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The anatomy of the penis refers to the shape and function of the male sex organ. The penis also functions to channel urine from the body. Internal portions of the penis are made up of the urethra and the corpus spongiosum. External portions include the foreskin and the glans. Understanding the anatomy of the penis helps to understand how the elements of this organ work together.
A glans, or head, of the penis is the round tip of the shaft, covered with tissue referred to as mucosa. The glans contains nerve endings that make it sensitive to touch, so it considered analogous to the female clitoris in terms of sexual sensation. A urethral opening in the middle of the glans allows semen, as well as urine, to be discharged from the body.
The penis shaft is the portion between the body and the head, or glans, of the penis. It is the longest part of the organ. A shaft contains the urethral tube, as well as the corpus spongiosum. When the penis is erect, the shaft becomes much larger and longer. Blood vessels called dorsal veins may protrude from the shaft of an erect penis.
Corpus cavernosum is the expandable spongy tissue that runs the length of the penis in columns. When the penis is flaccid, this tissue remains small, but once a man is aroused, it becomes larger. This is because blood fills up the tissue to make the penis erect. These blood-filled spaces are called endothelium. When nerves in the glans and shaft are stimulated, more blood flows through the blood vessels into these tissues.
Another functioning part of the anatomy of the penis is called corpus spongiosum. This spongy tissue inside of the shaft also helps to produce an erect penis. Unlike the corpus cavernosum, this portion of the anatomy of the penis also works to keep the urethra open during an erection.
The urethral tube in the penis runs from the opening of the glans to the bladder. It is approximately 9 inches (21 cm) long. Sections of the urethra are different depending on their location. A spongy urethra is located in the shaft and the membranous urethra is found near the urethra sphincter.