Overview of Male Sexual Function and Dysfunction

Libido is the conscious component of sexual function. Decreased libido manifests as a lack of sexual interest or a decrease in the frequency and intensity of sexual thoughts, either spontaneous or in response to erotic stimuli. Libido is sensitive to testosterone levels as well as to general nutrition, health, and drugs.

Conditions particularly likely to decrease libido include hypogonadism, chronic kidney disease, and depression; up to 25% of men with diabetes may meet the definition of hypogonadism.

prostate cancerbenign prostatic hyperplasia

Erection is a neurovascular response to certain psychologic and/or tactile stimuli. Higher cortical input and a sacral parasympathetic reflex arc mediate the erectile response. Neural output travels through the cavernous nerves, which traverse the posterolateral aspect of the prostate. Terminating in the penile vasculature, these nonadrenergic, noncholinergic nerves liberate nitric oxide, a gas. Nitric oxide diffuses into penile arterial smooth muscle cells, causing increased production of cyclic guanosine monophosphate (cGMP), which relaxes the arteries and allows more blood to flow through them and into the corpora cavernosa. As the corpora fill with blood, intracavernous pressure increases, which compresses surrounding venules, causing veno-occlusion and decreased venous outflow. The increased inflow of blood and decreased outflow further increase intracavernous pressure, contributing to erection. Many factors affect the ability to have an erection (see Erectile Dysfunction).

Ejaculation is controlled by the sympathetic nervous system. Neural stimulation of the alpha-adrenergic receptors in the male adnexa (eg, penis, testes, perineum, prostate, seminal vesicles) causes contractions of the epididymis, vas deferens, seminal vesicles, and prostate that transport semen to the posterior urethra. Then, rhythmic contractions of the pelvic floor muscles result in pulsatile ejaculation of the accumulated seminal fluid. At the same time, the neck of the bladder closes, preventing retrograde ejaculation of semen into the bladder. Selective serotonin reuptake inhibitors and alpha blockers may delay or inhibit ejaculation by receptor inhibition at these sites.

Orgasm is the pleasurable sensation that occurs in the brain generally simultaneously with ejaculation. Anorgasmia may be a physical phenomenon due to decreased penile sensation (eg, from neuropathy) or a neuropsychologic phenomenon due to psychiatric disorders or psychoactive drugs.