Epithelial tissue is a type of animal tissue that line the cavities and surfaces of blood vessels and organs in the body. Epithelial tissue originates from the ectoderm. All glands in our body are made of epithelial cells. Epithelial tissue cells are tightly packed and form a continuous sheet. They have no intercellular spaces between them. The shape of the cells depends on the location and function of the tissue.
They are classified as- Simple squamous epithelium, Stratified squamous epithelium, Columnar epithelium, and Cubodial epithelium.
1. Simple squamous epithelium- They are a single layer of thin flat, plate like cells. This type of epithelium is permeable and occurs where molecules can cross the membrane either via filtration or diffusion. Tongue, esophagus and the lining of the mouth are made up of squamous epithelium. It protects the underlying parts of body from mechanical injury, germs, and from drying.
2. Stratified squamous epithelium- it consists of squamous epithelial cells arranged in layers that protect from wear and tear. They lack intercellular spaces and are found in areas in body that are subject to constant abrasion. It forms the outermost layer of the skin and the inner lining of the mouth, esophagus and vagina.
3. Columnar epithelium are of two types, ciliated and non-ciliated. They are uni-layered. They line organs of the digestive tract including the stomach, small and large intestine and also the uterus. Ciliated epithelium helps the movement of ova in the fallopian tubes and the movement of mucus in the respiratory tract.
4. Cuboidal epithelium- They consists of single layers of cells that are equally tall and wide. They perform secretion and absorption and are found in the small collecting ducts of the kidneys, pancreas, and salivary glands.
5. Glandular epithelium- Epithelial cells that acquire properties of gland cells to secrete substances at the surface of the epithelial tissues are known as glandular epithelium. These substances are water based fluids and contain proteins.
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