Unit III Sexual Reproduction PDF

Republic of the Philippines NUEVA ECIJA UNIVERSITY OF SCIENCE AND TECHNOLOGY San Isidro Campus, San Isidro, Nueva Ecija, Philippines ISO 9001:2015 CERTIFIED COLLEGE OF EDUCATION UNIT III...

Republic of the Philippines NUEVA ECIJA UNIVERSITY OF SCIENCE AND TECHNOLOGY San Isidro Campus, San Isidro, Nueva Ecija, Philippines ISO 9001:2015 CERTIFIED COLLEGE OF EDUCATION UNIT III Sexual Reproduction Page | 1 Overview Sexual development refers to the series of physical, emotional, and psychological changes that take place as individuals grow and mature, ultimately shaping their sexual identity and capacity for reproduction. The physical aspects of sexual development are most prominent during puberty, a stage that typically occurs between ages 8 and 16. During this time, hormonal shifts trigger various bodily changes: in females, this includes the development of breasts, the start of menstruation, and the growth of pubic and underarm hair; in males, it involves the enlargement of the testes and penis, a deepening of the voice, and the growth of facial hair. These transformations reflect the body’s preparation for sexual maturity and reproduction. Alongside physical changes, sexual development also encompasses the formation of sexual identity and orientation, which evolves over time. Adolescents begin to recognize and explore their sexual feelings, attractions, and preferences, which may be influenced by a range of personal, social, and cultural factors. Emotional aspects of sexual development are equally significant, as individuals learn to navigate relationships, intimacy, and personal boundaries. Healthy sexual development often depends on supportive relationships, education, and self-reflection, while negative or confusing experiences can impact one's sense of sexual identity or expression. Overall, sexual development is a dynamic and multi- dimensional process that integrates physical, emotional, and social dimensions, guiding individuals as they come to understand their sexual selves. Learning Objectives At the end of the chapter, the students should be able to Outline how sexual development and differentiation happen. Describe puberty and its implications. Discuss the menstrual cycle and explain why it happens. “Nourishing the mind, nurturing the heart, leading the Future “ Telefax No. (044) 463-0226 [email protected] www.neust.edu.ph  Republic of the Philippines NUEVA ECIJA UNIVERSITY OF SCIENCE AND TECHNOLOGY San Isidro Campus, San Isidro, Nueva Ecija, Philippines ISO 9001:2015 CERTIFIED COLLEGE OF EDUCATION Lesson Proper Page | 2 Sexual Development and Differentiation Sexual development and differentiation are a dynamic biological process that begins at conception and continues through various stages of life. This process leads to the formation of sexual characteristics that define an individual’s ability to reproduce and also shape their sexual identity. It is influenced by genetic, hormonal, and environmental factors, and it occurs in several stages: from early embryonic development, through puberty, and into adulthood. This module will explore how sexual differentiation occurs during different stages of life, including the molecular, genetic, and hormonal processes that influence physical and sexual identity development. Genetic Sex Determination at Conception Sexual differentiation starts at conception, the moment when the sperm fertilizes the egg. The genetic material inherited from both parents determines the individual’s chromosomal sex and lays the foundation for future sexual development. XX and XY Chromosomes: The primary genetic determinant of sex lies in the sex chromosomes. Humans typically have 46 chromosomes, 23 of which are inherited from each parent. The X chromosome is larger and carries many genes, while the Y chromosome is smaller and contains fewer genes. A typical female has two X chromosomes (XX), and a typical male has one X and one Y “Nourishing the mind, nurturing the heart, leading the Future “ Telefax No. (044) 463-0226 [email protected] www.neust.edu.ph  Republic of the Philippines NUEVA ECIJA UNIVERSITY OF SCIENCE AND TECHNOLOGY San Isidro Campus, San Isidro, Nueva Ecija, Philippines ISO 9001:2015 CERTIFIED COLLEGE OF EDUCATION chromosome (XY). The Y chromosome carries a crucial gene, known as the SRY gene (Sex- determining Region Y), which is responsible for initiating the development of male characteristics. In the absence of a Y chromosome (XX combination), the pathway for female development is triggered. The Role of the SRY Gene: Page | 3 The SRY gene on the Y chromosome is pivotal in male differentiation. Around the 7th week of gestation, the SRY gene activates, triggering the differentiation of the gonads into testes rather than ovaries. These testes then begin to produce male hormones (androgens), primarily testosterone, which guide