Module 3 Reproductive System PDF

Module 3 — Reproductive System TLO 3.1 — DESCRIBE THE STRUCTURE AND FUNCTION OF THE MALE HUMAN REPRODUCTIVE SYSTEM The male human reproductive system consists of several organs and structures that work together to produce, store, and transport sperm cells, as well as to produce male hormones such as testosterone. The main components of the male reproductive system are: TESTES Structure: The testes (plural of testis) are oval-shaped glands located within the scrotum, a pouch of skin hanging outside the body. They are divided into lobules containing seminiferous tubules where sperm are produced. Function: The testes have two main functions: the production of sperm (spermatogenesis) and the secretion of testosterone, the primary male sex hormone responsible for the development of male secondary sexual characteristics. EPIDIDYMIS Structure: The epididymis is a coiled tube located on the surface of each testis. Function: The epididymis serves as a site for the maturation and storage of sperm. Sperm cells gain motility as they pass through the epididymis. VAS DEFERENS (DUCTUS DEFERENS) Structure: The vas deferens is a long, muscular tube that connects the epididymis to the urethra. Each testis has its own vas deferens. Function: The vas deferens transports mature sperm from the epididymis to the urethra during ejaculation. It is also involved in the storage of sperm. SEMINAL VESICLES Structure: The seminal vesicles are two small glands located behind the bladder. Function: They secrete a fluid that is rich in fructose, which provides energy for the sperm. This fluid combines with sperm to form semen. PROSTATE GLAND Structure: The prostate gland is a walnut-sized gland located beneath the bladder and surrounding the urethra. Function: The prostate secretes a slightly alkaline fluid that helps neutralise the acidic environment of the female reproductive tract, enhancing sperm viability. This fluid also contributes to semen. BULBOURETHRAL GLANDS (COWPER’S GLANDS) Structure: These are two small glands located below the prostate gland. Function: The bulbourethral glands secrete a clear fluid that lubricates the urethra and neutralises any acidic residue in the urethra before sperm travel through it. URETHRA Structure: The urethra is a tube that runs through the penis and serves as a passage for urine and semen. It is divided into the three parts: the prostatic urethra, the membranous urethra, and the spongy (penile) urethra. Function: The urethra carries semen during ejaculation and urine from the bladder. PENIS Structure: The penis is composed of erectile tissue that becomes engorged with blood during sexual arousal. The glans penis is the enlarged tip, and the shaft is the length of the organ. Function: The penis serves as the organ of copulation, allowing the transfer of sperm into the female reproductive tract during sexual intercourse. It also serves as the conduit for urine to exit the body. SCROTUM Structure: The scrotum is a pouch of skin and muscle that holds and protects the testes. Function: The scrotum helps regulate the temperature of the testes, which is crucial for the production of sperm. It does so by moving the testes closer to or farther from the body to maintain an optimal temperature for spermatogenesis. HORMONAL REGULATION The male reproductive system is regulated by hormones, including: Testosterone: Produced by the Leydig cells in the testes, testosterone is responsible for the development of male secondary sexual characteristics, such as facial hair, deep voice, and muscle mass. Follicle-Stimulating Hormone (FSH): Stimulates sperm production in the seminiferous tubules. Luteinising Hormone (LH): Stimulates the Leydig cells in the testes to produce testosterone. TLO 3.1.1 — FUNCTION OF THE VAS DEFERENS, EPIDIDYMIS, BULBOURETHRAL GLAND, PROSTATE GLAND, SEMINAL VESICLE, SCROTUM, TESTIS, EJACULATORY DUCT, URETHRA, CREMASTER AND DARTOS MUSCLES VAS DEFERENS (DUCTUS DEFERENS) Function: The vas deferens is a long, muscular tube that transports mature sperm from the epididymis to the urethra during ejaculation. It is the main pathway for sperm to travel from the testes to the ejaculatory duct. The vas deferens stores sperm temporarily before ejaculation. It is lined with smooth muscle that contracts in peristaltic waves during ejaculation to propel sperm forward. EPIDIDYMIS Function: The epididymis is a coiled tube located on the surface of each testis. It serves two primary functions: Sperm Maturation: Sperm produced in the seminiferous tubules of the testes are immature and non-motile. The epididymis provides an environment for sperm to mature and gain motility over a period of about 2-3 weeks. Sperm Storage: The epididymis also stores mature sperm until ejaculation. During this time, sperm are concentrated and stored in the tail of the epididymis. BULBOURETHRAL GLAND (COWPER’S GLAND) Function: The bulbourethral glands are pea-sized structures located beneath the prostate gland. They produce a clear, viscous secretion during sexual arousal, before ejaculation. This secretion: Lubricates the Urethra: The fluid neutralises any acidic residue left in the urethra from urine, creating a more suitable environment for sperm. Pre-Ejaculate: It also acts as a lubricant to ease the passage of sperm through the urethra during ejaculation. PROSTATE GLAND Function: The prostate gland is a walnut-sized gland located below the bladder, surrounding the urethra. It has several important functions: Secretion of Prostatic Fluid: The prostate produces a thin, milky fluid that is alkaline in nature. This fluid serves multiple purposes: o It neutralises the acidic environment of the female reproductive tract, helping to protect and sustain sperm viability. o It provides nourishment to sperm. The prostatic fluid accounts for about 20-30% of the total volume of semen. SEMINAL VESICLE Function: The seminal vesicles are two elongated, sac-like glands located behind the bladder, near the prostate. They secrete a thick, yellowish fluid that: Nourishes Sperm: The fluid contains fructose, a sugar that provides energy for sperm to move. Facilitates Sperm Motility: The seminal fluid also contains prostaglandins, which help increase sperm motility and promote smooth muscle contractions in the female reproductive tract, aiding in sperm transport. The seminal vesicle fluid makes up about 60-70% of the volume of semen. SCROTUM Function: The scrotum is a pouch of skin and muscle that contains and protects the testes. It has several key functions: Temperature Regulation: The scrotum helps maintain an optimal temperature for sperm production by controlling the distance of the testes from the body. Sperm production requires a temperature slightly lower than body temperature, so the scrotum contracts or relaxes to move the testes closer to or further from the body, respectively. Protection: The scrotum provides a physical barrier that protects the testes from trauma. TESTES (TESTIS) Function: The testes are the male gonads responsible for two key functions: Sperm Production (Spermatogenesis): The seminiferous tubules within the testes produce sperm through a process called spermatogenesis. Sperm production occurs in the presence of follicle-stimulating hormone (FSH) and testosterone. Testosterone Production: The Leydig cells in the testes produce testosterone, the primary male sex hormone. Testosterone plays a crucial role in the development of male secondary sexual characteristics (e.g. facial hair, deep voice) and regulates spermatogenesis. EJACULATORY DUCT Function: The ejaculatory ducts are formed by the joining of the vas deferens and the ducts of the seminal vesicles. They are located within the prostate gland, just before the urethra. The function of the ejaculatory ducts is to: Deliver Semen: During ejaculation, sperm from the vas deferens and fluid from the seminal vesicles combine in the ejaculatory ducts, which transport the semen into the prostatic urethra, where it is eventually expelled through the penis. URETHRA Function: The urethra is a tube that runs from the bladder to the tip of the penis and serves two functions: Excretion of Urine: It serves as the passageway for urine from the bladder to be excreted from the body. Passage of Semen: During ejaculation, the urethra carries semen from the ejaculatory duct to the outside of the body via the penis. It also transports sperm from the testes during sexual arousal. CREMASTER MUSCLE Function: The cremaster muscle is a thin layer of skeletal muscle that surrounds the testes and the spermatic cord. It plays a role in temperature regulation: Lifts the Testes: The cremaster muscle contracts to pull the testes closer to the body in response to cold temperatures, which helps preserve heat. Relaxes the Testes: In warm conditions, the muscle relaxes, allowing the testes to move farther from the body, promoting a cooler environment for sperm production. DARTOS MUSCLE Function: The dartos muscle is a layer of smooth muscle located beneath the skin of the scrotum. It has the following functions: Wrinkling of the Scrotum: The dartos muscle contracts in response to cold temperatures, causing the scrotum to wrinkle and reduce its surface area. This action helps conserve heat by reducing heat loss. Relaxation in Warmer Conditions: In warm conditions, the dartos muscle relaxes, allowing the scrotum to become smooth and expand, increasing the surface area for heat dissipation. SUMMARY TABLE STRUCTURE FUNCTION Vas Deferens Transports mature sperm from the epididymis to the urethra during ejaculation. Stores sperm temporarily. Uses smooth muscle contractions for sperm propulsion. Epididymis Matures sperm (gaining motility) and stores sperm until ejaculation. Bulbourethral Gland Secretes pre-ejaculate fluid to lubricate the urethra and neutralise any acidic residue from urine, providing a suitable environment for sperm. Prostate Gland Produces alkaline prostatic fluid that neutralises the acidic female reproductive tract, providing nourishment and protection for sperm. Seminal Vesicle Produces fructose-rich fluid that provides energy for sperm and contains prostaglandins to enhance motility, contributing to about 60-70% of semen volume. Scrotum Houses and protects the testes. Regulates temperature for optimal sperm production by moving the testes closer to or farther from the body. Testes Produce sperm (spermatogenesis) in the seminiferous tubules and secrete testosterone, which is essential for male sex characteristics and spermatogenesis. Ejaculatory Duct Transports semen (sperm and fluid from