Anatomy of the Penis

The internal structure of the penis consists of two cylinder-shaped vascular tissue bodies (corpora cavernosa) that run throughout the penis; the urethra (tube for expelling urine and ejaculate); erectile tissue surrounding the urethra; two main arteries; and several veins and nerves. The longest part of the penis is the shaft, at the end of which is the head, or glans penis. The opening at the tip of the glans, which allows for urination and ejaculation, is the meatus.

Physiology of Erection

The physiological process of erection begins in the brain and involves the nervous and vascular systems. Neurotransmitters in the brain (e.g., epinephrine, acetylcholine, nitric oxide) are some of the chemicals that initiate it. Physical or psychological stimulation (arousal) causes nerves to send messages to the vascular system, which results in significant blood flow to the penis. Two arteries in the penis supply blood to erectile tissue and the corpora cavernosa, which become engorged and expand as a result of increased blood flow and pressure.

Because blood must stay in the penis to maintain rigidity, erectile tissue is enclosed by fibrous elastic sheathes (tunicae) that cinch to prevent blood from leaving the penis during erection. When stimulation ends, or following ejaculation, pressure in the penis decreases, blood is released, and the penis resumes its normal shape.

Exercise & Sexual Function in Men

In March 2015, results of a study published in the Journal of Sexual Medicine indicated that men of all races who exercise more have improved erectile and sexual function. According to the study, men who reported more frequent exercise had higher sexual function scores and those who reported less exercise experienced lower sexual function. Higher rates of exercise involved a total of 18 metabolic equivalents (METS) per week, which involved 2 hours of strenuous exercise, 3.5 hours of moderate exercise, or 6 hours of light exercise.

Other factors that contribute to lower levels of sexual function include

  • Age
  • Cardiovascular disease
  • Diabetes
  • Past or current smoking

Updated by Remedy Health Media

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 10 Jun 1998

Last Modified: 31 Mar 2015