid growth and sexual maturation. These changes typically begin sometime between the ages of eight and fourteen, and start with an overall physical growth spurt, often most noticeable in the adolescent's increased height. Generally, girls begin puberty at around ten years of age and boys begin approximately two years later. Pubertal changes usually take around three to four years to complete.

    Typically, the physical growth spurt is followed by the development of sexual maturity. Changes in the primary sexual characteristics (reproductive organs) in males includes growth of the testes, penis, and scrotum, and in females the growth and maturation of the ovaries, uterus and external genitalia (vulva). Important signals of sexual maturity include spermarche or first ejaculation of semen in males, and menarche or the first menstrual period in females. Stress and higher percentage of body fat are correlated with menstruation at younger ages.

    Secondary sexual characteristics are visible physical changes not directly linked to reproduction, but that signal sexual maturity. For males this includes broader shoulders and a lower voice as the larynx grows. Body hair becomes coarser and darker, and hair growth occurs in the pubic area, under the arms and on the face. For females breast development occurs around age 10, although full development takes several years. Hips broaden and pubic and underarm hair develops and also becomes darker and coarser.

    Adult Sexual Anatomy and Physiology

    The Male Reproductive System

    The main structures of the male reproductive system are external to the body (Figure \(\PageIndex{4}\)). The two testes (singular, testis) hang between the thighs in a sac of skin called the scrotum. The testes produce both sperm and testosterone. Testosterone production is under the control of luteinizing hormone (LH) from the pituitary gland, which stimulates cells in the testes to secrete testosterone. Both follicle stimulating hormone (FSH) from the pituitary gland and testosterone are needed for normal spermatogenesis to be maintained in the testes. Additionally, testosterone maintains libido (sex drive) and plays a role in erection, allowing sperm to be deposited within the female reproductive tract. Testosterone is necessary for the proper functioning of the prostate gland, and is also important for muscle development and bone growth.

    Resting atop each testis is a coiled structure called the epididymis (plural, epididymes). The function of the epididymes is to mature and store sperm. The penis is a tubular organ that contains the urethra and has the ability to stiffen during sexual arousal. Sperm passes out of the body through the urethra during a sexual climax (orgasm). This release of sperm is called ejaculation.

    3D view of male reproductive structures; most structures are described in the text
    Sagittal view of male reproductive structures; most structures are described in the text
    Frontal view of male reproductive structures; most structures are described in the text
    Figure \(\PageIndex{4}\): The main structures of the male reproductive system in 3D view, sagittal view, and frontal view. Note that structures that are homologous to female structures (originating from the same embryonic tissue, such as the testes) are color-coded to match the female reproductive system diagrams in Figure \(\PageIndex{5}\).

    In addition to these external organs, there are several ducts and glands that are internal to the body. The ducts, which include the vas deferens (also called the ductus deferens), transport sperm from the epididymis to the urethra. The glands, which include the prostate gland and seminal vesicles, produce fluids that become part of semen. Semen is the fluid that carries sperm through the urethra and out of the body. It contains substances that control pH and provide sperm with nutrients for energy.

    The Female Reproductive System

    The main structures of the female reproductive system are internal to the body (Figure \(\PageIndex{5}\)). They include the paired ovaries, which are small, oval structures that produce eggs and secrete estrogens. The two uterine tubes (also known as Fallopian tubes or oviducts) start near the ovaries and end at the uterus. Their function is to transport eggs from the ovaries to the uterus. If fertilization of an egg occurs, it usually happens while it is traveling through the Fallopian tube. The uterus is a pear-shaped muscular organ that functions to carry a fetus until birth. It can expand greatly to accommodate a growing fetus, and its muscular walls can contract forcefully during labor to push the baby into the vagina. The vagina is a tubular tract connecting the uterus to the outside of the body. The vagina is where sperm are usually deposited during sexual intercourse (via ejaculation). The vagina is also called the birth canal because a baby travels through the vagina to leave the body during birth.

