Anatomy & Physiology: Tissues – Structure, Types, and Functions

Body Tissues

Introduction to Tissues

Tissues are groups of cells with similar structure and function, forming the basic building blocks of organs and body systems. There are four primary tissue types in the human body:

• Epithelial tissue (epithelium)

• Connective tissue

• Muscle tissue

• Nervous tissue

Epithelial Tissue

Locations and Functions

Epithelial tissue is found covering body surfaces, lining internal cavities, and forming glandular structures. Its main functions include:

• Protection – shields underlying tissues from mechanical and chemical damage

• Absorption – takes in substances such as nutrients and water

• Filtration – selectively allows substances to pass through

• Secretion – produces and releases substances like mucus and hormones

Key Characteristics of Epithelial Tissue

• Lines body surfaces – forms continuous sheets

• Polarity – has an apical surface (free, exposed) and a basement membrane (anchored to underlying tissue)

• Avascular – lacks direct blood supply

• Regenerates easily – especially when well-nourished

Classification of Epithelia

Epithelial tissues are classified based on two criteria: the number of cell layers and the shape of the cells.

• Number of cell layers:

  • Simple – one layer

  • Stratified – more than one layer

• Shape of cells:

  • Squamous – flattened, like fish scales

  • Cuboidal – cube-shaped, like dice

  • Columnar – tall, column-like

Examples and Applications

• Simple squamous epithelium – found in air sacs of lungs and lining of blood vessels; allows for rapid diffusion and filtration.

• Stratified squamous epithelium – found in skin, mouth, and esophagus; provides protection against abrasion.

• Simple cuboidal epithelium – lines kidney tubules and glandular ducts; involved in secretion and absorption.

• Simple columnar epithelium – lines digestive tract; specialized for absorption and secretion, often contains goblet cells that secrete mucus.

Table: Epithelial Tissue Classification

Type	Layers	Cell Shape	Main Locations	Main Functions
Simple Squamous	1	Flat	Lungs, blood vessels	Diffusion, filtration
Simple Cuboidal	1	Cube	Kidney tubules, glands	Secretion, absorption
Simple Columnar	1	Column	Digestive tract	Absorption, secretion
Stratified Squamous	Multiple	Flat (surface)	Skin, mouth, esophagus	Protection

Additional info: Epithelial tissues may also include pseudostratified and transitional types, which have specialized functions in the respiratory and urinary systems, respectively.