What is the significance of epithelial cells?

The significance of epithelial cells stems from their strategic locations within tissues and organs and their critical roles in various physiological processes that are essential to life. Depending on their structure, location, and specialized features, epithelial cells may have one or a combination of the following functions: 

• Barrier formation: Epithelial cells form protective barriers that separate and shield internal body environments from external factors. They also prevent harmful substances, pathogens, and toxins from entering sensitive tissues. 
• Surface protection: Epithelial cells provide a physical barrier on body surfaces, protecting against physical trauma, microbial invasion, and dehydration.
• Absorption and Secretion: Certain epithelial cells specialize in the absorption of nutrients, water, and electrolytes from the external environment while others are involved in secretion, producing and releasing substances such as mucus, hormones, and enzymes. 
• Filtration: Respiratory tract epithelium plays a key role in filtering out contaminants and particles from the air, so you only inhale clean air.
• Diffusion: Selective diffusion of materials from higher concentrations to lower concentrations through the squamous epithelial cells facilitates filtration, absorption, and secretion functions. 
• Excretion: Specialized epithelial cells in the sweat glands are responsible for excreting sweat while those in the kidneys are responsible for excreting waste products
• Sensory reception: The body receives external sensory stimuli though sensory nerve endings that are embedded in the epithelium. For example, stereocilia in the epithelium in the ear helps hearing and balance.