    3D view of female reproductive structures; most structures are described in the text
    Sagittal view of female reproductive structures; most structures are described in the text
    Frontal view of female reproductive structures; most structures are described in the text
    Inferior view (between legs) of female reproductive structures; most structures are described in the text
    Figure \(\PageIndex{5}\): The main structures of the female reproductive system in 3D view, sagittal view, frontal view, and inferior view (between the legs). Note that structures that are homologous to male structures (originating from the same embryonic tissue, such as the ovaries) are color-coded to match the male reproductive system diagrams in Figure \(\PageIndex{4}\).

    The external structures of the female reproductive system are referred to collectively as the vulva. The vulva includes the clitoris, which is homologous to the male penis (the erectile tissues of the penis and clitoris are colored dark green and light green in Figure \(\PageIndex{4}\) and Figure \(\PageIndex{5}\)), and the two pairs of labia (singular, labium), which surround and protect the openings of the urethra and vagina.

    The Menstrual Cycle

    The menstrual cycle refers to natural changes that occur in the female reproductive system each month during the reproductive years. The cycle is necessary for the production of eggs and the preparation of the uterus for pregnancy. It involves changes in both the ovaries and the uterus and is controlled by pituitary and ovarian hormones. Day 1 of the cycle is the first day of the menstrual period, when bleeding from the uterus begins as the built-up endometrium lining the uterus is shed. The endometrium builds up again during the remainder of the cycle, only to be shed again during the beginning of the next cycle if pregnancy does not occur. In the ovaries, the menstrual cycle includes the development of a follicle, ovulation of a secondary oocyte (the name given to an egg before maturation), and the degeneration of the follicle if pregnancy does not occur. Both uterine and ovarian changes during the menstrual cycle are generally divided into three phases, although the phases are not the same in the two organs.

    Ovarian Cycle

    The events of the menstrual cycle that take place in the ovaries make up the ovarian cycle. It consists of changes that occur in the follicles of one of the ovaries. The ovarian cycle is divided into the following three phases: 1) the follicular phase (several follicles begin maturing, but only one is selected to mature completely), 2) ovulation (the mature egg is released), and 3) the luteal phase (progesterone maintains the lining of the uterus for potential implantation of the fertilized egg).

    Follicle-stimulating hormone (FSH), secreted by the pituitary gland, rises and causes several follicles to begin to mature. One maturing follicle becomes dominant and starts releasing estrogen. The resulting rising levels of estrogen prevent multiple follicles from fully developing; non-dominant follicles undergo atresia, or degeneration. The continued rise in estrogen triggers a luteinizing hormone (LH) surge from the pituitary gland, which in turn stimulates ovulation. During the luteal phase, progesterone is secreted by the corpus luteum (a structure formed from the remnants of the follicle that released the egg) until the end of the cycle, when the corpus luteum either degenerates (if the egg was not fertilized) or is maintained by the new pregnancy.

    Uterine Cycle

    The events of the menstrual cycle that take place in the uterus make up the uterine cycle. This cycle consists of changes that occur mainly in the endometrium, which is the layer of tissue that lines the uterus. The uterine cycle is divided into the following three phases: 1) menstruation (shedding of the unfertilized egg and the endometrium lining that has built up), 2) the proliferative phase (the lining of the uterus grows again), and 3) the secretory phase (endometrium is prepared to receive a fertilized egg).

    The ovarian cycle, the uterine cycle, and the changes in hormone levels that occur during the menstrual cycle are illustrated in Figure \(\PageIndex{6}\). Note that the changes in the lining of the endometrium are illustrated in the part showing the uterine cycle phases.

    Diagrams of follicle development, ovarian and uterine cycle phases, and hormone levels, as described in the text
    Figure \(\PageIndex{6}\):

    The correlation of the hormone levels and their effects on the female reproductive system is shown in this timeline of the ovarian and menstrual cycles. The menstrual cycle begins at day one with the start of menses. Ovulation occurs around day 14 of a 28-day cycle, triggered by the LH surge.

    The Sexual Response Cycle

    In 1966, William Masters and Virginia Johnson published a book detailing the results of their observations of nearly 700 people who agreed to participate in their study of physiological responses during sexual behavior. Masters and Johnson observed people having intercourse in a variety of positions, as well as people masturbating, manually or with the aid of a device. Measurements of physiological variables, such as blood pressure and respiration rate, as well as measurements of sexual arousal, such as vaginal lubrication and penile tumescence (swelling associated with an erection) were recorded. In total, Masters and Johnson observed nearly 10,000 sexual acts as a part of their research (Hock, 2008).

