Penis, testes, and associated ducts
Overview
- The reproductive system facilitates sexual maturation of individuals and sexual reproduction of offspring.
- In the male, this includes the production of semen and its delivery to the outside environment.
- Specific anatomical adaptations, such as the penis, facilitate semen delivery close to the site of conception, within the female reproductive tract.
- Semen comprises sperm cells and seminal plasma, which nourishes and protects the sperm.
- Reproductive structures are classified as either primary or accessory (aka, secondary):
- The primary structures are referred to as gonads; their function is to produce gametes, aka, sex cells. In males, the primary structures are the testes (aka, testicles), which produce sperm and hormones.
- The accessory structures are the organs, ducts, and glands that facilitate delivery of the gametes to the external environment.
Ejaculation
- Emission is when semen is ushered into proximal urethra.
- Expulsion is when semen is projected through urethra.
- Suspended within the scrotum; produce sperm cells and hormones.
- Wraps over posterior-superior aspect of testis.
- Long coiled tube that stores developing sperm.
- Continuous with epididymis, ascends to enter the pelvis, then passes over the urinary bladder and ureter.
- It is a muscular tube that actively conducts sperm from the epididymis to the ejaculatory duct; this transport occurs during the emission phase of ejaculation.
- Ampulla is the widened end of the ductus deferens.
- Is adjacent to the ampulla.
- Contributes the majority of the total seminal plasma volume.
Ejaculatory duct
- Drains the ductus deferens and the seminal vesicle into the prostatic urethra.
Prostate gland
- Its secretions enter the prostatic urethra.
Bulbourethral glands (aka, Cowper's glands)
- Lie lateral to the prostate and secrete lubricating mucus into the spongy urethra.
- During the expulsion phase of ejaculation, secretions from the bulbourethral glands precede the rest of the seminal fluid.
Key Function:
Conduct urine and semen to the outside environment.
2ND CARD:
Key Anatomical Features of the Penis:
Skin
- Prepuce covers glans, is retractable in the adult.
Vessels
- Superficial dorsal vein and artery
- Deep dorsal vein
- Deep arteries within corpus cavernosa
Connective tissues
- Deep fascia surrounds erectile bodies and binds them together
- Intercavernous fascia separate corpora cavernosa from corpus spongiosum.
- Covered in tunica albuginea
- Comprise vascular tissues that engorge with blood upon arousal.
- Glans is distal expansion; corona is rim of glans
- Bulb is the widened proximal end
- The bulb anchors the corpus spongiosum to the perineal membrane (not shown);
- The bulb is wrapped in the bulbospongiosum muscle, which contracts to: force blood into the erectile tissues, eject residual urine from the urethra,
- Lie dorsal to corpus spongiosum
- Crus (singular = crura) of the corpus cavernosa extend laterally
- Crus attach to the pubic arch of the pelvis (not visible here), and are wrapped by ischiocavernosus muscles; like the bulbospongiosum, these muscles force blood into the erectile tissues.
Root
- Comprises bulb and crus of penis
Shaft
- Free, pendulous portion of penis between root and glans
Urethra
- Conducts semen to external environment
- Terminates at external urethral orifice
- Urethral glands secrete mucus to protect urethra from urine
Anatomical orientation
- Dorsal surface faces the torso
- Ventral surface faces away from the torso.
Clinical correlations:
- Vasectomy: the paired ductus deferens are surgically sealed shut; sperm is still produced, but cannot be transported to the ejaculatory ducts to join the seminal plasma.
- Thus, it is a highly effective form of contraception that is sometimes surgically reversed.
- Cryptorchidism, aka, undescended testis, is a common birth abnormality in boys; the testicles usually move into the scrotum on their own, but, if not, surgery may be necessary.
- Complications of cryptorchidism include increased likelihood of testicular cancer and reduced fertility.