Understanding the viral battleground
May 5, 2020 - Clinicians have traced the brutal rampage wrought by the coronavirus through the body, from the lungs -- ground zero -- to the heart and blood vessels, kidneys, gut, and brain.
The SARS-CoV-2 virus that causes Covid-19 enters human cells by attaching to a cell-surface receptor called angiotensin-converting enzyme 2 (ACE2). Once infected, the virus hijacks a host cell and turns it into a factory, making copies of itself to attack more cells.
Once in the nose and throat, the virus travels to the lungs. At the end of the lung’s respiratory tree lie the alveoli, tiny air sacs lined with a layer of cells that are also rich in ACE2 receptors.
Usually, oxygen crosses the alveoli into capillaries, tiny blood vessels, before being carried by the blood system to the rest of the body. As the immune system fights the virus, white blood cells release signalling molecules called cytokines. These proteins coordinate the body’s response against infection and trigger inflammation.
Vital organs throughout the body that are rich in ACE2 -- which helps regulate blood pressure -- are all targets for the virus. The lining of the heart and blood vessels, the kidneys and small intestine, along with the nose, throat and alveoli, are all rich in ACE2 receptors.
In some patients, an overreaction of the immune system known as a “cytokine storm” results in uncontrolled levels of cytokines which then activate more immune cells, resulting in hyperinflammation. Immune cells start to attack healthy tissues -- blood vessels leak, blood pressure drops, clots form, and catastrophic organ failure can ensue.
A newly observed threat from the SARS-CoV-2 virus that causes Covid-19 is an abnormal tendency to blood clotting. Blood clots can break apart and travel to the lungs, blocking vital arteries -- pulmonary embolism -- or lodge in the brain, causing a stroke.
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