response to decreased oxygen levels

Definition

Target type: biologicalprocess

Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a stimulus reflecting a decline in the level of oxygen. [GOC:al]

Response to decreased oxygen levels, also known as hypoxia, is a complex biological process that involves a cascade of cellular and physiological responses aimed at maintaining oxygen homeostasis. When oxygen levels fall below normal, cells activate a series of signaling pathways that lead to changes in gene expression, protein activity, and cellular metabolism.

One of the key players in the hypoxic response is the hypoxia-inducible factor (HIF) family of transcription factors. HIFs are heterodimers composed of an alpha subunit and a beta subunit. Under normoxic conditions, the alpha subunit of HIF is rapidly degraded by the proteasome. However, in hypoxic conditions, the alpha subunit is stabilized, allowing it to translocate to the nucleus and bind to specific DNA sequences known as hypoxia response elements (HREs). This binding activates the transcription of target genes involved in various aspects of the hypoxic response.

**Cellular and physiological responses to hypoxia include:**

* **Increased erythropoiesis:** HIF-1α stimulates the production of erythropoietin (EPO), a hormone that promotes the production of red blood cells in the bone marrow. This increase in red blood cell count enhances oxygen carrying capacity in the blood.
* **Angiogenesis:** HIF-1α promotes the formation of new blood vessels, which can improve blood flow and oxygen delivery to tissues.
* **Glucose metabolism:** HIF-1α alters glucose metabolism to favor glycolysis, a process that generates ATP (energy) in the absence of oxygen.
* **Cellular survival:** HIF-1α can activate genes that protect cells from damage caused by hypoxia, such as apoptosis (programmed cell death).
* **Changes in mitochondrial function:** HIF-1α can regulate mitochondrial function to reduce oxidative stress and preserve energy.

**Overall, the response to decreased oxygen levels is a highly coordinated process that involves multiple signaling pathways, cellular processes, and physiological adaptations. The primary goal of this response is to maintain oxygen homeostasis and ensure the survival of cells and tissues in the face of low oxygen conditions.**'
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