seminal vesicles) into the urethra during ejaculation. Urethra Carries urine from the bladder to the outside of the body and transports semen during ejaculation from the ejaculatory duct to the penis. Cremaster Muscle Contracts to pull the testes closer to the body in cold temperatures and relaxes to allow testes to move farther from the body in warm temperatures. Dartos Muscle Contracts to wrinkle the scrotum and reduce surface area in cold temperatures for heat retention; relaxes in warm temperatures to increase surface area. TLO 3.1.2 — HORMONAL CONTROL OF SPERMATOGENESIS The process of spermatogenesis—the production of sperm—requires precise hormonal control. These hormones regulate various stages of sperm development, including the production of sperm cells, their maturation, and the maintenance of male reproductive function. The hormonal regulation of spermatogenesis involves a complex interaction between the hypothalamus, pituitary gland, and the testes. Key hormones involved in this process include gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone. HYPOTHALAMIC-PITUITARY-GONADAL AXIS Spermatogenesis is regulated by a feedback system known as the hypothalamic-pituitary-gonadal (HPG) axis, which involves the release of hormones from the hypothalamus, pituitary gland, and testes. Gonadotropin-Releasing Hormone (GnRH): Source: The hypothalamus. Function: GnRH is released from the hypothalamus into the bloodstream and travels to the anterior pituitary gland, where it stimulates the release of luteinising hormone (LH) and follicle-stimulating hormone (FSH). Regulation: GnRH release is pulsatile and occurs in a cyclic pattern, typically every 60-90 minutes, which is essential for maintaining the proper levels of LH and FSH. PITUITARY GLAND AND GONADOTROPINS: The anterior pituitary gland releases two key gonadotropins that directly influence spermatogenesis: Luteinising Hormone (LH): Source: Anterior pituitary gland. Function: LH stimulates the Leydig cells in the testes to produce and secrete testosterone. Testosterone is essential for the initiation and maintenance of spermatogenesis and for the development of male secondary sexual characteristics. Role in Spermatogenesis: LH indirectly regulates spermatogenesis by increasing testosterone levels, which promote the function of Sertoli cells (the nurse cells that support and nourish developing sperm). Follicle-Stimulating Hormone (FSH): Source: Anterior pituitary gland. Function: FSH directly acts on the Sertoli cells in the seminiferous tubules of the testes, stimulating their activity. Sertoli cells play a critical role in spermatogenesis by providing physical support and nourishment to developing sperm cells. Role in Spermatogenesis: FSH promotes the development of spermatogonia (the sperm precursor cells) into mature sperm cells through a process known as spermatogenesis. It also stimulates the secretion of inhibin (a hormone that inhibits FSH production) from Sertoli cells, which provides a negative feedback mechanism for regulating spermatogenesis. TESTOSTERONE Testosterone is the primary male sex hormone and plays a central role in spermatogenesis. Source: Testosterone is produced by the Leydig cells located in the interstitial space of the testes. Function: Testosterone has several key functions in spermatogenesis: o It stimulates the Sertoli cells to support and nourish developing sperm cells. o It is essential for the maturation of spermatogonia (the diploid germ cells) into primary spermatocytes (the cells that will undergo meiosis to form haploid spermatids). o Testosterone also helps maintain the structure and function of the seminiferous tubules, which are the sites where sperm are produced. o It promotes the formation of the male secondary sexual characteristics, such as facial hair, muscle growth, and deepening of the voice. Regulation: Testosterone is regulated by a negative feedback mechanism. High levels of testosterone in the bloodstream inhibit the secretion of GnRH from the hypothalamus and LH from the anterior pituitary gland, reducing the stimulation of Leydig cells to produce testosterone. INHIBIN Source: Sertoli cells in the testes. Function: Inhibin is released by Sertoli cells in response to FSH stimulation. It acts to inhibit the secretion of FSH from the anterior pituitary gland. Role in Feedback Mechanism: By inhibiting FSH production, inhibin helps regulate the rate of spermatogenesis and prevents overproduction of sperm. STAGES OF SPERMATOGENESIS Spermatogenesis occurs in the seminiferous tubules of the testes and is a multistep process regulated by the hormonal signals described above. The stages of spermatogenesis are as follows: SPERMATOGONIAL PHASE Spermatogenesis begins with spermatogonia (stem cells) that reside along the basal membrane of the seminiferous tubules. Under the influence of testosterone and FSH, some spermatogonia undergo mitosis, producing primary spermatocytes. MEIOTIC PHASE Primary spermatocytes undergo meiosis I to form two secondary spermatocytes (haploid). These secondary spermatocytes then undergo meiosis II, resulting in spermatids (haploid). The process of meiosis ensures that sperm cells have half the number of chromosomes, which is crucial for fertilisation. SPERMIOGENESIS (DIFFERENTIATION) Spermatids undergo a process called spermiogenesis, where they differentiate into mature spermatozoa (sperm cells). This involves the development of a tail (flagellum), a condensed nucleus, and a midpiece containing mitochondria for energy production. NEGATIVE FEEDBACK AND REGULATION The hormonal regulation of spermatogenesis relies on negative feedback loops to maintain balanced hormone levels: Testosterone and Inhibin Negative Feedback: High levels of testosterone and inhibin reduce the secretion of GnRH, LH, and FSH, preventing excessive sperm production. FSH and LH Regulation: When sperm production is low, GnRH stimulates the release of LH and FSH from the anterior pituitary, which in turn increases testosterone and Sertoli cell activity to boost sperm production. SUMMARY TABLE HORMONE SOURCE FUNCTION Gonadotropin-Releasing Hormone (GnRH) Hypothalamus Stimulates the release of LH and FSH from the anterior pituitary. Luteinizing Hormone (LH) Anterior pituitary Stimulates Leydig cells in the testes to produce testosterone, which is essential for spermatogenesis. Follicle-Stimulating Hormone (FSH) Anterior pituitary Stimulates Sertoli cells to support spermatogenesis and promotes the production of inhibin. Testosterone Leydig cells Promotes spermatogenesis by stimulating Sertoli cells, supports the maturation of sperm, and maintains male sex characteristics. Inhibin Sertoli cells Inhibits FSH secretion to regulate the rate of spermatogenesis. TLO 3.1.2.1 — COMPONENTS AND FUNCTION OF SEMEN Semen is the fluid that is ejaculated during sexual climax, and it contains sperm cells along with several other components that contribute to its function in fertilisation. Semen is a complex mixture that plays a critical role in supporting, protecting, and transporting sperm as they travel through the female reproductive tract to reach and fertilise an egg. COMPONENTS OF SEMEN SPERM CELLS (SPERMATOZOA) Source: Produced in the seminiferous tubules of the testes through the process of spermatogenesis. Function: Sperm cells are the male gametes (reproductive cells) and their primary function is to fertilise the female egg (oocyte) during sexual reproduction. Each sperm contains 23 chromosomes, and it carries genetic information that combines with the egg's genetic material to form a zygote. Structure: Sperm cells have a head (containing the nucleus with DNA), a midpiece (packed with mitochondria for energy), and a tail (flagellum) that enables movement. SEMINAL FLUID (SEMINAL PLASMA) Seminal plasma is the liquid portion of semen and is composed of various fluids secreted by the accessory glands of the male reproductive system. This fluid provides nourishment and protection for sperm, enabling them to survive and move efficiently through the female reproductive tract. THE KEY COMPONENTS OF SEMINAL FLUID ARE PRODUCED BY THE FOLLOWING GLANDS: Seminal Vesicles: Contribution: The seminal vesicles contribute approximately 60-70% of the volume of semen. They secrete a thick, yellowish fluid that is rich in fructose, a sugar that provides energy for the sperm. This energy is necessary for sperm motility, particularly as they swim through the cervix and uterus towards the egg. Other Components: Seminal vesicles also produce prostaglandins, which are lipid compounds that play a role in increasing sperm motility and may help in the transport of sperm by causing smooth muscle contractions in the female reproductive tract. The fluid also contains vitamin C, amino acids, and other nutrients that nourish sperm. Prostate Gland: Contribution: The prostate gland secretes a slightly alkaline fluid that makes up about 20-30% of the semen volume. The prostate secretion helps to neutralise the acidic environment of the vagina, which can be harmful to sperm. This creates a more favourable environment for sperm survival. Other Components: The prostate fluid contains citric acid, which serves as a source of energy for sperm. It also contains enzymes such as prostate-specific antigen (PSA), which helps to liquefy the semen after ejaculation, allowing sperm to swim freely and more easily. Bulbourethral Glands (Cowper's Glands): Contribution: The bulbourethral glands contribute a small volume (approximately 1-5%) of the semen. They secrete a clear, viscous fluid known as pre-ejaculate or pre-cum. Function: The primary function of this fluid is to lubricate the urethra and neutralise any residual acidity left in the urethra from urine. This ensures that sperm are not damaged as they pass through the urethra during ejaculation. OTHER COMPONENTS OF SEMEN: Fructose: Source: Primarily from the seminal vesicles. Function: Fructose serves as the main energy source for sperm cells. It fuels their movement as they swim through the male and female reproductive tracts. Enzymes: Source: Prostate gland and other accessory glands. Function: Enzymes, such as prostate-specific antigen (PSA), help liquefy the semen after ejaculation, freeing sperm cells from the viscous semen and allowing them to move more easily. Other enzymes may assist in the breakdown of cervical mucus, facilitating sperm passage through the cervix. Prostaglandins: Source: Seminal vesicles. Function: Prostaglandins are lipid compounds that play several roles in semen function. They help sperm swim by promoting smooth muscle