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The Role of Testosterone in the Anatomy and Physiology of Normal Erectile Functioning
Role of Testosterone in Erectile Function
Testosterone, the primary male sex hormone, plays a crucial role in various aspects of male health, including sexual function. In this article we are doing to look at normal erectile function and how testosterone works to make it happen, support it and make it work best. We offer this information for two purposes. 1) So that you can have a sense of the amazing role testosterone plays in this function and 2) to better understand the relationship between testosterone levels and erectile function when diagnosing and treating erectile dysfunction (ED).
Functional Anatomy of the Penis
Anatomical and Physiological Steps from Arousal to Full Erection and Maintenance
- Arousal (Psychological and Sensory Stimuli): Arousal can be or is triggered most commonly in men relating to specific psychological stimuli, erotic thoughts, visual or auditory stimuli. Thinking About, seeing or meeting an attractive woman (or man) or by the occurrence of some sort of sensory stimuli, for example touching or being touched by someone who is attractive to you or who you fantasize or in the moment believe is attractive to you. Genital stimulation, being touched in the genital area or in or along an erogenous zone.
- Neural Activation: When you see, think of or are touched or stimulated by someone or something that arouses you the visual, auditory, touch or psychological stimuli is transmitted as a nervous system signal to your brain, which then responds and sends activation signal down your spinal cord to your pelvic nerves. During this process your Parasympathetic Nervous System is activated and triggers the releases of one or more neurotransmitters, most important of which is nitric oxide (NO) within the penile nerves.
- Nitric Oxide (NO) Release: As soon as NO is released from nerve endings within and around the corpus cavernosum, the NO stimulates the production of cyclic guanosine monophosphate (cGMP) within the smooth muscle cells of the corpus cavernosum.
- Vasodilation: The production of cGMP causes the smooth muscles in the walls of the arterioles supplying the corpus cavernosum to relax. This relaxation leads to vasodilation and increased blood flow into the corpus cavernosum.
- Engorgement and Erection: This increased blood flow fills the corpus cavernosum, causing it to swell and become rigid. The swelling compresses the veins that normally drain blood from the penis, reducing outflow and maintaining the erection.
- Role of Testosterone: Testosterone is crucial for triggering and maintaining libido as well as the sexual drive, both of which are necessary for initiating the arousal process. Testosterone acts to release and regulate the enzymes cGMP which is then involved in the cGMP pathway, and acts to enhance the erectile response.
- Maintenance of Erection: Once an erection is triggered, if there is adequate and ongoing testosterone release and hence stimulation, there is an ongoing and continuing sexual stimulation created by the ongoing release of NO and the production of cGMP. This allows the erection to be maintained over extended periods of time. At the same time Phosphodiesterase type 5 (PDE5) is being released and it acts to break down cGMP. Testosterone modulates the activity of PDE5, helping to sustain cGMP levels and maintain the erection.
- Erection Termination: With ejaculation or cessation of arousal (for any reason) this activates the sympathetic nervous system. PDE5 testosterone levels drop and this acts to increase PDE5 which then breaks down cGMP, leading to the contraction of smooth muscle and reduced blood inflow into the corpus cavernosum. Blood begins to drain from the corpus cavernosum, leading to detumescence, the loss of the erection.
Article by Dr. Allen Lawrence, M.A., M.D., Ph.D.
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