In human circulatory system, X are blood vessels which carry deoxygenated blood and have Y walls. Z carries blood from lungs to heart. X, Y, Z are:?

Option 2 : veins, thin, pulmonary vein

The correct answer is veins, thin, pulmonary vein.

Concept:

• Blood is the fluid that flows in blood vessels.
• It transports substances like digested food from the small intestine to the other parts of the body. 
• It carries oxygen from the lungs to the cells of the body. It also transports waste for removal from the body.

Explanation:

• Two types of blood vessels, arteries, and veins are present in the human body.
• Veins are blood vessels that carry deoxygenated blood from various parts of the body to the heart.
• Veins are thin and elastic, and they are found closer to the skin's surface.
• Pulmonary vein are the vessels that carry carbon dioxide-rich blood from all parts of the body back to the heart.
• There are valves present in pulmonary veins that allow blood to flow only towards the heart.

Hence, In human circulatory system, arteries are blood vessels which carry deoxygenated blood and have thick walls. Pulmonary vein carries blood from lungs to heart.

Arteries are blood vessels that carry oxygenated blood from the heart to different parts of the body. They are thick, elastic and are divided into a network of small blood vessels known as capillaries.