Abdominal Aorta

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The abdominal aorta is the largest artery in the abdomen that provides blood to the organs and tissues of the abdomen, pelvis, and legs. It descends from the thorax as a continuation of the thoracic aorta and branches several times to form the major arteries of the abdomen.

Anatomy

The abdominal aorta is about an inch in diameter and extends along the entire length of the abdomen, from the diaphragm to the pelvis. It enters the abdomen through a small opening at the posterior end of the diaphragm, just anterior to the spinal column. From this point, it descends along the spine parallel to the inferior vena cava until it reaches the pelvis, where it divides into the right and left common iliac arteries.

Many major arteries branch from the abdominal aorta to provide blood flow to the vital organs of the abdomen. Its visceral branches provide blood to organs, while its parietal branches supply blood to the tissues of the abdominal body wall.

• The inferior phrenic artery is a parietal artery, the most superior branch of the abdominal aorta. It extends superiorly to provide blood to the diaphragm muscle at the top of the abdomen. 
• The celiac trunk is a visceral artery that splits from the abdominal aorta below the inferior phrenic artery. It branches almost immediately into the left gastric, splenic, and common hepatic arteries. These arteries provide blood to the stomach, spleen, and liver.
• The superior mesenteric artery is a visceral artery that begins just inferior to the celiac trunk. It branches into the inferior pancreaticoduodenal, jejunal, ileal, ileocolic, and right and middle colic arteries. These branches spread throughout the middle abdomen to provide blood to the pancreas, small intestine, and large intestine.
• The suprarenal, renal, and gonadal arteries are visceral arteries that extend from the abdominal aorta below the superior mesenteric artery. They provide blood flow to the adrenal glands, kidneys, and gonads, respectively.
• The lumbar artery is a parietal artery that splits from the abdominal aorta inferior to the gonadal artery. It provides blood to the tissues and muscles of the abdominal wall.
• The inferior mesenteric artery is a visceral artery that arises inferior to the lumbar artery. It gives rise to three branches that form the left colic, sigmoid, and superior rectal arteries. These arteries provide blood to the large intestine and rectum.
• The median sacral artery is the most inferior artery that branches from the abdominal aorta. It is a parietal artery that descends into the pelvis and provides blood flow to the tissues of the lower back, sacral, and coccygeal regions.

Histology

The abdominal aorta is made of three distinct layers surrounding the lumen, or hollow center of the artery. The tunica intima is the innermost layer that is in contact with the lumen and the blood passing through it. It is made of endothelium, a specific type of stratified squamous epithelial cells that maintain the integrity of the vessel walls. Epithelium plays an important role in preventing blood cells from leaking out of the artery or sticking to the walls and forming clots. The next layer, the tunica media, is much thicker than the tunica intima and contains many elastin fibers and smooth muscle tissue. These structures work together to give the artery strength and elasticity and the ability to contract to help propel blood through the body. Finally, the tunica externa forms the outermost layer of the abdominal aorta and is made of dense irregular connective tissue containing many collagen fibers. This tissue gives the artery a strong but flexible outer coat and helps to attach the abdominal aorta to the surrounding tissues.

Physiology

The abdominal aorta provides all of the oxygenated blood to the tissues and organs of the abdomen as well as to the pelvis and lower limbs. It is an elastic artery, meaning that it has many elastic fibers in its walls that are able to expand to accommodate the large volume of blood pumped into the abdomen by the heart. These elastic fibers contract following each heartbeat to help propel blood away from the heart and toward organs and tissues. Oxygenated blood provides vital oxygen and nutrients to maintain the health and metabolism of the body's cells.