Male Hypogonadism and Impotence
posted in Male Hypogonadism and Impotence |Spermatogenesis is remarkably sustained throughout life if testicular androgen synthesis is adequate; however, androgen production does decline with age. The impact of this reduced androgen synthesis on health, well-being, and sexual function has not been determined.
As testosterone secretion diminishes, its diurnal variation is also blunted, resulting in a lower 6 to 8 AM peak. Mean gonadotropin levels rise slowly, but large pulses of luteinizing hormone are less frequent, which impairs pulsatile testicular response. Binding of testosterone to sex hormone-binding globulin increases with age, resulting in substantially less unbound, bioavailable testosterone. Also, metabolism of testosterone is slowed. Evidence suggests that androgens play an important role in libido (sexual appetite) and influence the frequency of nocturnal erections; however, erections produced by erotic stimuli can occur despite low levels of androgens.
Penile erection is accomplished through engorgement of the corpora cavernosa, two paired vascular bundles. Because each corpus caverno-sum is surrounded by a tough, fibrous sheath (the tunica albugineai. engorgement leads to rigidity. Erection occurs when arterial blood flow into the corpora cavernosa exceeds venous outflow. The pudendal artery supplies blood to the corpora, and blood flow is controlled by relaxation and contraction of arterial smooth muscle. Venous drainage occurs through venules just below the tunica albuginea. These venules are easily compressed as the corpora fill. The penis is innervated by the T11-L2 sympathetic nerves and the S2-4 somatic and parasympathetic nerves.
