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Hypoxia

Hypoxia is a physiological state characterized by decreased oxygen levels in organs and tissues. Low oxygenation plays a role in embryonic development and may be physiologically normal for some adult tissues which maintain a hypoxic environment (e.g., bone marrow microdomains and thymus). However, commonly oxygen deficiency affects cellular functions and disrupts various biological processes including cell proliferation and differentiation, angiogenesis, metabolism, and pH homeostasis. Therefore, hypoxia is associated with various pathophysiological conditions including chronic obstructive pulmonary disease, pulmonary hypertension, congenital heart disease, cerebral ischemia, and cancer.

Learn more about adaptations to hypoxia: The Cellular Response to Hypoxia in Cancer White Paper

Physiologic Median O2 Levels in Organs and Tissues

Median O2 Levels in Human Organs and Tissues

Cellular responses to hypoxia are critically dependent on the duration (acute vs chronic) and extent (hypoxia vs anoxia) of the low-oxygen state, and are predominantly mediated by hypoxia inducible factors (HIFs), considered to be “master regulators” of adaptations to low-oxygenation. However, currently it is well accepted that both HIF-dependent and -independent mechanisms play roles in shaping cellular responses to hypoxia in physiology and disease.

Defining Hypoxia States*

Duration

Extent

Acute
Low tissue oxygen from minutes to hours, due to temporary limitations in blood flow

Hypoxia
~ 1-2% O2

Chronic
Low tissue oxygen from hours to days, due to limitations in the diffusion of oxygen to distant tissues

Anoxia
~ 0.02% O2 and below

*Definitions for hypoxia are based on conditions used in cancer model systems.


Learn About HIFs