Mesothelial cells are a specialized type of cell that forms a protective, single-cell-thick layer known as the mesothelium. This membrane lines several of the body’s internal cavities and covers the outer surface of most internal organs. The primary purpose of this lining is to provide a smooth, non-stick surface that allows organs to move and glide against each other without causing friction or damage. This function is similar to the way a non-stick coating on a pan allows food to slide freely.
Location and Structure of the Mesothelium
Mesothelial cells form the lining of four main areas within the body. The pleura is the mesothelium associated with the lungs, lining the lung surface and the interior of the chest cavity. In the abdomen, the peritoneum covers the abdominal organs and lines the cavity walls. The heart is encased in a sac called the pericardium, which is also formed by mesothelial cells. A similar sac, the tunica vaginalis, surrounds the testes.
The structure of the mesothelium consists of two distinct layers. The visceral layer directly covers the surface of the organs, while the parietal layer lines the wall of the body cavity. Between these two layers is a small, fluid-filled space. This serous fluid is secreted by the mesothelial cells and is what allows the two layers to slide past one another smoothly. The cells themselves are flat and thin, a shape described as squamous, which helps create this smooth surface.
Functions of Mesothelial Cells
The most recognized function of mesothelial cells is providing lubrication. This fluid allows organs that are in constant motion, such as the expanding lungs and beating heart, to move without generating damaging friction.
Beyond lubrication, mesothelial cells are active participants in bodily transport and defense. They regulate the movement of fluids and cells across the mesothelial membrane. This is important for maintaining the correct fluid balance within the body’s cavities. These cells also play a role in the immune system by helping to detect and respond to infections and foreign materials.
When the body sustains an injury, mesothelial cells are involved in the subsequent healing process. They contribute to the inflammatory response, which is the body’s first step in addressing damage. Following inflammation, these cells aid in tissue repair and regeneration, working to restore the integrity of the affected area.
Mesothelial Cells and Disease
The primary disease associated with mesothelial cells is malignant mesothelioma, a cancer that arises from the mesothelium. This condition is strongly linked to asbestos exposure. When asbestos fibers are inhaled or ingested, they can travel to the mesothelial linings, particularly the pleura around the lungs or the peritoneum in the abdomen. The fibers become lodged in the tissue, causing chronic inflammation and DNA damage to the mesothelial cells over many decades, which can eventually lead to cancerous growth.
Damage to the mesothelium can also lead to non-cancerous conditions. After surgery or injury, the healing process can sometimes go awry, leading to the formation of fibrosis, or scar tissue. This can cause adhesions, where the visceral and parietal layers of the mesothelium stick together, restricting organ movement and potentially causing pain or dysfunction. An accumulation of excess fluid in the space between the layers, known as an effusion, can also occur.
Not all growths originating from mesothelial cells are cancerous. Benign tumors, such as mesothelial hyperplasia, can also develop. While these are not malignant, they can sometimes present symptoms or appear similar to cancerous growths in medical imaging, requiring further investigation to diagnose correctly.