Biology · Structural Organisation in Animals · NEET
Simple squamous epithelium is a SINGLE thin layer of flat cells. NCERT calls it 'simple' because there is only one layer resting on the basement membrane. When it is many layers thick it becomes COMPOUND (stratified) squamous epithelium, like the skin surface. For NEET, if the question says 'simple squamous', picture just one flat sheet.
Because it is very thin, materials can pass through it easily. In the alveoli of the lungs, oxygen and carbon dioxide diffuse across this thin layer. In blood vessel walls, the thin lining lets substances filter through. So the function (fast diffusion and filtration) matches the thin structure. This structure-function link is a favourite NEET point.
Endothelium is not a separate tissue type. It is the NAME given to the simple squamous epithelium that lines the inside of blood vessels and the heart. So 'endothelium' = simple squamous epithelium in a special location. NEET 2023 tested exactly this: Squamous epithelium matches with Endothelium.
The cells are flat, thin and plate-like (also called pavement or tile-like) with irregular, wavy boundaries. The nucleus is flattened and lies in the centre. 'Squamous' comes from a word meaning 'scale', so remember scale-like flat cells.
NCERT states two main sites: the walls of blood vessels and the air sacs (alveoli) of the lungs. It also lines body cavities and the heart (as endothelium). All these places need a thin surface for diffusion, filtration or a smooth lining.
Match List-I with List-II. List-I (A) Columnar epithelium (B) Ciliated epithelium (C) Squamous epithelium (D) Cuboidal epithelium List-II (I) Ducts of glands (II) Inner lining of stomach and intestine (III) Inner lining of bronchioles (IV) Endothelium Choose the correct answer from the options given below:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is a tissue made of a single thin layer of flat, tile-like cells. It is so thin that gases and fluids can pass through it quickly.
NCERT lists the walls of blood vessels and the air sacs (alveoli) of the lungs as the main sites of simple squamous epithelium.
Its thin structure allows diffusion of gases and filtration of substances. It also forms a smooth lining for cavities and blood vessels.
Endothelium is just the name for the simple squamous epithelium that lines the inside of blood vessels and the heart. Structure is the same; only the location gives it this special name.
The outer skin is made of COMPOUND (stratified) squamous epithelium, which is many layers thick for protection. This is different from the single-layered simple squamous epithelium in alveoli and vessels.
