Penile erection
Penile erection refers to the function of penis, to stand erect during copulation, to enhance penetration. The penile erectile tissue, plays the most important role in the erectile process. In the flaccid state, the smooth muscles of the penis are tonically contracted, allowing only a small amount of arterial flow for nutritional purposes. The partial pressure of blood oxygen (PO2) is about 35mm Hg range. It should be noted that the flaccid penis is in a moderate state of contraction, as evidenced by further shrinkage in cold weather. The angle at which penis will be erected is determined by its size and its attachment to the puboischial rami and the anterior surface of the pubic bone (funiform ligaments and the suspensory). In men possessing a long heavy penis or a loose suspensory ligament, the angle usually will not be more than 90 degrees, even at the full rigidity.