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Penis Anatomy

We invite you to a short lesson in anatomy. We think that you will find it rather useful, so, read carefully. The penis, the male organ of copulation, is partly inside and partly outside the body. The human penis is anatomically divided into two continuous areas - the body, or external portion, and the root, or internal portion. The body of the penis, sometimes referred to as the shaft, is cylindrical in shape when flaccid but when erect is somewhat triangular in cross section, with the angles rounded. The root of the penis begins directly below the bulb-urethral glands with a long cylindrical body of tissue known as the corpus spongiosum (or corpus cavernosum urethrae). This tissue extends through the body of the penis to the tip, where it expands into a mushroom-shaped structure called the glans penis. Running through the center of the corpus spongiosum is the urethra, a common passage for semen and urine; the urethra ends in a slit-like opening at the tip of the glans penis. Beginning alongside of the bulb-urethral glands is a pair of long cylindrical bodies called the corpora cavernosa penis. These continue through the body of the penis, occupying the sides and upper portion directly above the corpus spongiosum; they terminate immediately before the glans penis.

The base of the glans has a projecting margin, the corona, and the groove where the corona overhangs the corpora cavernosa is referred to as the neck of the penis. The corpora cavernosa consist of empty spaces divided by partitions of tissue. The tissue consists of muscle, collagen (a fibrous protein), and elastic fiber. The corpora cavernosa are termed erectile tissue, because during sexual excitation, their fibrous tissue is expanded by blood that flows into and fills their empty spaces. The blood is temporarily trapped in the penis by the constriction of blood vessels that would normally allow it to flow out. The penis becomes enlarged, hardened, and erect as a result of this increased blood pressure. The corpus spongiosum is also considered erectile tissue. This area, however, does not become as enlarged as the other two during erection, for it contains more fibrous tissue and less space; unlike the corpora cavernosa, the corpus spongiosum has a constant blood flow during erection. A circular layer of elastic tissue encloses the corpora cavernosa and corpus spongiosum. A thin layer of skin in turn covers this circular layer of tissue. The skin, which is slightly darker in color than the rest of the body, is loose and folded while the penis is in a flaccid state. At the beginning of the glans penis, a circular fold of skin, commonly called the foreskin (or prepuce), extends forward to cover the glans. A median fold, the frenulum of the prepuce, passes to the under surface of the glans to reach a point just behind the urethral opening. The prepuce can usually be readily drawn back to expose the glans.

The Physiology Of An Erection:

The creation of an erection is an extreme cascade of events that requires many different things to happen. There are numerous chemical transmitters involved in this including epinephrine, norepinephrine, acetylcholine, prostaglandin's and nitric oxide. An erection occurs when the nervous system activates a rapid increase in blood flow. Numerous sexual stimuli are processed by the brain and transmitted to the penis via the nervous system. Internally, the penis has three long masses of cylindrical tissue, known as erectile tissue, that are bound together by fibrous tissue. All three masses are sponge-like; they contain large spaces between loose networks of tissue. When the penis is in a flaccid, or resting, state, the spaces are collapsed and the tissue is condensed. During erection, blood flows into the spaces, causing distention and elevation of the penis. The amount of blood entering the penis can be increased by physical or psychological stimulation. As blood enters, there is a temporary reduction in the rate and volume of blood leaving the penis. The arteries carrying blood to the penis dilate; this, in turn, causes tissue expansion. The veins leading from the penis have funnel-shaped valves that reduce the outflow of blood. As the erectile tissue begins to enlarge, the additional pressure causes the veins to be squeezed against the surrounding fibrous tissue, and this further diminishes the outflow of blood. Essentially, blood becomes temporarily trapped in the organ.

 

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