Chapter 4: Histology

Introduction to Tissues

Histology is the study of tissues, which are groups of cells working together to perform specific functions. Understanding tissue structure and function is fundamental in Anatomy & Physiology.

• Tissue: A group of cells organized to perform specialized activities.

• Histology: The microscopic study of tissues.

• Biopsy: Removal of tissue for diagnostic examination.

• Autopsy: Examination of organs from a deceased body to determine cause of death.

There are four basic tissue types in the adult human body:

• Nervous tissue: Internal communication (brain, spinal cord, nerves)

• Muscle tissue: Contraction for movement (skeletal, cardiac, smooth muscle)

• Epithelial tissue: Forms boundaries between environments, covers surfaces, lines cavities, and forms glands

• Connective tissue: Supports, protects, and binds other tissues together (bones, tendons, fat, blood)

Organizational Levels in the Human Body

Tissues are a key level in the biological organization, situated between cells and organs.

• Atom → Molecule → Macromolecule → Organelle → Cell → Tissue → Organ → Organ System → Organism

Tissues are collections of similar cells and their extracellular matrix, working together for a common function.

Overview of Tissue Types

What Are We Expected to Learn?

For each of the four basic tissue types, study the following aspects:

• Location

• General characteristics

• Functions

• Classification

Epithelial Tissues

Major Types of Epithelial Tissues

• Covering and Lining Epithelium:

  • External surfaces: e.g., skin

  • Internal surfaces:

    1. Communicate with outside (digestive, respiratory, reproductive, urinary tracts)

    2. Do not communicate with outside (chest cavity, abdominal cavity, endothelium of blood vessels and heart)

• Glandular Epithelium:

  • Clusters deep to covering and lining epithelium

  • Specialized for secretion into ducts, onto surfaces, or into the blood

Functions of Epithelial Tissue

• Physical protection: Protects from abrasion, dehydration, and destruction by chemical or biological agents.

• Control of permeability: Regulates movement of substances by secretion, absorption, and filtration.

• Provide sensation: Extensively innervated by sensory nerves; may function in senses such as smell and taste.

• Glands provide specialized secretions: Epithelial cells form glands that secrete substances for various functions.

Key Characteristics of Epithelial Tissue

• Specialized contacts: Cells are closely joined by tight junctions and desmosomes.

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

• Avascularity: No direct blood supply; nutrients diffuse from underlying tissues.

• Regeneration: High mitotic rate; cells divide rapidly to replace lost or damaged cells.

• Cellularity: Composed almost entirely of cells with minimal extracellular material.

Classification of Epithelial Tissue

Epithelial tissues are classified by cell shape and number of layers:

• Cell shapes: Squamous (flat), Cuboidal (cube-shaped), Columnar (tall)

• Number of layers: Simple (one layer), Stratified (multiple layers), Pseudostratified (appears layered but all cells touch basement membrane)

Examples of Epithelial Tissue Types

Additional info:

• Epithelial tissues always have a free surface and a basement membrane (basal lamina).

• Basement membrane consists of lamina lucida (glycoproteins, fine filaments) and lamina densa (collagen bundles).