the development of male internal and external genitalia. Embryonic Development and Gonadal Differentiation (Weeks 1-8) In the early stages of embryonic development (from conception to the 8th week), the embryo has the potential to develop into either male or female. At this point, both males and females share the same early structures, known as indifferent gonads, which can develop into testes or ovaries. Gonadal Development: The presence of the SRY gene in the male embryo triggers the differentiation of these indifferent gonads into testes, which begin to secrete testosterone. In the absence of the SRY gene, the gonads develop into ovaries, and female reproductive structures begin to form. This differentiation is crucial, as the gonads are responsible for producing the hormones that will drive further sexual development. Müllerian and Wolffian Ducts: In the early stages of development, embryos possess both the Müllerian ducts and the Wolffian ducts. These ducts have the potential to form the internal reproductive structures. In male embryos, testosterone stimulates the development of the Wolffian ducts into male internal genitalia, including the epididymis, vas deferens, and seminal vesicles. The Müllerian ducts regress in males. In female embryos, in the absence of testosterone, the Müllerian ducts develop into the fallopian tubes, uterus, and vagina, while the Wolffian ducts regress. “Nourishing the mind, nurturing the heart, leading the Future “ Telefax No. (044) 463-0226 [email protected] www.neust.edu.ph  Republic of the Philippines NUEVA ECIJA UNIVERSITY OF SCIENCE AND TECHNOLOGY San Isidro Campus, San Isidro, Nueva Ecija, Philippines ISO 9001:2015 CERTIFIED COLLEGE OF EDUCATION External Genital Differentiation (Weeks 9-12) Between the 9th and 12th weeks of development, the external genitalia begin to form. Initially, male and female embryos have identical genital structures, but hormonal influences determine their differentiation. Page | 4 Male Genital Development: In male embryos, the presence of testosterone secreted by the testes causes the genital tubercle to elongate and form the penis, while the urethral folds fuse to create the urethra within the penis. The labioscrotal swellings become the scrotum, which eventually houses the testes. Testosterone also influences the descent of the testes into the scrotum. Female Genital Development: In female embryos, the absence of significant testosterone results in the genital tubercle developing into the clitoris, and the urethral folds becoming the labia minora. The labioscrotal swellings form the labia majora. The internal structures, including the vagina, continue to develop, forming the female external genitalia. Pubertal Hormonal Changes and Sexual Maturation (Ages 8-16) Puberty marks the onset of sexual maturation, triggered by the activation of the hypothalamic-pituitary-gonadal (HPG) axis. This hormonal system regulates the production of sex hormones and leads to the development of secondary sexual characteristics. Puberty typically begins between the ages of 8 and 16 and continues into early adulthood. Male Puberty: During male puberty, the brain signals the testes to produce testosterone in response to the release of gonadotropin-releasing hormone (GnRH) from the hypothalamus. Testosterone stimulates the development of male secondary sexual characteristics, such as muscle growth, voice deepening, facial and body hair growth, and penile growth. Spermatogenesis, or the production of sperm, also begins during puberty. Female Puberty: In females, the ovaries start to produce estrogen and progesterone, which are responsible for the development of breast tissue, the widening of the hips, and the initiation of menstrual cycles. These hormonal changes also influence the maturation of the uterus, vagina, and “Nourishing the mind, nurturing the heart, leading the Future “ Telefax No. (044) 463-0226 [email protected] www.neust.edu.ph  Republic of the Philippines NUEVA ECIJA UNIVERSITY OF SCIENCE AND TECHNOLOGY San Isidro Campus, San Isidro, Nueva Ecija, Philippines ISO 9001:2015 CERTIFIED COLLEGE OF EDUCATION fallopian tubes. The female body prepares for potential pregnancy, with the onset of menarche (first menstruation) signaling reproductive capability. Sexual Identity, Gender Identity, and Orientation Page | 5 While sexual development is often associated with biological processes, sexual identity and gender identity are shaped by a combination of biological, psychological, social, and cultural factors. These aspects of development evolve, influenced by personal experiences and societal norms. Sexual Identity: Sexual identity refers to how individuals perceive themselves in terms of their sexual preferences, behaviors, and attractions. This aspect of identity is often formed during adolescence as individuals begin exploring relationships, sexual