contractions in the female reproductive tract, particularly the cervix and uterus. This may facilitate sperm transport to the fallopian tubes, where fertilisation takes place. Prostaglandins also promote cervical mucus changes that can make it more favourable for sperm movement. Citric Acid: Source: Prostate gland. Function: Citric acid acts as a buffering agent to help neutralise the acidic environment of the vagina. This helps maintain sperm viability and motility by providing a more neutral pH. Zinc: Source: Prostate gland. Function: Zinc plays a role in stabilizing the sperm DNA and protecting the sperm from damage. It also supports sperm motility and function. Amino Acids: Source: Seminal vesicles and prostate. Function: Amino acids serve as nutrients for sperm, aiding their viability and motility during transit through the reproductive tract. Calcium: Source: Seminal fluid (from various glands). Function: Calcium is important for sperm motility and function. It plays a role in sperm capacitation (the process by which sperm gain the ability to fertilise an egg). SEMEN VOLUME The average volume of semen produced during an ejaculation is typically about 2 to 5 millilitres. However, semen volume can vary based on factors such as hydration, frequency of ejaculation, and individual health conditions. FUNCTION OF SEMEN The primary function of semen is to transport and protect sperm as they travel through the male and female reproductive tracts with the goal of fertilising an egg. Sperm Transport: The fluid components of semen (especially from the seminal vesicles) help propel sperm through the male reproductive system and into the female reproductive system. Sperm motility is enhanced by fructose, prostaglandins, and the neutralising effects of the prostate fluid. Sperm Protection: The alkaline environment provided by the prostate fluid helps protect sperm from the acidic vaginal environment, which can be harmful to sperm. The pre-ejaculate fluid from the bulbourethral glands also helps protect sperm by neutralising any residual acidity in the urethra, ensuring they are not damaged before ejaculation. Nutritional Support: The fructose, amino acids, and other nutrients in seminal fluid provide energy to sperm, which is essential for their movement through the female reproductive tract. This ensures sperm can swim towards the egg for fertilisation. Lubrication: The lubricating function of the bulbourethral glands aids in reducing friction as sperm travel through the urethra during ejaculation. This helps sperm move more easily and prevents any damage. Facilitating Fertilisation: The enzymes in semen help sperm swim through the female cervical mucus, which can otherwise be a barrier. Additionally, the prostaglandins in the seminal fluid may induce uterine contractions, facilitating sperm movement toward the fallopian tubes where fertilisation occurs. SUMMARY TABLE COMPONENT SOURCE FUNCTION Sperm Cells Testes (seminiferous tubules) Carry male genetic material, fertilise the egg, and contribute to the formation of the zygote. Fructose Seminal Vesicles Provides energy for sperm motility. Prostaglandins Seminal Vesicles Increase sperm motility and induce uterine contractions to aid sperm transport. Citric Acid Prostate Gland Neutralises vaginal acidity, providing a more favourable environment for sperm. Zinc Prostate Gland Protects sperm from DNA damage and supports sperm motility. Amino Acids Seminal Vesicles & Prostate Serve as nutrients to support sperm viability and function. Enzymes (e.g. PSA) Prostate Gland Liquefy semen post-ejaculation to release sperm and assist in sperm transport through the cervix. Calcium Seminal Fluid Important for sperm motility and capacitation (ability to fertilise). Bulbourethral Fluid Bulbourethral Glands Neutralises acidity in the urethra, lubricates the urethra for smoother sperm passage. Sperm Cells Testes (seminiferous tubules) Carry male genetic material, fertilise the egg, and contribute to the formation of the zygote. TLO 3.1.3 — FUNCTIONS OF TESTOSTERONE AND DHT Testosterone and dihydrotestosterone (DHT) are the two primary androgens (male sex hormones) responsible for the development and maintenance of male characteristics, reproductive function, and overall health. These hormones have overlapping yet distinct roles in various physiological processes. TESTOSTERONE Testosterone is the main male sex hormone produced primarily by the Leydig cells in the testes, with small amounts also produced by the adrenal glands. It is responsible for a wide range of physiological effects in both the development of male characteristics and the maintenance of various body functions. KEY FUNCTIONS OF TESTOSTERONE DEVELOPMENT OF MALE SEXUAL CHARACTERISTICS Embryonic and Foetal Development: Testosterone is essential for the development of male sexual organs during Foetal development. It contributes to the differentiation of the male reproductive tract, including the formation of the testes, seminal vesicles, prostate, and other male reproductive organs. Puberty and Secondary Sexual Characteristics: Testosterone triggers the physical changes during puberty, including the growth of the penis and testes, deepening of the voice, increase in muscle mass, and development of facial and body hair. It also stimulates the growth of the Adam's apple and broadening of the shoulders. Spermatogenesis: Testosterone is essential for the production of sperm in the testes. It acts on Sertoli cells in the seminiferous tubules, facilitating spermatogenesis (the process of sperm production). ANABOLIC EFFECTS (TISSUE GROWTH) Muscle Mass and Strength: Testosterone plays a crucial role in increasing muscle mass and strength by promoting protein synthesis in muscle tissue. This anabolic effect enhances muscle growth, which is why testosterone is often linked to increased physical performance and muscle hypertrophy. Bone Density: Testosterone helps maintain bone density by promoting osteoblast activity (cells that form bone) and inhibiting osteoclast activity (cells that break down bone). Low testosterone levels are associated with an increased risk of osteoporosis in men. METABOLISM AND FAT DISTRIBUTION Fat Metabolism: Testosterone influences fat metabolism by promoting lipolysis (the breakdown of fat). It also affects the distribution of body fat, promoting fat loss from the abdominal region and the accumulation of fat in the extremities. Energy Balance: Testosterone helps regulate overall energy balance, impacting factors like basal metabolic rate (BMR) and how the body processes nutrients. MOOD AND COGNITIVE FUNCTION Mood Regulation: Testosterone has an influence on mood and emotional well-being. Low testosterone levels are associated with symptoms of depression, irritability, and fatigue, whereas normal testosterone levels are linked to better mood and a sense of well-being. Cognitive Function: Testosterone plays a role in cognitive functions like memory, spatial abilities, and mental clarity. There is evidence suggesting that higher levels of testosterone may protect against cognitive decline as men age. LIBIDO AND SEXUAL FUNCTION Sex Drive: Testosterone is a key regulator of libido (sexual desire) in men. It promotes the desire for sexual activity and maintains erectile function. Erectile Function: Testosterone contributes to the ability to achieve and maintain an erection. While other factors such as nitric oxide are directly involved in the erectile process, testosterone helps maintain the overall function of the penis and penile tissues. RED BLOOD CELL PRODUCTION Erythropoiesis: Testosterone stimulates the production of erythropoietin, a hormone that promotes the production of red blood cells. As a result, men typically have a higher red blood cell count and haemoglobin levels compared to women, which is why testosterone levels influence overall oxygen-carrying capacity. DIHYDROTESTOSTERONE (DHT) DHT is a more potent androgen than testosterone, derived from testosterone through the action of the enzyme 5-alpha reductase. DHT binds more strongly to androgen receptors than testosterone and plays a more critical role in certain processes, especially in tissues like the prostate, skin, and hair follicles. KEY FUNCTIONS OF DHT DEVELOPMENT OF MALE SEXUAL CHARACTERISTICS Foetal Development: DHT is essential for the development of the male external genitalia during Foetal life. It promotes the differentiation of the penis, scrotum, and prostate. DHT also plays a role in the closure of the urethral tube in male foetuses. Pubertal Development: During puberty, DHT is responsible for the growth of the male external genitalia (e.g. penis and scrotum) and prostate. It also contributes to the development of body hair, including facial hair (e.g. beard and moustache), chest hair, and pubic hair. HAIR GROWTH AND LOSS Hair Follicle Regulation: DHT is a primary regulator of hair growth in certain areas of the body. It promotes the growth of facial and body hair during puberty. However, it is also a key factor in androgenic alopecia (male pattern baldness). DHT can shrink hair follicles on the scalp, shortening the hair growth cycle and leading to thinner hair and eventual baldness. Facial and Body Hair: DHT promotes the thickening and darkening of hair in areas like the face, chest, and back, contributing to male secondary sexual characteristics. PROSTATE GROWTH AND FUNCTION Prostate Development: DHT is essential for the normal development and growth of the prostate gland, including the seminal vesicles and the prostate itself. This growth is important for the production and secretion of prostatic fluid, which is a component of semen. Prostate Health: While DHT is crucial for the normal function of the prostate, an overabundance of DHT can contribute to benign prostatic hyperplasia (BPH), a non-cancerous enlargement of the prostate that occurs with aging. High levels of DHT are also implicated in prostate cancer development. SEXUAL FUNCTION Libido and Erectile Function: Like testosterone, DHT plays a role in male sexual function. DHT’s effects on the penis are more potent than testosterone’s, contributing to the maintenance of libido and the function of erectile tissue. It also influences the size of the penis during puberty and adulthood. SEBACEOUS GLAND ACTIVITY AND ACNE Skin and Acne: DHT stimulates the sebaceous (oil) glands in the skin, contributing to increased oil production. Excessive DHT activity is associated with acne, particularly during puberty when androgen levels increase. This is why androgen levels influence the development of acne, especially in