Question

Mammals are said to have double circulation. It means

• A. Blood vessels are paired
• B. There are two types of blood vessels attached to every organ
• C. There are two systems. One from the heart to the lungs and back to the rest of the body
• D. The blood circulates twice through the heart

Answer 1

The correct option is D The blood circulates twice through the heart

• Humans have double circulation. The blood pumped by the right ventricle enters the pulmonary artery, whereas the left ventricle pumps blood into the aorta.
• The deoxygenated blood pumped into the pulmonary artery is passed onto the lungs from where the oxygenated blood is carried by the pulmonary veins into the left atrium.
• This pathway constitutes the pulmonary circulation.

The oxygenated blood entering the aorta is carried by a network of arteries, arterioles and capillaries to the tissues from where the de-oxygenated blood is collected by a system of venules, veins and vena cava and emptied into the right atrium.

This is the systemic circulation.

So, the correct answer is option D.