The initial part of the aorta, the ascending aorta, rises out of the left ventricle, from which it is separated by the aortic valve. The two coronary arteries of the heart arise from the aortic root, just above the cusps of the aortic valve.
The aorta then descends to go down the trunk of the body. The portion above the diaphragm (in the thorax) is called the thoracic aorta and the portion below it (in the abdomen) the abdominal aorta.
As it travels down the posterior wall of the abdomen, the abdominal aorta runs on the left of the inferior vena cava, giving off major blood vessels to the gut organs and kidneys. There are many recognized variants in the vasculature of the gastrointestinal system. The most common arrangement is for the aorta to give off the celiac trunk, the superior mesenteric artery and the inferior mesenteric artery in turn. The renal arteries usually branch from the abdominal aorta in between the celiac trunk and the superior mesenteric artery.
The aorta is an elastic artery, and as such is quite distensible. When the left ventricle contracts to force blood into the aorta, the aorta expands. This stretching gives the potential energy that will help maintain blood pressure during diastole, as during this time the aorta contracts passively.
The abdominalaorta is a region of the descending aorta, originating superiorly as a continuation of the thoracic aorta as it passes through an opening in the diaphragm, and terminating inferiorly as the abdominalaorta bifurcates (divides into two structures) into the left and right common iliac arteries.
Lateral to the aorta are the inferior phrenics, middle supernal, renal, and ovarian or testicular arteries.
Because the branches from the abdominalaorta are large, the aorta rapidly decreases in size as it courses downward (inferiorly) through the abdomen.
The abdominalaorta is covered, anteriorly, by the lesser omentum and stomach, behind which are the branches of the celiac artery and the celiac plexus; below these, by the lienal vein, the pancreas, the left renal vein, the inferior part of the duodenum, the mesentery, and aortic plexus.
The right is longer than the left, on account of the position of the aorta; it passes behind the inferior vena cava, the right renal vein, the head of the pancreas, and the descending part of the duodenum.
Sometimes one is derived from the aorta, and the other from one of the renal arteries; they rarely arise as separate vessels from the aorta.
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