areas with a high density of sebaceous glands, like the face and back. MUSCLE MASS AND STRENGTH Anabolic Effects: Though testosterone has a more significant role in muscle mass development, DHT also exerts an anabolic effect on muscle tissue. However, DHT’s influence is generally less pronounced than that of testosterone. SUMMARY TABLE FUNCTION TESTOSTERONE DHT Sexual Development Development of male genitalia during Foetal life, puberty Development of external genitalia and prostate in utero and puberty Secondary Sexual Characteristics Deepening of voice, facial/body hair, muscle growth, bone density Facial and body hair growth, prostate development Spermatogenesis Stimulates sperm production in testes Less direct role, but maintains overall male fertility Anabolic Effects (Tissue Growth) Increases muscle mass and bone density Limited effect on muscle growth, but contributes to hair growth Libido and Sexual Function Maintains sexual desire and erectile function Potent influence on erectile function and sexual desire Hair Growth and Loss No direct effect on scalp hair, promotes body/facial hair Promotes facial/body hair growth, causes hair loss on scalp (baldness) Prostate Health Supports normal prostate function Essential for prostate growth, implicated in BPH and prostate cancer Skin and Sebaceous Glands Moderate effect on skin condition Increases sebum production, contributes to acne Mood and Cognitive Function Influences mood and cognitive function No significant role in mood/cognitive function TLO 3.2 — DESCRIBE THE STRUCTURE AND FUNCTION OF THE FEMALE HUMAN REPRODUCTIVE SYSTEM The female reproductive system is a complex and vital system responsible for reproduction, sexual function, and the production of hormones. It consists of both internal and external structures, each playing a role in various stages of reproduction, from the production of eggs (ova) to pregnancy and childbirth. EXTERNAL GENITALIA (VULVA) The external female reproductive structures are collectively referred to as the vulva. These structures protect the internal reproductive organs and are involved in sexual intercourse and childbirth. Mons Pubis: The rounded, fatty area above the pubic bone, which is covered with pubic hair after puberty. It cushions the pubic bone during intercourse. Labia Majora: These are the outer, thicker folds of skin that protect the internal reproductive organs. They contain sweat glands and sebaceous glands, which provide lubrication. Labia Minora: The inner, thinner folds of skin, located within the labia majora. They contain blood vessels, sebaceous glands, and erectile tissue. The labia minora protect the vaginal opening and urethral opening. Clitoris: A small, highly sensitive organ located at the top of the labia minora. It contains a dense concentration of nerve endings and is primarily responsible for female sexual pleasure. The clitoris consists of a glans (visible part) and two internal crura that extend along the pubic bone. Urethral Opening: The opening through which urine is expelled from the bladder. It is located below the clitoris and above the vaginal opening. Vaginal Opening: The entrance to the vagina, located between the urethral opening and the anus. It is also called the introitus and is part of the birth canal. The hymen, a thin membrane, partially covers the vaginal opening at birth but may be stretched or torn during sexual activity or physical activity. INTERNAL GENITALIA The internal female reproductive organs consist of the vagina, uterus, fallopian tubes, and ovaries. These structures are responsible for the production and transport of eggs, fertilisation, foetal development, and menstruation. VAGINA Structure: The vagina is a muscular, tubular organ that connects the external genitalia (vulva) to the uterus. It is approximately 8 to 10 cm in length but can expand during sexual intercourse and childbirth. Function: The vagina serves multiple functions: o It acts as the passage for menstrual blood to exit the body. o It is the canal through which sperm enter during sexual intercourse. o It forms part of the birth canal during childbirth, allowing the baby to pass from the uterus to the outside world. o The vaginal walls are lined with a mucous membrane that produces secretions for lubrication and protection from infections. UTERUS Structure: The uterus is a hollow, pear-shaped organ located in the pelvic cavity, between the bladder and rectum. It is about 7-8 cm long, 4-5 cm wide, and 2-3 cm thick. The uterus consists of three layers: o Endometrium: The innermost layer, which is made up of epithelial cells and blood vessels. This layer thickens and sheds during the menstrual cycle in response to hormonal changes. o Myometrium: The thick, muscular middle layer. It is responsible for uterine contractions during menstruation and childbirth. o Perimetrium: The outer serous layer, a thin membrane that helps protect and support the uterus. Function: The uterus has several vital functions: o Menstruation: If fertilisation does not occur, the endometrium sheds its lining, leading to menstruation. o Pregnancy: The uterus is where a fertilised egg implants and develops during pregnancy. The lining of the uterus (endometrium) provides a nutrient-rich environment for the embryo. o Childbirth: During labour, the myometrium contracts to help push the baby through the cervix and vagina. CERVIX Structure: The cervix is the lower, narrow portion of the uterus that connects to the vagina. It has an opening called the cervical os, which allows menstrual blood to flow out and sperm to enter. The cervix is composed of thick, muscular tissue and is lined with glandular tissue. Function: The cervix serves as a barrier that protects the uterus from infections. It also plays an essential role during childbirth, dilating to allow the baby to pass through the birth canal. The cervical mucus also varies in consistency throughout the menstrual cycle, helping or hindering sperm movement depending on the phase. FALLOPIAN TUBES (OVIDUCTS) Structure: The fallopian tubes are two narrow, muscular tubes that extend from the sides of the uterus toward the ovaries. Each tube is about 10-12 cm long and ends in a funnel-shaped structure called the fimbriae, which contains finger-like projections that help catch the released egg from the ovary. Function: The fallopian tubes are crucial for the transport of eggs and sperm. The functions of the fallopian tubes include: o Egg Transport: After ovulation, the fimbriae of the fallopian tube catch the egg and transport it through the tube toward the uterus. o Fertilisation Site: The fallopian tube is where fertilisation typically occurs. If sperm meet the egg in the tube, fertilisation happens, and the fertilised egg (zygote) continues its journey to the uterus for implantation. OVARIES Structure: The ovaries are a pair of small, almond-shaped organs located on either side of the uterus. They are about 3-5 cm in length and are composed of two main regions: o Cortex: The outer region, where eggs (ova) are stored and matured. o Medulla: The inner region, which contains blood vessels, nerves, and connective tissue. Function: The ovaries have two primary functions: o Oogenesis: The ovaries produce eggs (ova) through a process called oogenesis. A female is born with all the eggs she will ever have, and they mature throughout her reproductive years. Each month, during the menstrual cycle, one egg matures and is released from the ovary (ovulation). o Hormone Production: The ovaries produce hormones, including oestrogen and progesterone, which regulate the menstrual cycle, pregnancy, and the development of secondary sexual characteristics. HORMONAL REGULATION AND MENSTRUAL CYCLE The female reproductive system is regulated by hormonal signals from the brain, primarily involving the hypothalamus, pituitary gland, and ovaries. Hypothalamus releases GnRH (gonadotropin-releasing hormone), which stimulates the pituitary gland to release LH (luteinizing hormone) and FSH (follicle-stimulating hormone). FSH promotes the growth and maturation of ovarian follicles (which contain eggs), while LH triggers ovulation, the release of the egg from the ovary. Oestrogen and progesterone are produced by the ovaries and regulate the menstrual cycle. Oestrogen helps in the thickening of the endometrial lining, while progesterone prepares the uterus for pregnancy and supports the early stages of pregnancy if fertilisation occurs. PREGNANCY AND CHILDBIRTH Fertilisation: If sperm fertilises the egg in the fallopian tube, the resulting zygote travels down the tube to the uterus, where it implants in the endometrial lining. Pregnancy: If fertilisation occurs, the placenta begins to form, which produces human chorionic gonadotropin (hCG), a hormone that supports pregnancy by maintaining the production of progesterone and oestrogen. These hormones prevent menstruation and support Foetal development. Labour: During labour, the uterus contracts, and the cervix dilates to allow the baby to pass through the birth canal. TLO 3.2.1 — STRUCTURE AND FUNCTION OF THE FALLOPIAN TUBE, OVARY, UTERUS, CERVIX, VAGINA, ENDOMETRIUM, MYOMETRIUM, VULVA (CLITORIS, LABIUM MINORA AND MAJORA) The female reproductive system consists of both internal and external structures that are essential for reproduction, sexual function, and hormone regulation. FALLOPIAN TUBES (OVIDUCTS) Structure: Location: The fallopian tubes are a pair of muscular tubes, approximately 10-12 cm long, extending from the upper part of the uterus toward each ovary. Anatomy: Each fallopian tube has four parts: o Infundibulum: The funnel-shaped opening near the ovary, which contains finger-like projections called fimbriae that help capture the released egg. o Ampulla: The wide, central section where fertilisation usually occurs. o Isthmus: The narrow section that connects to the uterus. o Interstitial part: The segment of the fallopian tube that passes through the uterine wall. Function: Egg Transport: After ovulation, the fimbriae of the fallopian tubes catch the released egg and gently move it into the tube. The cilia lining the tube help propel the egg toward the uterus. Fertilisation: The fallopian tube is the site where fertilisation typically occurs. Sperm travel through the cervix and uterus to meet the egg in the ampulla. If fertilisation occurs, the fertilised egg (zygote) continues to the uterus for implantation. Conduit for Sperm: The fallopian tubes also serve as a pathway for sperm to reach the egg. OVARIES Structure: Location: The ovaries are almond-shaped organs located on either side of the