🫀Anatomy and Physiology II Unit 10 – Male Reproductive System Anatomy & Physiology

Overview and Key Structures

• Male reproductive system consists of internal and external structures that work together to produce, store, and transport sperm for reproduction
• Key structures include the testes, epididymis, vas deferens, seminal vesicles, prostate gland, bulbourethral glands, and penis
• Testes are the primary male reproductive organs responsible for producing sperm and testosterone
• Accessory glands (seminal vesicles, prostate, and bulbourethral glands) secrete fluids that nourish and protect sperm
• Ducts (epididymis, vas deferens, ejaculatory ducts, and urethra) transport and store sperm
• Penis is the external organ used for sexual intercourse and urination
• Scrotum is a skin-covered sac that contains the testes and helps regulate their temperature

Testes and Scrotum

• Testes are oval-shaped glands located in the scrotum that produce sperm and testosterone
• Each testis is divided into lobes, which contain seminiferous tubules where sperm production occurs
• Leydig cells, located between the seminiferous tubules, produce testosterone
• Sertoli cells, found within the seminiferous tubules, support and nourish developing sperm
• Scrotum is a skin-covered sac that hangs outside the body, providing a cooler environment for optimal sperm production
• Cremaster muscle in the scrotum can contract to pull the testes closer to the body for warmth or relax to allow them to hang lower for cooling
• Tunica albuginea is a tough, white fibrous capsule that surrounds each testis and provides protection

Sperm Production and Maturation

• Spermatogenesis is the process of sperm production that occurs in the seminiferous tubules of the testes
• Spermatogonia (stem cells) divide by mitosis to maintain their population and produce primary spermatocytes
• Primary spermatocytes undergo meiosis I to form secondary spermatocytes, which then undergo meiosis II to form spermatids
• Spermatids differentiate into mature spermatozoa (sperm) through the process of spermiogenesis
• Sperm structure includes a head (containing genetic material), midpiece (containing mitochondria for energy), and tail (for motility)
• Sperm maturation occurs in the epididymis, where they gain motility and the ability to fertilize an egg
• Spermatogenesis takes approximately 74 days in humans
• Sperm production is continuous throughout a male's reproductive life, with millions of sperm produced daily

Accessory Glands and Ducts

• Seminal vesicles are paired glands that produce a fluid rich in fructose, which provides energy for sperm
• Prostate gland surrounds the urethra and secretes an alkaline fluid that makes up about 30% of the semen volume
• Bulbourethral glands (Cowper's glands) secrete a clear, alkaline fluid that neutralizes any remaining acidity in the urethra
• Epididymis is a highly coiled tube that sits atop each testis, where sperm mature and are stored
• Vas deferens (ductus deferens) is a muscular tube that transports sperm from the epididymis to the ejaculatory ducts
• Ejaculatory ducts form by the joining of the vas deferens and the duct from the seminal vesicle, and they empty into the urethra
• Semen (seminal fluid) is the mixture of sperm and secretions from the accessory glands that is ejaculated during orgasm

Penis and Urethra

• Penis is the male external sexual organ composed of the root, body (shaft), and glans
• Corpora cavernosa are two columns of erectile tissue that run along the length of the penis and fill with blood during an erection
• Corpus spongiosum is a column of erectile tissue that surrounds the urethra and forms the glans penis at the tip
• Urethra is a tube that runs through the penis and serves as a passageway for both semen and urine (though not simultaneously)
• During sexual arousal, the penis becomes erect due to increased blood flow into the corpora cavernosa and corpus spongiosum
• Prepuce (foreskin) is a fold of skin that covers the glans penis in uncircumcised males
• Circumcision is the surgical removal of the foreskin, often performed for cultural, religious, or medical reasons

Hormonal Regulation

• Hypothalamus releases gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary gland to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
• FSH stimulates Sertoli cells to support spermatogenesis and secrete inhibin, which provides negative feedback on FSH secretion
• LH stimulates Leydig cells to produce testosterone, which is essential for spermatogenesis, male secondary sexual characteristics, and sex drive
• Testosterone provides negative feedback on the hypothalamus and anterior pituitary, regulating GnRH, FSH, and LH secretion
• Sertoli cells also produce anti-Müllerian hormone (AMH) during fetal development, which causes the regression of the female reproductive structures
• Puberty in males is initiated by an increase in GnRH, FSH, and LH secretion, leading to increased testosterone production and the development of secondary sexual characteristics
• Aging in males is associated with a gradual decline in testosterone levels (andropause), which can lead to reduced muscle mass, bone density, and sex drive

Common Disorders and Conditions

• Erectile dysfunction (ED) is the inability to achieve or maintain an erection sufficient for sexual intercourse
• Causes of ED include cardiovascular disease, diabetes, neurological disorders, hormonal imbalances, and psychological factors
• Premature ejaculation is a condition in which a man ejaculates sooner than he or his partner would like during sexual intercourse
• Testicular torsion occurs when the spermatic cord becomes twisted, cutting off blood supply to the testis and causing severe pain and swelling
• Varicocele is an enlargement of the veins in the scrotum that can lead to reduced sperm quality and infertility
• Prostatitis is inflammation of the prostate gland, which can cause pain, urinary symptoms, and sexual dysfunction
• Benign prostatic hyperplasia (BPH) is a non-cancerous enlargement of the prostate that can cause urinary difficulties
• Prostate cancer is a malignant growth in the prostate gland and is one of the most common cancers in men
• Testicular cancer is a malignant growth in the testes and is most common in young men aged 15-35 years

Clinical Applications and Research

• Semen analysis is a diagnostic test that evaluates sperm count, motility, and morphology to assess male fertility
• Vasectomy is a surgical procedure for male sterilization that involves cutting and sealing the vas deferens to prevent sperm from entering the semen
• Testicular self-examination is a technique men can use to detect lumps or abnormalities in the testes that may indicate testicular cancer
• Hormone replacement therapy (HRT) can be used to treat hypogonadism (low testosterone levels) and alleviate symptoms such as reduced libido, erectile dysfunction, and muscle weakness
• Phosphodiesterase type 5 (PDE5) inhibitors (sildenafil, tadalafil) are medications used to treat erectile dysfunction by increasing blood flow to the penis
• Research on male contraceptives focuses on developing methods to reversibly suppress sperm production or block sperm transport
• Stem cell research holds promise for treating male infertility by generating functional sperm or repairing damaged testicular tissue
• Genetic studies aim to identify genes associated with male reproductive disorders and develop targeted therapies
• Lifestyle factors such as obesity, smoking, and excessive alcohol consumption can negatively impact male reproductive health and are targets for preventive interventions