Male Reproductive Organs and Structures: Lecture Notes

Overview of Reproductive Systems

  • The primary function of reproductive systems is to create sex cells, also known as gametes, to produce offspring.
  • Primary organs in the reproductive system are responsible for producing sex cells and secreting hormones.
    • In males, the testes produce sperm and testosterone.
    • In females, the ovaries produce ova (eggs), estrogens, and progesterone.
  • Accessory sex organs support the movement of sex cells and create necessary fluids.
    • These include ducts, glands, and external genitalia.
  • The male reproductive system serves two main purposes: to create male characteristics and to produce sperm.
  • Outer structures aid in the movement of gametes.

Overview of the Male Reproductive System

The male reproductive system consists of several key components:

  • Testes: The primary organs where sperm is produced, located in the scrotum.
  • Spermatic Cord: Connects the testes to the body's inner workings.
  • Ducts: Facilitate the movement of sperm.
  • External Structures: Include the penis and scrotum.

Seminal fluid constitutes about 70% of the overall fluid and is released before ejaculation.

Testes

  • The testes are the primary reproductive organs in males, responsible for sperm and testosterone production.
  • They are housed within the scrotum in postnatal males.
  • The testes are connected to the body's internal systems via the spermatic cord.
  • Innervation:
    • Sympathetic innervation originates from spinal nerve level T12, utilizing the least splanchnic nerve.
    • Parasympathetic innervation arises from S2-4, part of the sacral outflow.
  • Arterial Supply:
    • The testicular artery, branching off the abdominal aorta, provides arterial supply.
  • Venous Drainage:
    • The testicular vein drains into the inferior vena cava or the left renal vein.

External Structures of the Male Reproductive System

  • Scrotum: The scrotum is composed of skin and fascia that surrounds the testes and epididymis; it is inferior to the abdominopelvic cavity.
    • It maintains the testes at approximately 2-3°F below normal body temperature, which is crucial for spermatogenesis.
  • Dartos Muscle:
    • A superficial smooth muscle that wrinkles the scrotal skin.
  • Cremaster Muscles:
    • Bands of deep skeletal muscle that elevate the testes when contracted which influences body temperature.

Testes Anatomy

  • The testes develop retroperitoneally in the abdominal cavity and descend into the scrotal sac.
  • Tunica Vaginalis: Covers the testes, consisting of parietal and visceral layers with a coelomic space between them.
    • This originates from the peritoneum and coelom of the abdominal cavity.
  • Tunica Albuginea: A connective tissue that surrounds the testes and divides it internally into lobules.
  • Seminiferous Tubules: Coiled tubules located within the lobules, where sperm is produced.

Seminiferous Tubules

  • Spermatogenic Cells (Spermatocytes): Undergo meiosis to produce sperm cells, halving the genetic material found in somatic cells.
    • These cells move toward the lumen of the tubule during their development.
  • The cells responsible for creating sperm or fluids differentiate from outside to inside.

Seminiferous Tubules - Sustentocytes

  • Sustentocytes (Sustentacular Cells): Surround and support spermatogenic cells.
    • Secrete lubricating fluid to facilitate sperm movement as they exit the seminiferous tubules and travel through the epididymis towards the ejaculatory duct.
    • Help provide nutrients to the lumen of the tubules.

Seminiferous Tubules - Interstitial Cells

  • Interstitial Endocrine Cells (Leydig Cells): Located in the soft tissue around the seminiferous tubules and produce testosterone.
  • Myoid Cells: Contract to move substances through the tubules.
    • These are modified muscle cells that aid in the contraction of the tubules.

Ducts of the Male Reproductive System

  • The seminiferous tubules merge into a larger network of tubules called the rete testis within the testes.
  • The rete testis allows for the transport of sperm into these tubules.

Ducts of the Male Reproductive System - Epididymis

  • Epididymis: A cup-shaped structure surrounding the testis, comprised of a head, body, and tail.
    • The rete testis drains into larger tubules located at the head of the epididymis.
    • Immature sperm move through the head and body, gaining the ability to swim.
    • Developed sperm are stored in the tail until ejaculation.

Ducts of the Male Reproductive System - Ductus Deferens

  • Ductus Deferens: The tail of the epididymis dilates into the ductus deferens (or vas deferens).
    • It has a thick muscular layer which constricts to facilitate sperm movement.
    • The ductus deferens passes up the spermatic cord and enters the body through the inguinal canal, running anterosuperior to the ureters inside the body.
    • The ampulla is an expansion of the ductus deferens before it terminates at the ejaculatory duct.
    • Sperm moves through the ductus deferens and is held in the ampulla temporarily.
    • The ejaculatory duct is where sperm and fluid mix together to form semen.

