Male Reproductive System PDF

Chapter 5 Describe the structure and function of the male human reproductive system. 1. Primary Sex Organs (Gonads) Testes: o The testes are the primary reproductive organs in males. They are oval-shaped glands housed in the scrotum, a sac that helps maintain the opti...

Chapter 5 Describe the structure and function of the male human reproductive system. 1. Primary Sex Organs (Gonads) Testes: o The testes are the primary reproductive organs in males. They are oval-shaped glands housed in the scrotum, a sac that helps maintain the optimal temperature for sperm production (approximately 1.1°C lower than the body’s core temperature). o The cremaster muscle within the scrotum contracts to raise the testes closer to the body when cold, helping regulate this temperature. o The seminiferous tubules within the testes are the specific sites of spermatogenesis (sperm production). The seminiferous tubules contain: § Leydig Cells (Interstitial Cells): These cells, found between the seminiferous tubules, produce testosterone, the primary male sex hormone. Testosterone is essential for the development of male secondary sexual characteristics (such as muscle growth and body hair) and regulates sperm production. § Sertoli Cells (Nurse Cells): Located within the seminiferous tubules, these cells support, nourish, and protect developing sperm cells, aiding in the process of spermatogenesis. 2. Duct System  Epididymis: o After sperm are produced in the seminiferous tubules, they move to the epididymis, a coiled tube located on the back of each testis. Here, sperm mature and gain the ability to swim, becoming capable of fertilizing an egg. Vas Deferens: o The vas deferens is a long, muscular tube that transports mature sperm from the epididymis to the ejaculatory ducts. During ejaculation, the vas deferens propels sperm forward toward the urethra, where they mix with fluid from the seminal vesicles, prostate gland, and bulbourethral glands. 3. Accessory Glands Seminal Vesicles: o These glands secrete a fluid rich in fructose that provides energy to sperm. This fluid makes up a significant portion of the semen, supporting sperm motility and viability. Prostate Gland: o Located just below the bladder, the prostate gland adds an alkaline fluid to semen, helping to neutralize the acidity of the female reproductive tract, which improves sperm survival. Bulbourethral Glands (Cowper’s Glands): o These glands produce a lubricating mucus that also neutralizes any acidic urine residue in the urethra, providing a safer environment for sperm during ejaculation. 4. External Genitalia Penis: o The penis serves as the external organ for delivering semen into the female reproductive tract. It contains erectile tissue that becomes engorged with blood, leading to an erection, which is necessary for the penetration required for sexual reproduction. Scrotum: o The scrotum is a sac that holds the testes outside the body cavity, maintaining the temperature necessary for sperm production. 5. Hormonal Regulation Hypothalamus and Pituitary Gland: o The hypothalamus releases Gonadotropin-Releasing Hormone (GnRH), which stimulates the anterior pituitary gland to release Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH). FSH: o This hormone targets the Sertoli cells in the seminiferous tubules, supporting the process of spermatogenesis. LH: o LH stimulates the Leydig cells to produce testosterone, which is essential for male reproductive function, promoting both sperm production and secondary sexual characteristics. Hormonal Regulation of Testicular Function The hormonal regulation of sperm production involves several key hormones: Gonadotropin-Releasing Hormone (GnRH): o Released by the hypothalamus and stimulates the anterior pituitary gland.  Follicle-Stimulating Hormone (FSH): o Released by the anterior pituitary in response to GnRH. o Targets the Sertoli cells in the testes to support spermatogenesis. Luteinizing Hormone (LH): o Also released by the anterior pituitary in response to GnRH. o Stimulates the Leydig cells to produce testosterone, which further promotes sperm production and influences male characteristics. Function of the vas deferens, epididymis, bulbourethral gland, prostate gland, seminal vesicle, scrotum, testis, ejaculatory duct, urethra. Vas Deferens Function: The vas deferens transports mature sperm from the epididymis to the ejaculatory ducts in preparation for ejaculation. Its muscular walls help propel sperm through peristaltic contractions. 