Tissue Organization: Structure and Function in Anatomy & Physiology

Chapter 05: Tissue Organization

Introduction to Tissues

Tissues are fundamental units in multicellular organisms, consisting of groups of similar cells and their associated extracellular material. The study of tissues is known as histology, which is essential for understanding the structure and function of organs and systems in the human body.

• Tissue: Groups of similar cells and extracellular matrix that perform a common function.

• Extracellular Matrix: Non-cellular material surrounding cells, providing structural and biochemical support.

• Histology: The scientific study of tissues.

• Four Major Tissue Types: Epithelial, Connective, Muscle, Nervous.

• Each tissue type has distinct structure and function.

Characteristics of Epithelial Tissue

Epithelial tissue (or epithelium) is specialized for covering surfaces, lining cavities, and forming glands. It is composed of tightly packed cells with minimal extracellular matrix and lacks blood vessels.

• Cellularity: Composed almost entirely of tightly packed cells.

• Polarity: Has an apical surface (exposed to environment or body space) and a basal surface (attached to underlying connective tissue).

• Attachment: Bound to a basement membrane, which acts as a barrier and anchor.

• Avascularity: No blood vessels; nutrients obtained by diffusion.

• Innervation: Highly innervated for sensory reception.

• Regeneration: High capacity for replacement of lost cells.

Locations:

• Covers body surfaces (e.g., skin)

• Lines body cavities (e.g., digestive tract)

• Forms majority of glands (e.g., sweat glands)

Functions:

• Physical protection (from dehydration, abrasion, destruction)

• Selective permeability (controls passage of substances)

• Secretion (specialized cells produce substances)

• Sensation (sensory reception and information transfer)

Classification of Epithelial Tissue

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

• By Number of Layers:

  • Simple Epithelium: Single layer; all cells contact basement membrane. Functions in absorption, secretion, filtration.

  • Stratified Epithelium: Multiple layers; only basal layer contacts basement membrane. Provides protection against mechanical stress.

  • Pseudostratified Epithelium: Appears layered but all cells contact basement membrane; not all reach apical surface.

• By Cell Shape:

  • Squamous: Flat, wide, irregular shape; nucleus flattened.

  • Cuboidal: As tall as wide; nucleus spherical and central.

  • Columnar: Taller than wide; nucleus oval, located in basal region.

  • Transitional: Cells change shape depending on stretch (e.g., bladder).

Example: Simple squamous epithelium lines air sacs of lungs, blood vessels, and serous membranes, allowing rapid movement of molecules.

Additional info: Classification is crucial for identifying tissue function and location in the body.