Question

The largest and thickest blood vessels are
a. Arteries
b. Veins
c. Capillaries
d. Venules

Answer 1

Hint: Blood vessels form a tubular network throughout the body that allows blood to flow from the heart to all living cells of the body and then back to the heart. Blood from the heart passes through vessels of progressively smaller diameters known as the arteries, arterioles, and capillaries.

Complete answer:
The walls of the arteries consist of three coats of tunics’.
• Tunica externa: The outermost layer is the tunica externa and is composed of connective tissues.
• Tunica media: The middle layer is the tunica media composed primarily of smooth muscles. It is thick, having more muscle fibers.
• Tunica interna: The inner layer is the tunica interna. It consists of two parts- the elastic membrane and endothelium. Tunica interna of arteries has a strong elastic membrane and more elongated endothelial cells.

Arteries distribute blood from the heart to the different parts of the body. They are not collapsible because they have thick muscular walls. Arteries have no valves. The flow of the blood is as fast as the blood in them is under great pressure.

Veins' tunica media is thin and has few muscle fibers. They are collapsible because they have thin walls. Capillaries are the narrowest blood vessels, through which the exchange of gases and nutrients between the blood and the tissue fluid occurs. The walls are composed of single simple squamous epithelium.
Venules are the small branch of veins.

Hence, the correct answer is option (A).

Note: Arteries have no valves. Except the pulmonary arteries, all the arteries carry oxygenated blood. Due to the difference in the thickness of the middle layer- tunica media, arteries are the thickest blood vessels.