Male Reproductive System Anatomy

Male Reproductive System

• The primary sex organs are the testes (in males) and ovaries (in females).
• Testes produce sperm (sex cells), and ovaries produce ova (sex cells).
• Testes secrete androgens (like testosterone in males), and ovaries secrete estrogens and progesterone (in females).
• Accessory reproductive organs include ducts, glands, and external genitalia, which transport and support gametes.
• Secondary sex organs facilitate the union of male and female gametes.

Anatomy of the Male Reproductive System

• Testes are located within the scrotum.
• They produce sperm.
• Sperm travels from the testes through a system of ducts: epididymis, ductus deferens, ejaculatory duct, and urethra.
• Accessory sex glands include seminal glands, prostate, and bulbourethral glands. Substances from these glands are added to the sperm and fluid creating semen.

Scrotum and Testes

• The scrotum is a sac of skin and superficial fascia.
• It hangs outside of the abdominopelvic cavity.
• The scrotum contains paired testes.
• The temperature of the testes is 3°C lower than core body temperature. This cooler temperature is necessary for sperm production.
• The dartos muscle is smooth muscle that wrinkles the scrotal skin. It pulls the scrotum close to the body.
• Cremaster muscles are bands of skeletal muscle. They elevate the testes.

Testes (cont.)

• Each testis is surrounded by two tunics. The outer layer is the tunica vaginalis, which derives from the peritoneum. The inner layer called tunica albuginea forms a fibrous capsule.
• Septa divide the testis into ~ 250 lobules. Each lobule contains one to four seminiferous tubules.
• Seminiferous tubules have a thick, stratified epithelium. This surrounds the central lumen.
• The epithelium contains spermatogenic cells (sperm-forming cells) and sustentocytes.
• Myoid cells surround the seminiferous tubules. They're smooth muscle-like cells and help squeeze sperm and tubular fluids out of the testes.
• Sperm travels from seminiferous tubules, to rete testis, efferent ductules, and then to the epididymis.
• The epididymis has a head, body, and tail.
• Sperm is stored in the epididymis' tail until ejaculation.
• Interstitial endocrine cells produce androgens, like testosterone, and secrete them into interstitial fluid.

Penis

• The penis is internally made up of spongy urethra and three cylindrical bodies of erectile tissue. A spongy network of connective tissue and smooth muscle with vascular spaces.
• The corpus spongiosum surrounds the urethra and expands into the glans and bulb.
• The paired corpora cavernosa are dorsal erectile bodies.
• Erection occurs when erectile tissue fills with blood, causing the penis to enlarge and become rigid.
• Crura are the proximal ends of corpora cavernosa, surrounded by the ischiocavernosus muscle. This anchors the penis to the pubic arch.

Epididymis

• The head of the epididymis contains efferent ductules.
• It is located on the superior aspect of the testis.
• The body and tail are on the posterolateral area of the testis.
• The duct of the epididymis is approximately 6 meters in length.
• Microvilli (stereocilia) absorb testicular fluid and pass nutrients to sperm.
• Nonmotile sperm enter; pass slowly through the epididymis (~ 20 days). They become motile.
• Sperm can be stored in the epididymis for several months.
• During ejaculation, the epididymis contracts to expel sperm into the ductus deferens.

Ductus Deferens and Ejaculatory Duct

• The ductus deferens (vas deferens) is about 45 centimeters long.
• It passes through the inguinal canal to the pelvic cavity.
• It expands to form the ampulla.
• It connects to the duct of the seminal vesicle to form the ejaculatory duct.
• Smooth muscle in the duct walls propels sperm from the epididymis to the urethra.
• Vasectomy involves cutting and ligating the ductus deferens. This is a nearly 100% effective form of birth control.

Male Accessory Glands

• Seminal glands: Located on the posterior bladder surface, these glands contain smooth muscle that contracts during ejaculation. They produce a viscous, alkaline seminal fluid which contains fructose (for ATP production), citric acid, coagulating enzymes, and prostaglandins. The seminal fluid makes up approximately 70% of the semen volume. The duct from the seminal gland joins the ductus deferens to form the ejaculatory duct.

