Why there is a liquid in the plural cavity?

You are likely referring to the pleural cavity, which is the space between the two layers of pleura that surround the lungs. This space is not normally filled with liquid.

There is a small amount of pleural fluid in the pleural cavity, which acts as a lubricant to allow the lungs to move freely during breathing. This fluid is constantly being produced and absorbed, maintaining a thin, even layer between the pleural membranes.

However, the presence of excess fluid in the pleural cavity is called a pleural effusion. This can be caused by various conditions, such as:

* Infection: Pneumonia, tuberculosis

* Heart failure: Fluid backs up into the lungs

* Cancer: Tumors can block lymphatic drainage

* Kidney failure: Fluid buildup in the body

* Trauma: Injury to the chest

* Autoimmune diseases: Rheumatoid arthritis, lupus

If there is excess fluid in the pleural cavity, it can cause shortness of breath, chest pain, and coughing. It is important to see a doctor if you experience these symptoms.