Module 4: Tissues – Structure and Function in Anatomy & Physiology

Introduction to Tissues

What is a Tissue?

A tissue is a group of closely associated cells that perform a specific function and are similar in structure. Tissues are fundamental building blocks in multicellular organisms, providing structure and function to organs and systems.

• Epithelial tissue – coverings and linings

• Connective tissue – support

• Nervous tissue – control

• Muscle tissue – movement

Tissues are composed of cells suspended in an extracellular matrix. The extracellular matrix is material outside the cell, made of proteins and fluid, and its composition varies by tissue type.

Epithelial Tissue

Introduction to Epithelial Tissue

Epithelial tissues cover the body surface or line body cavities. They form boundaries between different environments and regulate the passage of substances into and out of the body. Any substance that enters or leaves the body must pass through an epithelium.

• Main functions: Protection, absorption, secretion, and ion transport

• They line most body surfaces and cavities

• Contain little or no extracellular matrix

General Characteristics of Epithelial Tissue

• Cellularity: Epithelial cells are separated by minimal extracellular material; the tissue is mostly cells connected by specialized lateral junctions.

• Polarity: The apical (exposed) surface differs structurally and functionally from the basal (attached) surface.

• Regeneration: Epithelial tissues have a high regenerative capacity; lost cells are quickly replaced by cell division.

• Avascular but Innervated: Epithelia lack blood vessels and receive nutrients by diffusion from underlying connective tissue, but they are innervated (supplied by nerves).

• Support: All epithelial sheets are supported and attached to underlying connective tissue by a basal membrane.

Key Terms: apical (top/exposed), basal (bottom/attached), lateral junctions (connections between cells)

Additional info:

• Lateral junctions include tight junctions (prevent passage between cells), desmosomes (provide mechanical strength), and gap junctions (allow communication between cells).