Describe the structural and functional difference between arteries and veins in general. What is the "exception to the rule" as far as function of arteries and veins in the body?

Structurally, arteries and veins have several differences:

1. Wall Thickness: Arteries have thicker walls compared to veins. This is because arteries need to withstand the high pressure of blood pumped from the heart.

2. Lumen Size: The lumen, or the inside space of a blood vessel, is smaller in arteries and larger in veins. This helps veins hold a larger volume of blood.

3. Presence of Valves: Veins have valves to prevent the backflow of blood, while arteries do not have valves as the blood is pumped at high pressure from the heart.

Functionally, arteries and veins also differ:

1. Direction of Blood Flow: Arteries carry blood away from the heart to the rest of the body, while veins carry blood from the body back to the heart.

2. Oxygen Content: Arteries (except for the pulmonary artery) carry oxygenated blood, while veins (except for the pulmonary veins) carry deoxygenated blood.

The "exception to the rule" refers to the pulmonary artery and pulmonary veins. Unlike other arteries, the pulmonary artery carries deoxygenated blood from the heart to the lungs. Conversely, the pulmonary veins carry oxygenated blood from the lungs back to the heart, which is not typical of other veins.