Male Reproductive System PDF

**[Reproduction Introduction]** ***Sexual Reproductions involves*** - The formation of germ cells (aka gametogenesis). The female gamete (aka ovum), typically a large non-motile cell, whilst the male gamete (aka spermatozoon) is much smaller and highly motile when mature - Fusion...

**[Reproduction Introduction]** ***Sexual Reproductions involves*** - The formation of germ cells (aka gametogenesis). The female gamete (aka ovum), typically a large non-motile cell, whilst the male gamete (aka spermatozoon) is much smaller and highly motile when mature - Fusion of the two gametes (fertilisation) to form a zygote - The development of resultant offspring within the female reproductive system during pregnancy - The expulsion of the offspring once it is capable of surviving in the external environment which is known as parturition.   +-----------------+-----------------+-----------------+-----------------+ | **Term** | **Male** | **Female** | **Function** | +=================+=================+=================+=================+ | **Gametes** | Spermatozoa | Ova (ovum) | Germ cells with | | | (spermatozoon) | | a haploid | | | | | chromosome | | | | | number. | +-----------------+-----------------+-----------------+-----------------+ | **Gonads** | Testes (testis) | Ovaries (ovary) | Gametogenesis. | +-----------------+-----------------+-----------------+-----------------+ | **Sex | Testosterone | Oestrogen | Regulation of | | Hormones** | | | reproduction | | | | Progesterone | and | | | | | development. | +-----------------+-----------------+-----------------+-----------------+ | **Reproductive | Epididymis | Fallopian Tube | Male: Store and | | Tract** | | | deliver | | | Vas deferens | Uterus | gametes. | | | | | | | | Ejaculatory | Cervical Canal | Female: Receive | | | duct | | gametes, locus | | | | Vagina | for | | | Urethra | | fertilisation, | | | | | embryonic | | | | | development and | | | | | parturition. | +-----------------+-----------------+-----------------+-----------------+ | **Accessory Sex | Prostate Gland | Mammary Glands | Male:  Provide | | Organs** | | | support and | | | Seminal | | nourishment for | | | vesicles | | gametes. | | | | | | | | Bulbourethral | | Female: Provide | | | glands. | | nourishment for | | | | | post partum | | | | | offspring. | +-----------------+-----------------+-----------------+-----------------+     **[Structure]**   **Vas Deferens** - AKA Ductus Deferens - Continuous with the epididymis and is approximately 35cm long in humans and connects the epididymis to the urethra - The wall of the structure consists of an epithelial layer and three layers of smooth muscle. The layers of the smooth muscle work in a coordinated manner to propel spermatozoa along the length of the vas deferens during ejaculation - The vas deferens leaves the scrotum through the inguinal canal, then courses through the pelvic cavity and gives rise to a small swelling called the ampulla where it fuses with the duct from the seminal vesicle to form the ejaculatory duct   **Seminal Vesicle** - Glands are found on the posterior aspect of the bladder - Approximately 5cm long - The exocrine secretion of the seminal fluid and is secreted into the ejaculatory duct during ejaculation   **Ejaculatory duct** - Relatively short \~2cm long - Formed by the fusion of the vas deferens and the duct from seminal vesicles - Runs through the lateral wall of the prostate gland and fuses with the urethra   **Prostate gland** - Single, domed shaped gland found underneath the bladder and is penetrated by the prostatic urethra and the ejaculatory ducts - The prostate is made up of glandular epithelium surrounded by connective tissue and smooth muscle - Contraction of smooth muscle causes the exocrine secretions of the prostate gland (prostatic fluid) to flow through a series of small collecting ducts into the prostatic urethra during ejaculation   **Bulbourethral (Cowper\'s) Glands** - Pair of small exocrine located just underneath the prostate gland and at the base of the penis - The substances secreted by these gland flow into the penile urethra through small duct during ejaculation   **Epididymis** - C-shaped organ which usually lies on the posterior surface of each testis and is typically 3.5 cm long - It connects the testes to the vas deferens   **Urethra** - Terminal portion of the both the urinary and reproductive ductal system in the male. - Originates from the inferior portion of the urinary bladder - Is approximately 20cm long and is divided into three parts - *Prostatic Urethra*: The 2-3 cm portion which runs through the middle of the prostate gland where it fuses with the ejaculatory ducts. - *Membranous Urethra*: A short portion at the base of the prostate gland. - *Penile Urethra*: The major constituent of the urethra which runs through the penis. **Testis** - Pair of oval glands roughly 5cm by 2.5cm and weighs roughly 10-15g in adult humans - Each testis is subdivided into approx. 