Question

Use the coronavirus as a case study to illustrate major physiological concepts (“big ideas”). For example, how does it relate to biological levels, cell signaling, etc. Include specific details and examples in your answer for full credit

Answer 1

ACE Angiotensin converting enzyme catalyes the formation of angiotensin II from angiotensin I. ACE2 is one of the subtypes of ACE primarily acts to counterbalance the effect of ACE and generates angiotensin (1-7) from angiotensin II. These active form of hormones binds to Mas receptor and promotes vasodilation in the effected vascular bed. It is predomiantly used in the treatment of hypertension as it lowers the BP by increasing the stroke volume and vasodilating effect induced decreased resistance. ACE2 receptors are found widely in the surface of heart, kidney, stomach, intestine, and lungs. Studies reported that ACEi/ARBs stimulate the upregualtion of ACE2 and these medications might increase the potential risk of SARS-CoV-2 infection is still in debate.

The pathogenecity of human corona virus SARS-CoV-2 target the host receptor called as angiotensin-converting enzyme 2 (ACE2) predominantly on the epithelial layer of the lungs. SARS-CoV-2 not only uses the SARS-CoV receptor ACE2 for entry and the serine protease TMPRSS2 for S protein priming

Substantial increased expression of ACE2 is also observed in individuals with type 1 or type 2 diabetes who are under the ACEi/ARB therapy. ACEi- ACE inhibitors and ARB - angiotensin II type-I receptor blockers. ACE inhibitors used as therapeutic drug in the hypertension because of its vasodialtion promoting properties as seen earlier, which results in an upregulation of ACE2. Research suggesting that the increased ACE2 expression is seen in individuals treated with ACE inhibitors and ARBs. It leads to the hypothesis that ACE2 would facilitate and increase the risk of infection with COVID-19. This is evident from the fact that the possible negative feedback loop which could eventually upregulates more ACE2 receptor since the ACEi initially inhibits ACE which results in decreased angiotensin I. This upregualtion of ACE2 receptor increses the available binding sites for SARS-CoV-2.

Diagnosis of SARS Covid-2 by radiograph characterized with 'ground-glass opacities' a hallmark of Covid19 lung infection. The GGO is mostly bilateral but at times it is also subpleural or peripheral. ‘Ground glass’ means the hazy lung opacity on chest radiograph. It does not enable to obscure any underlying pulmonary vessels or bronchial walls due to lesser density. The crazy paving appearance because of the inter-/intra-lobular septal thickening. It is also characterized by air space consolidation, bronchovascular thickening in the lesion and traction bronchiectasis. Reports says that the consolidative opacities is seen in 54% of asymptomatic patients had pneumonic changes.

ACE2 receptor play major role in severity of the disease and the pneumonia. Virus affect the pneumocytes which play an important role in producing surfactant in order to maintain the surface tension so that the alveoli sac remains open for gas exchange. The virus gets entry to these cells by binding to ACE2 receptors and elicit the immune response: IgM-type antibodies as a first line and also the the longer term antibodies IgG type. Infection in lung cells causes pneumonia and collapse of lungs as the alvoli also collapse which makes the breathing difficult leading to breathlessness. This signals the accumulation of inflammatory immune responses, fibrin clots form in the alveoli, and fibrin-platelet microthrombi and all these contributes for the hazy appearance of chest radipgraph.