explain the differences in the thickness of the walls of the: atria and ventricles, left ventricle and right ventricle

Published by Patrick Mutisya · 14 days ago

Cambridge A‑Level Biology 9700 – The Heart: Wall Thickness

The Heart

Objective

Explain the differences in the thickness of the walls of the:

  • atria and ventricles

  • left ventricle and right ventricle

Why Wall Thickness \cdot aries

The thickness of a cardiac chamber wall is determined by the pressure that the chamber must generate to overcome the resistance of the downstream circulation. Greater pressure requirements lead to a thicker muscular wall.

Atria vs. Ventricles

• The atria receive blood from the veins and act mainly as passive reservoirs. Their contraction only needs to push blood into the ventricles, which are already at a relatively low pressure.

• The ventricles pump blood into the high‑resistance arterial systems (pulmonary artery and aorta). To generate the required pressures, the ventricular walls contain a much larger amount of cardiac muscle.

Left \cdot entricle vs. Right \cdot entricle

• The left ventricle pumps oxygen‑rich blood into the systemic circulation via the aorta. Systemic vascular resistance is high, so the left ventricle must develop a systolic pressure of about 120 mm Hg.

• The right ventricle pumps deoxygenated blood into the pulmonary circulation via the pulmonary artery. Pulmonary vascular resistance is much lower, and the right ventricle only needs to generate a systolic pressure of about 25 mm Hg.

Consequently, the left ventricular wall is considerably thicker than that of the right ventricle.

Comparative Summary

ChamberTypical Wall Thickness (mm)Primary FunctionPressure Generated (mm Hg)
Right Atrium2–3Collects systemic venous blood≈ 5 (venous pressure)
Left Atrium2–3Collects pulmonary venous blood≈ 5–8 (pulmonary venous pressure)
Right \cdot entricle4–5Propels blood to lungs≈ 25 (pulmonary arterial pressure)
Left \cdot entricle10–12Propels blood to systemic body≈ 120 (systemic arterial pressure)

Suggested diagram: Cross‑sectional view of the heart showing relative wall thickness of the atria, right ventricle and left ventricle.

Key Points to Remember

  1. Wall thickness correlates with the pressure a chamber must generate.

  2. Atria have thin walls because they operate at low pressure.

  3. The left ventricle has the thickest wall to overcome high systemic resistance.

  4. The right ventricle is thinner than the left because pulmonary resistance is lower.