A simple squamous epithelium refers to a single layer of thin, flat cells that line body surfaces which are not exposed to substantially abrasive forces. One side of a simple squamous epithelium opens to the local environment while the other is anchored to a thin support layer called a basement membrane. These cells provide a thin surface that facilitates the easy passage of small molecules across the epithelium. For example, simple squamous epithelium is found in the air sacs of the lungs, at the interface of blood filtration in the kidneys, and in minute blood vessels called capillaries.
A simple squamous epithelium called the endothelium lines the inner surfaces of arteries, veins and capillaries. In arteries and veins, the endothelium reduces friction and allows for smooth blood flow. Endothelial cells in arteries and veins also aid in the constriction or dilation of the blood vessels, which regulates blood flow and pressure. The walls of capillaries consist of a single layer of endothelial cells. This allows for the easy exchange of nutrients and oxygen into the body tissues, and the outflow of waste products.
Simple squamous epithelium lines the air sacs, or alveoli, of the lungs. The alveoli are the sites where gases are exchanged in the lungs. Simple squamous epithelial cells in the alveoli allow oxygen from the air to enter the blood in the capillaries of the lung. Carbon dioxide, a metabolic waste product, passes across the epithelium of the alveoli to be removed from the body by exhalation.
Simple squamous epithelial cells in the functional units of the kidneys, called the glomeruli, enable rapid filtration of the blood and diffusion of small molecules. This process enables the kidneys to remove waste products and excess water from the body through the urine.
Reviewed by: Tina M. St. John, M.D.