400 lobules, each containing between 1 and 4 seminiferous tubule, the double ended tubules are typically 200-350 microns in diameter and both ends empty into a series of ducts that deliver spermatozoa to the epididymis - The seminiferous tubules are responsible for spermatogenesis. The spaces between the tubules are filled with connective tissue, blood and lymph vessels and the Leydig (aka interstitial) cells which are responsible for production of testosterone   **[Spermatogenesis ]** - Occurs in the seminiferous tubules beginning at puberty, this continues until late in life - Involves the process by which primordial germ cells are transformed into spermatozoa - Most effective rates of spermatogenesis occur at environmental temperatures of 3-5*ºC* below core body temp - This is why the testes are located within the scrotum exterior to the pelvic cavity - The failure or testes to descend (cryptorchidism) can result in attenuated spermatogenesis - Tested of prepubertal males - Simple seminiferous tubules - Small numbers of germ cells arranged around the periphery of the tubules and positioned between supporting Sertoli cells, these are attached to the basal surface of the tubule and project towards the lumen - Beginning at puberty (11-14 years old) - Spermatogonia divide and dramatically increase the number of cells at the base of the tubule - Spermatogonia begin the sequence of events by which they are transformed into spermatazoa - The developing cells (positioned between the sertoli cells) move away from the periphery of the seminiferous tubules towards the lumen - If you observe a cross section, there will be more developed cells towards the periphery to the tubule lumen ***Mitosis*** - Spermatagonia located close to the peripherly of the seminiferous tubule and have a fairly large oval-shaped nuclei - The cells undergo mitotic division - Gives rise to two daughter cell - One remains at the periphery (retains germ cell stocks) - Second undergoes a further two mitotic divisions ***Meiosis*** - Following mitotic division, the spermatogonia continues to grow and become primary spermatocytes - These are typically larger than spermatogonia but have the same central nucleus - Primary spermatocytes undergo meiosis to form two secondary spermatocytes - Typically smaller diameter and remain coupled by narrow cytoplasmic bridges - Secondary spermatocytes undergo second meiotic division giving rise to two spermatids each - Spermatids remain coupled by narrow cytoplasmic bridges ***Spermiogenesis*** - The final stage in spermatogenesis - The process by which spermatids metamorphose - Throughout the process, the maturing spermatozoa remain associated with the Sertoli cells. - Most action takes place towards the luminal surface of the seminiferous tubules - Key elements - *Nuclear reorganisation* - Early in process, centrally located spermatid nucleus begins to move and takes up a position on the non-luminal side of the spermatid cytoplasm - The nucleus begins to elongate and the chromatin becomes much denser - *Acrosome Formation* - The acrosome is formed as the spermatid Golgi apparatus takes up position between the migrating nucleus and plasma membrane - As the spermiogenesis progresses the acrosome grows around the elongating nucleus and ultimately covers its anterior and lateral surfaces - *Tail assembly* - The motility of spermatozoa is of course enabled by their tail - The formation of tail involves reorganisation the remaining cytoplasm and plasma membrane around the long microtubule core - Microtubule core arises from one of the spermatids centrioles and consequently has the typical arrangement of two microtubules surrounded by nine pairs of microtubules arranged equidistant from each other. - Movement of tail is enabled by formation of transient cross-bridges between microtubules which cause them to slide relative to each other - The process is powered by ATP generated by the large number of mitochondria found in initial portion of the tail (midpiece) 1. **Spermiogenesis** - **Cytoplasmic Bridge: Spermatids from a single primary spermatocyte remain connected by a cytoplasmic bridge during spermiogenesis.