Body Tissues: Structure, Classification, and Function in Human Anatomy & Physiology

Body Tissues

Overview of Body Tissues

Body tissues are groups of cells with similar structure and function. In human anatomy and physiology, tissues are classified into four primary types, each with distinct roles in the body.

• Epithelial tissue (epithelium): Covers body surfaces and lines cavities.

• Connective tissue: Supports, connects, and protects body parts.

• Muscle tissue: Responsible for movement.

• Nervous tissue: Receives and transmits nerve impulses.

Epithelial Tissue

General Characteristics of Epithelial Tissue

Epithelial tissues are specialized to line body surfaces and form protective sheets. They have unique structural and functional properties:

• Cellularity: Composed of closely packed cells with minimal extracellular material.

• Polarity: Each sheet has an exposed apical surface and an attached basement membrane.

• Avascularity: Epithelial tissues lack a direct blood supply.

• Regeneration: Cells divide rapidly to replace lost or damaged cells, especially if 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 epithelium: One layer of cells.

  • Stratified epithelium: More than one layer of cells.

• Cell shape:

  • Squamous: Flattened, scale-like cells.

  • Cuboidal: Cube-shaped cells.

  • Columnar: Tall, column-shaped cells.

Visual Classification

Simple epithelium has a single layer of cells, while stratified epithelium has multiple layers. Cell shapes include squamous (flat), cuboidal (cube-like), and columnar (tall).

Functional Classification of Epithelial Tissue

The function of epithelial tissue is closely related to its structure and type.

Cell Type	Number of Layers One layer: simple epithelial tissues	Number of Layers More than one layer: stratified epithelial tissues
Squamous	Diffusion and filtration; secretion in serous membranes	Protection
Cuboidal	Secretion and absorption; ciliated types propel mucus or reproductive cells	Protection; these tissue types are rare in humans
Columnar	Secretion and absorption; ciliated types propel mucus or reproductive cells	Protection; these tissue types are rare in humans
Transitional	No simple transitional epithelium exists	Protection; stretching to accommodate distension of urinary structures

Simple Epithelia

Simple epithelia are specialized for absorption, secretion, and filtration. They are not suited for protection due to their thinness.

Simple Squamous Epithelium

• Structure: Single layer of flat cells.

• Locations:

  • Air sacs of the lungs (alveoli)

  • Walls of capillaries (Endothelium)

  • Serous membranes (Serosae or Mesothelium) lining and covering organs

• Function: Allows rapid diffusion, filtration, or secretion in membranes.

Example

Simple squamous epithelium forms the thin walls of alveoli in the lungs, facilitating gas exchange.

Additional info:

• Other simple epithelia include simple cuboidal (found in kidney tubules and glands) and simple columnar (lining the digestive tract).

• Stratified epithelia provide protection, especially in areas subject to abrasion (e.g., skin, esophagus).

• Transitional epithelium is specialized for stretching, found in the urinary bladder.