Epithelial tissues

• Epithelial tissues cover body surfaces, line cavities and form glands.
• They function in protection, secretion, absorption, and transportation.

Epithelial tissues are classified based on the number of cell layers and cell shape

Simple Epithelium tissue

• Single layers of cells primarily functions in absorption, secretion, and filtration.

Types

Simple Squamous Epithelium

• • Structure: Single layer of flat cells.
  • Location: Alveoli of lungs, glomeruli of kidneys, lining of blood vessels (endothelium), and lining of body cavities (mesothelium).
  • Function: Allows for rapid diffusion and filtration.

Simple Cuboidal Epithelium

• • Structure: Single layer of cube-shaped cells.
  • Location: Kidney tubules, ducts of small glands, ovary surface.
  • Function: Secretion and absorption.

Simple Columnar Epithelium

• • Structure: Single layer of tall, column-shaped cells.
  • Location: Lining of the gastrointestinal tract, gallbladder, and some ducts of glands.
  • Function: Absorption and secretion; may have microvilli for increased surface area or cilia for movement of substances.

Stratified Epithelium tissue

• Multiple layers of cells, primarily functions in protection against abrasion.

Types

Stratified Squamous Epithelium

• • Structure: Multiple layers with flat apical cells.
  • Location:
    • Keratinized: Epidermis of the skin.
    • Non-keratinized: Lining of the mouth, esophagus, and vagina.
  • Function: Protects underlying tissues from abrasion and pathogens.

Stratified Cuboidal Epithelium

• • Structure: Typically, two layers of cube-shaped cells.
  • Location: Ducts of sweat glands, mammary glands, and salivary glands.
  • Function: Protection and limited secretion/absorption.

Stratified Columnar Epithelium

• • Structure: Multiple layers with columnar apical cells.
  • Location: Rare; found in the male urethra and large ducts of some glands.
  • Function: Protection and secretion.

Structure

• Epithelial cells are closely packed together with little extracellular matrix, and they form a continuous sheet held together by cell junctions such as tight junctions, gap junctions, and desmosomes.
• They have an apical surface facing the body cavity or external environment and a basal surface attached to the underlying connective tissue via a basement membrane.

Location

1. Surface epithelium: External body surfaces (skin), internal cavities (mouth, respiratory tract, and gastrointestinal tract)
2. Glandular epithelium: Forms glands (e.g., sweat glands, salivary glands, thyroid gland)

Functions

1. Protection: Epithelial tissues protect the body from mechanical injury, harmful substances, and pathogens.
2. Secretion: Glandular epithelium secretes substances like hormones, enzymes, and mucus.
3. Absorption: Simple columnar and simple cuboidal epithelia help absorb nutrients in the gastrointestinal tract and kidney tubules.
4. Transportation: Ciliated epithelial cells help transport particles and mucus across their surfaces.

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