Oxygenation
- Oxygen is important for the metabolic conversion of energy substrates
- Without oxygen, cells are severely limited in their potential in
producing energy vital for cellular processes (i.e. anaerobic versus aerobic
metabolism)
- Ultimately fuel e.g. carbohydrates, fat +/- protein can be used to
produce ATP via different biochemical pathways.
- ATP is the 'universal currency' of energy within the cell that powers
enzymes, transport proteins etc.
- Oxygen delivery begins at the mouth and nose, transmitted via the
airways to the lungs, enters the bloodstream where it is predominantly
carried by haemoglobin where it then enters the tissues.
Oxygen follows the pressure gradient starting at the mouth and ending at the
mitochondria in each cell.
At each point the oxygen content falls.These are the following
contributors
- Upper airways - humification (partial pressure of water vapour)
- Alveoli - addition of exiting CO2 (alveolar gas equation)
- Alveolar-arterial gradient - shunt (physiological and anatomical),
diffusion (usually small effect except in disease)
- Haemoglobin binding capacity (based on the oxy-dissociation curve and
the absolute concentration of haemoglobin)
- Tissue oxygen extraction via internal biochemical pathways
Lack of oxygen at the cellular level can be due to impairment at any point
along this path
One classification (there are other systems)
- Hypoxic hypoxia - inadequate oxygen intake into the lungs or entering
the bloodstream (e.g. breathing at altitude, pneumonia)
- Anaemic hypoxia - insufficient haemoglobin to carry oxygen (e.g. blood
loss)
- Hypemic hypoxia - impaired ability for haemoglobin to bind oxygen (e.g.
carbon monoxide poisoning)
- Stagnant hypoxia - impaired flow of oxygenated blood (e.g. circulatory
failure, obstructed arteries)
- Histotoxic hypoxia - impaired biochemical processes to utilise oxygen
(e.g. cyanide poisoning)
In pathological terms, cellular hypoxia is called
ischaemia. This leads to either temporary dysfunction and if prolonged or
severe, death.