Epithelium

Epithelium is a type of body tissue that forms a continuous sheet-like covering on the exterior surfaces of the body (skin), internal surfaces of cavities and organs (lining of the digestive tract), and forms glands. Its primary functions include protection, absorption, secretion, and sensation. Epithelial cells are tightly packed, connected by specialized junctions, and avascular (lacking blood vessels), relying on underlying connective tissue for nutrients. The classification of epithelium is based on the shape of the cells (squamous, cuboidal, columnar) and the number of cell layers (simple, stratified). This arrangement and cellular specialization allow for diverse functional roles in various body systems. Specific types include the epidermis of the skin, the lining of the respiratory tract, and the specialized cells of glands like those that secrete hormones.

Epithelium meaning with examples

• The respiratory system's epithelium, a pseudostratified columnar type, is lined with cilia and goblet cells. These goblet cells secrete mucus that traps inhaled particles. Cilia then sweep the mucus upwards, clearing the airways of dust and pathogens. This process protects the lungs and facilitates efficient gas exchange in alveoli.
• The digestive system's epithelium, specifically the simple columnar type lining the small intestine, plays a vital role in nutrient absorption. Its microvilli increase the surface area, optimizing uptake from digested food. This efficient absorption is essential to providing the body with necessary energy and building blocks.
• The epidermis, a stratified squamous epithelium, forms a protective barrier against the external environment. Its multiple layers and keratinization (hardening) help prevent water loss and protect against abrasion, UV radiation, and infection. This ensures the integrity of the skin as a crucial defense.
• Glandular epithelium, found within glands like the thyroid, is responsible for secretion. Thyroid epithelium secretes hormones (e.g., thyroxine) directly into the bloodstream. These hormones regulate metabolism and play a key role in other essential bodily functions and are controlled by the hypothalamus.