The Circulatory System: Structure and Function in Transporting Oxygen, Nutrients, and Waste

The circulatory (cardiovascular) system is a closed network transporting blood throughout the body.

Components

• Heart: Four-chambered pump (right/left atria, right/left ventricles). Right side: pulmonary circuit. Left side: systemic circuit.
• Blood Vessels:
  • Arteries: High-pressure, thick-walled, carry blood away from heart.
  • Capillaries: Microscopic, single-cell walls, exchange site.
  • Veins: Low-pressure, thin-walled, valves, return blood to heart.
• Blood: Plasma (55%) + formed elements (RBCs, WBCs, platelets).

Key Functions

• O₂/CO₂ transport (RBCs/hemoglobin)
• Nutrient delivery (glucose, amino acids, fatty acids)
• Waste removal (CO₂, urea, creatinine → lungs/kidneys)
• Hormone distribution
• Thermoregulation (vasodilation/constriction)
• Immune surveillance (WBCs, antibodies)
• Hemostasis (platelets, coagulation factors)

Homeostasis

Continuous flow maintains stable internal environment. Baroreceptors, chemoreceptors, and hormonal signals (RAAS, ADH, ANP) regulate pressure and volume.