Template:Normoxia - state or rate

Aerobic and anaerobic from normoxia to anoxia: oxygen availability and metabolic state or rate

Oxygen availability: state

• Normoxic
• Hyperoxic - Hyperoxic conditions may impose oxidative stress and may increase maximum aerobic performance.
• Hypoxic - "Metabolic hypoxia is indicated as a reduced oxygen flux below the critical oxygen pressure and is either fully or partially anaerobic" [1]. This functional or physiological definition of hypoxia is compared to environmental hypoxia defined as environmental oxygen pressures below the normoxic reference level. "The high efficiency of oxidative phosphorylation at low oxygen emphasizes that even trace amounts of oxygen can make a vital energetic contribution when ATP limitation threatens cellular survival under severe hypoxia encountered at high altitude, in aquatic habitats, and during pathological states of ischemia" [2].
• Microxic - "Microxic regulation .. effectively increases the slope of the flux-pressure relation in the microxic region" [1].
• Anoxic - "When strictly anoxic conditions are not achieved, anaerobic metabolism proceeds simultaneously with oxygen consumption" [3]. "The difficulties involved in defining an absolute limit between microxic and anoxic conditions are best illustrated by a logarithmic p_O2 scale [1].

Metabolism: state or rate

• Aerobic - Whereas anaerobic metabolism may proceed in the absence or presence of oxygen (anoxic or oxic conditions), aerobic metabolism is restricted to oxic conditions.
• Anaerobic - "In zoophysiology, 'anaerobic' (without air) is rarely defined in terms of controlled measurements of the actual extent of anaerobic conditions [1].

Critical and limiting p_O2

• Critical oxygen pressure - "Metabolic hypoxia is indicated as a reduced oxygen flux below the critical oxygen pressure [1].
• Limiting oxygen pressure - "Below the critical oxygen pressure, the aerobic ATP production decreases, and below the limiting oxygen pressure anaerobic processes compensate increasingly for the diminished aerobic flux." Then "there is an extended phase of fully aerobic hypoxia" [1].

References

1. Gnaiger E (1991) Animal energetics at very low oxygen: Information from calorimetry and respirometry. In: Strategies for gas exchange and metabolism. Woakes R, Grieshaber M, Bridges CR (eds), Soc Exp Biol Seminar Series 44, Cambridge Univ Press, London:149-71. - »Bioblast link«
2. Gnaiger E, Méndez G, Hand SC (2000) High phosphorylation efficiency and depression of uncoupled respiration in mitochondria under hypoxia. Proc Natl Acad Sci U S A 97:11080-5. - »Bioblast link«
3. Gnaiger E, Staudigl I (1987) Aerobic metabolism and physiological responses of aquatic oligochaetes to environmental anoxia. Heat dissipation, oxygen consumption, feeding and defecation. Physiol Zool 60:659-77. - »Bioblast link«