uterus, within the pelvic cavity. Anatomy: o Cortex: The outer region of the ovary, which contains ovarian follicles in various stages of development. o Medulla: The inner region of the ovary, containing blood vessels, lymphatics, and nerves. o Follicles: Ovarian follicles are fluid-filled sacs that contain immature eggs (ova). Each month, one follicle matures and releases an egg during ovulation. Function: Oogenesis: The ovaries produce and store eggs, which are released during ovulation. A female is born with all the eggs she will ever have, and they mature throughout her life. Hormone Production: The ovaries produce key reproductive hormones such as: Oestrogen: Regulates the menstrual cycle, helps develop secondary sexual characteristics, and prepares the body for pregnancy. Progesterone: Prepares the uterus for pregnancy and maintains the early stages of pregnancy. Inhibin: Regulates the secretion of FSH from the pituitary gland. Ovulation: The mature egg is released from the ovary during ovulation, usually once a month, into the fallopian tube where it may be fertilised. UTERUS Structure: Location: The uterus is a hollow, pear-shaped organ located in the pelvic cavity, between the bladder and the rectum. Anatomy: o Fundus: The upper part of the uterus, above the openings of the fallopian tubes. o Body: The central part of the uterus where the embryo implants. o Cervix: The lower, narrow portion of the uterus that connects to the vagina. o Endometrium: The inner lining of the uterus, which thickens each month in preparation for implantation. o Myometrium: The thick, muscular layer that contracts during labour. o Perimetrium: The outer serous layer that provides a protective covering. Function: Menstruation: If fertilisation does not occur, the endometrium is shed during menstruation, leading to the monthly menstrual flow. Pregnancy: The uterus provides a site for implantation of a fertilised egg. The endometrium thickens to support the developing embryo. The uterus grows and expands as the foetus develops during pregnancy. Labour: The uterus contracts during labour to help expel the foetus during childbirth. Support for the Foetus: The uterus provides a protected environment for Foetal development, providing nutrients and oxygen, and eliminating waste. CERVIX Structure: Location: The cervix is the lower part of the uterus, connecting the uterus to the vagina. It is about 2-3 cm long. Anatomy: o Cervical Canal: The narrow passage within the cervix that connects the uterus to the vagina. o External Os: The opening at the end of the cervix that leads into the vagina. o Cervical Mucus: The cervical canal produces mucus, which varies in consistency during the menstrual cycle. The mucus is thicker and more acidic outside of ovulation, and thinner and more alkaline during ovulation to facilitate sperm passage. Function: Barrier and Protection: The cervix acts as a barrier to prevent infections from reaching the uterus. The cervical mucus helps protect against bacterial invasion. Sperm Passage: The cervix serves as the pathway for sperm to travel from the vagina into the uterus during sexual intercourse. Menstrual Flow: During menstruation, the cervix allows the shedding of the endometrial lining to exit the uterus. Childbirth: The cervix dilates (opens) during labour to allow the passage of the baby from the uterus into the birth canal. VAGINA Structure: Location: The vagina is a muscular, tubular organ that extends from the external genitalia to the cervix, measuring about 8-10 cm in length. Anatomy: o Vaginal Canal: The vaginal canal is lined with a mucous membrane and contains folds (rugae) that allow for stretching during intercourse and childbirth. o Vaginal Opening (Introitus): The external opening of the vagina, located between the labia minora and above the anus. Function: Sexual Intercourse: The vagina is the organ through which sperm is deposited during intercourse. It is also involved in sexual pleasure. Birth Canal: During childbirth, the vagina serves as the passage through which the baby is delivered from the uterus to the outside world. Menstrual Flow: The vagina is the exit route for menstrual blood during the menstrual cycle. Protection: The vaginal lining produces natural lubrication and contains acidic secretions that help protect against infections. ENDOMETRIUM Structure: Location: The endometrium is the inner lining of the uterus, which changes throughout the menstrual cycle. Anatomy: It consists of two layers: o Stratum Functionalis: The functional layer that thickens in preparation for implantation and is shed during menstruation if no pregnancy occurs. o Stratum Basalis: The basal layer that remains after menstruation and regenerates the functionalis layer. Function: Menstruation: The endometrium sheds its superficial layer during menstruation if fertilisation does not occur. Pregnancy: The endometrium provides a nutrient-rich environment for the implantation of a fertilised egg. It supports the early development of the embryo and is involved in the formation of the placenta. MYOMETRIUM Structure: Location: The myometrium is the thick middle layer of the uterus, made of smooth muscle tissue. Anatomy: It consists of three layers of smooth muscle fibres that are oriented in different directions: longitudinal, circular, and oblique. Function: Contractions: The myometrium is responsible for the powerful contractions that occur during labour to help expel the foetus from the uterus. Menstrual Flow: The myometrium contracts during menstruation to help expel the shed endometrial lining. Support During Pregnancy: During pregnancy, the myometrium provides structural support to the growing uterus and foetus. VULVA (EXTERNAL GENITALIA) Structure: Location: The vulva is the external portion of the female reproductive system, located between the legs. Anatomy: o Labia Majora: The larger, outer folds of skin that enclose the other external genitalia. They contain sweat and sebaceous glands and provide protection. o Labia Minora: The inner, smaller folds of skin, which surround the vaginal and urethral openings. They are more sensitive than the labia majora and contain erectile tissue. o Clitoris: A small, highly sensitive organ located at the top of the labia minora. It is primarily involved in sexual pleasure. The clitoris has a glans (visible portion) and internal crura that extend along the pubic bone. Function: Sexual Stimulation: The vulva, particularly the clitoris, is highly sensitive and plays a key role in sexual arousal and pleasure. Protection: The labia majora and minora protect the internal reproductive organs from infection and physical damage. Lubrication: The labia minora contain sebaceous glands that secrete oils, and during sexual arousal, the vulva secretes lubrication that aids in intercourse. SUMMARY TABLE STRUCTURE ANATOMY FUNCTION Egg transport from ovary to uterus Fallopian Tubes 10-12 cm long, with parts: infundibulum, ampulla, isthmus, interstitial part Site of fertilisation Sperm pathway Oogenesis (egg production) Ovary Almond-shaped, with cortex (follicles) and medulla (blood vessels, nerves) Hormone production (oestrogen, progesterone, inhibin) Menstruation Uterus Hollow, pear-shaped, with fundus, body, cervix, endometrium, myometrium, perimetrium Site for implantation and foetal development Labour contractions Barrier to infection Pathway for sperm Cervix Lower part of uterus, with cervical canal and external os Allows menstrual flow Dilates during labour Sexual intercourse Birth canal Vagina Muscular, tubular, 8-10 cm in length Menstrual flow exit Protection from infections Thickens for implantation Endometrium Inner uterine lining, with stratum functionalis and basalis Shed during menstruation if no pregnancy Uterine contractions during labour Myometrium Middle layer of smooth muscle in the uterus Expels endometrial lining during menstruation Sexual arousal and pleasure Vulva (External Genitalia) Labia majora, labia minora, clitoris Protection of internal organs Lubrication during intercourse Protection of internal genitalia Labia Majora Larger outer folds of skin Contain sweat and sebaceous glands Sensory function Labia Minora Smaller inner folds, surround vaginal and urethral openings Contain erectile tissue Clitoris Small organ at the top of labia minora Primary organ for sexual pleasure TLO 3.2.2 — FUNCTIONS OF OOESTROGEN AND PROGESTERONE OESTROGEN Oestrogen is a group of hormones, primarily oestradiol in females of reproductive age, produced mainly by the ovaries, with smaller amounts produced by the adrenal glands and placenta during pregnancy. Oestrogen is responsible for the development and maintenance of female secondary sexual characteristics and the regulation of the menstrual cycle. Key Functions of Oestrogen: DEVELOPMENT OF SECONDARY SEXUAL CHARACTERISTICS Breast Development: Oestrogen stimulates the growth of the mammary glands, contributing to breast development during puberty and pregnancy. Widening of the Hips: Oestrogen causes widening of the pelvic bones and hips, which is an important change for childbirth. Pubic and Axillary Hair Growth: Oestrogen promotes the growth of pubic and underarm hair. Fat Distribution: Oestrogen contributes to the distribution of fat in the breasts, hips, and thighs, creating the typical female body shape. REGULATION OF THE MENSTRUAL CYCLE Follicular Phase: Oestrogen is responsible for the growth and maturation of ovarian follicles during the follicular phase of the menstrual cycle. It also promotes the thickening of the endometrium (uterine lining) to prepare for potential pregnancy. Positive Feedback on LH Surge: Just before ovulation, a rise in oestrogen levels signals the pituitary gland to release a surge of luteinizing hormone (LH), which triggers ovulation (the release of a mature egg from the ovary). BONE HEALTH Bone Density: Oestrogen plays a critical role in maintaining bone density by promoting osteoblast (bone-building cells) activity and inhibiting osteoclast (bone-resorbing cells) activity. Oestrogen deficiency after menopause can lead to a decrease in bone mass, increasing the risk of osteoporosis. CARDIOVASCULAR HEALTH Cholesterol Regulation: Oestrogen helps maintain healthy cholesterol levels by reducing LDL (low-density lipoprotein) and increasing HDL (high-density lipoprotein). This provides some cardiovascular protection in premenopausal women. Vasodilation: Oestrogen also promotes vasodilation, enhancing blood flow and reducing blood pressure. SKIN AND HAIR HEALTH Collagen Production: Oestrogen supports the production of collagen, contributing