Circulatory System Functions: Blood Pressure, Oxygen Delivery, Waste Removal, and Temperature Control

The Circulatory System: Homeostasis Engine

Heart, blood vessels, and blood form a closed loop maintaining internal equilibrium.

1. Blood Pressure Regulation

Baroreflex (carotid sinus/aortic arch) adjusts heart rate, contractility, vascular tone. Renin-angiotensin-aldosterone system (RAAS) controls volume. Together they ensure perfusion pressure.

2. Oxygen & Nutrient Delivery

O₂ from lungs → arterial blood → capillaries → tissues. Nutrients (glucose, amino acids, fatty acids) from gut → liver → systemic circulation. Hormones also distributed.

3. Waste Removal

• CO₂ → lungs → exhalation.
• Metabolic wastes (urea, creatinine) → kidneys → urine.
• Liver clears toxins, bilirubin.

4. Immune Defense

Leukocytes (neutrophils, lymphocytes, monocytes) patrol vessels, extravasate at infection sites. Complement and antibodies circulate. Lymphatic system returns interstitial fluid and immune cells.

5. Thermoregulation

• Heat stress → cutaneous vasodilation + sweating → heat loss.
• Cold stress → vasoconstriction + shivering → heat conservation.

6. Acid-Base Balance

CO₂/HCO₃⁻ buffer system. Lungs adjust pCO₂ (minutes); kidneys adjust HCO₃⁻ (hours/days). Maintains pH 7.35–7.45.

7. Hormone Distribution

Endocrine glands → bloodstream → target cells. Rapid, systemic signaling.

Disturbances (shock, heart failure, anemia, sepsis) disrupt homeostasis → multi-organ dysfunction.