Editing Hypoxia (medicine) (section)

===Acute===
{{see also|Hypoxic ventilatory response#Acute hypoxic ventilatory response}}
If oxygen delivery to cells is insufficient for the demand (hypoxia), electrons will be shifted to [[pyruvic acid]] in the process of [[lactic acid fermentation]].  This temporary measure (anaerobic metabolism) allows small amounts of energy to be released.  Lactic acid build up (in tissues and blood) is a sign of inadequate mitochondrial oxygenation, which may be due to hypoxemia, poor blood flow (e.g., shock) or a combination of both.<ref name="Hobler and Carey 1973" /> If severe or prolonged it could lead to cell death.<ref name="Fulda et al 2010" />

In humans, hypoxia is detected by the peripheral chemoreceptors in the [[carotid body]] and [[aortic body]], with the carotid body chemoreceptors being the major mediators of reflex responses to hypoxia.<ref name="Arieff 2013" /> This response does not control ventilation rate at normal P<sub>O<sub>2</sub></sub>, but below normal the activity of neurons innervating these receptors increases dramatically, so much as to override the signals from central chemoreceptors in the [[hypothalamus]], increasing P<sub>O<sub>2</sub></sub> despite a falling P<sub>CO<sub>2</sub></sub>{{citation needed|date=September 2022}}

In most tissues of the body, the response to hypoxia is [[vasodilation]]. By widening the blood vessels, the tissue allows greater perfusion.

By contrast, in the [[lung]]s, the response to hypoxia is vasoconstriction. This is known as [[hypoxic pulmonary vasoconstriction]], or "HPV", and has the effect of redirecting blood away from poorly ventilated regions, which helps match perfusion to ventilation, giving a more even oxygenation of blood from different parts of the lungs.<ref name="Michiels 2004" /> In conditions of hypoxic breathing gas, such as at high altitude, HPV is generalized over the entire lung, but with sustained exposure to generalized hypoxia, HPV is suppressed.<ref name="Gao et al 2021" />
Hypoxic ventilatory response (HVR) is the increase in [[ventilation (physiology)|ventilation]] induced by hypoxia that allows the body to take in and transport lower concentrations of oxygen at higher rates.  It is initially elevated in lowlanders who travel to high altitude, but reduces significantly over time as people [[acclimatize]].<ref name="Cymerman and Rock" /><ref name="Teppema and Dahan 2010" />