Hypoxia - classification, etiology, adaptive -compensatory mechanisms, pathogenesis, clinical manifestations.
Hypoxia is a condition in which there is insufficient oxygen supply to tissues, impairing cellular metabolism.
Etiology
Hypoxic hypoxia
- High altitude (low atmospheric O₂).
- Respiratory disorders (COPD, severe pneumonia).
- Hypoventilation (CNS depression).
Anemic hypoxia
- Anemia (iron deficiency, hemolysis).
- Carbon monoxide poisoning (Hb blocked by CO).
- Methemoglobinemia.
Circulatory (ischemic) hypoxia
- Heart failure.
- Shock.
- Local arterial occlusion (e.g., thrombosis).
Histotoxic hypoxia
- Cyanide poisoning (inhibits cytochrome oxidase).
- Severe sepsis affecting mitochondria.
Pathogenesis
- Reduced oxygen delivery or utilization → ↓ oxidative phosphorylation in mitochondria.
- ATP depletion → failure of Na /K ATPase → cellular swelling, ion imbalance.
- Switch to anaerobic glycolysis → lactate accumulation → metabolic acidosis.
- Cellular and eventually organ dysfunction or death.
Adaptive- compensatory mechanisms
Immediate (acute) responses
- Hyperventilation → increases alveolar and arterial pO ₂.
- Tachycardia, increased cardiac output → improve tissue perfusion.
Medium- term (hours to days)
- Increased 2,3-BPG in red cells → right shift of O₂ dissociation curve → enhanced O₂ unloading to tissues.
- Splenic contraction → release of stored RBCs.
Long- term (days to weeks)
- Increased erythropoietin production → polycythemia → increased oxygen-carrying capacity.
- Angiogenesis → improved microcirculation.