** - **Duration: The process takes 64-74 days from the initial mitotic division of a spermatogonium to the release of mature spermatozoa into the lumen of the seminiferous tubule.** - **Maturity: Although spermatozoa are structurally mature at this stage, they are non-motile and incapable of fertilization.**   1. **Epididymal Maturation** - **Transport Mechanism: Spermatozoa are moved through the epididymis by tubular fluid flow and peristaltic contractions of smooth muscle.** - **Fluid Reabsorption: A significant portion of the seminiferous tubular fluid is reabsorbed during transport.** - **Transport Time: Average epididymal transport time is 12 days.** - **Impact of Ejaculation Frequency: Increased ejaculation frequency can enhance the rate of transport without causing a significant decline in sperm concentration or motility. Slight differences in concentration may occur between the first and second ejaculate.**   1. **Storage in the Vas Deferens** - **Final Stage: Fully motile spermatozoa are stored in the vas deferens until ejaculation.**   **[Sertoli cells ]** - Large cells that are attached to peripheral edge of the seminiferous tubule that project up upwards to the lumen - Development of spermatogonia, spermatocytes and spermatids occur in pockets between adjacent Sertoli cells. - Functions A. Formation of blood-testes barrier - There is a tight junction between the plasma membrane of adjacent Sertoli cells - This prevents movement of blood borne substances into the lumen of the seminiferous tubules - Acts as an immunological barrier - Developing spermatogonia are permitted to move past the barriers by remodelling of the barrier B. Supply of nutrients to developing sperm cells - All nutrients required by developing sperm cells are Sertoli cells - This is due to the blood-testes barrier - The Sertoli cells regulate the nutrients for the sperm cells C. Phagocytosis of cellular debris - Sertoli cells are responsible for phagocytosis of developing sperm cells that die before reaching maturity as well as other cellular debris D. Secretion of seminiferous tubule fluid - This is secreted by the Sertoli cells - This washes the spermatozoa along the length of tubules towards epididymis E. Regulation of spermatogenesis - Hormonal control   **[Control of spermatogenesis ]** - Initiated by an increase in gonadotropin-releasing hormone (GnRH) secretion by the hypothalamis (at onset of puberty) - GnRH stimulates secretion of the gonadotropins, follicle -stimulating hormone and luteinising hormone by the anterior pituitary gland - ***Lutenising hormone*** - Binds to specific receptors on the leydig cells of interstial space of the testes and stimu;ates their initial development and the secretion of testosterone by these cells - ***Follicle stimulating hormone*** - Acts on sertoli cells of seminefeorus tubu;es causing them to mature (together with testosterone - leydig cells) -\> this initiates spermatogenesis - FSH stimulates the secretion of inhibin and androgen binding protein (ABP) by the sertoli cells - ***Testosterone*** - Secreted by the leydig cells under the influence of LH - Responsible for: - \'masculinisation of the brain\' - musculoskeletal growth - enlargement of the accessory organs - development of male secondary sex characteristics - the stimulation of spermatogenesis (together with FSH). - Effects of testosterone on spermatogenesis are enhancesd by the secretion of ABP by the sertoli cells - Binding testosterone ABP enhances the local concentration of testosterone causing the stimulatory effect on spermatogensis - Negative feedback mechanisms in spermatogensis - ***Testosterone*** - Inhibirotry effect on the hypothalamus which results in a decline in GnRH causes a decline in circulating levels of both FSH and LH - Direct inhibitory effect of testosterone on LH secretion by the anterior pituitary - If testosterone levels increase the feedback loop will reduce LH levels and subsequently testosterone secretion by the Leydig cells - If testosterone levels begin to drop, the inhibitory influence will decline and LHG lebels willrise to stimulate testosterone secretion restoring stasis - The net effect of both these actions is that circulating testosterone levels are very precisely controlled - ***Inhibin*** - Inhibin released by sertoli cells also exhibits a poweful inhibitory influence on the anterior pituitary which primarily inhibits FSH secretion Regulation and Production of Spermatozoa 1. Initiation of Spermatogenesis - Triggered at puberty by increased levels of GnRH, LH, FSH, testosterone, and ABP - Regulated by negative feedback from testosterone and inhibin. 