Simple squamous epithelium is a type of epithelial tissue characterized by a single layer of squamous epithelial cells. Epithelium lines most of the body’s organs and constitutes one of the body’s main tissue types, along with nervous, connective, and muscle tissue. Epithelium is divided by form and function into three main types: cuboidal, squamous, and columnar. Squamous cells are flat and primarily function in processes of secretion, diffusion, and filtration. Epithelial cells arranged in one layer are called simple epithelium, and epithelial tissue with more than one layer is considered stratified.
Under a microscope, simple squamous epithelium appears flat and irregular, much like scales or fried eggs laid side by side. One can also see a round, dark stained spot in the middle of each cell, which is the nucleus. Because there is only one layer of cells, each cell is in contact with the basement membrane, or basal lamina, a fibrous sheet that anchors the epithelium to the underlying organ. The side facing the basement membrane is called the basal surface and the exposed surface is called the apical surface. Like other types of epithelia, simple squamous epithelium is arranged with very little intercellular space, or gaps between cells, and the cells are attached laterally, or on the sides.
Simple squamous epithelium has the unique characteristic of a very large surface area relative to its width. This makes it suited for rapid diffusion and filtration. Diffusion is the process of particles moving from a place of higher concentration to a place of a lower concentration. For example, when well-nourished blood passes a hungry cell, the nutrients diffuse through the wall of the blood vessel into the cell, because the blood has a higher concentration of nutrients than the cell. Filtration is a process in which fluids move due to hydrostatic pressure.
Simple squamous epithelium is found in the alveoli in the lungs, the endothelium of the blood vessels, the glomerulus and tubules in the kidneys, mesothelium. In the alveoli, or the grape-like structures in the lungs, simple squamous epithelium helps diffuse gases in and out of the blood stream as part of respiration. Simple squamous epithelia in the endothelium, or the thin interior lining of all blood vessels, aids blood flow and regulates the passage of white blood cells and other substances out of the bloodstream. In the glomerulus and tubules in the kidney, this epithelium conducts filtration and diffusion to regulate the body’s water and excrete wastes. The mesothelium, or the thin membrane that surrounds the heart, lungs, and many organs in the abdomen, protects the organs by forming a lubricated film that prevents the organs from rubbing or sticking together.