Circulation of blood
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Learning Objectives
- 1Describe how blood circulates through the heart and body
- 2Identify the four chambers of the heart and their roles
- 3Distinguish between pulmonary and systemic circulation
- 4Name the main blood vessels and explain what they carry
Mini Lesson
Your heart is a powerful muscle that pumps blood around your body all day, every day. Blood carries oxygen and nutrients to every cell and brings waste gases back to be removed. This non-stop journey is called blood circulation, and it follows two connected loops.
The Heart
The heart is divided into four chambers. The two upper chambers are called atria (singular: atrium) and the two lower chambers are called ventricles. A thick wall called the septum separates the left side from the right side.
- Right atrium — receives oxygen-poor blood returning from the body.
- Right ventricle — pumps oxygen-poor blood to the lungs.
- Left atrium — receives oxygen-rich blood returning from the lungs.
- Left ventricle — pumps oxygen-rich blood out to the whole body.
Two Circulation Loops
Blood travels in two main loops: pulmonary circulation (heart to lungs and back) and systemic circulation (heart to body and back).
- Heart pumps oxygen-poor blood to lungs (pulmonary circulation begins).
- Lungs add oxygen to the blood and remove carbon dioxide.
- Oxygen-rich blood returns to the left side of the heart.
- Heart pumps oxygen-rich blood out to the whole body (systemic circulation begins).
- Body cells use the oxygen and release carbon dioxide.
- Oxygen-poor blood returns to the right side of the heart.
Blood Vessels
Blood travels through a network of tubes called blood vessels. The three main types are arteries, veins, and capillaries.
- Arteries — carry blood away from the heart; walls are thick and muscular.
- Veins — carry blood back to the heart; have valves to prevent backflow.
- Capillaries — tiny vessels connecting arteries to veins; where oxygen and nutrients pass into cells.
Tip: remember the order with HLHB — Heart to Lungs, Lungs to Heart, Heart to Body, Body back to Heart.
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