THE MANNER OF DEVELOPMENT OF COVID-19 FROM INFECTION TILL APPEARANCE OF SYMPTOMS
Pathogenesis of COVID-19
After the virus enters the body, it needs a special receptor to help it enter the cell. This receptor is called (Angiotensin Converting Enzymes_2) Symbolized by ACE_2.
The ACE_2 is present on the surface of the alveolar cells in the lung.
We have 3 types of alveolar cells:
Type1: Responsible for gas exchange.
Type2: It is responsible for producing “surfactant” which is a mixture of proteins and fats that reduce the surface tension of the alveoli.
Type3: Dust cell, which is macrophages.
The ACE_2 is found on type2 of these cells.
Corona virus envelope contains proteins called spikes and special (S_Spike) that help the virus bind to ACE_2.
When the above association occurs, the genetic material of the virus enters the cell and the cell is harnessed to produce viral proteins, thus the virus multiplies and the cell dies.
When (type 2 alveolar cells)die, they release substances called specific inflammatory mediators.
These substances stimulate the existing immune cells “macrophages” and when they stimulate the macrophages, they secrete 3 immune substances called “cytokines” which are:
Tumor Necrosis Factor (TNF_α).
These three substances, when they reach the bloodstream, cause the symptoms associated with infection with Corona virus.
First - at the level of lungs:
1)These substances cause expansion of the blood vessels surrounding the vesicle, as well as increased permeability of the wall of these vessels
Capillary permeability increased. and thus leads to “alveolar edema”, which leads to hypoxia and shortness of breath.
2)The loss of surfactant leads to an increase in the surface tension of the vesicle and consequently leads to Alveolar collapse. It also leads to Hypoxia and shortness of breath.
3)These three substances also lead to an increase in the flow of “neutrophils” cells to the place of the viral infection as an immune response. Neutrophils cells kill some viruses by secreting two substances such as:
Reactive Oxygen Species “ROS”
But the above articles also destroy some of the alveolar cells responsible for gaseous exchange and cause a condition called consolidation that causes cough symptoms.
The virus also affects gastrointestinal organs as ACE2 is abundantly expressed in the glandular cells of gastric, duodenal and rectal epithelium as well as endothelial cells and enterocytes of the small intestine. The virus has been found in the faeces of as many as 53%of hospitalised people and more anal swab positives have been found than oral swab positives in the later stages of infection
Second: At the CNS level:
The three substances “IL_1, IL_6, TNF” go to the “hypothalamus” and thus increase the body temperature and cause the symptoms of “Fever”.
Third: In the case of severe infection “SIRS” will occur (Systemic inflammatory response syndrome.)
That lead to septic shock.
Multiple organ dysfunction syndrome.
Especially the kidney and kidney failure.