2. Epididymis Function: The epididymis is where sperm mature and gain the ability to swim. It also serves as a storage site for sperm until ejaculation. 3. Bulbourethral Glands (Cowper’s Glands) Function: These glands produce an alkaline mucus-like fluid that neutralizes acidic urine residue in the urethra and lubricates the tip of the penis, making it easier for sperm to travel during ejaculation. 4. Prostate Gland  Function: The prostate gland secretes a slightly alkaline fluid that makes up about one-third of semen volume. This fluid contains prostate-specific antigen (PSA), which helps liquefy semen and increase sperm mobility, and has antibiotic properties that protect sperm from bacterial infection. 5. Seminal Vesicles Function: Seminal vesicles contribute about 60% of the semen volume. Their fluid contains fructose, which provides energy for sperm, as well as other substances that promote sperm motility and success in the female reproductive tract by neutralizing its acidic environment. 6. Scrotum Function: The scrotum is a sac-like structure that houses the testes and regulates their temperature to ensure optimal sperm production, keeping it slightly cooler than body temperature. 7. Testis (Plural: Testes) Function: The testes produce sperm through spermatogenesis in the seminiferous tubules and synthesize testosterone, which is crucial for male reproductive development and secondary sexual characteristics. 8. Ejaculatory Duct Function: The ejaculatory duct is formed by the merging of the vas deferens and seminal vesicle duct, and it passes through the prostate gland to join the urethra. During ejaculation, it serves as a conduit through which semen is expelled. 9. Urethra Function: The urethra is a dual-purpose duct that carries urine from the bladder and semen from the reproductive tract to the external urethral orifice at the tip of the penis. Additional Note: Components of Semen Semen, composed of sperm and fluids from the accessory glands, provides nutrients (such as fructose), activates and protects sperm, and facilitates their movement through the male and female reproductive tracts. Sperm Production in Seminiferous Tubules: Sperm is produced in the seminiferous tubules within the testes through a process called spermatogenesis. Maturation in the Epididymis: Sperm exits the seminiferous tubules and enters the epididymis, where it matures and gains motility, becoming capable of fertilizing an egg. Transport through the Vas Deferens: Mature sperm are then transported from the epididymis through the vas deferens. Fluid Addition from Seminal Vesicles: As sperm reaches the seminal vesicles, seminal fluid is added. This fluid contains fructose, which provides energy for the sperm, and other substances that aid sperm motility and protect against the acidic environment of the female reproductive tract. Ejaculatory Duct: Sperm and seminal fluid combine in the ejaculatory duct, which passes through the prostate. Additional Fluid from Prostate and Bulbourethral Glands: As the mixture enters the urethra, fluids from the prostate gland and bulbourethral glands are added. The prostate fluid helps protect sperm from bacteria and increases sperm motility, while the bulbourethral glands secrete an alkaline fluid to neutralize any acidic residue in the urethra. Ejaculation through the Urethra: The final semen mixture (containing sperm and glandular fluids) is expelled from the body through the urethra and out of the penis during ejaculation. Hormonal control of spermatogenesis (Gonadotropin-releasing hormone (GnRH), LH, FSH, inhibin, testosterone, oestrogen, Dihydrotestosterone (DHT)). Spermatogenesis, the process of sperm production in males, is regulated by a complex interplay of hormones. Here’s how the primary hormones contribute to the control of spermatogenesis: 1. Gonadotropin-Releasing Hormone (GnRH): o Released from the hypothalamus in pulses. o Stimulates the anterior pituitary gland to release two key gonadotropins: luteinizing hormone (LH) and follicle-stimulating hormone (FSH). 2. Luteinizing Hormone (LH): o Targets Leydig cells (also called interstitial cells) in the testes. o Stimulates Leydig cells to produce testosterone, the primary male sex hormone essential for spermatogenesis and development of secondary sexual characteristics. 3. Follicle-Stimulating Hormone (FSH): o Targets Sertoli cells (also known as nurse cells) within the seminiferous tubules of the testes. o Promotes spermatogenesis by stimulating Sertoli cells to support sperm development and maturation. o Encourages the secretion of inhibin by Sertoli cells. 