In Depth: Organs and Inner Muscles
The pelvic region holds major organs under its layers of muscles. Some of the most important include the major digestive organs, the intestines.
The small intestine is the longest part of the digestive tract. It receives food from the stomach and begins breaking down the food while absorbing the majority of its nutrients. The mucus this long hollow organ secretes breaks down proteins and carbohydrates and protects the small intestine from harmful stomach enzymes. Enzymes secreted by the liver and pancreas further aid digestion.
The small intestine is longer of the two, so the large intestine earned its name because it is much wider in diameter.
The large intestine connects to the small intestine in the lower right section of the abdominal cavity. A muscular sphincter, the ileocecal, prevents food from traveling back up the small intestine.
The large intestine is filled with billions of bacteria that turn food into solid feces and remove water and electrolytes. As food travels up and around, muscles in the large intestine break down the material before it descends down the colon, the last part of the digestive tract. From there, it travels through the rectum and out of the anus.
The pelvis also houses the reproductive organs, which have their own muscles.
The muscles of the penis include the corpora cavernosa, two cylinder-like chambers that run down the sides of the penis. Upon arousal, the corpora cavernosa fill with blood, and the penis becomes firm. This is known as an erection.
While the penis is erect, an inner layer, the corpus sponginosum, remains spongy and limber. This protects the urethra—a tube that carries urine and semen out of the body— from closing during an erection so that semen can exit the body upon ejaculation.
During ejaculation, semen travels from the testes through the epididymis, a long twisted tube on both sides of the testes. It then moves up to the vas deferens and behind the bladder. From there, it travels to the seminal vesicle and out through the urethra.
The prostate is a walnut-sized gland that controls the release of urine from the bladder. It also secretes a milky fluid that is the major component in semen: the part that helps nourish and transport the sperm.
Above the prostate is the bladder. Also known as the urinary bladder, it is an expandable muscular sac that stores urine. When signaled, the bladder releases the urine into the urethra.