While discussing the physiological process behind penile erection, the anatomy and physiology instructor mentions that what substance is released to facilitate smooth muscle relaxation and shunting of blood into the sinusoids?
A) Norepinephrine
B) Nitroglycerine
C) Nitric oxide
D) Nicotinic acid
Ans: C
Feedback:
Parasympathetic innervation must be intact and nitric oxide synthesis must be active for erection to occur. Parasympathetic stimulation results in release of nitric oxide, a nonadrenergic–noncholinergic neurotransmitter, which causes relaxation of the trabecular smooth muscle of the corpora cavernosa. This relaxation permits inflow of blood into the sinuses of the cavernosa at pressures approaching those of the arterial system. The nicotinic acid in cigarette smoke can induce vasoconstriction and penile venous leakage because of its effects on cavernous smooth muscle. Nitroglycerine is a vasodilator that has no effect on trabecular smooth muscle. A norepinephrine action is vasoconstriction, rather than relaxation, as part of sympathetic nervous system response.
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