orientation, and intimacy. Gender Identity: Gender identity refers to an individual’s internal sense of being male, female, or another gender, and it may or may not align with the sex assigned at birth. While biological sex is determined by chromosomes and hormones, gender identity is a deeply personal understanding of one’s gender. Some individuals may identify as transgender, meaning their gender identity does not match the sex assigned at birth. Sexual Orientation: Sexual orientation refers to whom a person is romantically or sexually attracted to. Common categories include heterosexual, homosexual, and bisexual, though sexual orientation exists on a spectrum and can be fluid over time. Disorders of Sexual Development (DSDs) Disorders of Sexual Development (DSDs) are conditions where an individual’s sexual differentiation does not follow the typical developmental pathway. These conditions may be caused by chromosomal abnormalities, hormonal imbalances, or genetic mutations. Androgen Insensitivity Syndrome (AIS): Individuals with XY chromosomes who are affected by AIS have a mutation in the androgen receptor, preventing their bodies from responding to male hormones (androgens). As a result, “Nourishing the mind, nurturing the heart, leading the Future “ Telefax No. (044) 463-0226 [email protected] www.neust.edu.ph  Republic of the Philippines NUEVA ECIJA UNIVERSITY OF SCIENCE AND TECHNOLOGY San Isidro Campus, San Isidro, Nueva Ecija, Philippines ISO 9001:2015 CERTIFIED COLLEGE OF EDUCATION despite having male chromosomes and internal testes, their external genitalia develop in a typically female pattern. Congenital Adrenal Hyperplasia (CAH): CAH is a genetic disorder that causes the adrenal glands to overproduce androgens (male hormones). In female individuals, this Page | 6 can lead to ambiguous genitalia at birth, with characteristics that may appear more male than female. This condition requires medical attention and sometimes surgical intervention. Puberty and Its Implications Puberty is a pivotal stage in human development, marking the transition from childhood to adulthood. This period is characterized by a series of physical, emotional, and psychological changes that prepare the body for reproduction. Puberty is driven by hormonal changes that lead to the development of secondary sexual characteristics and the maturation of the reproductive system. These changes also influence cognitive and social development, shaping an individual’s identity and emotional well-being. This module will provide a detailed description of puberty, its biological processes, and the psychological and social implications it has on adolescents. The Biological Process of Puberty Puberty is initiated by the activation of the hypothalamic-pituitary-gonadal (HPG) axis, a complex system that regulates the release of sex hormones. The timing and progression of puberty can vary among individuals, typically occurring between the ages of 8 and 16. The changes that take place during puberty are primarily influenced by genetic, hormonal, and environmental factors. The Role of Hormones: The hypothalamus begins to release gonadotropin-releasing hormone (GnRH), which stimulates the pituitary gland to produce luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These hormones, in turn, signal the gonads (testes in males, ovaries in females) to produce sex hormones (testosterone in males, estrogen in females). These hormones drive the physical changes associated with puberty. In Males: The testes begin producing testosterone, which stimulates the development of secondary sexual characteristics such as increased muscle mass, facial and body hair, deepening of the voice, and the growth of the penis and testes. Testosterone also stimulates the production of sperm, marking the onset of fertility. Puberty in males is often signaled by the first ejaculation or the appearance of pubic hair. In Females: The ovaries begin producing estrogen and progesterone, hormones that lead to the development of secondary sexual characteristics like breast development, widening of the hips, and the onset of menstruation (menarche). The uterus, vagina, and fallopian tubes also mature “Nourishing the mind, nurturing the heart, leading the Future “ Telefax No. (044) 463-0226 [email protected] www.neust.edu.ph  Republic of the Philippines NUEVA ECIJA UNIVERSITY OF SCIENCE AND TECHNOLOGY San Isidro Campus, San Isidro, Nueva Ecija, Philippines ISO 9001:2015 CERTIFIED COLLEGE OF EDUCATION during this time, preparing the body for potential reproduction. The menstrual cycle becomes regular, and females become capable of bearing children. Physical Changes During Puberty Page | 7 Puberty involves numerous physical changes, many of which are directly linked to the development of secondary sexual characteristics and the maturation of the reproductive system. These changes not