Deficiency of oxygen causes cell injury by reducing aerobic oxidative respiration.
May be generalized or regional in nature and it implies a deprivation of adequate oxygen supply.
Adaptation to hypoxia is associated with increased respiration, blood flow and survival responses.
Other adaptation mechanisms rely on oxygen-sensing prolyl hydroxylases, which hydroxylate prolines in the alpha subunit of the hypoxia-inducible transcription factor(HIF).
HIF is a heterodimer transcription factor with 2 subunits: HIF-1alpha or HIF-2alpha and HIF-1Beta.
HIF-1beta is ubiquitous, whereas HIF-2alpha is restricted to certain tissues.
Complete deprivation of oxygen is known as anoxia.
Apoxemia is the presence of an abnormally low concentration of oxygen in the arterial blood.
Generalized process at high altitude, where it can cause altitude sickness.
Occurs while diving underwater and breathing mixtures of gases with a low oxygen content.
Symptoms may develop suddenly or gradually.
Symptoms include headaches, fatigue, shortness of breath, nausea and possibly euphoria.
Severe or sudden onset of hypoxia associated with change in levels of consciousness, seizures, coma and death.
When severe it induces blue discoloration of the skin, cyanosis.
Acute causes of hypoxia such as pneumonia and pulmonary embolism are frequently associated with clinical signs and symptoms which include air hunger, diaphoresis, tachypnea, and tachycardia.
In chronic hypoxia the above clinical markers may be masked by chronic pulmonary and cardiovascular conditions, despite low pulse oximetry readings.
Types: hypoxic hypoxia-a generalized hypoxia as a result of low partial pressure of oxygen in arterial blood.
Hypoxic hypoxia may be due to low partial pressure of atmospheric oxygen found at high altitude or by replacement of oxygen as in modified atmosphere of a sewer or recreational use of nitrous oxide, in the presence of sleep apnea, inadequate pulmonary ventilation, right to left heart shunts and lack of ventilation.
Type: anemic hypoxemia-arterial oxygen pressure is normal but total oxygen content of the blood is reduced.
Type: hypemic hypoxemia-inability of oxygenated blood to be delivered to tissues and occurs with carbon monoxide poisoning or methemoglobinemia.
Types: histotoxic hypoxia-cells unable to use oxygen secondary to impaired oxidative phosphorylation enzymes.
Types: ischemic hypoxia-restricted blood flow to tissue.
Hypoxia can induce inflammation: in mountain sickness circulating proinflammatory cytokines are increased and vascular leakage causes pulmonary edema.
Ischemia in organ grafts increases the risk of inflammation and graft failure or rejection.
In obesity adipocyte demand for oxygen causes hypoxia and increases inflammatory adipokines in fat: this results in infiltration of macrophages, low grade inlammation which promotes insulin resistance.