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Cerebral hypoxia is a form of hypoxia (reduced supply of oxygen), specifically involving the brain; when the brain is completely deprived of oxygen, it is called cerebral anoxia. There are four categories of cerebral hypoxia; they are, in order of increasing severity: diffuse cerebral hypoxia (DCH), focal cerebral ischemia , cerebral infarction ...
Anoxic events with euxinic (anoxic, sulfidic) conditions have been linked to extreme episodes of volcanic outgassing. Volcanism contributed to the buildup of CO 2 in the atmosphere and increased global temperatures, causing an accelerated hydrological cycle that introduced nutrients into the oceans (stimulating planktonic productivity).
Within a few minutes of anoxia onset in the turtle's brain there is decreased cerebral blood flow that eventually ceases. Meanwhile, glycolysis is stimulated to maintain a near optimum ATP production. [3] This compensatory stimulation of glycolysis occurs because, in the turtle's brain, cytochrome a and a 3 have a low affinity for oxygen. [13]
Possible causes include cerebral ischemia, hypoxia (inadequate oxygen supply to tissue), or anoxia (total oxygen depletion). Agonal breathing is a severe medical sign requiring immediate medical attention, as the condition generally progresses to complete apnea and preludes death .
Anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: Anoxic waters, sea water, fresh water or groundwater that are depleted of dissolved oxygen; Anoxic event, when the Earth's oceans become completely depleted of oxygen below the surface levels
The Toarcian extinction event, also called the Pliensbachian-Toarcian extinction event, [1] [2] the Early Toarcian mass extinction, [3] the Early Toarcian palaeoenvironmental crisis, [4] or the Jenkyns Event, [5] [6] [7] was an extinction event that occurred during the early part of the Toarcian age, approximately 183 million years ago, during the Early Jurassic.
Anoxic waters are a natural phenomenon, [3] and have occurred throughout geological history. The Permian–Triassic extinction event, a mass extinction of species from the world's oceans, may have resulted from widespread anoxic conditions combined with ocean acidification driven by a massive release of carbon dioxide into Earth's atmosphere. [4]
Hypoxia differs from hypoxemia and anoxemia, in that hypoxia refers to a state in which oxygen present in a tissue or the whole body is insufficient, whereas hypoxemia and anoxemia refer specifically to states that have low or no oxygen in the blood. [3] Hypoxia in which there is complete absence of oxygen supply is referred to as anoxia.