only signify physical maturation but also contribute to the development of body image and self-esteem. Growth Spurts: One of the most noticeable aspects of puberty is the growth spurt, which typically occurs earlier in females than in males. This rapid increase in height and weight is driven by the release of growth hormones and sex hormones. In females, growth spurt usually occurs before menstruation begins, while in males, it often occurs later in puberty. Development of Secondary Sexual Characteristics: o In Males: Puberty leads to the growth of facial and body hair (underarms, chest, and pubic area), voice deepening, and the development of broader shoulders. o In Females: Estrogen causes the development of breasts and the broadening of the hips, and the appearance of pubic hair marks the development of female sexual maturity. Reproductive Maturation: In both males and females, the development of reproductive organs progresses. In males, the testes begin producing sperm, while in females, the menstrual cycle starts, signifying the ability to ovulate and conceive. Emotional and Psychological Changes During Puberty Puberty does not only affect physical growth but also brings about significant emotional and psychological changes. Adolescents undergo fluctuating moods, increased emotional intensity, and a heightened need for independence. These changes are largely due to hormonal shifts but are also influenced by social and environmental factors. Mood Swings and Emotional Regulation: During puberty, fluctuations in estrogen and testosterone can lead to mood swings, irritability, and heightened emotions. Adolescents may experience a range of intense feelings as they navigate new experiences and challenges in their social and academic lives. Increased Self-awareness and Identity Formation: Puberty is a critical period for the development of self-identity. As physical changes “Nourishing the mind, nurturing the heart, leading the Future “ Telefax No. (044) 463-0226 [email protected] www.neust.edu.ph  Republic of the Philippines NUEVA ECIJA UNIVERSITY OF SCIENCE AND TECHNOLOGY San Isidro Campus, San Isidro, Nueva Ecija, Philippines ISO 9001:2015 CERTIFIED COLLEGE OF EDUCATION occur, adolescents begin to explore their sexual identity, gender identity, and personal values. This period can also be marked by increased peer pressure, as adolescents start to define their place in the social structure and seek acceptance from others. Cognitive and Social Development: During puberty, adolescents experience significant changes in cognitive development, Page | 8 moving from concrete thinking to more abstract reasoning. They begin to develop the ability to think critically, consider multiple perspectives, and make decisions that can impact their future. Puberty also ushers in a greater desire for independence from parents and a stronger focus on peer relationships, which play a central role in shaping their social lives. The Implications of Puberty Health and Well-being: While puberty is a natural and necessary stage of life, it can come with certain challenges. Adolescents may struggle with issues such as body image, particularly in cultures that place significant emphasis on physical appearance. Girls may face societal pressures related to beauty standards, while boys may feel expectations regarding strength and masculinity. Puberty can also trigger issues like acne, menstrual discomfort, or changes in appetite. Sexuality and Reproductive Health: Puberty is the time when adolescents begin to explore their sexual identities and may experience their first sexual feelings and attractions. This period of increased sexual awareness comes with the need for education about sexual health, contraception, and consent. Inadequate knowledge about these topics can lead to risky behaviors, unintended pregnancies, or sexually transmitted infections (STIs). It is critical that adolescents receive accurate and comprehensive sexual education to navigate this complex phase healthily. Mental Health: Adolescence is a period of emotional turbulence, and the hormonal changes associated with puberty can contribute to feelings of anxiety, depression, or self-doubt. Mental health challenges may arise, particularly as adolescents cope with the stresses of growing up, academic pressures, and evolving social dynamics. It is important for educators, parents, and health professionals to support adolescents through these changes and provide resources to help manage mental health concerns. “Nourishing the mind, nurturing the heart, leading the Future “ Telefax No. (044) 463-0226 [email protected] www.neust.edu.ph  Republic of the Philippines NUEVA ECIJA UNIVERSITY OF SCIENCE AND TECHNOLOGY San Isidro Campus, San Isidro, Nueva Ecija, Philippines ISO 9001:2015 CERTIFIED COLLEGE OF EDUCATION Puberty in Different Populations Puberty does not occur in the