Epithelial Tissue: Cell Differentiation and Specialization

• Epithelial tissue is one type of mammalian tissue.

Cell Differentiation and Specialization

• In unicellular organisms, a single cell performs all necessary life functions.
• In multicellular organisms, cells differentiate and specialize as they mature.
• Cells develop specific shapes and structures for particular functions.
• Tissue development allows multicellular organisms to perform life functions efficiently.

Epithelial Tissue

• It forms continuous sheets of cells that cover the body's external and internal surfaces, including skin, the gut, and blood vessels.
• Epithelial tissue attaches to underlying tissue via a basement membrane.
• It does not contain blood vessels and is classified as simple or compound based on its structure.

Simple Epithelium

• Consists of a single layer of cells.

Squamous Epithelium

• Found in the inner lining of the mouth, vagina, oesophagus, blood vessels, and alveoli of the lungs.
• It features thin, large, flattened, irregularly shaped cells.
• Cells are closely packed in a mosaic pattern and contain spherical, centrally positioned nuclei.
• Functions include protecting and supporting underlying tissue, reducing friction in blood vessels, and facilitating gas diffusion with a moist environment.

Cuboidal Epithelium

• Located in various glands with secretory functions, such as the salivary glands and liver, and in the lining of ducts like renal tubules.
• Cells have approximately equal length and width, with no intercellular spaces.
• They feature large, round, centrally situated nuclei.
• Cuboidal epithelium secretes or absorbs various substances based on the organ's function.

Columnar Epithelium

• Lines the stomach, small intestine, urethra, vas deferens (sperm duct), prostate gland, and part of the uterus.
• Columnar cells are elongated and column-shaped with an oval nucleus near the base.
• These often contain goblet cells, which are column-shaped epithelial cells that secrete mucus.
• Functions include secreting mucus, absorbing digested food, and providing protection and support.

Ciliated Epithelium

• Found in the nasal cavity, trachea, bronchi, fallopian tubes, vas deferens, the central canal of the spinal cord, and sense organs like ears, eyes, and noses.
• Ciliated epithelium is made of columnar cells with a brush border of cilia (short, hair-like organelles) at their free ends, and this tissue also contains goblet cells.
• Dust particles get trapped in the mucus secreted by the goblet cells.
• Cilia beat rhythmically to move mucus and trapped dust away from the lungs towards the throat, where it can be swallowed or coughed out.
• This tissue also helps move cerebrospinal fluid along the spinal cord's central canal and moves ova along the fallopian tubes in females.

Compound Epithelium

• Consists of numerous layers of cells, including stratified squamous, cuboidal, and columnar epithelium.
• Stratified epithelial tissue is found on the surface of the skin, rectum, anus, tongue, pharynx, sweat gland ducts, and bladder.
• Cells have varied shapes and sizes, arranged in layers, and new cells are formed closest to the basement membrane.
• Outer layers wear off, causing deeper cells to flatten, harden, and move closer to the surface.
• Functions in protection, excretion, feeding, and thermoregulation.