Lock and Key Model. Each type of enzyme has a unique 3-D shape, including a surface groove called an active site, which fits its target substrate much like a key fits in a lock. Other substances that donât fit can't enter the active site and no reaction occurs.
Some of the many causes of hypoxia are the following: 1  Chemical or gas poisoning (for example cyanide, carbon monoxide) 2  Low or absent concentration of oxygen (for example, high altitudes reached without supplemental oxygen as seen in mountain climbing, and aviation, drowning or fires)  Lung problems, for example:
anemic hypoxia hypoxia due to reduction of the oxygen-carrying capacity of the blood as a result of a decrease in the total hemoglobin or an alteration of the hemoglobin constituents.circulatory hypoxia stagnant hypoxia. histotoxic hypoxia that due to impaired utilization of oxygen by tissues, as in cyanide poisoning. a type brought about by a reduction of the oxygen-carrying capacity of the blood because of a decrease in the complete blood counts or an alteration of the hemoglobin constituents. hypoxia, anoxic, n a type resulting from inadequate oxygen in inspired air or interference with gaseous exchange in the lungs.