PHYSICAL EXAMINATION

LABORATORY STUDIES

DIAGNOSIS

Erectile dysfunction

PATHOPHYSIOLOGY OF KEY SYMPTOMS

The male erection response is due to the engorgement of blood vessels in the corpus cavernosa (see Fig. 87-1). These vascular changes require the interplay of the vascular endothelial cells, sympathetic and parasympathetic nervous system, the central nervous system, and a permissive role played by the endocrine system. Disorders in any of these systems can result in erectile dysfunction, defined as “an inability to achieve and maintain an erection sufficient for satisfactory sexual performance.”

The penis is normally in a flaccid state, in which sympathetic nervous system tone constricts the smooth muscle of the penile erectile tissue, limiting blood flow into the corpus cavernosa. Endothelin and prostaglandins produced in the vascular wall augment the arteriolar vasoconstriction.

Appropriate psychologic or tactile stimulation causes an increase in parasympathetic activity and a withdrawal of sympathetic tone. The neurally mediated vasodilation causes blood to become trapped in the corpus cavernosa, leading to an erection.

The erectile response is initiated by an increase in parasympathetic nerve activity working through the NANC (nonadrenergic, noncholinergic) neurotransmitters, predominantly nitric oxide (NO) and vasoactive intestinal peptide (VIP). An increase in the activity of the NANC nerves dilates the vascular smooth muscle and causes an increase in blood flow. The increase in blood flow creates a shear stress on the vascular endothelium, stimulating NO production by the endothelial cells. It is the endothelial NO that mediates the maintenance of an erection (Fig. 88-1).

FIGURE 88–1 Lipophilic signaling molecules (H) bind to intracellular receptors (R). About half of the steroid receptors are coupled to heat-shock proteins (HSPs), which dissociate when the steroid binds the receptor. Nitric oxide binds to soluble guanylyl cyclase, generating cGMP and, from that point, follow the normal G protein–coupled second messenger pathway.