The possibility of achieving an erection without testes highlights the difference between the body’s physical mechanics and its hormonal system. The ability to “get hard” relies on an intricate network of nerves and blood vessels, which are physically separate from the hormone-producing glands. While the testes provide the primary hormonal fuel for sexual desire and function, the core mechanical process of an erection is a neurological and vascular event.
The Physical Process of Achieving an Erection
The physical act of an erection is primarily a hydraulic event orchestrated by the nervous system. Sexual stimulation, whether physical or psychological, triggers signals from the brain and spinal cord that activate the parasympathetic nervous system. This activation causes the release of chemical messengers in the penile tissue, most importantly nitric oxide (NO).
Nitric oxide is the signaling molecule that initiates the cascade leading to engorgement. It acts on the smooth muscle cells lining the arteries and the spongy tissue of the corpora cavernosa, causing them to relax. This relaxation allows a massive surge of arterial blood flow into the erectile chambers, increasing blood flow up to 20 to 40 times the resting rate.
As the erectile tissue rapidly fills with blood, the expansion compresses the veins responsible for draining blood away, a mechanism known as venous occlusion. This trapping of blood creates the rigidity and firmness of a full erection. The entire process is a local neuro-vascular reflex, meaning the physical structures—nerves, blood vessels, and smooth muscle—are the sole requirements for the mechanical event.
How Testosterone Influences Sexual Function
Testosterone, the primary androgen produced by the testes, does not directly cause the physical erection but acts as a prerequisite for function. Its most well-known influence is on libido, or sexual desire, which initiates the neurological and vascular sequence. A decline in this hormone often results in a measurable reduction in the motivation for sexual activity.
Beyond desire, testosterone maintains the health and responsiveness of the penile tissue. It helps support the production of nitric oxide and enhances the sensitivity of the smooth muscle to its relaxing effects. Adequate hormone levels are required to keep the smooth muscle and endothelial cells within the corpora cavernosa in a healthy, functional state.
Without sufficient testosterone, the erectile tissue may become less responsive to the chemical signals that trigger relaxation and blood flow, leading to diminished erection quality. The hormone ensures that the mechanical system is primed and ready to respond robustly when the nervous system sends the signal.
Maintaining Erectile Function After Testicular Loss
A person can achieve an erection after the loss of the testes because the physical machinery—the nerves and blood vessels—remains intact. However, the removal of both testes (bilateral orchiectomy) eliminates the body’s main source of testosterone, causing a rapid drop in hormone levels. While the adrenal glands produce trace amounts of androgens, this is insufficient to maintain normal function.
This resulting state of low testosterone, or hypogonadism, causes significant impairment in sexual function. Symptoms include a near-total loss of libido and a marked decrease in erection quality and frequency. Although the mechanical ability is present, the hormonal fuel and tissue responsiveness are gone. To counteract this, Hormone Replacement Therapy (HRT) or Testosterone Replacement Therapy (TRT) is required.
TRT successfully restores testosterone levels to a normal range, reinstating libido and maintaining the health of the erectile tissues. This treatment is delivered through various methods, such as injections, gels, or patches. TRT is crucial for maintaining sexual function after testicular loss. For some, TRT alone is sufficient, while others may find that TRT helps medications, like PDE5 inhibitors, work more effectively to ensure a firm erection.