字幕表 動画を再生する 英語字幕をプリント Coronaviruses are a large family of viruses that are known to cause illness ranging from the common cold to more severe diseases such as Middle East Respiratory Syndrome and Severe Acute Respiratory Syndrome. A novel coronavirus or the SARS CoV-2 is a new strain of coronavirus that has not been previously identified in humans. Coronavirus spreads from person to person through small air droplets. Let us say a person with Covid-19 sneezes or exhales in front of you and you inhale the viral particles coming out of his mouth. The virus will then travel to the respiratory system. Epithelial cells of your bronchi which are the main airways in your lungs, bronchiole , the smaller passageways and most important the tiny air sacs at the end called the alveoli, are the main targets. Epithelial Cells are like the safety shields of the body, forming a covering of all the body surfaces. Unfortunately, they are the prime cellular targets of the novel coronavirus because of the ACE-2 receptors which acts as the entry point. The virus enters the cell using the spike protein on its surface that binds on a receptor of the target cells. Viruses have their own genetic code but they lack the machinery to copy their DNA. So once inside like a Trojan horse, the virus then hijacks and transforms the cell into a viral protein making factory. The infected cells now serves the virus, synthesizing thousands and thousands of viral proteins and assembling them, which are later released to enslave more cells and the process continues. As the infected cells die, they release proteins called Cytokines and Damage-associated molecular patterns. Cytokines are like messenger proteins which acts as a signal to activate the immune system. Macrophages, one of the most specialised cells of the immune system gets activated. The macrophages then begin to secrete inflammatory cytokines which results into acute inflammation inside the lung. To be specific, they release, IL-1, IL-6, IL-8, TNF alpha and IFN gamma. These cytokines migrate to the capillaries that line the alveoli. Capillaries are the smallest blood vessels having an endothelial lining comprised of endothelial cells. The inflammatory cytokines increase the spaces between endothelial cells causing the capillaries to leak. As the fluid from the capillaries, starts accumulating inside the alveoli it becomes difficult to breath. This condition is called as Pneumonia. The inability to get enough oxygen into the lungs raises the risk for developing hypoxemia, where the blood oxygen level drops. Also carbon dioxide will start accumulating inside which is called as respiratory acidosis. As there is increase in the secretion of cytokines, it will induce the expression of a very important molecule on the endothelial lining of blood vessels, called Vascular cell adhesion protein. This acts as a magnet, it attracts neutrophils to the site of the injury, inside the alveoli. Neutrophils are white blood cells whose main function is to kill and clean out the invading pathogens. They kill the virus by secreting proteases and reactive oxygen species, but it comes with a price, which is the damage of the tissue itself. The cycle will repeat leading to more inflammation and fluid accumulation. Type 1 alveolar cells, which are involved in the process of gas exchange between the alveoli and the blood, are damaged. Type 2 alveolar cells, which are responsible for making the alveoli open, also gets damaged. As a result alveoli will collapse which will further contribute to hypoxemia. Additionally, the cytokines secreted by the macrophage will result in the microscopic clotting of platelets and red blood cells called as microthrombus or the blood clot. This will lead to more hypoxemia and complete lung failure. As all these cytokines are secreted into the system circulation, they will have a very bad effect causing abnormal blood clotting. Blood clots starts forming throughout the body, blocking small blood vessels. This is known as Disseminated intravascular coagulation, which is a serious disorder. So it all began with a nasty cold and a viral pneumonia, from acute respiratory distress syndrome it progressed to pulmonary embolism and then ultimately led to multi organ failure due to abnormal blood clotting. It isn't the virus that kills you, but the way your body reacts or fails to react against the virus that causes death. There is no 100 percent effective treatment as of yet, but we don't need to panic as stress is going to help the virus more. Remember 94 percent of the patients recover from it despite the type of symptoms they show. Thoroughly wash your hands with alcohol-based hand rubs or soaps, avoid any physical contact and stay away from crowds and if you have any symptoms remain calm and contact your health services. It is really not the end of the world, we just need to break the chain. Don't you all think our so body is amazing, constantly fighting off infection and disease? Comment below your thoughts and subscribe for more such wonderful videos. Thank you for watching, Stay happy Stay Curious.