Pathophysiology of Pneumonia

Pneumonia is an inflammatory lung condition that is characterized by parenchyma of the lung and abnormal alveolar fluid retention. There are many factors that can result in developing pneumonia. These factors include bacterial, viral, fungal infections. The other factors include flea bites or a chemical or physical injury to the lungs. Many times the cause of pneumonia is idiopathic, that is, unknown origin. In this article, we shall learn the pathophysiology of pneumonia.

What is the Pathophysiology of Pneumonia?
Pneumonia is a commonly occurring serious disease that affects about 1 out 100 people every year. As mentioned above, many factors are responsible for development of pneumonia. Pneumonia can be divided into various categories like community acquired and hospital acquired infection. The common type of community acquired infection is pneumococcal pneumonia and Mycoplasma pneumonia. Many times in people with lowered immunity or geriatric patients, pneumonia is seen after a bout of influenza. Most of the hospital acquired infections of pneumonia are the serious infections, as they body lacks the mechanism to fight against the condition. Aspirational pneumonia, pneumonia in immunocompromised host and viral pneumonia are some of the pneumonia related specific disorders.

The causative agent or organism gains entry into the body through the respiratory tract by way of inspiration or aspiration of oral secretions. The organisms that can reach the lungs through blood circulation are staphylococcus and gram negative bacilli.

The body's defense mechanism, that is, pulmonary defense mechanism in case of lungs comes into action. A cough reflex, mucociliary transport and pulmonary macrophages try to protect the body against the infection. However, in some people their defense mechanism is either suppressed or overwhelmed by the invading agent and leads to development of infection.

The invading organism starts to multiply and release damaging toxins that cause inflammation and edema of the lung parenchyma. This action leads to accumulation of cellular debris and exudes within the lungs. Soon the airless state of the lungs is changed to a consolidated state due to the fluid and exudate filling up.

The ciliated epithelial cells are damaged in case of viral pneumonia. The virus reach the lungs through air-borne droplets inhaled through the mouth and nose. The virus after gaining entry into the lungs, begins an invasion of the cell lining of the airways and alveoli. This leads to cell death by direct action of the virus or through a cell controlled self-destruction called apoptosis. With the body's response to the invasion, there is further damage to the lungs as the fluid is leaked into the alveoli. Viral infection of the lungs damages the lungs and makes them even more susceptible to bacterial infections. This complicated the matters even more in viral pneumonia.

The fungal pneumonia is a rare condition, and is often seen in individuals with compromised immune system like AIDS, etc. The pathophysiology of fungal pneumonia is very much similar to bacterial pneumonia. The most common fungal agents that cause pneumonia are Histoplasma capsulatum, Cryptococcus neoformans, Pneumocystis jiroveci, blastomyces and Coccidioides immitis.

Pneumonia caused by parasites occurs when they travel to the lungs by gaining entry through skin or begin swallowed. There is cellular destruction and immune response that leads to disruption of oxygen transportation. The common parasite that causes pneumonia are Toxoplasma gondii, Strongyloides stercoralis and Ascariasis.

Pneumonia in Children
Pneumonia in children is basically a self-limiting condition most of the time. Recurrent cases of pneumonia are seen in chronic cases of asthma or cystic fibrosis. The pathophysiology of pneumonia in children is described in 4 stages, the 24-hour congestion stage, the red hepatization stage, the gray hepatization stage and the resolution stage.

24 Hour Congestion Stage
This is the first stage of pneumonia that occurs within 24 hours of infection. The lung is characterized by vascular congestion and alveolar edema. Microscopic examination shows the presence of many bacteria and few neutrophils.

Red Hepatization
The red hepatization stage is seen when the red blood cells and fibrin enters the alveoli. The lung tissue becomes red and firm that leads to difficulty in breathing or rapid breathing.

Gray Hepatization Stage
The fibrin and dying red and white blood cells collects in the alveolar spaces in the gray hepatization stage. The sputum contains a tinge of blood or purulent discharge. In this stage, atelectasis, that is, reduction of available area within the lung for gas exchange may also be seen.

Resolution Stage
This is the last stage of pneumonia in children. The enzymes in the lungs are brake down the substances causing inflammation. The white blood cells fight off the invading organism and the remains may be coughed up.

This was some information related to pathophysiology of pneumonia. You can also find more information of pneumonia prevention in the article on pneumonia shot. I hope this article has helped you understand the normal mechanical, physical and biochemical functions caused by the disease.