Chapter 4: Tissue – The Living Fabric (Anatomy & Physiology Study Notes)

Tissues: The Living Fabric

Introduction to Tissues

Tissues are groups of cells that are similar in structure and perform a common function. The human body is composed of four primary types of tissues, each with specialized roles essential for maintaining homeostasis and overall function.

• Epithelial tissue: Covers body surfaces and lines cavities.

• Connective tissue: Supports, protects, and binds other tissues together.

• Muscle tissue: Contracts to produce movement.

• Nervous tissue: Enables internal communication via electrical impulses.

Primary Tissues of the Human Body

Overview and Functions

• Nervous tissue: Found in the brain, spinal cord, and nerves; responsible for transmitting electrical signals from sensory receptors to effectors.

• Muscle tissue: Includes skeletal muscles (attached to bones), cardiac muscle (heart), and smooth muscle (walls of hollow organs); contracts to cause movement.

• Epithelial tissue: Forms boundaries between environments, protects, secretes, absorbs, and filters; lines digestive tract organs and other hollow organs, glands (e.g., pancreas), and skin surface (epidermis).

• Connective tissue: Supports, protects, and binds other tissues; found in bones, tendons, and fat/soft padding tissue.

Epithelial Tissue (Epithelium)

Main Types by Location

• Covering and lining epithelia: Located on external and internal surfaces (e.g., skin, lining of organs).

• Glandular epithelia: Forms the secretory tissue in glands.

Characteristics of Epithelial Tissue

• Polarity: Cells have an apical (free) surface and a basal (attached) surface.

• Specialized surfaces:

  • Apical surfaces may have microvilli (brush border of intestinal lining) or cilia (lining of trachea).

  • Basal surface rests on a basement membrane composed of glycoproteins and collagen fibers.

• Cellularity: Composed of closely packed cells forming continuous sheets held together by tight junctions and desmosomes.

• Support: Supported by a connective tissue reticular lamina beneath the basement membrane.

• Avascular but innervated: Contains no blood vessels but is supplied by nerve fibers.

• Regeneration: High rate of cell division and repair.

Classification of Epithelia

Epithelia are classified based on two criteria:

• Number of cell layers:

  • Simple epithelium: Single cell layer thick.

  • Stratified epithelium: Two or more cell layers.

• Cell shape:

  • Squamous: Flattened cells.

  • Cuboidal: Cube-shaped cells.

  • Columnar: Column-shaped cells.

Example: Simple squamous epithelium consists of a single layer of flat cells, while stratified columnar epithelium has multiple layers of tall, column-shaped cells.

Types of Epithelial Tissue

Type	Structure	Main Functions	Locations
Simple Squamous	Single layer of flattened cells	Diffusion, filtration, friction reduction	Kidney, lining of heart, blood vessels, lymphatic vessels, serosae
Simple Cuboidal	Single layer of cube-shaped cells	Secretion, absorption	Kidney tubules, ducts and secretory portions of small glands, ovary surface
Simple Columnar	Single layer of column-shaped cells; often with goblet cells, microvilli, or cilia	Secretion, absorption, movement of substances	Digestive tract (microvilli), small bronchi, uterine tubes, regions of uterus (ciliated)

Additional info:

• Goblet cells are specialized for mucus secretion and are commonly found in simple columnar epithelium.

• Microvilli increase surface area for absorption, while cilia aid in moving substances across the epithelial surface.