Anatomy of an Erection

Erectile dysfunction: the mechanism of an erection

What is the penis?

The penis is a male reproductive organ. It consists of the following:

  • 2 cylindrical cavities named cavernous bodies, spanning the entire length of the penis, that connect to intertwined vessels for the blood and sinuses (cavities);
  • Urethra: a duct from which urine and semen are ejected. This is located within the cavernous bodies;
  • Erectile tissues which are located above the urethra and inside the cavernous bodies, consisting of two arteries and several blood vessels with nerve tissue;
  • Penile trunk, which is the longest part of the penis;
  • Trunk head, which is situated at the end of the penis;
  • An aperture on top of the penile head through which urine and semen fluid are excreted.

The elements of the penis are: Anatomy of an erection

  • Vein
  • Nerve
  • Cavernous bodies (known as corpora cavernosa in Latin)
  • Penile head
  • Aperture
  • Arteries
  • Skin
  • Urethra

The mechanism of an erection

Swelling of the penis actually starts in the brain. Physical and mental stimuli cause chemical signals to be sent from the brain’s nerve tissue to the penile nerve tissue, thus instructing the penile vessels to fill with blood. Once it’s filled the penis, the blood is held in the cavernous bodies due to the high pressure, therefore maintaining the erection. This causes the penis to increase in size and results in an erection. The erection ends when the inflow of blood ceases, opening the urinary canal and returning the penis to its normal state.

How ejaculation occurs

Ejaculation or ejection of the sperm occurs during orgasm — at the moment a male reaches the climax of his arousal. Due to sexual stimulation, the nerve endings send chemical signals (impulses) to the spinal cord and brain. Impulses are then sent back to the penis causing ejaculation.

Ejaculation consists of two phases. First, the tube through which the seminal fluid comes from the testicles is constricted, which directs the sperm to the prostate and urethra. Seminal vesicles produce fluids, which create the seminal fluid. During the second phase, muscles in the base of the penis start to constrict with a speed of once every 0.8 seconds, and this pushes the sperm out of the penis.