to skin elasticity and reducing wrinkles. This is why skin tends to lose elasticity and becomes thinner after menopause, when oestrogen levels decline. Hair Growth: Oestrogen influences hair growth, and its lower levels can lead to thinning hair, especially after menopause. NEUROLOGICAL EFFECTS Mood Regulation: Oestrogen has been shown to have mood-stabilizing effects, likely through its influence on neurotransmitters such as serotonin. It is also linked to a decreased risk of depression during the reproductive years. Cognitive Function: Oestrogen has neuroprotective effects and has been associated with improved cognitive function, including memory. Its decline post-menopause has been linked to an increased risk of cognitive decline and Alzheimer’s disease. PREGNANCY Placental Development: Oestrogen plays a key role in the development of the placenta during pregnancy, supporting Foetal development. Uterine Growth: It promotes the growth and stretching of the uterus during pregnancy to accommodate the growing foetus. Preparation for Labour: Oestrogen levels rise significantly in the final weeks of pregnancy, contributing to the softening of the cervix and preparing the body for labour. PROGESTERONE Progesterone is another critical hormone primarily produced by the corpus luteum (the structure that forms in the ovary after ovulation) and the placenta during pregnancy. It plays a central role in regulating the menstrual cycle and supporting pregnancy. Key Functions of Progesterone: REGULATION OF THE MENSTRUAL CYCLE Luteal Phase: After ovulation, progesterone levels rise as the corpus luteum secretes the hormone. Progesterone stabilizes the thickened endometrium, making it ready for implantation of a fertilised egg. If pregnancy does not occur, progesterone levels drop, leading to menstruation. Prevents Premature Menstruation: By maintaining the endometrial lining and preventing its shedding during the luteal phase, progesterone ensures that menstruation does not occur prematurely. PREPARATION FOR PREGNANCY Uterine Lining Maintenance: Progesterone is crucial for maintaining the endometrial lining of the uterus, ensuring it remains thick and supportive of a developing embryo. Immune System Regulation: Progesterone helps to modulate the immune system during pregnancy to prevent rejection of the developing foetus, which is genetically distinct from the mother. PREGNANCY SUPPORT Relaxation of Uterine Muscles: Progesterone prevents uterine contractions during pregnancy, reducing the risk of preterm labour. Breast Preparation: Progesterone stimulates the development of milk-producing glands in the breasts, preparing the body for breastfeeding after childbirth. Prevents Ovulation: During pregnancy, high levels of progesterone prevent further ovulation, ensuring that only one pregnancy occurs at a time. CERVICAL MUCUS CHANGES Thickening of Cervical Mucus: Progesterone thickens the cervical mucus, which helps prevent the entry of pathogens into the uterus and also creates a barrier that prevents sperm from reaching the egg during the luteal phase of the menstrual cycle. BREAST DEVELOPMENT Lobular-Alveolar Development: Progesterone works alongside oestrogen to develop the lobules and alveoli (milk-producing glands) in the breast tissue. However, progesterone inhibits milk production until after birth when its levels decrease. NEUROENDOCRINE EFFECTS Mood and Behaviour: Progesterone can have a calming or sedative effect on the body, influencing mood and sleep. It may also have an impact on anxiety levels, with some women experiencing premenstrual symptoms (PMS) linked to fluctuating progesterone levels. METABOLIC EFFECTS Body Temperature Regulation: Progesterone raises the body’s core temperature slightly, which is why women often experience a slight rise in temperature during the luteal phase of their menstrual cycle. Appetite Changes: Progesterone can increase appetite and cravings, particularly for carbohydrate-rich foods. INTERACTION BETWEEN OESTROGEN AND PROGESTERONE Oestrogen and progesterone have complementary yet opposing effects on the reproductive system, particularly in the menstrual cycle and pregnancy: Menstrual Cycle: Oestrogen promotes the growth and development of the endometrium, while progesterone stabilizes and maintains it. The balance between these two hormones is crucial for the proper regulation of the menstrual cycle. The abrupt decline in both hormones is what triggers menstruation. Pregnancy: Oestrogen supports the growth and development of the foetus, while progesterone maintains the uterine environment, prevents preterm labour, and ensures proper immune responses. SUMMARY TABLE HORMONE FUNCTION Oestrogen Development of Secondary Sexual Characteristics: Regulation of the Menstrual Cycle: Breast development Growth and maturation of ovarian follicles Widening of hips Thickening of the endometrium Pubic and axillary hair growth Positive feedback on LH surge for ovulation Fat distribution in breasts, hips, and thighs Bone Health: Cardiovascular Health: Maintains bone density by promoting osteoblast activity and inhibiting osteoclast activity Improves cholesterol levels (lowers LDL, raises HDL) Prevents osteoporosis post-menopause Promotes vasodilation and lowers blood pressure Skin and Hair Health: Neurological Effects: Supports collagen production, maintaining skin elasticity Regulates mood and reduces the risk of depression Influences hair growth, preventing thinning Linked to improved cognitive function and memory Pregnancy: Supports placental development and foetal growth Promotes uterine growth and prepares the body for labour Progesterone Regulation of the Menstrual Cycle: Preparation for Pregnancy: Stabilizes and maintains the endometrial lining after ovulation Maintains the endometrial lining for implantation Prevents premature menstruation Modulates the immune system to prevent rejection of the foetus Pregnancy Support: Cervical Mucus Changes: Prevents uterine contractions during pregnancy Thickens cervical mucus to prevent pathogens and sperm entry Prepares breasts for milk production- Prevents further ovulation during pregnancy Neuroendocrine Effects: Breast Development: Has a calming, sedative effect on mood and anxiety Stimulates the development of milk-producing glands in the breasts Affects sleep patterns Metabolic Effects: Raises body temperature slightly during the luteal phase Increases appetite, especially for carbohydrate-rich foods TLO 3.3 — DESCRIBE THE REGULATION OF THE MENSTRUAL CYCLE AND UTERINE CYCLE The menstrual cycle and the uterine cycle are closely intertwined, regulated by the interaction of hormones from the hypothalamus, pituitary gland, and ovaries. These cycles prepare the female body for potential pregnancy and occur in a regular pattern, typically lasting about 28 days, although it can vary among individuals. MENSTRUAL CYCLE OVERVIEW The menstrual cycle consists of a series of physiological events that regulate the function of the ovaries and the uterus. It is controlled by a feedback mechanism involving hormones, and it is divided into four main phases: Menstrual Phase (Days 1-5) Follicular Phase (Days 1-13) Ovulation (Day 14) Luteal Phase (Days 15-28) HORMONAL REGULATION OF THE MENSTRUAL CYCLE The menstrual cycle is controlled by the hypothalamic-pituitary-gonadal axis: Hypothalamus: The hypothalamus releases gonadotropin-releasing hormone (GnRH). Pituitary Gland: GnRH stimulates the anterior pituitary to release two hormones: o Follicle-stimulating hormone (FSH): Stimulates the growth and maturation of ovarian follicles. o Luteinizing hormone (LH): Triggers ovulation and supports the luteal phase. Ovaries: The ovaries produce hormones that regulate the cycle: o Oestrogen: Produced by growing follicles and the corpus luteum, it stimulates the growth of the endometrium and regulates the release of FSH and LH. o Progesterone: Produced by the corpus luteum after ovulation, it stabilizes the endometrial lining and maintains pregnancy if fertilisation occurs. PHASES OF THE MENSTRUAL CYCLE MENSTRUAL PHASE (DAYS 1-5) Hormonal Events: Low Oestrogen and Progesterone: If fertilisation does not occur, the corpus luteum degenerates, causing a drop in oestrogen and progesterone levels. This hormonal decline triggers menstruation, where the endometrial lining (stratum functionalis) is shed. Endometrial Events: The endometrial lining is shed as blood and tissue, marking the start of a new cycle. FOLLICULAR PHASE (DAYS 1-13) Hormonal Events: FSH stimulates the growth of ovarian follicles. Oestrogen is secreted by developing follicles, particularly oestradiol, which encourages further growth and thickening of the endometrium (preparing it for possible implantation). Low levels of oestrogen during early follicular phase inhibit LH and FSH secretion. As the follicle matures, oestrogen levels rise, which eventually leads to a positive feedback loop with the hypothalamus and pituitary, stimulating a surge in LH. Ovarian Events: Follicular development: Multiple follicles grow, but usually, one becomes dominant and fully matures. Endometrial Events: The endometrial lining begins to proliferate and thicken in response to increasing oestrogen levels, preparing for potential implantation. OVULATION (DAY 14) Hormonal Events: LH Surge: The peak of oestrogen secretion from the dominant follicle triggers the LH surge from the pituitary gland. This surge causes the mature follicle to rupture and release the egg (ovum) in a process called ovulation. FSH also increases slightly, supporting follicular growth but is less significant than LH at this stage. Ovarian Events: Egg release: The ovary releases the matured egg, which then enters the fallopian tube for possible fertilisation. Endometrial Events: The endometrial lining continues to thicken under the influence of oestrogen in preparation for implantation. LUTEAL PHASE (DAYS 15-28) Hormonal Events: After ovulation, the ruptured follicle transforms into the corpus luteum, which secretes progesterone and small amounts of oestrogen. Progesterone is the dominant hormone in the luteal phase, and it promotes the thickening of the endometrium, making it more receptive to a fertilised egg. If pregnancy does not occur, the corpus luteum degenerates after about 10-14 days, and progesterone levels drop, signalling the start of a new menstrual cycle. Ovarian Events: Corpus luteum forms and produces progesterone. Endometrial Events: The endometrium continues to prepare for possible implantation, with increased vascularity and glandular secretion. If no fertilisation occurs, the