Before a male has an orgasm and ejaculates, his penis gets hard. During an erection, the blood vessels in the spongy tissue of the penis fill with blood. This causes the penis to become stiff and stand out from the body.

An erection can happen very quickly, in response to physical stimulation, sexual thoughts, or nothing at all. When a penis gets erect, it also gets longer and wider, and may even change color. Some penises are quite straight when erect, others are slightly curved, or even bent.
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Impotence

Impotence, also known as erectile dysfunction, is the failure to attain or maintain an erection firm enough for intercourse. Most men experience occasional erectile failures, usually because they are tired, stressed, or intoxicated. Causes of long-term erectile dysfunction include:

• Blockage in the arteries


• Diabetes


• Side effects of medications


• Kidney or liver failure


• Hormonal abnormalities


• Alcoholism and drug abuse

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