84. Functional Organization of Cardiovascular System – Quiz

📌 Professor’s Notes: Quick Revision

High-yield revision notes for rapid review before university examinations.

• The cardiovascular system (CVS) maintains homeostasis by transporting oxygen, nutrients, hormones, and metabolic wastes. It also regulates body temperature, tissue perfusion, and fluid balance. The heart functions as the central pump, generating the pressure required for blood circulation. Resting cardiac output is about 5 L/min and increases during exercise and stress.
• The heart functions as a dual pump.
  • The right heart pumps deoxygenated blood to the lungs through the pulmonary circulation.
  • The left heart pumps oxygenated blood to the body through the systemic circulation.
  • The left ventricle has a thicker wall because it pumps against much higher resistance than the right ventricle.
• Blood vessels consist of three layers:
  • Tunica intima: Endothelium that regulates vascular permeability, coagulation, and vascular tone.
  • Tunica media: Smooth muscle and elastic tissue responsible for vasoconstriction and vasodilation.
  • Tunica externa: Connective tissue providing strength and support.
    The proportions of these layers vary according to the function of each vessel.
• Based on function, blood vessels are classified as:
  • Elastic (Windkessel) vessels: Aorta and large arteries. Their elastic recoil maintains continuous blood flow during diastole and reduces fluctuations in arterial pressure (Windkessel effect).
  • Resistance vessels: Small arteries and arterioles. They produce the greatest peripheral resistance and are the main regulators of blood pressure.
  • Exchange vessels: Capillaries, where gases, nutrients, and waste products are exchanged because of their thin endothelial wall.
  • Capacitance vessels: Veins and venules, which contain 60–70% of total blood volume and serve as the body’s major blood reservoir.
• Arteries have thick muscular walls and receive sympathetic innervation that regulates vascular tone. Arterioles are the principal resistance vessels. Metarterioles and precapillary sphincters regulate blood flow into capillary beds. Veins have thin walls, large lumens, venous valves, and high compliance. Venous return is assisted by the skeletal muscle pump and respiratory movements.
• Systemic circulation is a high-pressure, high-resistance circuit that supplies body tissues and contains about 80–85% of total blood volume. Pulmonary circulation is a low-pressure, low-resistance circuit that carries blood to the lungs for gas exchange and contains about 10–12% of total blood volume. Under normal conditions, the outputs of both ventricles are equal.
• Central blood volume includes blood within the heart, pulmonary circulation, thoracic aorta, superior vena cava, and intrathoracic inferior vena cava. It constitutes about 20–25% of total blood volume and is an important determinant of venous return, central venous pressure, stroke volume, and cardiac output. Peripheral blood volume (75–80%) is mainly present in the veins of the limbs and abdomen. During hemorrhage, venoconstriction shifts blood from peripheral to central circulation to maintain cardiac output.