The penis is the copulatory organ in male mammals and is also the organ responsible for urine discharge from their body. While in higher vertebrates this organ is called the penis, in lower invertebrates the corresponding structure is often referred to as cirrus.
A part of the penis is outside the body and the other part is inside. The internal part of the penis is attached to the bony edges of the pubic arch which is the front part of the pelvis, at the base of the trunk. This internal part is called the root of the penis. The external part of the penis, called the body of the penis, is pendulous and is covered by skin.
The penis anatomy is segregated into two parts: the external portion or the body and the root. The root of the penis has two projections (crura) and the bulb of the penis. The crura are joined to the edges of the pubic arch and the bulb is attached to the perineal membrane that makes the base of the trunk. The location of the penis root is right under the bulbourethral glands with the corpus spongiosum (or corpus cavernosum urethrae). It is a long cylindrical body of tissue that runs through the body of the penis right to its tip. At this point, it forms a mushroom-shaped structure that is termed a glans penis. The base of the glans penis has the corona (projecting margin).
The urethra is a tube that passes through the center of the corpus spongiosum. It provides the common route for the passage of both urine and semen. At the tip of the glans penis, the urethra provides a slit-like opening. At the sides of the bulbourethral glands, there is a pair of long cylindrical parts called the corpora cavernosa. They course through the body of the penis and located at the sides and in the area directly above the corpus spongiosum. The corpora cavernosa ends right before the glans penis. The groove where the corona is overhanging the corpora cavernosa is called the neck of the penis.
The penis anatomy has been illustrated in the penis diagram below.
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The corpora cavernosa has empty spaces that are divided by tissue partitions. These are made of collagen (fibrous protein), muscle, and elastic fiber. The corpora cavernosa are called erectile tissue since, at the time of sexual excitation, blood flows and fills their empty spaces, expanding their fibrous tissue. This blood is normally allowed to flow out by the blood vessels but their constriction holds the bloods in the penis for some time. This process enlarges and hardens the penis, making it erect due to the increased blood pressure.
The corpora cavernosa and corpus spongiosum are both covered by a circular layer of elastic tissue that is covered by a thin layer of skin. This skin is slightly darker than the rest of the body, is loose, and gets folded when the penis is in a flaccid state. The glans penis has a circular fold of skin where it begins. This skin is commonly known as the foreskin (prepuce) and it extends further to cover the glans.
Blood Supply to the Penis
The penis gets its blood supply from the internal pudendal artery which is a branch of the internal iliac artery. This artery supplies blood to the pelvic structures and organs and the inside of the thighs. The penis also has sensory and autonomic (involuntary) nerves. In the autonomic nerve fibers, the parasympathetic fibers cause the dilation of the blood vessels while the sympathetic fibers cause their constriction. The sympathetic system causes ejaculation which inhibits the desire to urinate at the time of erection and prevents the semen from entering the bladder at the same time.
Types of Penis
Some penises are straight at the time of erection while others have s slight curvature. Both types of penis are perfectly normal. There are three categories of a curved penis:
Curved downward from the base of penis.
Curved upwards from the base.
Curved to the left or right.