    Based on these observations, Masters and Johnson divided the sexual response cycle (Masters & Johnson, 1966) into four phases that are fairly similar in men and women:

    1. Excitement: Activation of the sympathetic branch of the autonomic nervous system defines the excitement phase; heart rate and breathing accelerates, along with increased blood flow to the penis, vaginal walls, clitoris, and nipples. Involuntary muscular movements (myotonia), such as facial grimaces, also occur during this phase.
    2. Plateau: Blood flow, heart rate, and breathing intensify during the plateau phase. During this phase females experience an orgasmic platform—the outer third of the vaginal walls tightening—and males often exhibit a release of pre-ejaculatory fluid.
    3. Orgasm: The shortest but most pleasurable phase is the orgasm phase. After reaching its climax, neuromuscular tension is released and the hormone oxytocin floods the bloodstream—facilitating emotional bonding. Although the rhythmic muscular contractions of an orgasm are temporally associated with ejaculation in males, orgasm and ejaculation are actually two separate physiological processes (and can thus occur independently).
    4. Resolution: The body returns to a pre-aroused state in the resolution phase.

    The final phase, resolution, is where the main differences between males and females occur. Males enter a refractory period of being unresponsive to sexual stimuli. The length of this period depends on age, frequency of recent sexual behavior, level of intimacy with a partner, and novelty. Because females do not have a refractory period, they have a greater potential—physiologically—of having multiple orgasms. Ironically, females are also more likely to “fake” having orgasms (Opperman et al., 2014). As such, whereas the graph for the male sexual response cycle shows only the most common progression through the four phases including orgasm (with a potential partial second cycle starting after the refractory period ends), the graph for the female sexual response cycle shows three alternative patterns- A. progression through all four stages with multiple orgasms, B. prolonged time in the plateau phase with no orgasm, and C. progression through all four stages with a single orgasm (Figure \(\PageIndex{7}\)).

    Graphs of the human male and female sexual response cycles, as described in the text
    Figure \(\PageIndex{7}\):

    Diagram of the common human sexual response cycles as described by Masters and Johnson

    Of interest to note, the sexual response cycle is a universal response to sexual stimuli, and occurs regardless of the type of sexual behavior—whether the behavior is masturbation; romantic kissing; or oral, vaginal, or anal sex (Masters & Johnson, 1966). Further, a partner (of any sex/gender) or environmental object is sufficient, but not necessary, for the sexual response cycle to occur.

    Feature: Human Biology in the News

    Lung, heart, kidney, and other organ transplants have become relatively commonplace, so when they occur, they are unlikely to make the news. However, when America's first penis transplant took place, it was considered very newsworthy.

    In 2016, Massachusetts General Hospital in Boston announced that a team of its surgeons had performed the first penis transplant in the United States. The patient who received the donated penis was a 64-year-old cancer patient. During the 15-hour procedure, the intricate network of nerves and blood vessels of the donor penis were connected with those of the penis recipient. The surgery went well, but doctors reported it would be a few weeks until they would know if normal urination would be possible, and even longer before they would know if sexual functioning would be possible. At the time that news of the surgery was reported in the media, the patient had not shown any signs of rejecting the donated organ. The surgeons also reported they were hopeful that such transplants would become relatively common, and that patient populations would expand to include wounded warriors and transgender males seeking to transition.

    The 2016 Massachusetts operation was not the first penis transplant ever undertaken. The world’s first successful penis transplant was actually performed in 2014 in Cape Town, South Africa. A young man who had lost his penis from complications of a botched circumcision at age 18 was given a donor penis three years later. That surgery lasted nine hours and was highly successful. The young man made a full recovery and regained both urinary and sexual functions in the transplanted organ.

    In 2005, a man in China also received a donated penis in a technically successful operation. However, the patient asked doctors to reverse the procedure just two weeks later, because of psychological problems associated with the transplanted organ for both himself and his wife.

