Biology – 8.2 Transport in humans | e-Consult

The heart wall is composed of three layers: the epicardium (also known as the visceral pericardium), the myocardium, and the endocardium.

The myocardium is the thickest layer and is responsible for the heart's pumping action. It is made up of cardiac muscle cells, which are specialized for rhythmic contraction. The atrial wall is thinner than the ventricular wall because the atria only need to pump blood to the ventricles. The ventricular wall, particularly the left ventricle, is significantly thicker than the atrial wall. This is because the left ventricle must pump blood to the entire body, requiring greater force. The ventricular wall is composed of more cardiac muscle cells and is therefore thicker and stronger.

The endocardium is a thin layer of endothelium that lines the heart chambers and covers the heart valves. It helps to reduce friction during blood flow. The epicardium is the outer layer of the heart wall and contains blood vessels and nerves that supply the heart.

Adaptations of the heart wall to its function:

• Thick muscular wall (myocardium) in ventricles: Provides the force needed to pump blood to the entire body.
• Thinner wall in atria: Reflects the lower pressure required to pump blood into the ventricles.
• Strong, interconnected cardiac muscle cells: Allows for coordinated and powerful contractions.
• Elasticity of the heart wall: Allows the heart to expand and fill with blood during diastole.