4. Testosterone: o Produced by Leydig cells in response to LH stimulation. o Necessary for the initiation and maintenance of spermatogenesis. o Helps maintain the male reproductive organs and secondary sexual characteristics. o Testosterone, in its active form, Dihydrotestosterone (DHT), is more potent and binds more effectively to androgen receptors, further promoting sperm development and growth of male secondary sexual traits. 5. Dihydrotestosterone (DHT): o Formed when testosterone is converted by the enzyme 5α-reductase in certain tissues, including the prostate and hair follicles. o Binds more strongly to androgen receptors than testosterone and is important in developing male secondary sex characteristics. o Plays a role in supporting spermatogenesis within the testes. 6. Oestrogen: o Small amounts of testosterone are converted into oestrogen by Sertoli cells via the enzyme aromatase.  o While primarily considered a female hormone, oestrogen is involved in regulating fluid reabsorption in the epididymis, which is necessary for creating the optimal environment for sperm maturation. 7. Inhibin: o Produced by Sertoli cells in response to FSH stimulation. o Provides negative feedback to the anterior pituitary, selectively inhibiting the release of FSH. o Helps regulate sperm production by controlling FSH levels, ensuring that the rate of spermatogenesis remains balanced. Feedback Loops: Negative Feedback of Testosterone and Inhibin: Testosterone provides negative feedback to the hypothalamus and pituitary gland to reduce GnRH and LH secretion, keeping testosterone levels stable. Similarly, inhibin provides negative feedback to inhibit FSH release, maintaining balanced sperm production. Functions of testosterone and DHT Testosterone and dihydrotestosterone (DHT) are both androgens (male sex hormones) that play crucial roles in male development and reproductive function. Although closely related, they have distinct roles based on their effects in different tissues. Functions of Testosterone 1. Spermatogenesis and Fertility: o Essential for the initiation and maintenance of sperm production in the testes. o Supports Sertoli cells in the seminiferous tubules, which provide a nurturing environment for developing sperm. 2. Development of Male Reproductive Organs: o Promotes the growth and development of primary male sex organs (testes and penis) during fetal development and puberty. 3. Secondary Sexual Characteristics: o Responsible for male physical features that emerge during puberty, such as increased muscle mass, deeper voice (due to the growth of the larynx), and facial/body hair. o Increases bone density and contributes to male body structure. 4. Libido and Sexual Function: o Drives sexual desire (libido) and contributes to the maintenance of erectile function. 5. Behavioral Effects: o Influences behaviors related to aggression, mood, and energy levels. o Contributes to cognitive functions such as spatial ability and mental acuity. 6. Anabolic Effects: o Promotes protein synthesis, increasing muscle mass and strength. o Plays a role in the distribution of body fat and helps regulate red blood cell production. Functions of Dihydrotestosterone (DHT) DHT is derived from testosterone via the action of the enzyme 5-alpha reductase. It is more potent than testosterone and binds more strongly to androgen receptors, which amplifies its effects. 1. Fetal Development of External Genitalia: o Crucial for the development of male external genitalia (penis, scrotum, and prostate) in the fetus. o Any deficiency in DHT during fetal development can result in ambiguous genitalia or underdeveloped male characteristics. 2. Male Pattern Baldness: o Influences hair follicles and is associated with androgenic alopecia (male pattern baldness). o In genetically predisposed individuals, DHT causes hair follicles to shrink, leading to thinning hair and eventual hair loss. 3. Development of Secondary Sexual Characteristics: o Similar to testosterone but with more significant effects on body and facial hair growth. o Plays a role in sebum production (oil production in the skin), which can influence skin texture and acne development during puberty. 4. Prostate Health: o Stimulates the growth of the prostate gland, which is essential during male development. o In adulthood, elevated levels of DHT may contribute to conditions like benign prostatic hyperplasia (BPH) due to its strong influence on prostate cell growth. Summary of Differences Testosterone primarily promotes spermatogenesis, muscle mass, libido, and broader systemic effects. DHT is more specific in its potent effects on external genitalia development, hair growth patterns, and prostate health.  - Describe the structure and function of the female human reproductive system Structure and function of the fallopian tube, ovary, uterus, cervix, vagina, endometrium, myometrium, vulva (clitoris, labium minora and majora) Structure and Function of Female Reproductive System Components 1. Fallopian Tubes (Oviducts): o Structure: Two thin tubes extending from the ovaries to the uterus; lined with ciliated epithelial cells. o Function: Site of fertilization where the sperm meets the egg. The cilia and muscular contractions help move the fertilized egg (zygote) toward the uterus. 2. Ovaries: o Structure: Paired, almond-shaped organs located on either side of the uterus. o Function: Produce ova (eggs) and secrete hormones (estrogen and progesterone). They contain follicles that mature and release eggs during ovulation. 3. Uterus:  o Structure: A hollow, muscular organ with three layers: endometrium (inner), myometrium (middle), and perimetrium (outer). o Function: Site for implantation of the fertilized egg, supports fetal development during pregnancy, and facilitates menstruation when pregnancy does not occur. 4. Cervix: o Structure: The lower part of the uterus, which opens into the vagina; has a narrow canal lined with mucus-secreting glands. o Function: Acts as a barrier to protect the uterus from bacteria; during ovulation, the cervical mucus becomes thinner to allow sperm passage. 5. Vagina: o Structure: A muscular, elastic tube extending from the cervix to the external genitalia. o Function: Serves as the birth canal during childbirth, the passageway for menstrual fluid, and the receptacle for the penis during intercourse. 6. Endometrium: o Structure: The inner lining of the uterus, which undergoes cyclic changes during the menstrual cycle. o Function: Provides a suitable environment for embryo implantation; thickens in response to hormonal changes and sheds during menstruation if fertilization does not occur. 7. Myometrium: o Structure: The middle layer of the uterus, composed of smooth muscle. o Function: Contracts during childbirth to help push the baby out and during menstruation to help expel the endometrial lining. 8. Vulva: o Structure: The external female genitalia, including: § Clitoris: A small, sensitive organ responsible for sexual arousal. § Labia Minora: Thin, inner folds that protect the vaginal opening and urethra. § Labia Majora: The outer folds of skin that encase the labia minora and protect the internal structures. o Function: Protects the internal reproductive organs, contributes to sexual arousal, and assists in childbirth. Functions of oestrogen and progesterone Estrogen: Functions: o Promotes the development of female secondary sexual characteristics (e.g., breast development, wider hips). o Regulates the menstrual cycle, stimulating the growth of the endometrium during the follicular phase. o Enhances the proliferation of ovarian follicles and regulates their maturation. o Affects metabolism, bone density, and cardiovascular health. Progesterone: Functions:  o Prepares the endometrium for implantation after ovulation; thickens the lining and increases blood supply. o Inhibits further ovulation during pregnancy and maintains pregnancy by suppressing uterine contractions. o Plays a role in breast development for milk production during lactation. Describe the regulation of the menstrual cycle and uterine cycle Regulation of the Menstrual Cycle and Uterine Cycle 1. Menstrual Cycle: o The menstrual cycle is approximately 28 days long and can be divided into four main phases: § Menstrual Phase: Shedding of the endometrial lining if no fertilization occurs. § Follicular Phase: Follicle-stimulating hormone (FSH) stimulates the growth of ovarian follicles; estrogen levels rise. § Ovulation: A surge in luteinizing hormone (LH) triggers ovulation, releasing a mature egg. § Luteal Phase: After ovulation, the corpus luteum forms, secreting progesterone and estrogen. If no fertilization occurs, hormone levels decline, leading to menstruation. 