The types of Hypoxia...

1. Anoxic hypoxia or Diffusion hypoxia
Anoxic hypoxia also called as diffusion hypoxia is essentially due to the deficency of oxygen being absorbed by the lungs. This is either due to a decrease in the inspired concentration of oxygen in the air which can result in suffocation.
Another reason is due to a defect in the absorption of oxygen by the lungs due to some pathology or defect at the alveolo cappilary membrane of the lungs, where the real gas exchange takes place.

2. Anaemic hypoxia
Another among the 4 Types of Hypoxia is the Anemic hypoxia. This is due to decreases oxygen binding capacity of the lungs, most commonly due to a decrease in the hemoglobin concentration. Hemoglobin is the main carrier of oxygen in the circulation throughout the body. Hence, if hemoglobin is less, the supply of oxygen to the tissues is decreased.

3. Stagnant hypoxia
The next among the 4 Types of Hypoxia is stagnant hypoxia. This is due to decrease in the flow of blood, that carries the oxygen. For example as in Cardiac arrest or in circulatory shock, the decreased supply of oxygen due to cessation or slowing down of blood circulation causes hypoxia to the body tissues.

4. Histotoxic hypoxia
The last among the 4 Types of Hypoxia is the histotoxic hypoxia. this occurs due to defect in the extraction of oxygen from the circulation by the body tissues. An example of histotoxic hypoxia is cyanide poisoning