What are free radicals in the body
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Understanding Free Radicals in the Human Body
What Are Free Radicals?
Definition and Chemical Nature
Free radicals are highly reactive chemical species that contain one or more unpaired electrons in their outer orbitals. This unique structure makes them extremely reactive with other molecules 146. They can be atoms, molecules, or ions and are produced both endogenously within the body and from external sources such as pollution, radiation, and cigarette smoke 189.
Sources and Formation of Free Radicals
Endogenous Production
Within the body, free radicals are continuously generated as by-products of normal metabolic processes, particularly during the reduction of oxygen in the mitochondria. This process produces reactive oxygen species (ROS) such as superoxide anion (O2·−) and hydrogen peroxide (H2O2) 247. Enzymes like NAD(P)H oxidase and nitric oxide synthase (NOS) are also involved in the regulated production of these radicals .
Exogenous Sources
External factors such as ionizing radiation, pollution, and certain medications can also lead to the formation of free radicals. These external sources contribute to the overall oxidative burden on the body 49.
Dual Role of Free Radicals
Harmful Effects
At high concentrations, free radicals can cause significant damage to cellular components, including lipids, proteins, and DNA. This oxidative damage is implicated in the pathogenesis of various diseases such as cancer, diabetes, atherosclerosis, neurodegenerative disorders, and rheumatoid arthritis 2367. The process of aging is also thought to be influenced by the accumulation of oxidative damage over time .
Beneficial Roles
Interestingly, free radicals also play essential roles in normal physiological processes. At moderate concentrations, they act as signaling molecules that regulate vascular tone, oxygen tension, and various cellular signaling pathways. These functions are crucial for maintaining redox homeostasis and protecting cells against oxidative stress 267. For example, nitric oxide (NO) and superoxide anion are involved in critical signaling processes that help regulate blood flow and immune responses .
Antioxidant Defense Mechanisms
Endogenous Antioxidants
The body has evolved several antioxidant defense mechanisms to neutralize free radicals and mitigate their harmful effects. Key antioxidant enzymes include superoxide dismutase (SOD), which converts superoxide anion into hydrogen peroxide, and catalase and glutathione peroxidase, which further break down hydrogen peroxide into water and oxygen 47.
Exogenous Antioxidants
In addition to endogenous defenses, antioxidants can be obtained from dietary sources. Vitamins such as vitamin E, flavonoids, and polyphenols found in fruits and vegetables are potent antioxidants that help neutralize free radicals 39. These dietary antioxidants are crucial for supplementing the body's natural defenses, especially under conditions of increased oxidative stress.
Conclusion
Free radicals are a double-edged sword in the human body. While they are essential for various physiological functions and signaling processes, their excessive accumulation can lead to oxidative stress and contribute to the development of numerous diseases. Understanding the balance between free radical production and antioxidant defenses is key to maintaining health and preventing disease.
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