2. Uterine Cycle: o Corresponds with the menstrual cycle and is divided into three phases: § Menstrual Phase: Shedding of the endometrium, resulting in menstrual bleeding. § Proliferative Phase: Estrogen promotes the rebuilding of the endometrial lining. § Secretory Phase: Progesterone prepares the endometrium for possible implantation, increasing glandular activity. Follicular and luteal phases of menstrual cycle Cervical mucus and endometrium changes follicular Phase: Duration: Days 1-14 of the cycle. Changes:  o Ovarian Changes: Follicles develop in response to FSH; one becomes dominant and matures. o Endometrial Changes: Estrogen levels rise, stimulating the thickening of the endometrium in preparation for a potential pregnancy. Luteal Phase: Duration: Days 15-28 of the cycle. Changes: o Ovarian Changes: The dominant follicle transforms into the corpus luteum, which secretes progesterone. o Cervical Mucus: Becomes thicker and more viscous due to increased progesterone, creating a barrier to sperm and pathogens. o Endometrial Changes: The endometrium continues to thicken and becomes more vascularized in preparation for implantation Menopause is a natural biological process that marks the end of a woman’s reproductive years. It typically occurs between the ages of 45 to 55, with the average age being around 51. Here's a more detailed breakdown of the process and its effects: 1. Ovulation and Menstruation Stop: o As women approach menopause, the ovaries gradually decrease the production of eggs and hormones (such as estrogen and progesterone). o Eventually, ovulation ceases, and menstruation stops entirely, marking the end of the menstrual cycle. 2. Decreased Estrogen: o The decline in estrogen levels is a hallmark of menopause, contributing to a variety of physical and emotional changes. o Estrogen plays a crucial role in maintaining bone density, regulating mood, and supporting cardiovascular health. 3. Shortage of Primordial Follicles: o Women are born with a finite number of primordial follicles (early-stage eggs) in their ovaries. o Over time, these follicles decrease in number, and by the time menopause is reached, very few remain. 4. Physical and Health Effects: o Osteoporosis: Decreased estrogen leads to a loss of bone density, increasing the risk of fractures and bone weakening. o Neural Effects: Hot flashes, night sweats, and mood changes (such as depression) are common during menopause due to hormonal fluctuations. o Atherosclerosis Risk: With estrogen levels dropping, the risk of developing cardiovascular issues, such as atherosclerosis (hardening of the arteries), increases. 5. Symptoms: o Hot flashes: Sudden feelings of heat, often accompanied by sweating and redness of the skin. o Vaginal Dryness: Reduced estrogen can cause the vaginal walls to become thinner and less lubricated, leading to discomfort during intercourse.  oSleep disturbances: Hormonal changes may contribute to insomnia or disrupted sleep patterns. 6. Long-term Effects: o Cardiovascular Health: The decline in estrogen may increase the risk of heart disease and high blood pressure. o Mood and Cognitive Effects: Some women experience changes in mood, depression, and difficulty concentrating during menopause. Fertilisation (site of fertilisation, implantation, hCG) 1. Timing of Fertilization: o Fertilization must occur within 24 hours of ovulation (when the egg is released from the ovary). The ovumis viable for only 24 hours after ovulation. o Sperm, on the other hand, can survive for approximately 48 hours within the female reproductive tract, but their ability to fertilize the egg is dependent on proper conditions and timing. 2. Sperm Migration: o After ejaculation, sperm are deposited in the vagina and must travel through the cervical canal, into the uterus, and up into the oviducts (fallopian tubes) to meet the egg. o Contractions of the myometrium (muscular layer of the uterus) assist in the migration of sperm towards the egg. 3. Capacitation of Sperm: o Before sperm can fertilize the egg, they must undergo capacitation, a maturation process. o Capacitation involves two main factors: § Exposure to seminal gland secretions in the male reproductive tract. § Exposure to the female reproductive tract, which removes a glycoprotein coat covering the sperm, allowing it to interact with the egg more effectively. Acrosomal Reaction and Fertilization: 1. Acrosomal Reaction: o The acrosome is a cap-like structure on the sperm that contains enzymes such as hyaluronidase and acrosin. o These enzymes are essential for the sperm to penetrate the zona pellucida (the outer protective layer of the egg) and allow the sperm to bind to the egg membrane. 