3.5.3 The Walls of the Heart

Structure and Function of the Heart Walls:

1. Atrium Walls:

• Thin and elastic to allow stretching as blood flows in from veins.
• Right Atrium:
• Receives deoxygenated blood from the vena cava.
• Left Atrium:
• Receives oxygenated blood from the pulmonary vein.

2. Ventricle Walls:

• Thicker and more muscular than atria to generate the force needed to pump blood out of the heart.
• Right Ventricle:
• Pumps deoxygenated blood to the lungs via the pulmonary artery.
• Wall is thinner than the left ventricle as it pumps blood over a shorter distance (to the lungs).
• Left Ventricle:
• Pumps oxygenated blood to the body via the aorta.
• Wall is very thick to generate the high pressure required to pump blood around the body.

Adaptations of the Heart Walls:

3. Left Ventricle Wall:

• Thickest wall in the heart.
• Contains large amounts of cardiac muscle to create the high pressure needed for systemic circulation.

4. Right Ventricle Wall:

• Thinner than the left ventricle.
• Generates lower pressure to pump blood to the lungs, preventing damage to the delicate capillaries in the lungs.

5. Cardiac Muscle:

• Found in all heart walls.
• Myogenic: Generates its own electrical impulses to coordinate contractions without external stimulation.
• Rich in mitochondria, providing the energy needed for continuous contractions.

Summary of Wall Thickness:

Chamber	Wall Thickness	Reason
Left Atrium	Thin	Receives blood from the pulmonary vein.
Right Atrium	Thin	Receives blood from the vena cava.
Left Ventricle	Very Thick	Pumps oxygenated blood under high pressure to the body.
Right Ventricle	Thicker than atria but thinner than left ventricle	Pumps blood at low pressure to the lungs.

Role of the Septum:

• The septum separates the left and right sides of the heart.
• Prevents the mixing of oxygenated and deoxygenated blood, ensuring efficient gas exchange.

Key Terms:

• Cardiac Muscle: Specialised muscle that contracts to pump blood.
• Myogenic: Ability to contract without external stimulation.
• Septum: Muscular wall separating the left and right sides of the heart.