Final answer:
Penile tumescence involves vasocongestion, where nitric oxide release leads to the dilation of penile arteries and increased blood flow, causing an erection. Testosterone regulates this process along with the sex drive, and sexual response during intercourse occurs in four phases.
Step-by-step explanation:
Mechanisms of Penile Tumescence
The mechanisms responsible for penile tumescence, commonly known as an erection, involve a vascular process called vasocongestion. This process begins with sexual arousal or REM sleep, which triggers the release of nitric oxide (NO) from nerve endings in the phallus. NO activates a signaling pathway causing the relaxation of the surrounding smooth muscles and dilation of penile arteries, increasing blood flow into the corpora cavernosa and corpus spongiosum. The rise in blood volume compresses the thin-walled penile venules, reducing blood outflow, and resulting in an erection. The average length of an erect phallus is approximately 15 cm.
Testosterone plays a crucial role in regulating sex organs and sex drive, and its production is controlled by a negative feedback loop involving the testes and the endocrine system. Understanding the interplay of these physiological responses to sexual arousal provides insights into the sexual response during intercourse, with phases of excitement, plateau and resolution.