2. Fertilization Process: o Thousands of sperm are needed to break down the barriers surrounding the egg, but only one sperm will successfully fertilize the egg. o Once a sperm penetrates the zona pellucida, the egg undergoes a reaction that hardens the zona pellucida, preventing polyspermy (fertilization by multiple sperm). o The entry of the sperm triggers the completion of meiosis in the oocyte, and the egg’s genetic material combines with that of the sperm to form a zygote. Cleavage and Implantation: 1. Cleavage: o After fertilization, the zygote undergoes rapid cell division known as cleavage, which results in the formation of a blastocyst. 2. Implantation: o Around Day 6-7, the blastocyst reaches the uterus and begins to implant into the endometrium (uterine lining). o The embryo secretes hyaluronidase, which erodes a path through the uterine epithelium, allowing it to embed itself into the uterine lining. o By Day 10, the embryo is completely encased in the endometrial lining and begins to develop a connection to the maternal blood supply. Pregnancy Hormones and Maintenance of Pregnancy: 1. Human Chorionic Gonadotropin (hCG): o After implantation, the developing embryo produces hCG (Human Chorionic Gonadotropin), which is critical for maintaining the corpus luteum (CL). o The CL produces progesterone and estrogen, which are essential for maintaining the endometrium and supporting the pregnancy. 2. Decline of Corpus Luteum: o As pregnancy progresses, the corpus luteum gradually declines in size and function, while the placentatakes over hormone production. 3. Placenta Hormones: o The placenta produces estrogen and progesterone during pregnancy, maintaining the endometrium, supporting fetal development, and preventing menstruation. Discuss the physiological adaptations that occur during pregnancy Circulatory System: Increased Blood Volume: Maternal blood volume increases by 30-50% to meet the demands of both the mother and the growing fetus. Reduced Blood Flow to Placenta: The blood flow to the placenta can reduce blood volume in the systemic circulation. However, this is countered by the increased maternal blood volume. Changes in Oxygen and CO2: The fetus' metabolic activity leads to reduced PO2 and increased PCO2 in the maternal blood. Heart Rate: The heart rate increases by about 15 bpm, driven by increased sympathetic nervous system activity. Progesterone: Stimulates the production of erythropoietin (EPO) from the kidneys, enhancing red blood cell production. Coagulation: Coagulation factors are elevated, helping prevent excessive bleeding during delivery. Relaxin: Increases cardiac output and vasodilation, particularly to the kidneys and placenta. Kidneys: Increased Glomerular Filtration Rate (GFR): The GFR increases by about 50% due to increased blood volume and the need to excrete wastes from fetal metabolism. Increased Urinary Frequency: Pregnant women often experience frequent urination, partly because of the increased volume of urine and the pressure from the growing fetus on the bladder. Respiratory System: Increased Tidal Volume: The amount of air breathed in and out with each breath increases to meet the higher oxygen demand. Progesterone Effect: Progesterone increases sensitivity to carbon dioxide (CO2), leading to deeper and more frequent breathing. This helps to lower PCO2 in the blood, facilitating CO2 diffusion from the fetus. Higher Oxygen Demand: As the maternal metabolic rate rises, the body adjusts to ensure sufficient oxygen is delivered to both the mother and fetus. Mammary Glands: Hormonal Influence: The development of mammary glands involves various hormones, including oxytocin for milk "let-down". Colostrum Production: The first milk produced, known as colostrum, is rich in antibodies and provides passive immunity to the newborn. Gastrointestinal System: Constipation: Caused by progesterone, which relaxes smooth muscles, as well as pressure from the enlarging uterus. Heartburn: As the uterus expands, it pushes up on the stomach, causing acid reflux and heartburn. Nausea and Vomiting: Often associated with hCG (human chorionic gonadotropin), which is produced early in pregnancy. Endocrine System: Pituitary Gland: Increases in size by 30-50% due to progesterone-stimulated synthesis of prolactin, which helps prepare the body for breastfeeding. Progesterone: Plays a major role in the enlargement of mammary glands and the preparation for milk synthesis. Corticotropin-Releasing Hormone (CRH): Released by the placenta, stimulating the anterior pituitary to secrete ACTH, which leads to increased cortisol levels, playing a role in stress