same way for everyone, and factors like genetics, nutrition, and health conditions can influence the timing and experience of puberty. Page | 9 Early or Delayed Puberty: Some adolescents experience precocious puberty, where puberty begins earlier than usual (before age 8 in girls and before age 9 in boys). This can be challenging, both socially and emotionally, as early physical maturation may lead to feelings of awkwardness or isolation. Conversely, delayed puberty can lead to feelings of self-consciousness or frustration, especially if peers are maturing at a faster rate. Cultural and Societal Influences: The experience of puberty is also shaped by cultural, familial, and societal expectations. In some cultures, puberty is associated with particular rites of passage or celebrations. In others, the focus may be on personal responsibility, academic achievement, or future planning. Adolescents who grow up in cultures with restrictive views on sexuality or gender may face unique challenges in navigating puberty and identity development. The Menstrual Cycle – An Overview and Its Biological Significance The menstrual cycle is a fundamental process in female reproductive biology, marking the monthly preparation of the body for a potential pregnancy. Understanding the menstrual cycle is crucial not only for recognizing reproductive health but also for understanding hormonal balance, fertility, and overall well-being. In this module, we will explore the menstrual cycle in detail—its phases, hormonal regulation, and the physiological changes that occur. We will also discuss why the menstrual cycle happens and its significance in human reproduction. What Is the Menstrual Cycle? The menstrual cycle is a recurring process that involves the shedding of the uterine lining (endometrium) when pregnancy has not occurred. It typically lasts about 28 days, though it can vary from person to person. The cycle prepares the female reproductive system for a potential pregnancy, and when fertilization does not take place, the cycle culminates in menstruation—commonly referred to as a period. The menstrual cycle is controlled by a complex interplay of hormones and takes place in the ovaries and the uterus. It involves the maturation of an egg (or ovum) within the ovaries and the preparation of the uterus for possible implantation of a fertilized egg. “Nourishing the mind, nurturing the heart, leading the Future “ Telefax No. (044) 463-0226 [email protected] www.neust.edu.ph  Republic of the Philippines NUEVA ECIJA UNIVERSITY OF SCIENCE AND TECHNOLOGY San Isidro Campus, San Isidro, Nueva Ecija, Philippines ISO 9001:2015 CERTIFIED COLLEGE OF EDUCATION The Phases of the Menstrual Cycle The menstrual cycle can be divided into four distinct phases, each driven by hormonal fluctuations and corresponding physical changes: Page | 10 A. Menstrual Phase (Day 1–5) What Happens: The menstrual phase is the beginning of the cycle, marked by the shedding of the uterine lining. This is when a woman experiences her period. If the egg released in the previous cycle is not fertilized, the hormone levels (estrogen and progesterone) drop, causing the thickened endometrium (uterine lining) to break down and be expelled from the body through the vagina. This shedding is what is known as menstruation. Hormonal Changes: The drop in progesterone and estrogen levels signals the shedding of the endometrial lining. B. Follicular Phase (Day 1–13) What Happens: This phase overlaps with the menstrual phase at the start. During the follicular phase, the follicles in the ovaries begin to mature under the influence of follicle-stimulating hormone (FSH), which is released from the pituitary gland. One follicle becomes dominant and prepares to release an egg (ovum). The uterus also begins to rebuild its lining in anticipation of a possible pregnancy. Hormonal Changes: As the follicles mature, they produce increasing amounts of estrogen, which helps rebuild the endometrium and stimulates the release of luteinizing hormone (LH). The rising estrogen also signals the pituitary to prepare for ovulation. C. Ovulatory Phase (Day 14) What Happens: Ovulation is the release of a mature egg from the dominant follicle in the ovary. This occurs around day 14 of a 28-day cycle (though this can vary). The egg is released into the fallopian tube, where it may meet sperm for fertilization. The time of ovulation is the most fertile period of the menstrual cycle. Hormonal Changes: The surge in LH triggered by high estrogen levels causes ovulation. The egg is released and moves down the fallopian tube toward the uterus. At the same time, estrogen levels begin to decrease, and progesterone starts to rise in preparation for the next phase of the cycle. D. Luteal Phase (Day 15–28) What Happens: After ovulation, the ruptured follicle transforms into a structure called the corpus luteum, which