Epithelial tissue is composed of cells that are laid together in sheets, with its cells being closely connected to one another. The epithelial layers are avascular but innervated. The cells of the epithelium have two surfaces, the structure, and function of which can vary1. Such glands as the exocrine and endocrine are made up of epithelial tissue and are differentiated based on the manner of secretions’ release. There are eight types of epithelia, with six of them being identified on the basis of the number of cells and their shape and two being named by the type of cells found in them. They include simple squamous epithelium, simple cuboidal epithelium, simple columnar epithelium, pseudostratified columnar epithelium, stratified squamous epithelium, stratified cuboidal epithelium, stratified columnar epithelium, and transitional epithelium. Among the mentioned types of epithelia, the simple squamous epithelium will be discussed further. Simple squamous epithelium represents a single layer of flat cells that have the shape of scales. This type of epithelial lines the inner surfaces of all blood vessels make up the wall of alveolar sacs in the lungs and lines the cavities in the body2. The cells of the epithelium have a flat shape and are arranged using a single layer. This layer is thin enough that it allows forming of a membrane through which the compounds can move with the help of diffusion. Simple squamous epithelia allow for facilitating gas diffusion as well as small molecules. Simple squamous epithelium tends to be permeable and occurs where small molecules require passing quickly through membranes through diffusion or filtration. The epithelium falls under the physiological category of exchange epithelium because of its capacity to transport molecules promptly across the tissue level. To enable this movement, some kinds of simple squamous epithelium can be porous, which allows molecules to pass through it, thus enabling a leaky epithelium. Simple squamous epithelium is best located in the air sacs of the lungs, the lining of the heart, as well as lymphatic and blood vessels. Therefore, the primary function of this type of epithelium entails allowing materials to pass by means of diffusion and filtration and secrete lubricating substances. Because simple squamous epithelium is involved in the composition of the lungs, the heart, blood, and lymphatic vessels, it plays crucial functions in the body. The lungs are a vital body organ, which is a part of the respiratory system, allowing a person to breathe. They will enable the inflow of oxygen into the body (inhalation) and send carbon dioxide out (exhalation), while the exchange of oxygen and carbon dioxide is called respiration. Besides, the simple squamous epithelium is included in the composition of the heart, which is the most critical organ in the body which sends blood around it. Blood functions as the key provider of the body with oxygen and much-needed nutrients and also carries waste. The blood and lymphatic vessels also play vital roles in the human organism, with simple squamous epithelium representing their core component. The lymphatic system represents the component of the immune s