Last Updated on September 27, 2020 by Sagar Aryal
Simple squamous epithelium definition
Simple squamous epithelium is a type of simple epithelium that is formed by a single layer of cells on a basement membrane. It is a type of epithelium formed by a single layer of squamous or flat cells present on a thin extracellular layer, called the basement membrane. This epithelium is also termed the pavement epithelium because the cells appear like tiles on a floor when viewed from the apical surface.
Structure of the simple squamous epithelium
- The simple squamous epithelium consists of cells that are thinly walled with a dense nucleus.
- The position of the nucleus depends on the form of the cells where the nucleus is mostly randomly oriented towards the periphery.
- The cells appear like scales that provide a smooth low-friction surface over which fluids can move quickly.
- The thinness of the cells and the presence of a single layer facilitate the transfer and exchange of molecules across the membrane.
- The cells are tightly packed with almost no intracellular spaces, forming a continuous sheet.
- The shape and size of the cells are more or less similar to one another, although they are not identical to each other.
- All types of epithelium are separated from the underlying tissue by a basement membrane.
- The apical surface of the tissue faces the lumen of the organs while the lateral surfaces are provided with a variety of adhesions and junctions.
- These junctions ensure the connection between the adjacent cells and aid the transfer of water and other molecules between them.
- Membrane carrier proteins are found in this layer that function to facilitate the movement of ions, gases, small molecules, or water through the cells.
- Like all other epithelial tissues, the simple squamous epithelium is also avascular with no supply of blood vessels. The cells in this epithelium rely on the blood vessels of the adjacent connective tissues for oxygen, nutrients, and excretion.
- However, the cells do have a distinct nerve supply.
- Based on the location of the epithelium and its primary function, the squamous epithelium has two types.
- The first type is the endothelium, which lines the areas that require a rapid exchange of chemical substances.
- Endothelium arises from the ectoderm layer in the embryo.
- Endothelium provides protection while ensuring the movement of molecules in and out of the layer.
- The second type is the mesothelium that lines the surface layer of the serous membrane, consisting of cells that secrete a fluid to lubricate the surface.
- The mesothelium arises from the mesoderm layer of the embryo.
Functions of the simple squamous epithelium
As a part of the covering and lining epithelium, the first and most crucial function of simple squamous epithelium is the exchange of molecules. However, the epithelium also has a number of other functions, some of which are:
- They provide a smooth, frictionless surface in sites where secretion takes place.
- The epithelium also somewhat protects the underlying tissues against factors like desiccation, invasion by foreign invaders, toxins, and less intense physical trauma.
- However, because the epithelium is of a single layer, it cannot provide protection in areas subjected to extreme mechanical stress.
- The absence of blood vessels in the epithelial tissue thus prevents bleeding in the tissue during abrasion.
2. Absorption and Transportation
- They are particularly important in places where absorption and transportation of molecules take place.
- The simple epithelia are typically specialized as the lining of vessels and cavities, where they regulate the passage of substances into the underlying tissue.
- Different physiological processes like osmosis, diffusion, and filtration take place across the surface of this tissue.
- The processes like filtration of blood in the Bowman’s capsule of the kidneys and diffusion of oxygen and carbon dioxide between organs and blood vessels are all performed through the simple squamous epithelium.
- The singular layer of thin flat cells makes the simple squamous epithelium an ideal tissue for these processes.
- Epithelium in some parts like the intestinal wall consists of specialized membrane proteins, which facilitated diffusion of molecules and ions across the membrane.
- The simple squamous epithelium forming the mesothelium facilitated the movement of the viscera and the active transport of fluid by the process of pinocytosis.
- Some cells in the simple squamous epithelium are also known to produce some fluids like the mucus that acts as a lubricating agent against the inevitable friction.
- Mesothelium in different parts of the body is involved in the secretion of biologically active molecules.
- One example of this is the simple squamous epithelium in the intestine, where the cells produce mucus, reducing the friction created due to the movement of food particles through the intestine.
Location and Examples
- They are found throughout the body ranging from the blood vessels like arteries and veins to the nephrons in the kidneys.
- The endothelium lines the organs of the cardiovascular and lymphatic system of the body like the heart, blood vessels, and lymphatic vessels.
- Another example of the simple squamous epithelium is the alveoli of the lungs which are made up of a single layer of squamous cells surrounded by a network of capillaries.
- Peritoneum in the intestine is an example of the mesothelium that forms the epithelia of the serous intestinal membrane.
- The simple squamous epithelium also lines the Bowman’s capsule of the nephrons in the kidney. The outer wall of the Bowman’s capsule is bordered by a single layer of squamous cells. At the same time, the capillaries present inside the capsule are also made up of a modified form of the simple squamous epithelium.
- In addition, the loops of Henle in the kidneys are also lined by the simple squamous epithelium.
- Simple squamous epithelium is also found in the tympanic membrane of the ear and also lines the inner surface of the cornea.
- Besides, the lining of the common bile duct, oviduct, and ovary is also of the simple squamous epithelium.
References and Sources
- Mescher AL (2016). Basic Histology. Fourteenth Edition. McGraw-Hill Education.
- Tortora GJ and Derrickson B (2017). Principles of Physiology and Anatomy. Fifteenth Edition. John Wiley & Sons, Inc.
- Waugh A and Grant A. (2004) Anatomy and Physiology. Ninth Edition. Churchill Livingstone.
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