response and pigmentation changes (e.g., darkening of areolae and nipples). Insulin Resistance: Pregnancy leads to a mild insulin resistance, which increases maternal glucose levels and ensures glucose delivery to the fetus. Parathyroid Hormone-related Peptide (PTHrp): Released from the placenta and breasts during lactation, promoting calcium absorption from the gut and facilitating bone mineralization in the fetus. Thyroid Gland: The thyroid increases in size, and hCG stimulates thyroxine (T4 and T3) release, promoting fetal growth and development, particularly the central nervous system (CNS). Metabolic Changes: Increased Nutrient Requirements: The need for nutrients increases by 10-30% due to the demands of pregnancy and fetal growth. Basal Metabolic Rate (BMR): BMR can increase by 15%, contributing to an overall increased energy demand. Feeling Overheated: Due to increased metabolic rate and carrying extra weight, pregnant women often feel overheated and may sweat more. Parturition (relaxin, contractions and oxytocin, baby and placenta delivery) Parturition, or childbirth, is the process of delivering a baby. It involves a series of coordinated events that include cervical dilation, uterine contractions, and the expulsion of the fetus and placenta. The process is divided into three main stages: Stages of Parturition:  1. First Stage: Contractions o Cervical Dilation: The first stage involves the gradual dilation (opening) of the cervical canal. o Hormonal Changes: High Estrogen: Increases oxytocin receptor density in the uterus, making the uterus more responsive to oxytocin. Oxytocin: Stimulates uterine contractions. As the cervix stretches, it triggers the release of oxytocin, initiating contractions in a neuroendocrine reflex. Positive Feedback Cycle: Contractions begin mild and infrequent (less than 30 seconds every 30 minutes) but progressively become stronger and more frequent (lasting 60-90 seconds every 2-3 minutes). Uterine contractions: Begin at the top of the uterus and move down, pushing the fetus against the cervix, which further stimulates oxytocin release. 2. Second Stage: Delivery of the Baby Neural Reflex Activation: Stretching of the cervix and uterine walls triggers neural reflexes that stimulate contractions in the abdominal muscles, leading the mother to voluntarily push. Pushing: The mother actively contracts her abdominal muscles to help push the baby through the birth canal. Duration: This stage usually lasts 30-90 minutes. Umbilical Cord: After the baby is delivered, the umbilical cord is clamped, tied, and severed. The stump forms the navel (umbilicus). 3. Third Stage: Delivery of the Placenta Placenta Separation: Contractions after the birth of the baby help to separate the placenta from the uterine wall (myometrium). Blood Loss: The detachment of the placenta causes uterine blood vessels to tear, leading to some blood loss. The uterus continues to contract to compress these blood vessels and reduce the bleeding. Expulsion of the Afterbirth: The placenta is expelled from the uterus, typically 15-30 minutes after the birth of the baby.  Relaxin's Role: This hormone plays a key role in pregnancy and childbirth by: o Stimulating the breakdown of collagen in the pelvis to help the birth canal expand. o Softening and widening the cervix to facilitate delivery. o Inhibiting uterine contractions during most of pregnancy to prevent premature labor. Labour Pain: Hypoxia (Ischemia) of Myometrium: During contractions, uterine blood flow is temporarily restricted, leading to hypoxia, which causes pain in a manner similar to angina (heart pain due to reduced blood supply). Pressure: The large fetal head pressing against a narrow pelvic outlet can cause additional discomfort. Cervical Dilation and Vaginal Stretching: Pain is also caused by the stretching and distension of the cervix, vagina, and perineum. Episiotomy: A surgical cut made in the perineum to prevent tearing during childbirth. Circulatory, respiratory, GI tract, endocrine (CRH, ACTH, cortisol) CRH, ACTH, and cortisol help regulate fetal development, maternal metabolism, and stress response. Progesterone maintains pregnancy by reducing uterine contractility and stimulating breast tissue development. Estrogen promotes uterine and mammary gland growth, and is involved in labor induction. Relaxin prepares the pelvic region for childbirth and contributes to cardiovascular changes. hCG maintains the corpus luteum early in pregnancy and stimulates other hormones like thyroid hormones.