Identify and describe What is the Circulatory System?, The Double Circulatory System and The Four Chambers of the Heart in the context of the heart and blood vessels.
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GCSE Biology Revision
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GCSE Biology revision
The heart and blood vessels
Animal tissues, organs and organ systems
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Explain the relationships between What is the Circulatory System?, The Double Circulatory System and The Four Chambers of the Heart and how they contribute to the heart and blood vessels.
Apply and analyse knowledge of What is the Circulatory System?, The Double Circulatory System and The Four Chambers of the Heart to interpret unfamiliar information about the heart and blood vessels.
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What is the Circulatory System?
- The circulatory system, also called the cardiovascular system, is an organ system made up of the heart, blood vessels, and blood
- Its main function is to transport substances such as oxygen, nutrients, cells, and waste products around the body
- The heart pumps blood, blood vessels direct it, and blood acts as the fluid carrying all the essential substances
The Double Circulatory System
- Mammals like humans have a double circulatory system because it contains two separate circuits
- The pulmonary circuit carries blood from the heart to the lungs and back to the heart, where it becomes oxygenated
- The systemic circuit carries blood from the heart to all body tissues, such as muscles, brain, and liver, and then back to the heart
- Having two circuits means oxygenated and deoxygenated blood are kept separate, making the system more efficient
The Four Chambers of the Heart
- The heart is a muscular organ containing four chambers: two atria (upper chambers) and two ventricles (lower chambers)
- The right atrium and right ventricle are on the right side of the heart, and the left atrium and left ventricle are on the left side
- When viewing a diagram of the heart, left and right refer to the owner's left and right, so they appear reversed to the viewer
- The left ventricle has a thicker muscular wall than the right ventricle because it must pump blood all the way around the body, not just to the nearby lungs
The Valves of the Heart
- Between each atrium and ventricle on both sides are the atrioventricular valves
- These valves ensure blood flows in only one direction — from the atria down into the ventricles — preventing backflow
Blood Vessels Entering and Leaving the Heart
- The vena cava is the body's largest vein and carries deoxygenated blood from the body into the right atrium
- The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs to become oxygenated
- The pulmonary vein carries oxygenated blood from the lungs back to the left atrium
- The aorta is the body's largest artery and carries oxygenated blood from the left ventricle out to all body tissues
The Journey of Blood Through the Heart
- Deoxygenated blood enters the right atrium via the vena cava, which contracts to push blood into the right ventricle
- The right ventricle contracts and pumps blood through the pulmonary artery to the lungs, where it picks up oxygen
- Oxygenated blood returns via the pulmonary vein to the left atrium, which contracts to fill the left ventricle
- The left ventricle contracts and pumps oxygenated blood into the aorta, sending it around the body before it returns to restart the cycle
Coronary Arteries
- The heart muscle itself requires a constant supply of oxygenated blood, which it receives from the coronary arteries
- Coronary arteries are small arteries that branch off the aorta and encircle the heart, supplying oxygen and nutrients to the cardiac muscle
- If the coronary arteries become blocked, it can lead to coronary artery disease or a heart attack
Key Terminology Summary
- Arteries carry blood away from the heart, while veins carry blood back towards the heart
- Oxygenated blood travels in the pulmonary vein and aorta, while deoxygenated blood travels in the vena cava and pulmonary artery — note that the pulmonary vessels are exceptions to the usual artery/vein oxygen rule
- The terms atria (singular: atrium) and ventricles refer to the upper and lower chambers of the heart respectively