7/30/2023 0 Comments Pathological condition researchThe heart then pumps out the oxygenated blood from left ventricle to its periphery to maintain the proper function of every single cell. The oxygenated blood returns to left atrium through pulmonary vein. Oxygen exchange occurs in the alveoli of lung with more than 95% of oxygen diffuses into the capillary vessels via the alveolar-capillary exchange system and then binds to hemoglobin. Taking human as an example, the central and peripheral chemoreceptors sense the reduction of oxygen tension and send signals to respiratory center in medulla and pons, where a series of processes are initiated to increase pulmonary ventilation and cardiac output to maintain normal functions of human body. Hypoxia is usually considered to have pathological effects however, it also involves in maintaining normal physiological functions. Therefore, a wider range of oxygen concentrations and feedback to acute stresses from seconds to days, even weeks to months, shall be put into consideration when referring the mechanisms of pathophysiological relevancies. Hypoxia is a state of continuously lack of oxygen for a short (acute hypoxia, e.g., ischemia) or long (chronic hypoxia, e.g., chronic kidney disease, cancer) period of time. Mostly, hypoxia is referred to the relatively low (generally < 2%) oxygen content compared to normal status in a given organ, tissue, or cell type. Hypoxia may not be considered as the inequivalent to ambient oxygen concentration (21% oxygen) as many tissues physiologically function at levels equal to 5% oxygen or even as low as 1% oxygen. Lack of oxygen supply or an excessive oxygen consumption could result in insufficient oxygen levels for maintaining normal cellular function, a condition defined as hypoxia. In metazoan organisms, the oxygen delivery and cellular adaptation to oxygen deprivation are accelerated through the hypoxic signaling pathway in order to sustain oxygen homeostasis. This review article will summarize current understandings regarding the molecular mechanism of hypoxia in these common and important diseases. A growing body of evidence implicates that hypoxia plays critical roles in the pathogenesis of major causes of mortality including cancer, myocardial ischemia, metabolic diseases, and chronic heart and kidney diseases, and in reproductive diseases such as preeclampsia and endometriosis. As a result, irreversible processes occur that may cause physiological disorder or even pathological consequences. A series of chain reaction-like gene expression cascade, termed hypoxia-mediated gene regulatory network, will be initiated under such prolonged or intermittent hypoxic conditions and subsequently leads to alteration of cellular function and/or behaviors. However, the situation becomes complicated if hypoxic stress persists (chronic hypoxia) or cyclic normoxia-hypoxia phenomenon occurs (intermittent hypoxia). Normally, such hypoxic response will cease when oxygen level is restored. When oxygen delivery is disrupted or reduced, the organisms will develop numerous adaptive mechanisms to facilitate cells survived in the hypoxic condition. All nucleated cells can sense oxygen concentration and respond to reduced oxygen availability (hypoxia). Oxygen is essentially required by most eukaryotic organisms as a scavenger to remove harmful electron and hydrogen ions or as a critical substrate to ensure the proper execution of enzymatic reactions.
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