Definition and Causes of hypoxia or anoxia
What is hypoxia?
Hypoxia is a relative deficiency of oxygen recognizable as a disproportion between the need for oxygen and its availability. It may result from a reduced supply or increased demand that cannot be satisfied. Complete block in the oxygen supply is called anoxia.
What could cause hypoxia or anoxia?
- Hypoxia and anoxia can result from the following:
- Inadequate supply of oxygen (e.g., low concentration of oxygen in air at high altitude)
- Obstruction of airways (e.g., strangulation and drowning)
- Inadequate oxygenation of blood in the lungs (e.g., lung diseases)
- Inadequate oxygen transport in blood (e.g., anemia)
- Inadequate perfusion of blood in the tissues (ischemia resulting from heart failure)
- Inhibition of cellular respiration—that is, blocked utilization of oxygen (e.g., cyanide poisoning of respiratory enzymes)
How does hypoxia cause cell injury?
Oxygen is essential for aerobic respiration. Hypoxia prevents normal oxidative phosphorylation, thus reducing the capacity of mitochondria to generate adenosine triphosphate (ATP). Without ATP, the cell cannot maintain its vital functions. Hypoxic cells swell. This change is called hydropic or vacuolar change and is typically reversible.