External Structures of the Male Reproductive System - Spermatic Cord

  • Spermatic Cord: Includes the skin and muscle surrounding the ductus deferens, testicular artery, pampiniform venous plexus, and nerves.
    • Passes through the inguinal canal, which may be slightly larger in men.
  • Pampiniform Venous Plexus: A network of testicular veins that surrounds the testicular artery.
    • It facilitates countercurrent exchange, influencing temperature regulation.

Clinical Implications - Inguinal Hernia

  • Inguinal Hernia: Contents of the spermatic cord pass from the pelvic cavity through the inguinal canal down the spermatic cord into the scrotal sac to reach the testis.
    • The opening is normally narrow to guard against dangers.
    • If the opening is too wide, loops of the intestine could slip out, causing a herniation or hernia.
    • This can lead to constriction or strangulation of the intestines and often requires surgical correction.

Ducts of the Male Reproductive System - Urethra

  • Urethra: The urethra carries semen from the ejaculatory ducts or urine from the bladder outside the body.
    • Prostatic Urethra: Surrounded by the prostate gland.
    • Membranous or Intermediate Urethra: The shortest portion, located in the urogenital diaphragm.
    • Spongy (Penile) Urethra: Runs through the penis, opening to the external urethral orifice.

Clinical Implications - Vasectomy

  • Vasectomy: A portion of the ductus deferens (or vas deferens) is in the scrotal sac.
    • A small incision is made in the scrotal sac to cut or ligate the ductus deferens.
    • Almost 100% effective in preventing pregnancy because the sperm has nowhere to go.

Accessory Glands of the Male Reproductive System - Seminal Vesicles

  • Seminal Vesicles: Paired glands on the posterior surface of the urinary bladder whose duct joins the ductus deferens to form the ejaculatory duct.
    • Produces 70% of seminal fluid.
      • High in sugar to nourish sperm.
      • Contains prostaglandins to promote uterine contractions.
      • Alkaline to neutralize the acidic environment of the vagina.

Accessory Glands of the Male Reproductive System - Prostate

  • Prostate: Encircles the urethra inferior to the urinary bladder.
    • Ejaculatory ducts join with the urethra within the mass of the prostate gland.
    • Produces 30% of seminal fluid which is slightly acidic with enzymes to liquefy semen.
    • Plays a role in activating sperm once in the female reproductive tract.

Accessory Glands of the Male Reproductive System - Bulbourethral Glands

  • Bulbourethral Glands: Paired, pea-sized glands inferior to the prostate gland in the urogenital diaphragm.
    • Produces thick, clear mucus during sexual arousal to lubricate the glans penis and clean the urethra before ejaculation.
    • Alkaline and ejaculated before ejaculation.

External Structures of the Male Reproductive System - Penis

  • Penis: Delivers sperm into the female reproductive tract.
    • Composed of erectile tissue, not muscle.

External Structures of the Male Reproductive System - Root

  • The root consists of:
    • Crura: Enlargements of the corpora cavernosa anchored to the pubic arch by ischiocavernosus muscles.
    • Bulbs: Continuous with the corpus spongiosum and anchored to the urogenital diaphragm by bulbospongiosus muscles.

Muscles That Support the External Genitalia

  • Superficial Transverse Perineal
    • Origin: Ischial tuberosities
    • Insertion: Perineal body
    • Function: Supports pelvic organs
  • Ischiocavernosus
    • Origin: Ischial tuberosities
    • Insertion: Crus of the penis or clitoris
    • Function: Assists with ejaculation
    • Innervation: Pudendal nerve (S2-4)
  • Bulbospongiosus
    • Origin: Perineal body
    • Insertion: the bulb of the penis or clitoris
    • Function: Assists with ejaculation
    • Innervation: Pudendal nerve (S2-4)

External Structures of the Male Reproductive System - Body

  • The body of the penis is made up of erectile tissues:

    1. Corpora Cavernosa: Paired columns of erectile tissues on the dorsal aspect.

    2. Corpus Spongiosum: A single mid-ventral column of erectile tissue that surrounds the urethra.

      • Prevents the urethra from collapsing.
      • Ensures that the return stays open during ejaculation.

External Structures of the Male Reproductive System - Glans and Prepuce

  • Glans Penis: The enlarged tip of the penis is composed of corpus spongiosum tissue.
  • Prepuce (Foreskin): The loose covering of skin that cuffs over the glans.
    • Circumcision is the removal of the prepuce.