Lesson Topics

1 | Overview of the Circulatory System

2 | Double Circulation

3 | The Movement of Oxygen and Carbon Dioxide Around the Body

4 | The Heart

5 | Blood Vessels

6 | Blood

7 | Circulatory Systems in Other Animals

8 | Summary

Lesson Summary

• The circulatory system (cardiovascular system) transports substances around the body including food molecules, oxygen, carbon dioxide and other waste materials.

• The circulatory system consists of blood vessels, blood and the heart.

• Blood vessels form a transportation network throughout the body.

• Blood carries substances through blood vessels.

• The heart drives the movement of blood through blood vessels.

• Humans and other animals with lungs have a double circulatory system, consisting of a pulmonary circuit and a systemic circuit.

• The pulmonary circuit moves deoxygenated blood from the heart to the lungs and oxygenated blood from the lungs to the heart.

• Oxygen diffuses from the lungs into the bloodstream and carbon dioxide diffuses from the bloodstream into the lungs.

• The systemic circuit moves oxygenated blood from the heart to the body and deoxygenated blood from the body to the heart.

• Oxygen diffuses from the bloodstream into cells and carbon dioxide diffuses from cells into the bloodstream.

• The human heart consists of two sides, each divided into two chambers.

• The left side of the heart drives systemic circulation.

• The right side of the heart drives pulmonary circulation.

• The atria are the upper chambers of the heart, where blood enters.

• The left atrium receives blood from the lungs.

• The right atrium receives blood from the body.

• The ventricles are the lower chambers of the heart, where blood exits.

• The left ventricle pumps blood to the body.

• The right ventricle pumps blood to the lungs.

• Movement of blood between the atria and ventricles, and out of each ventricle, occurs via one-way valves.

• There are three types of blood vessels – arteries, veins and capillaries.

• Arteries carry blood away from the heart.

• The main arteries leading from the heart are the pulmonary arteries, which carry blood to the lungs, and the aorta, which carries blood to the rest of the body.

• Veins carry blood towards the heart.

• The main veins leading to the heart are the pulmonary veins, which carry blood from the lungs, and the vena cavae, which carry blood from the rest of the body.

• Capillaries connect arteries and veins.

• Blood consists of plasma, red blood cells, white blood cells and platelets.

• Plasma is the liquid component of blood, carrying suspended cells and platelets and containing dissolved substances.

• Red blood cells transport oxygen bound to haemoglobin molecules.

• White blood cells form part of the body’s immune system.

• Platelets are fragments of cells involved in blood clotting when blood vessels are damaged.

• All vertebrates and some invertebrates have a closed circulatory system, where blood is contained within blood vessels, keeping it separate from other bodily fluids.

• Most invertebrates have an open circulatory system, where haemolymph moves through the body cavity, where it mixes with other bodily fluids.

• Mammals and birds have a four-chambered heart consisting of two atria and two ventricles.

• Amphibians and reptiles have a three-chambered heart consisting of two atria and one ventricle.

• Fish have a two-chambered heart, consisting of one atrium and one ventricle. They have a single circulatory system.

Fish have a two-chambered heart and a single circulatory system.
Amphibians and reptiles have a three-chambered heart and a double circulatory system.
Mammals and birds have a four-chambered heart and a double circulatory system.

(Image: paveu, Adobe Stock)

(Header image: abhijith3747, Adobe Stock)