EPITHELIAL TISSUE

Epithelial tissue

Epithelial tissue is a type of connective tissue that forms the covering of external and internal surfaces of the body.

Functions of Epithelial tissue :

• Forms a covering for external and internal surfaces of the body
• Lines the cavities of organs and glands
• Lines the surfaces of hollow organs
• Forms glands

Structure of Epithelial tissue :

• Composed of epithelial cells
• Epithelial cells are closely packed to form a layer
• Layer may be single or multiple
• Epithelial cells are attached to each other by desmosomes and to the basement membrane by hemidesmosomes

Types of Epithelial tissue :

• Simple epithelium :
  • Composed of single layer of epithelial cells
  • Types : Simple squamous, Simple cuboidal and Simple columnar
• Stratified epithelium :
  • Composed of multiple layers of epithelial cells
  • Types : Stratified squamous, Stratified cuboidal and Stratified columnar

Simple Epithelium

Types of simple epithelium :

• Simple squamous :
  • Composed of flat epithelial cells
  • Found in areas where filtration and diffusion occur
  • Examples : Lungs, kidneys
• Simple cuboidal :
  • Composed of cube-shaped epithelial cells
  • Found in areas where secretion and absorption occur
  • Examples : Ovaries, pancreas
• Simple columnar :
  • Composed of column-shaped epithelial cells
  • Found in areas where secretion and absorption occur
  • Examples : Intestine, stomach

Stratified Epithelium

Types of stratified epithelium :

• Stratified squamous :
  • Composed of multiple layers of flat epithelial cells
  • Found in areas where friction and abrasion occur
  • Examples : Skin, esophagus
• Stratified cuboidal :
  • Composed of multiple layers of cube-shaped epithelial cells
  • Found in areas where secretion and absorption occur
  • Examples : Salivary glands, sweat glands
• Stratified columnar :
  • Composed of multiple layers of column-shaped epithelial cells
  • Found in areas where secretion and absorption occur
  • Examples : Trachea, bronchi

Glandular Epithelium

Types of glandular epithelium :

• Endocrine glands :
  • Composed of epithelial cells that secrete hormones
  • Examples : Pituitary gland, thyroid gland
• Exocrine glands :
  • Composed of epithelial cells that secrete substances through ducts
  • Examples : Salivary glands, pancreas

Lining of body cavities

Types of lining :

• Serous lining :
  • Secretes mucus or a watery fluid
  • Examples : Lungs, digestive tract
• Mucous lining :
  • Secretes mucus
  • Examples : Nasal cavity, vagina
• Ciliated lining :
  • Has cilia that move secretions
  • Examples : Lungs, oviducts

Functions of Epithelial tissue in body cavities :

• Protection
• Absorption
• Secretion
• Filtration
• Excretion

Epithelial Tissue

1. Define Epithelium

Epithelium is a type of connective tissue that forms the lining of various organs, glands, and body surfaces. It is composed of closely packed cells that perform specific functions such as protection, secretion, absorption, filtration, and diffusion.

2. Characteristics of Epithelial Tissue

• Simple or stratified
• Pseudostratified or stratified
• Cuboidal or squamous
• Keratinized or non-keratinized
• Ciliated or non-ciliated
• Glandular or non-glandular

3. Classification of Epithelia

• Simple Epithelia
  • Simple Squamous Epithelium
  • Simple Cuboidal Epithelium
  • Simple Columnar Epithelium
• Stratified Epithelia
  • Stratified Squamous Epithelium
  • Stratified Cuboidal Epithelium
  • Stratified Columnar Epithelium
• Pseudostratified Epithelia
  • Pseudostratified Columnar Epithelium

Simple Squamous Epithelium

• Forms lining of blood vessels and alveoli
• Allows for easy diffusion of gases and nutrients
• Examples: endothelium and mesothelium

Simple Cuboidal Epithelium

• Forms lining of kidney tubules and ducts
• Allows for secretion and absorption
• Examples: renal tubules and sweat glands

Simple Columnar Epithelium

• Forms lining of intestine and respiratory tract
• Allows for absorption and secretion
• Examples: intestinal epithelium and respiratory epithelium

Stratified Squamous Epithelium

• Forms lining of skin and esophagus
• Provides protection and resistance to wear and tear
• Examples: skin and esophageal mucosa

Stratified Cuboidal Epithelium

• Forms lining of sweat glands and salivary glands
• Allows for secretion and absorption
• Examples: sweat glands and salivary glands

Stratified Columnar Epithelium

• Forms lining of trachea and bronchi
• Allows for secretion and absorption
• Examples: tracheal and bronchial epithelium

Pseudostratified Columnar Epithelium

• Forms lining of respiratory tract and urethra
• Allows for secretion and absorption
• Examples: respiratory epithelium and urethral epithelium