    Summary

    The reproductive system is responsible for the production of gametes (sperm or eggs), the meeting of gametes during fertilization, and the carrying of an embryo/fetus. The gonads (the testes in males and the ovaries in females) produce gametes and sex hormones. Sex hormones (androgens and estrogens) control the development of sex organs before birth, sexual maturation at puberty, and reproduction once sexual maturation has occurred.

    Sexual differentiation is the process of becoming male or female. A gene on the Y chromosome called SRY is critical for stimulating testis development and subsequently the development of male reproductive structures. Without a Y chromosome, the embryo develops a female body plan.

    Undifferentiated embryonic tissues develop into different homologous structures in male and female fetuses, such as the testes and ovaries, or the penis and clitoris. However, the tissue that forms the internal reproductive structures stems from ducts that will develop into only male (Wolffian) or only female (Müllerian) structures. To be able to reproduce as an adult, one of these systems must develop properly and the other must degrade.

    Further development of the reproductive systems occurs at puberty. The increase in sex steroid hormones leads to maturation of the gonads and other reproductive organs. Important signals of sexual maturity include spermarche (first ejaculation of semen) in males, and menarche (first menstrual period) in females. 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.

    The main male reproductive structures are external to the body: the penis and the paired testes. The penis contains the urethra and is able to stiffen during sexual arousal. Sperm passes out of the body through the urethra during orgasm, called ejaculation. The testes produce sperm and testosterone, and are located in the scrotum. Luteinizing hormone (LH) stimulates cells in the testes to secrete testosterone. Both follicle stimulating hormone (FSH) and testosterone are needed for spermatogenesis. Additionally, testosterone maintains libido (sex drive), plays a role in erection, is necessary for prostate gland function, and is important for muscle development and bone growth. Internal ducts and glands include the vas deferens (which transports sperm from the epididymis to the urethra), the prostate gland and the seminal vesicles (which produce fluids that become part of semen).

    The external structures of the female reproductive system are referred to as the vulva: the clitoris and the two pairs of labia surrounding and protecting the openings of the urethra and vagina. The main female reproductive structures are internal to the body and include the paired ovaries (which produce eggs and secrete estrogens), the two Fallopian tubes (which transport eggs from the ovaries to the uterus), the uterus (a muscular organ that carries a fetus until birth), and the vagina. The vagina is a tubular tract connecting the uterus to the outside of the body. Sperm are usually deposited in the vagina during sexual intercourse (via ejaculation), and a baby travels through the vagina (also called the birth canal) to leave the body.

    The menstrual cycle in females is necessary for the production of eggs and the preparation of the uterus for pregnancy. It involves changes in both the ovaries and the uterus and is controlled by pituitary and ovarian hormones. The ovarian cycle is divided into the follicular phase (several follicles begin maturing, but only one is selected to mature completely), ovulation (the mature egg is released), and the luteal phase (progesterone maintains the lining of the uterus for potential implantation of the fertilized egg). The uterine cycle is divided into menstruation (shedding of the unfertilized egg and the endometrium lining that has built up), the proliferative phase (the lining of the uterus grows again), and the secretory phase (endometrium is prepared to receive a fertilized egg).

    Masters and Johnson (1966) divided the sexual response cycle into four phases that are fairly similar in men and women: excitement (heart rate and breathing accelerates, increased blood flow to the penis, vaginal walls, clitoris, and nipples), plateau (blood flow, heart rate, and breathing intensify; females experience an orgasmic platform—the outer third of the vaginal walls tightening—and males often exhibit a release of pre-ejaculatory fluid), orgasm (shortest but most pleasurable phase), and resolution (the body returns to a pre-aroused state). The main differences between males and females occur during resolution. Males enter a refractory period of being unresponsive to sexual stimuli. Females do not have a refractory period, so they have a greater potential for having multiple orgasms.

    References

    Note: These are no references added to the content of this page. Refer to the text attributions to locate citations for articles from outside sources used.

