The penile shaft consists of two corpora cavernosa that fill with blood to cause an erection
The penis is a male reproductive organ located within the scrotum and extends from the pelvic bone. It consists of three parts: the root, shaft, and glans (head) (1). The corpus cavernosum makes up most of the length of the shaft and contains spongy tissue made of smooth muscle cells and elastic fibers (2). During sexual arousal, these cells become engorged with blood, causing the corpus cavernosum to swell and increase in size (3). This results in an erection.
When a man becomes sexually aroused, his brain sends signals to the penis via nerves, which trigger the release of nitric oxide in the corpus cavernosum (4). Nitric oxide causes the endothelial cells lining the walls of the penis' blood vessels to relax, allowing more blood to flow into the penis (5). As the blood fills the corpora cavernosa, they expand and create pressure on the fibrous sheath surrounding them, leading to rigidity and an erection.
While both corpora cavernosa contribute to an erection, their exact roles are not fully understood (6). Studies have shown that each corpora cavernosum has its own unique properties, including sensory nerve endings that may play a role in maintaining proper arterial blood supply (7). Additionally, some evidence suggests that the right corpus cavernosum may be larger than the left due to variations in anatomical structure and vascularization (8).
However, the specific differences between the two sides remain unclear, although researchers believe there is likely some degree of asymmetry present (9). In addition to their structural differences, the corpora cavernosa also differ in terms of their responses to different types of stimuli. For example, one study found that electrical stimulation of one side of the penis led to greater stiffness than the other (10), suggesting that each side may respond differently to certain types of stimuli.
Overall, further research is needed to better understand the exact function and interplay of the two corpora cavernosa in causing an erection. Nevertheless, this vital organ plays a crucial role in male sexual health and satisfaction, as well as overall physical and mental well-being. A healthy penis should feel firm when flaccid and elastic during an erection.