2. Production Rates - Healthy 20-year-old men produce approximately 6.5 million sperm/gram testis/day. - This rate declines with age, reaching about 3.8 million sperm/gram testis/day in men aged 50-90 years.   **[Male sexual Function]** A. ***Erection*** - ***Enabled by engorgment of three columns of penile erectile tissue with blood*** - ***Typicallt the penile erectile tissue are relatively empty (large venous sinusoids)*** - ***Due to the arterioles that supply them being constricted under the influence of noradrenaline released from the post-ganglionic neurones of the sympathetic division of the ANS*** - ***Consequently in the absences of any stimulation the penis is flaccid*** - ***During arousal there are changes in ANS tone brought about by psychogenic stimuli (seeing someone attractive) and a direct spinal reflex activated by mechanoreceptors in the penis*** - ***Changes in the autonomic tone causes an increased blood flow to the penis and a concomitant relaxating of the smooth musle of the penile erectile tissue to accommodate the nlood*** - ***Both diameter and length of penis increase*** - ***Process is enhanced firther by decreased venous outflow*** - ***Can be the result of occlusion of the veins as a result of rigidity of the penis*** - ***The parasympatheitc division of the autonomic nervous system stimulates secretion of mucus from the bulbourethral glands which flows thrpough the urethra*** - ***Acts as a lubricant during interocurse*** - Cellular mechanism of relaxation of smooth muscle of the penile erectile tissue - Acetylcholine released from parasympathetic postganglionic neurones bind to muscanaric receptors on the endothelial cells that line venous sunsoids of the erectile tissues - Triggers synthesis of nitric oxide (NO) by endothelial cells - NO released difuses into adjacent smooth muscles of erectile tissue and stimulates the intracellular enzyme guanylate cyclase to produce elevtated levels of cyclic guanosis monophosphate (cGMP) - cGMP activates a complex intracellular-messenger cascade that causees relaxation of smooth muscle cells and permits the erectile tissue to become engorged with blood - NO-induced elevation in cGMP levels is a significant step in the erection of the penis - Smooth muscle cells have the enzyme phosphodiesterase type-5 (PDE5) this breaks down the cGMP, inhibiting smooth muscle relaxation and enabling the penis to become flacid A. ***Emission*** - The transfer of spermatozoa, prostatic fluid, seminal fluid and mucus from the bulbourethral glands to mix (forming semen) in the urethra. from the vas deferens - Caused by heightened tactile and psychogenic stimuli and are mediated by increase in sympatheitc activity to smooth muscle within the lining of the vas deferens , ejaculatory duct, prostate gland and seminal deferens B. ***Ejaculation*** - Rapid filling of urethra during emission causing further sensory outflow from penis - increased afferent activity reflexly enhances further the sympathetically mediated contraction of the smooth muscle of the male ductal system and stimulates the rhythmic contraction of a number of skeletal muscles at the base of the penis which further increases the pressure in the erectile tissue - Net effect of all increased reflex activity is rapid explusion of semen from urethra - Urtehtra closest to bladded constricts to prevent back flow of semen into bladder - The volume of semen ejaculated is in the order of 2-6 mL with the average around 3 mL. The major contribution of this volume is from seminal fluid followed by prostatic fluid with the remaining volume consisting of the mucus secreted by the bulbourethral glands and the spermatozoa themselves.   **[Accessory Sex Organs ]**   A. Seminal Vesicles - Volume Contribution: Approximately 65% of semen volume. - Key Components: - Fructose: - Concentration: 3 mg/mLFunction: Main energy source for sperm post-ejaculation. - Prostaglandins: - High concentration in seminal fluid. - Functions: - Stimulate male ductal system during emission and ejaculation. - Enhance sperm motility. - Induce contraction of the female ductal system. - Semenogelin: - Protein causing semen coagulation into a gel-like mass. - Function: Helps semen adhere to the vaginal wall, retaining it within the female reproductive tract. A. Prostate Gland - Volume Contribution: About 25% of semen volume. - Key Characteristics: - Alkaline Fluid: Neutralizes acidic secretions of vas deferens and vagina. - Optimal pH for Sperm Motility: Around 6.0. - Prostate-Specific Antigen (PSA): - Proteolytic enzyme - Function: Breaks down semen clot formed by semenogelin, releasing spermatozoa. A. Bulbourethral Glands - Volume Contribution: Approximately 5% of semen volume. - Secretions: - Clear alkaline mucus secreted during sexual arousal. - Functions: - Neutralizes acidity from residual urine in the urethra. - Acts as a lubricant for intercourse and semen flow during ejaculation. **[ Male Sexual Function]** Overview: Male sexual function encompasses the physiological processes involved in erection, emission, and ejaculation. It is regulated by hormonal signals and nervous system control, ensuring proper reproductive capabilities and sexual health. *Erection*: - Engorgement of penile erectile tissue with blood. - Initiated by decreased sympathetic tone and increased parasympathetic activity. - Smooth muscle relaxation facilitated by nitric oxide (NO) and cyclic guanosine monophosphate (cGMP). - Increased blood flow leads to penis rigidity; venous outflow is reduced. *Emission*: - Transfer of spermatozoa and fluids from accessory glands into the urethra. - Triggered by tactile and psychogenic stimuli. - Mediated by sympathetic nervous system activity affecting smooth muscles in the vas deferens and prostate. *Ejaculation*: - Rapid filling of the urethra during emission stimulates further contractions. - Involves rhythmic contraction of skeletal muscles at the base of the penis. - Prevents backflow of semen into the bladder through urethral constriction. - Average semen volume is 2-6 mL, primarily from seminal fluid. *Nervous System Control*: - Autonomic nervous system regulates erection (parasympathetic) and emission/ejaculation (sympathetic). - Psychogenic stimuli and mechanical stimulation activate reflex pathways for sexual function. *Physiological Mechanisms*: - Erection involves NO release leading to cGMP production, causing smooth muscle relaxation. - Emission combines sperm and fluids via muscular contractions. - Ejaculation results from coordinated muscle contractions and nerve reflexes, expelling semen effectively. **[Male Reproductive Anatomy]** *Overview: The male reproductive anatomy consists of various structures that play crucial roles in the production, maturation, and transportation of sperm. Key components include the testes, ducts, glands, and external genitalia, all working together to facilitate reproduction.* *Vas Deferens:* - Duct that transports sperm from the epididymis to the ejaculatory duct. *Seminal Vesicle:* - Gland that produces seminal fluid, which nourishes and helps transport sperm. *Ejaculatory Duct:* - Formed by the union of the vas deferens and the duct from the seminal vesicle; it carries sperm and seminal fluid into the urethra. *Prostate Gland:* - Produces a fluid that nourishes and protects sperm; contributes to semen volume. *Bulbourethral Glands (Cowper\'s Glands):* - Secrete a pre-ejaculate fluid that lubricates the urethra and neutralizes acidity. *Epididymis:* - Coiled tube where sperm mature and are stored after being produced in the testes. *Urethra:* - Tube that carries urine from the bladder and semen from the reproductive tract out of the body. *Testis:* - Primary male reproductive organ responsible for producing sperm and hormones like testosterone. **[Semen Composition]** - Overview: Semen is a complex fluid composed of spermatozoa and various secretions from accessory glands. It plays a crucial role in reproduction by providing the medium for sperm transport and nourishment, with contributions from seminal vesicles, prostate gland, and bulbourethral glands. *Seminal Fluid*: - Major component contributing approximately 65% of semen volume. - Contains fructose (energy source), prostaglandins (enhance motility), and semenogelin (causes coagulation). *Prostatic Fluid:* - Contributes about 25% of semen