Epithelial Tissue

Diverse group that includes 

  • Surface -Covers body surfaces; lines body cavities, hollow organs, and ducts;  Ex: Skin 

  • Glands/ solid organs

  • As its name suggests, covering and lining epithelium forms the outer covering of the skin and the outer covering of some internal organs. 



  • It also lines body cavities; blood vessels; ducts; and the interiors of the respiratory, digestive, urinary, and reproductive systems. 



  •  The cells of epithelial tissue have an apical surface, which is exposed to a body cavity, lining of an internal organ, or the exterior of the body; lateral surfaces, which face cells on either side; and a basal surface, which is deep




Epithelial Tissue



Functions 

Protection 

  • Barrier 

  • Exchange between compartments 

Secretion 

  • By glandular products 

Absorption 

 Ex: Intestines




Epithelial Tissue Cell shapes



Squamous cells – thin, and this allows for the rapid passage of substances through them 



Cuboidal cells – as tall as they are wide and are shaped like cubes or hexagons. They may have microvilli at their apical surface and function in either secretion or absorption. 



Columnar cells – much taller than they are wide, like columns, and protect underlying tissues. Their apical surfaces may have cilia or microvilli, and they often are specialized for secretion and absorption.





Types of Epithelial Tissue 



Simple 

  • Single layer of identical cells 

Simple squamous 

  • Flat cells 

  • Ex: Heart, BVs, LVs, Lung alveoli 

Simple cuboidal 

  • Cube-shaped 

  • Secretion, absorption, excretion

Simple columnar 

  • Rectangular-shaped 

  • Alimentary tract 

  • Absorption, secretion 

  • Goblet cells





Simple ciliated

  • With fine hair-like processes – CILIA 

  • Movement 

  • Respiratory passages

Stratified - Layers

  • Stratified Epithelium 

  • Keratinized 

  • Dry surfaces 

  • Wear and tear 

  • Skin, hair, nails  



  • Non-keratinized 

  • Wet surfaces  Lining of mouth, pharynx, esophagus, vagina



Transitional

  • Transitional Epithelium

  • Pear-shaped cell 

  • Urinary system 

  • Stretches as urine passes

Epithelial Tissue 

  • A gland may consist of one cell or a group of highly specialized epithelial cells that secrete substances into ducts, onto a surface, or into the blood. All glands of the body are classified as either endocrine or exocrine: 



Endocrine glands enter the interstitial fluid and then diffuse into the bloodstream without flowing through a duct. These secretions are called hormones. 



Exocrine glands secrete their products into ducts that empty at the surface of covering and lining epithelium such as the skin surface or the lumen of a hollow organ. The secretions of exocrine glands include mucus, perspiration, oil, earwax, milk, saliva, and digestive enzymes.