Hey,
Mean total diameter of ascending aorta in females: 33.5 mm, and 36 mm in males.
Total diameter of abdominal aorta: 19 - 25 mm.
Basically, the aorta is the largest single blood vessel in the body. It is approximately the diameter of your thumb. This vessel carries oxygen-rich blood from the left ventricle to the various parts of the body.
The aorta is thicker than the wall of the pulmonary trunk. The reason for this is that the blood in the aorta has to go all around the body. Blood in the pulmonary trunk has to go all around the lungs. The body is, obviously, larger than the lungs. This means blood going around the body needs to be "pushed" more. This is because there is more resistance. For example, it's harder to push a car for 1 mile, then it is to push it 1 metre. Because the blood has to be pushed more, the heart (left ventricle) pumps it out at a higher pressure. Similarly, because the blood going around the lungs doesn't need to go so far, the heart (right ventricle) pumps it out at a lower pressure. Because the blood in the aorta is at higher pressure than the pulmonary trunk, it needs to have thicker walls. For example a fire hose is thicker than a garden hose because it needs to transports water at a higher pressure. The aorta contains large amount of smooth muscle and elastic tissue to help it cope with the high blood pressure.
Since the main coronary trunk emerges directly from the proximal portion of the aorta, it receives a strong forward pressure of blood due to the pressure exerted by each beat of the left ventricle. likewise the blood reaches the left myocardial muscles first where it is most needed due to the bigger size and larger amount of work exerted by the left ventricle. This is the advantage of the coronary artery originating from the left rather than the right side.
Do a search, I think the latter question as been asked before and answered in full.
thanks, but i still don't really understand the last question.