Circulatory System Questions & MCQ — Practice with Answers

What the circulatory system does

The circulatory system is the body's transport system. Its main job is to carry nutrients, oxygen, and waste products to and from all parts of the body. Oxygen and digested food are delivered to every cell, while waste products like carbon dioxide are carried away to be removed.

The heart

The heart is a muscular organ about the size of your fist. It pumps blood continuously throughout the body. The heart has four chambers: two upper chambers (called atria) that receive blood, and two lower chambers (called ventricles) that pump blood out. The heart never stops working — it beats about 100,000 times a day to keep blood flowing.

Blood vessels

Blood travels through the body in tubes called blood vessels. There are three types:

• Arteries carry blood away from the heart to all parts of the body. They have thick, muscular walls to withstand the high pressure of blood being pumped from the heart.
• Veins carry blood back to the heart from all parts of the body. They have thinner walls and contain valves to prevent blood from flowing backwards.
• Capillaries are tiny blood vessels that connect arteries and veins. They have very thin walls, allowing exchange of substances (such as oxygen, nutrients, and waste) between the blood and body cells.

Blood

Blood is the fluid that flows through the circulatory system. It carries oxygen from the lungs and nutrients from the digestive system to all body cells. At the same time, blood picks up waste products such as carbon dioxide from the cells and carries them to the lungs (for carbon dioxide) or kidneys (for other waste) to be removed from the body.

How the circulatory system works with other systems

The circulatory system does not work alone. It depends on other body systems:

• Respiratory system: The blood picks up oxygen in the lungs and releases carbon dioxide to be breathed out. Without the respiratory system, the blood would have no oxygen to deliver.
• Digestive system: Digested nutrients are absorbed into the blood through the walls of the small intestine. The blood then carries these nutrients to all body cells. Without the digestive system, the blood would have no nutrients to transport.

“Veins carry only blue blood.” Blood is never actually blue. In diagrams, veins are drawn in blue to show they carry oxygen-poor blood, but the blood itself is dark red, not blue. The blue colour is just a convention used in science diagrams to make it easy to tell arteries and veins apart.

“The heart is on the left side of the body.” The heart is actually located near the centre of the chest, slightly tilted to the left. People often think it is entirely on the left side because they can feel the heartbeat more strongly on the left, but most of the heart sits in the middle of the chest between the two lungs.

“Arteries always carry oxygen-rich blood.” Most arteries carry oxygen-rich blood, but there is one important exception: the pulmonary artery carries oxygen-poor blood from the heart to the lungs. What defines an artery is that it carries blood away from the heart, not whether that blood is oxygen-rich or oxygen-poor.

“The heart only pumps blood to the muscles.” The heart pumps blood to every part of the body — including the brain, skin, organs, and even the heart itself. Every cell in the body needs a constant supply of oxygen and nutrients, so blood must reach all parts, not just the muscles.