Ventricular wall thickness indicates pressure differences for pulmonary and systemic circulation

Steps:

• Blood to lungs exits right ventricle at lower pressure; to body, left ventricle at higher pressure.
• Heart walls' muscularity correlates with force needed to pump blood.
• Option D compares wall T (likely left ventricle) and U (right ventricle).
• Greater muscularity in T suggests higher pressure to body versus lungs.

Why D is correct:

• Cardiac muscle thickness determines ejection pressure per Laplace's law: wall stress = (pressure × radius) / (2 × thickness), so thicker walls handle/generate higher systemic pressure.

Why the others are wrong:

• A: Atrial walls are thin for filling, not ejection pressure to lungs/body.
• B: Atria fill ventricles; thinner walls irrelevant to outflow pressures.
• C: Valve strength prevents backflow, not indicative of forward pressure differences.

Final answer: D