Hypoxia

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A cell or organism can be described as being hypoxic if they are in an environment that has a lower pO2 than the environment the cells are usually exposed to. This is with regards to the levels of pO2 found at sea level in comparison to the concentration found in cells. At sea level, the pO2 is 150 mmHg, so this is the usual level of oxygen for a human, so falling below that level, by climbing a mountain, for example, will cause hypoxia. This is because the pO2 drops the further above sea level you get, dropping to about 40 mmHg at the peak of Mount Everest.

Human cells, however, aren't usually exposed to 150 mmHg of pO2. The pressure drops between different compartments in the body so that the tissues only have around 10 to 18 mmHg pO2. This means that if you're growing these cells as a culture outside of the body, then having them at a pO2 of 15 mmHg wouldn't cause them to become hypoxic. Hypoxia is all relative to the cell or organism and it's natural environment.

Hypoxia has medical relevance with regards to cancer (among other notable diseases including Rheumatoid Arthritis and Chronic Kidney Disease). This is that the lowering of oxygen concentration below that of sea level works to increase the resilience and aggressiveness of certain malignant tumours[1]., due to the physiological stress placed on cells, which leads to adaptations resulting in the proliferation of the cancerous cells[2].

Although hypoxia may sound dangerous it is very important in the formation of the placenta, heart, bone and vasculature in embryos. This is done by using the Hypoxia Inducible Cascade (HIF) signalling cascade. The HIF Cascade controls many pathways and so targets the following: cellular metabolism, cell death, cell growth, oxygen supply and transcription.

References

  1. Menard JA, Christianson HC, Kucharezewska P, Bourseau-Guilmain E, Svensson KJ, Lindqvist E, Indira Chandran V, Kjellén L, Welinder C, Bengzon J, Johansson MC, Belting M. Metastasis Stimulation by Hypoxia and Acidosis-Induced Extracellular Lipid Uptake Is Mediated by Proteoglycan-Dependent Endocytosis. Cancer Research 2016; 76(16): 4828-40
  2. Harris AL. Hypoxia — a key regulatory factor in tumour growth. Nature Reviews Cancer 2002; 2: 38-47
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