Male Reproductive System

Male Reproductive System

Components & Functions

• Production of Gametes: Testes produce sperm, which are male gametes.
• Production of Sex Hormones:
  • Testes produce androgens, the most common being testosterone.
  • Testosterone affects the development, maturation, and activity of male reproductive organs.
• Facilitation of Fertilization:
  • The penis is the male copulatory organ, received by the vagina during sexual intercourse.
  • Semen, containing sperm, is ejaculated from the penis and enters the female reproductive tract.
  • Sperm travels towards the ovulated oocyte to fertilize it.

Embryological Development of Testes

• Primary Germ Layer: The mesoderm.
• Develops from primitive structures that differentiate into either male or female structures depending on genetic expression.
• 5th Week: Paired structures called genital ridges or gonadal ridges form within the mesoderm.
  • Forms the gonads (testes for men).
  • Genital ridges form in the abdominal cavity around the 10th thoracic vertebrae.
• During development, the resulting gonads descend to their final position in the scrotum through the inguinal canal (canal in the groin).
• Each gonad is guided to its final position by a thin band of connective tissue called the gubernaculum.
  • In men, this forms the scrotal ligament, which tethers each testis to the scrotum internally.

Scrotum & Spermatic Cord

• Scrotum: A cutaneous sac that houses the testes; together with the penis, it forms the external genitalia of the male.
  • The testes are located outside the trunk of the body in the scrotum to provide a cooler environment needed for normal sperm production.
• Spermatic Cord: A structure that carries the ductus deferens (accessory male reproductive structure), as well as blood vessels, nerves, and lymphatic vessels between the testes and the abdominopelvic region.
  • It travels through the inguinal canal (the canal in the groin region that the testes pass through during their descent to the scrotum).
• Dartos muscle and cremaster muscle respond to temperature changes to keep the testes at an ideal temperature.

Cremaster Muscle

• Skeletal muscle located within the wall of the spermatic cord, derived from the internal oblique muscle of the abdominal wall.
• When exposed to cold air, the cremaster muscle contracts, pulling the testes closer to the trunk of the body to conserve heat.
• When exposed to hot temperatures, the cremaster muscle relaxes, moving the testes away from the trunk to facilitate cooling.

Dartos Muscle

• Smooth muscle located within the wall of the scrotum.
• When exposed to cold temperatures, the dartos muscle contracts, wrinkling the scrotal skin and reducing heat loss.
• When exposed to hot temperatures, the dartos muscle relaxes, unwrinkling the scrotal skin and increasing heat loss.

Testes

• Paired, oval-shaped organs located in the scrotum.
• Function: Produce male gametes (sperm) and sex hormones (androgens, like testosterone).
• Covered by a serous membrane called the tunica vaginalis and another layer of tissue called the tunica albuginea.
• Internally divided into smaller sections called lobules, which contain highly coiled structures called seminiferous tubules.

Seminiferous Tubules

• Highly coiled structures where sperm is produced.
• In the spaces between the seminiferous tubules are cells that produce androgens, the most common of which is testosterone.

Lobule

• Smaller sections that each testis is divided into by connective tissue septa formed by projections of the tunica albuginea into the testis.

Tunica Albuginea

• Fibrous capsule of the testis.
• Deep to the visceral layer of the tunica vaginalis and composed of dense irregular connective tissue.

Epididymis, Ductus Deferens, & Ejaculatory Duct

• The duct system begins in the testes, and the union of many small ducts in each testis ultimately forms a highly coiled duct within the epididymis.
• The duct of the epididymis is continuous with the ductus deferens.
• The ductus deferens then unites with the duct of one of the accessory glands in the male reproductive system to form the ejaculatory duct.
• The ejaculatory duct opens into the prostatic urethra, through which sperm is ultimately ejaculated.

Ejaculatory Duct

• Formed by the union of the ampulla of the ductus deferens and the duct of the seminal vesicles.
• The seminal vesicle is one of the accessory glands of the male reproductive system and is located lateral to the ampulla of the ductus deferens on the posterior surface of the urinary bladder.
• The formation of the ejaculatory duct occurs within the prostate gland (accessory gland) and is located inferior to the urinary bladder.
• The ejaculatory duct opens into the prostatic urethra.

Ductus Deferens

• Also known as the vas deferens; a continuation of the duct of the epididymis; one of the structures that runs within the spermatic cord.
• Once the ductus deferens enters the pelvic cavity via the spermatic cord, it travels to the posterior surface (base) of the urinary bladder, terminating as a dilated part called the ampulla.

Epididymis

• A comma-shaped structure that sits along the posterior surface of each testis.
• It has a head, body, and tail, and it is at the tail that the duct of the epididymis is continuous with the ductus deferens.
• The epididymis is the site of sperm storage and maturation.

Accessory Glands

• Function: Produce secretions that collectively form seminal fluid.
• When seminal fluid is combined with sperm, it forms semen, which is ejaculated.
• Secretions within seminal fluid provide nourishment to sperm as they travel through the female reproductive tract and neutralize the acidity of the vagina to protect sperm.

Seminal Vesicles

• Paired, elongated glands located lateral to the ampulla of each ductus deferens on the posterior surface of the urinary bladder.
• The duct of each seminal vesicle unites with the ampulla of each ductus deferens to form two ejaculatory ducts.
• Seminal vesicles secrete a viscous, alkaline fluid rich in fructose.
  • The alkalinity of this fluid neutralizes the acidity of the vagina.
  • Fructose provides nourishment to sperm.
• Secretions of seminal vesicles also contain prostaglandins, which are hormone-like substances that promote dilation of the external os of the cervix, facilitating the entry of sperm into the uterus.

Prostate Gland

• A single, walnut-shaped gland located directly inferior to the urinary bladder.
  • The prostatic urethra passes through it, and this is where the two ejaculatory ducts open.
• The prostate gland secretes a slightly milky fluid that is weakly acidic due to its citric acid content, which is important for sperm health.
• The fluid also contains an antibacterial agent to fight urinary tract infections in the male, as well as a substance called prostate-specific antigen (PSA) which acts as an enzyme to help liquefy ejaculated semen once it enters the female reproductive tract.

Bulbourethral Glands

• Paired, pea-shaped glands located on either side of the membranous urethra within the urogenital diaphragm.
• Secrete a clear, viscous fluid into the urethra to lubricate it prior to ejaculation.

Penis

• The male copulatory organ.
• Composed of erectile tissue that contains a network of venous spaces that fill with blood during sexual arousal, causing an erection.

Body of Penis

• Composed of 3 cylindrical masses of erectile tissue that are continuations of the root structures of the penis.
• Include a single corpus spongiosum, which is a continuation of the bulb of the penis, and a paired corpora cavernosa (singular = corpus cavernosum) which are continuations of crura of the penis (singular = crus).
• The corpus spongiosum dilates distally to form the glans, and the spongy urethra runs within the corpus spongiosum.

Root of Penis

• The attached part of the penis, which anchors it to the pelvis inferiorly.
• Composed of a single mass of erectile tissue called the bulb of the penis and 2 elongated masses of erectile tissue called crura (singular = crus).

Glans

• The dilated, distal portion of the penis formed by the corpus spongiosum and contains the external urethral orifice.
• Covered by a circular fold of skin called the prepuce (foreskin).