The cardiovascular system and blood
The cardiovascular system, also called the circulatory system, transports blood throughout the body. Its central pump is the heart, a muscular organ divided into four chambers: two upper atria that receive blood and two lower ventricles that pump it out. One-way valves between the chambers and at the exits keep blood flowing in a single direction. With each heartbeat the heart drives blood through a network of vessels, and animations are well suited to showing this continuous, rhythmic flow that is hard to convey with a still picture.
Blood travels in a double circuit. The pulmonary circulation carries oxygen-poor blood from the right side of the heart to the lungs, where it releases carbon dioxide and takes up oxygen, then returns to the left side. The systemic circulation then pumps this oxygen-rich blood from the left side out to the rest of the body and back again. Arteries carry blood away from the heart under high pressure, veins return it, and tiny capillaries connect the two and allow the exchange of oxygen, nutrients and waste with the surrounding tissues.
Blood itself is a tissue made of liquid plasma carrying red blood cells, which contain haemoglobin and transport oxygen; white blood cells, which defend against infection; and platelets, which help blood to clot. Together the heart, vessels and blood deliver oxygen and nutrients to every cell, remove waste, distribute heat and hormones, and carry the immune defences that protect the body.
Frequently asked questions
- What are the four chambers of the heart?
- Two atria, which receive incoming blood, and two ventricles, which pump blood out. The right side serves the lungs and the left side serves the rest of the body.
- What is the difference between arteries and veins?
- Arteries carry blood away from the heart, usually under high pressure, while veins return blood to the heart. Capillaries link them and allow exchange with tissues.
- What does blood carry?
- Blood transports oxygen and nutrients to cells, removes carbon dioxide and waste, and carries immune cells, hormones and heat around the body.
