Cartoon of an oxygen molecule by Ulflund via Wikimedia Commons

Although oxygen is essential for air-breathing species and allowed for the evolution of multicellular organisms, it is also a dangerous molecule that can lead to cellular toxicity through the generation of reactive oxygen species (ROS). However, it is important to point out that cellular ROS also play several physiological roles in the body.

I just read an interesting review article published in Physiological Reviews that explored natural oxygen delivery and availability to tissues and organs in the body and how to replicate those natural levels in cell culture. Once entering the body, oxygen levels become quite different from levels found in the atmosphere and it is important to understand these differences to know what “normal” is for various tissues of the body. The review article did a great job exploring variations in oxygen levels in multiple tissues.

Animals come equipped with several biological sensors to detect variations in oxygen concentrations. Hypoxia Inducible Factors (HIFs), for examples can be found in all eukaryotic animals. As the name implies, HIFs are responsible for regulating the body’s response to hypoxia by turning on production of red blood cells (to carry more oxygen) and stimulating the growth of new blood vessels to transport oxygen, among other effects. Mitochondria also serve as biological oxygen sensors that can change how cells produce energy in hypoxic conditions and how much ROS cells produce. Carbon monoxide and hydrogen sulfide are also naturally produced in the body and are thought to serve as oxygen sensors.

Just how did animals evolve the ability to breathe air? Find out in this nifty YouTube video:

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