• Prostate: This gland encircles the urethra inferior to the bladder; it's about the size of a peach pit. It consists of smooth muscle which contracts during ejaculation and secretes a milky, slightly acidic fluid. This fluid contains citrate, enzymes, and the prostate-specific antigen (PSA). The prostate fluid plays a role in sperm activation and accounts for about one-third of the semen volume.

• Bulbourethral glands: Pea-sized glands inferior to the prostate. They secrete a thick, clear mucus during sexual arousal to lubricate the glans of the penis. The mucus also neutralizes traces of acidic urine in the urethra prior to ejaculation.

• Benign prostatic hyperplasia (BPH): A common age-related condition that can distort the urethra. Treatments include surgery or newer options like microwaves, drugs, balloon compression, or radio-frequency radiation.

• Prostate cancer: The second most common cause of cancer death in men. Early screening includes digital exams and PSA levels. Biopsies are conducted for abnormalities. Treatment often involves surgery, radiation, castration, and/or drugs; some clinical trials also explore cryosurgery, chemotherapy, ultrasound, or proton beam therapy.

Semen

• Semen is a milky-white mixture of sperm and secretions from accessory glands.
• The ejaculated volume is 2-5 ml, containing 20-150 million sperm/ml.
• Semen contains fructose for ATP production, protects and activates sperm, and facilitates sperm movement.
• Alkaline fluid neutralizes acidity in the male urethra and female vagina, enhancing sperm motility.

Semen (cont.)

• Semen contains prostaglandins to decrease mucus viscosity in the cervix and stimulate reverse peristalsis in the uterus.
• It contains the hormone relaxin and other enzymes to enhance sperm motility.
• Semen contains ATP for energy; can suppress the female immune response.
• Some antibiotic chemicals destroy some bacteria.
• Clotting factors coagulate semen initially to prevent draining, then liquefy it by the enzyme fibrinolysin, so sperm can continue its journey.

Male Sexual Response (Erection)

• An erection is the enlargement and stiffening of the penis.
• Arterioles that supply blood to the penis are typically constricted.
• Sexual excitement activates the central nervous system causing parasympathetic neurons to release nitric oxide (NO).
• NO then relaxes the local vascular smooth muscle, allowing blood to flow into the penis. This causes enlargement and stiffening.

Ejaculation

• Ejaculation is the propulsion of semen from the male duct system through a sympathetic spinal reflex.
• Bladder sphincter muscle constricts to prevent urine expulsion.
• Ducts and accessory glands contract and empty their contents.
• Bulbospongiosus muscles undergo rapid contractions that expel semen at approximately 500 cm/s (close to 11 mph).
• The climax (orgasm) phase of ejaculation follows.

Spermatogenesis

• Spermatogenesis is the production of sperm (spermatozoa) within seminiferous tubules.
• Most bodily cells have 46 chromosomes (diploid).
• Diploid means two chromosomes for each gene; one maternal and one paternal.
• Gametes (sperm cells or ova = egg cells = sex cells) only have 23 chromosomes (haploid).
• Spermatogenesis involves meiosis, which reduces the chromosome number to haploid form and introduces genetic diversity in the process.
• Meiosis I reduces the chromosome number.
• Synapsis occurs where homologous chromosomes pair up.
• Crossover (Chiasmata) involves genetic material exchange between homologous chromosomes.
• Meiosis II is just like mitosis, separating the sister chromatids to generate four unique haploid cells from the original diploid cell.
• Spermatogenesis takes 64–72 days if conditions are hospitable.

Mechanism and Effects of Testosterone Activity

• Testosterone, synthesized from cholesterol, is converted into dihydrotestosterone (DHT) in the prostate. Estradiol forms in some brain neurons. Testosterone promotes spermatogenesis and targets accessory organs.
• Testosterone also has widespread anabolic effects on the body. Deficiency leads to atrophy of accessory organs, decreased semen volume and impaired erection/ejaculation.
• Replenishing testosterone can reverse these deficits.
• Male secondary sex characteristics include features/traits like pubic, axillary, and facial hair; enhanced chest hair growth; a deeper voice; thicker/oilier skin; greater bone density; larger/more massive skeletal muscles and an enhanced sex drive (libido).

Explore the intricacies of the male reproductive system in this quiz. From the primary sex organs like testes to the essential ducts and glands involved in sperm production and transport, this quiz covers the vital anatomy involved. Test your knowledge on the function and structure of each component.