decline in progesterone leads to the shedding of the endometrial lining, beginning the menstrual phase. UTERINE CYCLE The uterine cycle corresponds to the changes in the uterus and its endometrium during the menstrual cycle. It is divided into three phases: Menstrual Phase (Days 1-5): Shedding of the endometrial lining (stratum functionalis). Proliferative Phase (Days 6-14): The endometrium rebuilds and thickens in response to rising oestrogen levels. Secretory Phase (Days 15-28): The endometrium becomes more vascular and glandular under the influence of progesterone, preparing for implantation. KEY HORMONES SUMMARY TABLE HORMONE SOURCE FUNCTION GnRH (Gonadotropin-Releasing Hormone) Hypothalamus Stimulates the release of FSH and LH from the anterior pituitary. FSH (Follicle-Stimulating Hormone) Anterior Pituitary Stimulates the growth and maturation of ovarian follicles. LH (Luteinizing Hormone) Anterior Pituitary Triggers ovulation and supports corpus luteum formation. Oestrogen Ovaries (Follicles) Stimulates follicular development, thickens the endometrial lining, and promotes the LH surge. Progesterone Ovaries (Corpus Luteum) Prepares the endometrium for implantation, maintains the uterine lining, and prevents further ovulation. TLO 3.3.1 — FOLLICULAR AND LUTEAL PHASES OF MENSTRUAL CYCLE The menstrual cycle is divided into two primary phases: the follicular phase and the luteal phase. These phases are regulated by hormonal fluctuations and coordinate with ovarian and endometrial changes to prepare the body for pregnancy. Both phases are essential for proper reproductive function. FOLLICULAR PHASE (DAYS 1-13) The follicular phase begins on the first day of menstruation and ends with ovulation (Day 14). It involves the development and maturation of ovarian follicles, culminating in the release of an egg during ovulation. This phase is characterized by increasing oestrogen levels and low progesterone levels. KEY EVENTS OF THE FOLLICULAR PHASE Menstruation (Days 1-5): The first part of the follicular phase is marked by menstruation, where the endometrial lining (stratum functionalis) is shed due to a decrease in oestrogen and progesterone if fertilisation has not occurred. GnRH (Gonadotropin-Releasing Hormone) is secreted by the hypothalamus, which stimulates the anterior pituitary to release FSH (Follicle-Stimulating Hormone) and LH (Luteinizing Hormone). Follicular Recruitment and Growth (Days 1-7): FSH stimulates the growth of several ovarian follicles (each containing an immature egg). At the start of the follicular phase, several primordial follicles begin to mature, but only one (dominant follicle) will continue to grow. As the follicles grow, they begin to secrete oestrogen (oestradiol), which is responsible for stimulating the regeneration of the endometrial lining. The endometrial tissue thickens and becomes more vascular to prepare for possible implantation. Dominant Follicle Selection (Days 7-13): As the follicles mature, one follicle becomes the dominant follicle (usually the largest), and the others undergo atresia (degeneration). The dominant follicle secretes high levels of oestrogen, which further stimulates the endometrial lining to grow and prepares it for potential implantation. Oestrogen also plays a key role in regulating the secretion of FSH and LH through a negative feedback loop. Initially, high oestrogen levels inhibit FSH production to prevent the maturation of additional follicles. On Day 12-13, rising oestrogen levels induce a positive feedback mechanism that causes a sharp increase in LH levels, known as the LH surge. This surge triggers ovulation (the release of the egg) at the end of the follicular phase. KEY HORMONES SUMMARY TABLE HORMONE SOURCE ROLE GnRH Hypothalamus Stimulates release of FSH and LH from the pituitary gland. FSH Anterior Pituitary Stimulates the growth of ovarian follicles and the secretion of oestrogen by granulosa cells. Oestrogen (Oestradiol) Ovarian Follicles Stimulates the regeneration and thickening of the endometrial lining; inhibits FSH and stimulates LH surge. OVULATION (DAY 14) Ovulation marks the transition between the follicular and luteal phases. The LH surge triggered by high levels of oestrogen from the dominant follicle causes the mature follicle to rupture and release an egg into the fallopian tube. This is the only phase in the menstrual cycle when fertilisation can occur. LUTEAL PHASE (DAYS 15-28) The luteal phase begins immediately after ovulation and lasts until the start of menstruation (Days 15-28). The luteal phase is characterized by the formation of the corpus luteum and the secretion of progesterone, which prepares the endometrium for potential embryo implantation. KEY EVENTS OF THE LUTEAL PHASE Formation of the Corpus Luteum (Days 15-17): After ovulation, the ruptured follicle transforms into the corpus luteum, a temporary endocrine structure. The corpus luteum secretes progesterone, along with a small amount of oestrogen, to stabilize the endometrial lining. Progesterone is the dominant hormone in this phase, and it increases the blood supply to the endometrium, making it thicker and more glandular to support implantation. Oestrogen levels also remain elevated, though they are lower than during the follicular phase. Maintenance of the Endometrium (Days 18-25): The endometrium continues to develop and becomes more vascular under the influence of progesterone. Progesterone also suppresses FSH and LH to prevent further ovulation during this phase. If fertilisation occurs, the embryo will produce human chorionic gonadotropin (hCG), which signals the corpus luteum to continue producing progesterone and prevents its degeneration. If no fertilisation occurs, the corpus luteum begins to degenerate (Days 24-28), leading to a drop in progesterone and oestrogen levels. Pre-menstruation (Days 26-28): As progesterone and oestrogen levels fall, the endometrial lining begins to break down. The drop in hormones signals the start of the menstrual phase (Day 1 of the next cycle), and the shedding of the endometrial lining occurs. KEY HORMONES SUMMARY TABLE HORMONE SOURCE ROLE LH Anterior Pituitary Triggered by oestrogen, leads to ovulation; remains low in luteal phase. Progesterone Corpus Luteum Maintains and stabilizes the endometrial lining, inhibits further ovulation. Oestrogen Corpus Luteum Supports the action of progesterone, helps maintain the endometrial lining. COMPARISON OF FOLLICULAR AND LUTEAL PHASES CHARACTERISTIC FOLLICULAR PHASE LUTEAL PHASE Duration 1-13 days 15-28 days Dominant Hormones Oestrogen (oestradiol), FSH Progesterone, Oestrogen Key Events Follicle growth, oestrogen production, endometrial regeneration Corpus luteum formation, progesterone production, endometrial preparation for implantation Endometrial Changes Thickening of the endometrial lining Further thickening and glandular secretion in preparation for implantation Ovarian Events Follicle maturation, ovulation at the end of the phase Corpus luteum forms, secretes progesterone Hormonal Feedback Oestrogen stimulates LH surge; negative feedback on FSH Progesterone suppresses LH and FSH to prevent further ovulation Fertilisation Egg is prepared for release during ovulation If fertilisation occurs, pregnancy is established; if not, progesterone levels drop, and menstruation begins TLO 3.3.2 — ENDOMETRIUM CHANGES The endometrium, the lining of the uterus, undergoes dynamic changes throughout the menstrual cycle in response to fluctuating hormone levels. These changes are crucial for preparing the uterus for potential implantation of a fertilised egg and, if fertilisation does not occur, for shedding the lining during menstruation. The endometrial changes are coordinated with the follicular phase, ovulation, luteal phase, and menstruation to ensure reproductive success. PHASES OF ENDOMETRIAL CHANGES The endometrial changes are typically classified into three main phases: Menstrual Phase (Days 1-5) Proliferative Phase (Follicular Phase) (Days 6-14) Secretory Phase (Luteal Phase) (Days 15-28) Each of these phases corresponds to specific hormonal fluctuations and structural changes in the endometrial tissue. MENSTRUAL PHASE (DAYS 1-5) The menstrual phase marks the beginning of the cycle and is characterized by the shedding of the functional layer (stratum functionalis) of the endometrium. This phase occurs when implantation has not taken place and is primarily triggered by a decline in oestrogen and progesterone levels. Key Events: Hormonal Influence: Following the degeneration of the corpus luteum, levels of progesterone and oestrogen drop significantly, leading to the constriction of blood vessels supplying the endometrial tissue. Shedding of Endometrial Tissue: As a result of the reduced blood flow, the functional layer of the endometrium (the innermost layer) begins to break down and is eventually shed, which constitutes menstruation. Endometrial Appearance: During menstruation, the endometrium is largely denuded, and the functional layer is lost, leaving the deeper basal layer (stratum basalis) intact. The basal layer remains, serving as the source for regenerating the functional layer in the next cycle. PROLIFERATIVE PHASE (FOLLICULAR PHASE) (DAYS 6-14) The proliferative phase corresponds to the follicular phase of the menstrual cycle and is characterized by the regeneration and growth of the endometrial lining. This phase is under the influence of oestrogen, which is secreted by the developing ovarian follicles. The proliferative phase prepares the endometrium to receive a fertilised egg should conception occur. Key Events: Hormonal Influence: As oestrogen levels rise due to the maturation of ovarian follicles, it stimulates the endometrial cells to proliferate and rebuild the functional layer. Endometrial Changes: o The functional layer of the endometrium begins to regenerate and thicken, with new glandular and vascular structures developing. o The endometrium becomes increasingly vascularized, and spiral arteries grow to provide a rich blood supply to the developing tissue. o The basal layer (which remains from the menstrual phase) serves as a foundation for the regeneration of the functional layer. Glandular Development: The endometrial glands (in the functional layer) begin to elongate, becoming more complex and forming an intricate network of glands to secrete various substances if pregnancy occurs. Endometrial Appearance: The endometrium is thickening, and the functional layer becomes more granular as glandular structures become more pronounced. SECRETORY PHASE (LUTEAL PHASE) (DAYS 15-28) The secretory