Which blood vessels have the smallest diameter?

Correct option is A

The correct answer is (a) Capillaries

Explanation:
• Capillaries are the smallest and thinnest blood vessels in the body.
• Their walls are only one cell thick, which allows for the efficient exchange of oxygen, carbon dioxide, nutrients, and waste between blood and tissues.
• The average diameter of a capillary is about 5 to 10 micrometers, which is just enough for a single red blood cell to pass through.
• They connect arterioles (small arteries) to venules (small veins).
• The total network of capillaries is called a capillary bed.

Information Booster:
• Blood flows most slowly through capillaries to provide maximum time for diffusion/exchange.
• Arterioles are known as 'resistance vessels' because they regulate blood flow into capillaries.

Additional Knowledge:
Arterioles (Option b)
• Smallest branches of arteries; they are larger than capillaries and have muscular walls.

Venules (Option c)
• Small vessels that drain blood from capillaries and join to form veins.

Lymphatic (Option d)
• These vessels carry lymph, not blood, and are generally larger in diameter than capillaries.

So the correct answer is (a)