volume. - Alkaline nature neutralizes acidity in the urethra and vagina. - Contains prostate-specific antigen (PSA) which breaks down semen clot to release sperm. *Bulbourethral Secretions*: - Contribute approximately 5% of semen volume. - Clear alkaline mucus that neutralizes residual urine acidity and acts as a lubricant during intercourse. *Semen Volume Contribution*: - Average ejaculate volume ranges from 2-6 mL, typically around 3 mL. - Major contributions come from seminal fluid, followed by prostatic fluid and bulbourethral secretions. - Key Components: - Spermatozoa: Male gametes produced in the testes. - Fructose: Main energy source for sperm post-ejaculation. - Prostaglandins: Stimulate male ductal system and enhance sperm motility. - PSA: Enzyme that aids in sperm mobility by breaking down clots formed by semenogelin. **[Spermatogenesis]** - Overview: Spermatogenesis is the process of sperm cell development in males, occurring in the testes. It involves several stages, including mitosis and meiosis, leading to the formation of mature spermatozoa from spermatogonia under hormonal regulation. *Spermatogonia*: - The initial germ cells that undergo division to produce sperm. - Located in the seminiferous tubules of the testes. *Mitosis*: - Spermatogonia divide by mitosis to produce primary spermatocytes. - Ensures a continuous supply of germ cells. *Meiosis*: - Primary spermatocytes undergo meiosis I and II to form secondary spermatocytes and then spermatids. - Reduces chromosome number by half, creating haploid cells. **[Spermiogenesis:]** - The final stage where spermatids mature into spermatozoa. - Involves morphological changes, including the development of a flagellum and condensation of the nucleus. *Sertoli Cells:* - Supportive cells within the seminiferous tubules. - Provide nourishment, structural support, and regulate the environment for developing sperm. *Leydig Cells:* - Located in the interstitial tissue of the testes. - Produce testosterone, which is crucial for the regulation of spermatogenesis. *Hormonal Regulation:* - Controlled by hormones such as Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH). - Testosterone plays a key role in stimulating spermatogenesis and maintaining male reproductive functions. **[Hormonal Control of Reproduction]** Overview: Hormonal control of reproduction involves a complex interplay of hormones that regulate spermatogenesis and male sexual function. Key hormones include GnRH, FSH, LH, testosterone, and inhibin, which work through feedback mechanisms to maintain reproductive health. *GnRH (Gonadotropin-Releasing Hormone):* - Secreted by the hypothalamus. - Stimulates the anterior pituitary gland to release FSH and LH. *FSH (Follicle-Stimulating Hormone*): - Acts on Sertoli cells in seminiferous tubules. - Promotes maturation of sperm and secretion of inhibin and ABP (androgen-binding protein). *LH (Luteinizing Hormone):* - Binds to Leydig cells in testes. - Stimulates testosterone production. *Testosterone*: - Produced by Leydig cells under LH influence. - Responsible for masculinization, musculoskeletal growth, secondary sex characteristics, and stimulation of spermatogenesis. *Inhibin*: - Released by Sertoli cells. - Inhibits FSH secretion from the anterior pituitary. *Feedback Mechanisms:* - Negative Feedback: - Testosterone inhibits GnRH and LH secretion when levels are high. - Inhibin primarily inhibits FSH secretion. - Maintains stable circulating levels of testosterone and regulates spermatogenesis. Regulation and Production of Spermatozoa: - Initiated at puberty with increased GnRH, LH, FSH, testosterone, and ABP. - Healthy young men produce approximately 6.5 million sperm/gram testis/day; this declines with age. Male Sexual Function: - *Erection*: - Blood engorgement in erectile tissue due to decreased sympathetic tone and increased parasympathetic activity. - Nitric oxide (NO) plays a key role in smooth muscle relaxation. - *Emission and Ejaculation*: - Emission involves mixing sperm with seminal fluid. - Ejaculation is the expulsion of semen, facilitated by rhythmic contractions of smooth and skeletal muscles. - *Accessory Sex Organs*: - Seminal Vesicles: Contribute \~65% of semen volume; provide fructose and prostaglandins. - Prostate Gland: Contributes \~25% of semen volume; produces alkaline fluid and PSA. - Bulbourethral Glands: Contribute \~5% of semen volume; secrete mucus for lubrication.