Yes capillary has no muscular wall because it is smallest blood vessels and made up of single layer wall not that of muscular type...

The Answer:
The correct answer is option 'A' - Capillary. Capillaries are the only blood vessels that lack muscular walls.

Explanation:
Blood vessels are tubular structures that carry blood throughout the body. They are classified into three main types: arteries, veins, and capillaries. Each type of blood vessel has distinct characteristics and functions.

1. Capillaries:
- Capillaries are the smallest blood vessels in the body and connect arterioles to venules.
- They have a diameter of about 5-10 micrometers, which is similar to the size of a single red blood cell.
- Capillaries are the site of exchange of nutrients, gases, and waste products between the blood and surrounding tissues.
- Unlike arteries and veins, capillaries lack muscular walls. Instead, their walls are composed of a single layer of endothelial cells, which are thin, flat cells that allow for efficient exchange of substances.
- The absence of muscular walls in capillaries allows them to be highly permeable and facilitates the exchange of oxygen, carbon dioxide, nutrients, and waste products between the blood and surrounding tissues.

2. Arteries:
- Arteries are blood vessels that carry oxygenated blood away from the heart and towards the tissues.
- Arteries have thicker, more elastic walls compared to other blood vessels.
- The walls of arteries consist of three layers: the outermost tunica adventitia, the middle tunica media (which contains smooth muscle), and the innermost tunica intima.
- The smooth muscle in the tunica media allows arteries to contract and relax, regulating blood flow and maintaining blood pressure.
- Arteries have a pulsatile flow of blood due to the rhythmic contraction of the heart.

3. Veins:
- Veins are blood vessels that carry deoxygenated blood back to the heart from the tissues.
- Veins have thinner walls compared to arteries and contain valves to prevent backflow of blood.
- The walls of veins also contain smooth muscle, but it is less developed than in arteries.
- Veins have a lower blood pressure compared to arteries and rely on skeletal muscle contractions and one-way valves to move blood towards the heart.

Conclusion:
In summary, capillaries are the only blood vessels that lack muscular walls. Capillaries have thin walls consisting of a single layer of endothelial cells, allowing for efficient exchange of substances between the blood and surrounding tissues. Arteries and veins, on the other hand, have thicker walls containing smooth muscle that helps regulate blood flow and maintain blood pressure.