begins producing progesterone. Progesterone thickens the uterine lining, making it receptive for a fertilized egg. If fertilization does not occur, the corpus luteum breaks down, leading to a drop in progesterone and estrogen levels, which triggers the shedding of the uterine lining, and the cycle starts again. Hormonal Changes: High levels of progesterone from the corpus luteum maintain the thickened endometrial lining. If pregnancy does not occur, the corpus luteum degenerates, leading to a drop in progesterone and estrogen levels, signaling the beginning of menstruation. “Nourishing the mind, nurturing the heart, leading the Future “ Telefax No. (044) 463-0226 [email protected] www.neust.edu.ph  Republic of the Philippines NUEVA ECIJA UNIVERSITY OF SCIENCE AND TECHNOLOGY San Isidro Campus, San Isidro, Nueva Ecija, Philippines ISO 9001:2015 CERTIFIED COLLEGE OF EDUCATION Why Does the Menstrual Cycle Happen? The menstrual cycle occurs as part of the body’s reproductive system, preparing the female body for pregnancy each month. It is driven by a combination of hormonal signals that coordinate the processes of ovulation (the release of an egg from the ovaries) and the preparation of the uterus Page | 11 (endometrial thickening) for implantation. The cycle exists for the following reasons: To Produce Eggs for Fertilization: The primary biological purpose of the menstrual cycle is to prepare the body for reproduction. The cycle ensures that a mature egg is available each month for potential fertilization by sperm. If the egg is fertilized, it can implant in the uterus and develop into a pregnancy. To Prepare the Uterus for Pregnancy: The thickening of the uterine lining each cycle ensures that if fertilization occurs, there is a nutrient-rich environment to support the embryo. The endometrium is designed to nourish and protect the developing fetus during the early stages of pregnancy. To Shed the Uterine Lining if Pregnancy Does Not Occur: If the egg is not fertilized, the body must "reset" and prepare for the next cycle. This is done by shedding the uterine lining, which is no longer needed, leading to menstruation. This process allows the uterus to start fresh, making it ready for another possible pregnancy. Hormonal Regulation and Feedback Mechanisms The menstrual cycle is tightly controlled by hormones, with a feedback loop between the hypothalamus, pituitary gland, ovaries, and uterus. Hypothalamus: The hypothalamus in the brain releases gonadotropin-releasing hormone (GnRH), which signals the pituitary gland to release FSH and LH, hormones that regulate the ovaries. Pituitary Gland: The pituitary secretes FSH to stimulate follicle development in the ovaries, and LH to trigger ovulation. Ovaries: The ovaries produce estrogen and progesterone in response to FSH and LH. These hormones help regulate the thickening of the uterine lining, ovulation, and the maintenance of the corpus luteum. Uterus: The uterine lining (endometrium) changes in response to hormonal signals, thickening in the first half of the cycle in anticipation of pregnancy and shedding in the event of no pregnancy. This hormonal regulation is a classic example of a negative feedback loop: for example, rising estrogen levels lead to the release of LH, which then triggers ovulation. Once ovulation occurs, estrogen and progesterone levels rise, leading to the thickening of the uterine lining, and if no pregnancy occurs, these hormone levels drop, triggering menstruation. “Nourishing the mind, nurturing the heart, leading the Future “ Telefax No. (044) 463-0226 [email protected] www.neust.edu.ph  Republic of the Philippines NUEVA ECIJA UNIVERSITY OF SCIENCE AND TECHNOLOGY San Isidro Campus, San Isidro, Nueva Ecija, Philippines ISO 9001:2015 CERTIFIED COLLEGE OF EDUCATION Common Irregularities and Health Implications The menstrual cycle can sometimes be irregular or abnormal, which may reflect underlying health issues. Some common menstrual irregularities include: Page | 12 Amenorrhea: The absence of menstruation, which can be caused by factors such as pregnancy, hormonal imbalances, excessive exercise, or eating disorders. Dysmenorrhea: Painful menstruation, often associated with cramps caused by uterine contractions. It can also be a sign of conditions such as endometriosis or fibroids. Menorrhagia: Excessive menstrual bleeding, which could indicate conditions like fibroids, polyps, or hormonal imbalances. Polycystic Ovary Syndrome (PCOS): A condition that affects hormone levels, leading to irregular periods, ovarian cysts, and sometimes infertility. Regular cycles are generally a sign of reproductive health, but any significant changes should be discussed with a healthcare provider for proper diagnosis and treatment. “Nourishing the mind, nurturing the heart, leading the Future “ Telefax No. (044) 463-0226 [email protected] www.neust.edu.ph