    Additional Resources

    Sex determination may be more complicated than originally thought. Check out this video to learn more:

    Have you ever heard of premenstrual syndrome, also known as PMS? Learn more about what it is and why some women get it here:

    Morning erections are part of the normal sleep cycle in men. Learn more here:

    Attributions

    Figures:

    1. Reproductive systems figure- cropped from Organ Systems of the Human Body: Organs that work together are grouped into organ systems. (https://open.oregonstate.education/aandp); Reproductive figure https://open.oregonstate.education/a...ody/#fig_1_2_2; originally found in "Human Organs and Organ Systems" by Suzanne Wakim & Mandeep Grewal, LibreTexts is licensed under CC BY-NC.
    2. Human chromosome Y by National Center for Biotechnology Information, Public domain, via Wikimedia Commons
    3. Sexual differentiation by OpenStax College, CC BY 3.0, via Wikimedia Commons
    4. Male reproductive system: 3D view, Sagittal view, and Frontal view by R. Dewaele (Bioscope, Unige), J. Abdulcadir (HUG), C. Brockmann (Bioscope, Unige), O. Fillod, S. Valera-Kummer (DIP), www.unige.ch/ssi, CC BY-SA 4.0, via Wikimedia Commons
    5. Female reproductive system: 3D view, Sagittal view, Frontal view 1, and Frontal view 2 by R. Dewaele (Bioscope, Unige), J. Abdulcadir (HUG), C. Brockmann (Bioscope, Unige), O. Fillod, S. Valera-Kummer (DIP), www.unige.ch/ssi, CC BY-SA 4.0, via Wikimedia Commons
    6. Menstrual cycle timeline- from " Anatomy and Physiology of the Female Reproductive System" by LibreTexts is licensed under notset .
    7. Sexual response cycle by Avril1975, Public domain, via Wikimedia Commons

    Text adapted from:

    1. "Introduction to the Reproductive System" by Suzanne Wakim & Mandeep Grewal, LibreTexts is licensed under CC BY-NC.
    2. "Anatomy of the Male Reproductive System" by Whitney Menefee, Julie Jenks, Chiara Mazzasette, & Kim-Leiloni Nguyen, LibreTexts is licensed under CC BY.
    3. "Human Organs and Organ Systems" by Suzanne Wakim & Mandeep Grewal, LibreTexts is licensed under CC BY-NC.
    4. Hormones & Behavior by Randy J. Nelson, licensed CC BY-NC-SA 4.0 via Noba Project.
    5. "Development of the Male and Female Reproductive Systems" by Whitney Menefee, Julie Jenks, Chiara Mazzasette, & Kim-Leiloni Nguyen, LibreTexts is licensed under CC BY.
    6. Sexual Maturation during Puberty section (heavily edited): " Growth in Adolescence" by Martha Lally & Suzanne Valentine-French, LibreTexts is licensed under CC BY-NC-SA.
    7. "Physical Changes in Adolescence" by Paris, Ricardo, Raymond, & Johnson, LibreTexts is licensed under CC BY .
    8. "Functions of the Male Reproductive System" by Suzanne Wakim & Mandeep Grewal, LibreTexts is licensed under CC BY-NC.
    9. "Menstrual Cycle" by Suzanne Wakim & Mandeep Grewal, LibreTexts is licensed under CC BY-NC .
    10. 10.3 Sexual Behavior (Psychology 2e) by Rose M. Spielman, William J. Jenkins, and Marilyn D. Lovett, licensed CC BY 4.0 via OpenStax.
    11. Human Sexual Anatomy and Physiology by Don Lucas and Jennifer Fox, licensed CC BY-NC-SA 4.0 via Noba Project.
    12. Human Biology in the News feature: "Structures of the Male Reproductive System" by Suzanne Wakim & Mandeep Grewal, LibreTexts is licensed under CC BY-NC.

    Changes: Text (and images) from above twelve sources pieced together with some modifications, transitions and additional content added by Naomi I. Gribneau Bahm, PhD., Psychology Professor at Cosumnes River College, Sacramento, CA.


    This page titled 13.2: Sexual Development, Anatomy and Physiology is shared under a mixed license and was authored, remixed, and/or curated by Naomi Bahm (ASCCC Open Educational Resources Initiative (OERI)) .