In Depth: Bones, Vessels, and Nerves
Oxygenated blood begins its trip down the chest through the thoracic aorta, the major blood vessel with branches that serve the chest muscles and lungs. It’s the same aorta that becomes the abdominal aorta.
The abdominal aorta’s largest branch, the superior mesenteric artery, supplies blood to most of the small intestine and the first half of the large intestine. The inferior mesenteric artery handles the second half of the large intestine’s blood supply.
In the pelvis, the abdominal aorta splits into two main branches called common iliac arteries. These travel down each leg, where they branch into internal and external iliac arteries. These branch further to supply the legs, and the largest of these branches are the femoral arteries.
Branching from the internal iliac artery, the internal pudendal artery is the main vessel that supplies oxygenated blood to the penis and makes erections possible. The testicular arteries, also known as the internal spermatic arteries, supply blood to the testes. They branch from the abdominal aorta.
Veins are the blood vessels that return oxygen-depleted blood back to the heart for reuse. They typically follow the same path as arteries. Similar to the arteries in the pelvis, veins branch within the legs. As blood returns to the heart these branches — the external iliac veins — feed into the inferior vena cava, the large vessel that travels parallel to the abdominal aorta.
Nerves branch from the spinal column. There are three types of nerves:
- Autonomic nerves: These control involuntary or partially voluntary actions such as heartbeat.
- Motor nerves: These signal muscles to move.
- Sensory nerves: These relay information from the skin and muscles, such as heat and pain.
In the pelvis, the spinal column ends in the sacrum, five fused vertebral bones that form the back of the pelvis. Behind it is the sacral plexus, a collection of nerves that serve the pelvic area, genitals, buttocks, and some parts of the legs and feet.
The sciatic nerve is the largest nerve stemming from the sacral plexus. This large nerve fiber begins in the lower back at the spinal column, runs through the buttocks beneath the gluteus maximus muscle, and extends down the back of the thigh. There is one sciatic nerve in each leg, and each is about one inch wide in the pelvis.