There is also evidence that a full bladder can contribute to morning wood.
还有证据表明，充盈的膀胱有助于早起。
AsapSCIENCE - Human
Now that we got the one obligatory joke out of the way, we can get to the hard facts of nocturnal penile tumescence, otherwise known as " morning wood" .
既然我们已经开玩笑了，我们就可以了解夜间阴茎勃起的事实， 也就是所谓的“晨勃” 。
中文百科
晨勃
晨勃，即晨间勃起，为男性阴茎或女性阴蒂在睡眠中或早晨刚睡醒时的自发性勃起反应，可以指：
夜间阴茎勃起（简称NPT）
夜间阴蒂勃起（简称NCT）
英语百科
Morning wood 晨勃
Morning wood is one of several similar slang or colloquial terms referring to the phenomenon of nocturnal penile tumescence (erection) during and immediately following sleep.