Edexcel iGCSE Biology-3.15 Structure & Function of the Heart- Study Notes- New Syllabus

Structure & Function of the Heart

📝 Introduction

• The heart is a muscular organ that pumps blood around the body.
• Works as a double circulatory system → blood passes through the heart twice in one complete circuit.
• Right side → pumps blood to the lungs (pulmonary circulation).
• Left side → pumps blood to the rest of the body (systemic circulation).

📍 Location

• The heart is located in the thorax (chest cavity).
• It lies between the lungs and is slightly towards the left side of the body.
• It is protected by the rib cage.

🫀 Chambers of the Heart

• The heart has four chambers.
• The upper chambers are called atria (singular: atrium).
• The lower chambers are called ventricles.

🔵 Right Atrium

Structure

• Thin-walled upper chamber on the right side of the heart.

Function

• Receives deoxygenated blood returning from the body.
• Blood enters through the vena cava.
• Passes blood into the right ventricle.

🔵 Right Ventricle

Structure

• Lower chamber on the right side.
• Wall is thicker than the atrium but thinner than the left ventricle.

Function

• Pumps deoxygenated blood to the lungs through the pulmonary artery.
• Blood travels to the lungs to collect oxygen and release carbon dioxide.

🔴 Left Atrium

Structure

• Thin-walled upper chamber on the left side.

Function

• Receives oxygenated blood from the lungs.
• Blood enters through the pulmonary vein.
• Passes blood into the left ventricle.

🔴 Left Ventricle

Structure

• Lower chamber on the left side.
• Has the thickest muscular wall of all four chambers.

Function

• Pumps oxygenated blood to all parts of the body through the aorta.

Why is the Wall Thicker?

• Blood must travel to every part of the body.
• A higher pressure is needed to push blood over a much greater distance.
• The thicker muscle produces a more powerful contraction.

🧱 Septum

Structure

• The septum is a thick muscular wall running down the centre of the heart.

Function

• Separates the right and left sides of the heart.
• Prevents oxygenated blood from mixing with deoxygenated blood.
• Ensures body tissues receive fully oxygenated blood.

🚪 Heart Valves

Function of Valves

• Valves ensure that blood flows in one direction only.
• They prevent blood from flowing backwards when the heart contracts.

There are two main types of valves.

Atrioventricular (AV) Valves

Location

• Between each atrium and ventricle.

Function

• Open to allow blood to flow from the atria into the ventricles.
• Close when the ventricles contract.
• Prevent blood from flowing back into the atria.

Semilunar Valves

Location

• At the openings of the aorta and pulmonary artery.

Function

• Open when the ventricles pump blood into the arteries.
• Close after contraction.
• Prevent blood from flowing back into the ventricles.

🩸 Major Blood Vessels Connected to the Heart

Vena Cava

• Carries deoxygenated blood from the body to the right atrium.

Pulmonary Artery

• Carries deoxygenated blood from the right ventricle to the lungs.

Pulmonary Vein

• Carries oxygenated blood from the lungs to the left atrium.

Aorta

• Carries oxygenated blood from the left ventricle to the rest of the body.

❤️ Coronary Arteries

Function

• The heart muscle needs a constant supply of oxygen and nutrients because it works continuously.
• Coronary arteries supply oxygenated blood directly to the heart muscle.
• This enables the heart muscle to carry out aerobic respiration and contract continuously.

⚙️ How the Heart Functions

The heart works through a repeating sequence of contraction and relaxation called the cardiac cycle.

Step 1: Atrial Systole

• Both atria contract.
• Blood is pushed into the ventricles through the atrioventricular valves.
• The ventricles fill with blood.

Step 2: Ventricular Systole

• Both ventricles contract.
• The atrioventricular valves close to prevent backflow.
• Blood is pumped:
  • From the right ventricle into the pulmonary artery.
  • From the left ventricle into the aorta.
• The semilunar valves open to allow blood to leave the heart.

Step 3: Diastole

• The atria and ventricles relax.
• The semilunar valves close to stop blood flowing back into the ventricles.
• Fresh blood enters the atria from the veins.
• The next heartbeat begins.

Blood Flow Through the Heart

🌟 Importance of the Heart

The heart is essential because it:

• Pumps blood continuously around the body.
• Delivers oxygen and nutrients to cells.
• Removes carbon dioxide and other waste products.
• Maintains blood circulation.
• Supplies the heart muscle itself through the coronary arteries.

📊 Summary Table

⚡ Quick Recap
Heart = double pump → right side (lungs), left side (body).
Left ventricle thicker → needs more force.
Valves stop backflow → ensure one-way flow.
Cardiac cycle = atrial systole → ventricular systole → diastole.
Coronary arteries keep heart alive.