phase aligns with the luteal phase of the menstrual cycle, following ovulation. During this phase, the corpus luteum in the ovary secretes progesterone, which is the dominant hormone during this phase. Progesterone acts to further prepare the endometrium for a potential pregnancy by making the environment more suitable for embryo implantation. Key Events: Hormonal Influence: The corpus luteum secretes high levels of progesterone and a smaller amount of oestrogen. Progesterone stimulates the endometrial glands to secrete nutrients and substances that support a potential pregnancy. Endometrial Changes: o The endometrial lining continues to thicken as secretory activity in the glands increases. The glands become more coiled and filled with secretions, providing a nutrient-rich environment for a fertilised egg. o The spiral arteries become more developed and dilated, improving the blood supply to the endometrium. o Progesterone also causes the endometrium to become more oedematous (fluid-filled), softening and increasing in volume to facilitate the implantation of an embryo if fertilisation has occurred. o Increased Vascularity: The endometrium becomes highly vascularized and more receptive to the embryo. Endometrial Appearance: The endometrium appears thick, velvety, and glandular. It is now richly prepared to support an embryo if implantation occurs. If Pregnancy Does Not Occur: As the luteal phase progresses, the corpus luteum degenerates, leading to a decline in progesterone and oestrogen levels. The loss of progesterone causes the functional layer of the endometrium to break down, initiating the shedding of the lining and the start of a new menstrual cycle (via menstruation). HORMONAL REGULATION OF ENDOMETRIAL CHANGES The regulation of endometrial changes is controlled by the interplay of hormones, primarily oestrogen and progesterone, in response to the phases of the menstrual cycle. HORMONE SOURCE ROLE IN ENDOMETRIAL CHANGES Oestrogen Ovarian Follicles Stimulates the regeneration and thickening of the endometrial lining in the proliferative phase. Progesterone Corpus Luteum Prepares the endometrium for potential implantation by increasing glandular secretion, vascularization, and oedema during the secretory phase. FSH Anterior Pituitary Stimulates follicle development and oestrogen production during the early menstrual cycle. LH Anterior Pituitary Stimulates ovulation and the formation of the corpus luteum. SUMMARY OF ENDOMETRIAL CHANGES PHASE HORMONAL INFLUENCE ENDOMETRIAL CHANGES Menstrual Phase Decreased oestrogen and progesterone Shedding of the functional layer, leaving the basal layer intact. Proliferative Phase Rising oestrogen Regeneration of the endometrial lining, increased glandular and vascular growth. Secretory Phase Rising progesterone and oestrogen Endometrial thickening, glandular secretion, increased vascularization in preparation for implantation. TLO 3.3.3 — FERTILISATION (SITE OF FERTILISATION, IMPLANTATION, HCG). Fertilisation, implantation, and the secretion of human chorionic gonadotropin (hCG) are critical processes in early pregnancy. These events occur in specific stages, with hormones playing a vital role in supporting pregnancy, regulating the menstrual cycle, and ensuring successful implantation of the embryo. FERTILISATION Definition: Fertilisation is the process in which a sperm cell from a male merges with an oocyte (egg cell) from a female to form a zygote, which contains a complete set of chromosomes. Site of Fertilisation: Fertilisation typically occurs in the fallopian tube, specifically in the ampulla (the widest part of the fallopian tube) which is situated near the ovary. o After ovulation, the oocyte is captured by the fimbriae (finger-like projections) of the fallopian tube and is directed into the tube. o Sperm cells, following ejaculation into the female reproductive tract, travel through the cervix and uterus to reach the fallopian tube. o Fertilisation usually occurs within 12–24 hours after ovulation when the oocyte is viable and can be fertilised by sperm. Process of Fertilisation: Sperm Penetration: o The sperm must penetrate the corona radiata (the layer of follicular cells surrounding the oocyte) and the zona pellucida (a glycoprotein layer) to reach the egg. o The sperm head binds to and penetrates the zona pellucida via enzymes in the acrosome (a cap-like structure at the sperm's head), allowing the sperm to reach the egg's plasma membrane. Fusion of Sperm and Egg: Once the sperm binds with the egg, the membranes of the sperm and egg fuse, allowing the sperm's nucleus to enter the oocyte, forming the zygote. Completion of Meiosis in Oocyte: The egg completes the second meiotic division upon fertilisation, forming a second polar body. Zygote Formation: The sperm and egg nuclei merge to form a diploid zygote (46 chromosomes—23 from the sperm and 23 from the egg), which will undergo mitotic divisions (cleavage) as it begins its journey to the uterus. IMPLANTATION Definition: Implantation is the process in which the fertilised egg (now a blastocyst) attaches to and embeds itself into the endometrial lining of the uterus, beginning the development of pregnancy. Timing of Implantation: o Implantation typically occurs 6–10 days after fertilisation, once the blastocyst has divided and matured into a form that can attach to the endometrium. o The endometrial lining must be in the secretory phase (after ovulation) to be receptive to the implanting embryo, which is supported by the hormones oestrogen and progesterone. Steps in Implantation: Blastocyst Hatching: o After fertilisation, the zygote undergoes cleavage, becoming a morula and then a blastocyst. The blastocyst is a hollow ball of cells with an inner cell mass (which will develop into the embryo) and an outer layer of cells (trophoblast, which will contribute to the placenta). o The blastocyst "hatches" from the zona pellucida to allow the trophoblast cells to interact with the endometrium. Attachment to Endometrium: The trophoblast cells secrete enzymes that allow them to invade the endometrial lining, attaching to and embedding into the endometrial tissue. Syncytiotrophoblast Formation: The trophoblast differentiates into two layers: the cytotrophoblast (inner layer) and the syncytiotrophoblast (outer layer). The syncytiotrophoblast is responsible for secreting human chorionic gonadotropin (hCG) and forming the placenta. Implantation and Formation of Placenta: As implantation progresses, the blastocyst becomes surrounded by the endometrial tissue, and villi form, which will eventually contribute to the placenta, allowing for nutrient and waste exchange between the mother and the developing embryo. HUMAN CHORIONIC GONADOTROPIN (HCG) Definition and Role: hCG is a hormone secreted by the syncytiotrophoblast (cells from the outer layer of the blastocyst) soon after implantation, and it plays a crucial role in supporting pregnancy during its early stages. Function of hCG: Maintains the Corpus Luteum: o hCG signals the corpus luteum (the structure formed from the ruptured follicle after ovulation) to continue producing progesterone. o Progesterone is essential to maintain the endometrial lining and prevent menstruation, thus allowing the embryo to implant and continue to develop. Supports Placental Development: hCG stimulates the growth and maintenance of the placenta, which will eventually take over the production of progesterone after the first trimester. Detectable in Pregnancy Tests: hCG levels rise rapidly in the early weeks of pregnancy, making it a key marker for pregnancy tests. These tests detect hCG in urine or blood. hCG Levels: After implantation, hCG levels begin to rise dramatically, doubling every 48–72 hours during the first weeks of pregnancy. The peak of hCG levels typically occurs between the 8th and 10th week of pregnancy, after which they gradually decline and plateau as the placenta takes over progesterone production. SUMMARY PROCESS LOCATION KEY EVENTS Fertilisation Fallopian tube (ampulla) Sperm fuses with egg to form a zygote; completes meiosis and begins cleavage. Implantation Uterus (endometrial lining) Blastocyst attaches to and invades the endometrial lining; trophoblast secretes hCG to support pregnancy. hCG Production Placenta (syncytiotrophoblast) hCG maintains corpus luteum, stimulates progesterone production, and supports early placental development. TLO 3.4 — DISCUSS THE PHYSIOLOGICAL ADAPTATIONS THAT OCCUR DURING PREGNANCY Pregnancy involves profound physiological changes across multiple systems in the mother’s body to support Foetal growth, prepare for delivery, and accommodate the metabolic needs of both the mother and foetus. These changes are driven by hormonal, mechanical, and metabolic factors and are generally divided into adaptations in various body systems and the process of parturition. TLO 3.4.1 — PARTURITION (RELAXIN, CONTRACTIONS AND OXYTOCIN, BABY, AND PLACENTA DELIVERY) Parturition refers to the process of childbirth, which involves uterine contractions, cervical dilation, and the delivery of the baby and placenta. Hormones such as relaxin and oxytocin play pivotal roles. RELAXIN Source: Secreted by the corpus luteum, placenta, and decidua. Function: o Softens and relaxes the cervix to facilitate dilation during labour. o Relaxes pelvic ligaments and the pubic symphysis to prepare for childbirth. o May reduce uterine contractions in early pregnancy to prevent preterm labour. CONTRACTIONS AND OXYTOCIN Uterine Contractions: Braxton Hicks contractions (false labour) occur sporadically during pregnancy and help tone the uterus. True labour contractions are regular, strong, and increase in intensity, aiding in cervical dilation and delivery. Oxytocin: Released from the posterior pituitary. Stimulates myometrium contractions during labour. Positive feedback loop: Foetal pressure on the cervix increases oxytocin secretion, amplifying contractions (Ferguson reflex). DELIVERY OF THE BABY Stage 1: Cervical dilation and effacement (thinning of the cervix). o Regular uterine contractions gradually dilate the cervix to 10 cm. Stage 2: Delivery of the baby. o Involves intense uterine contractions and maternal effort (pushing). o The baby moves through the birth canal (vagina) aided by uterine contractions and relaxation of pelvic ligaments. Stage 3: Delivery of the placenta. o After the baby is delivered, uterine contractions continue to detach and expel the placenta. o Oxytocin helps clamp down the uterus, reducing blood loss and promoting haemostasis. TL

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