Epithelial tissue

Ciliated epithelium lines the inner surface of hollow organs like bronchioles and Fallopian tubes.

Cuboidal epithelium lines the tubular parts of nephrons, where it helps in secretion and absorption.
Bronchioles are lined by ciliated epithelium, and the moist surface of the buccal cavity by compound epithelium.

The inner lining of blood vessels (the endothelium) is made of a single thin layer of flattened cells with irregular boundaries.
Such a tissue is simple squamous epithelium.
NCERT states that squamous epithelium is found in the walls of blood vessels and the air sacs of lungs, where it is involved in forming a diffusion boundary.
Columnar epithelium lines the stomach and intestine; connective tissue and smooth muscle form the outer layers of the vessel wall, not its lining.
Hence the cells lining the blood vessels belong to squamous epithelium.

When columnar or cuboidal cells bear cilia on their free surface, the tissue is called ciliated epithelium.
Its function is to move particles or mucus in a specific direction over the epithelium.
It is mainly present on the inner surface of hollow organs like the bronchioles and the Fallopian tubes.
The stomach is lined by non-ciliated columnar epithelium, the oesophagus by stratified squamous epithelium, and the urethra and bile duct are not lined by ciliated columnar cells.
Hence ciliated columnar epithelial cells occur in bronchioles and Fallopian tubes.

Simple squamous epithelium is made of a single thin layer of flattened cells with irregular boundaries.
It is found in the walls of blood vessels and the air sacs of lungs, where it forms a diffusion boundary.
The inner lining of blood vessels (endothelium) is therefore squamous epithelium.
Cuboidal epithelium lines ducts of glands and kidney tubules, columnar epithelium lines the stomach and intestine, and ciliated epithelium lines bronchioles and Fallopian tubes.
Hence the inner walls of blood vessels are formed of squamous epithelium.

In epithelial tissue the cells are compactly packed with little intercellular matrix, and specialised junctions provide structural and functional links between the cells.
Tight junctions help to stop substances from leaking across the tissue.
Adhering junctions cement the neighbouring cells together.
Gap junctions connect the cytoplasm of adjoining cells for the rapid transfer of ions, small molecules and sometimes big molecules.
NCERT states that these three types of junctions are found in the epithelium and other tissues, and describes them under epithelial tissue.
Hence these junctions are found in epithelial tissue.

If columnar or cuboidal cells bear cilia on their free surface, the tissue is called ciliated epithelium.
Its function is to move particles or mucus in a specific direction over the epithelium.
It is mainly present on the inner surface of hollow organs like the bronchioles and the fallopian tubes: in the bronchioles it sweeps mucus and dust outwards, and in the fallopian tubes it moves the ovum towards the uterus.
Hence the epithelium is ciliated.

Simple epithelium consists of a single layer of cells resting on a basement membrane, with very little intercellular material.
The cells are closely packed in a definite layer (squamous, cuboidal or columnar).
It lines body cavities, ducts and tubes, and functions in diffusion, secretion and absorption.
So the characteristic of simple epithelium is that the cells form a definite layer.