Human Histology: Epithelial Tissue Types and Functions

Introduction to Histology

Tissues are groups of similar cells specialized to carry out a specific function.

• Histology: The study of tissues.
• Cytology: The study of cells.

There are 4 primary types of tissues in the human body: Epithelial, Connective, Muscle, and Nervous.

Epithelial Tissue Overview

Epithelial tissue covers organs and lines cavities to form barriers; these tissues absorb, secrete, and excrete substances.

• Glandular Tissue: Secretes substances needed by the body.
• Characteristics: Avascular, high mitotic rate, tightly packed, possesses a basement membrane and one free surface.

Extracellular Matrix: All material outside of and between non-living cells.

Classification of Epithelial Tissue

Epithelial tissues are classified by shape: Squamous, Cuboidal, Columnar, and Transitional.

Simple Epithelium

• Simple Squamous: Single layer of flat cells. Function: Absorption. Example: Alveoli of lungs.
• Simple Cuboidal: Single layer of cube-shaped cells. Function: Secretion and absorption. Example: Kidney tubules, salivary glands.
• Simple Columnar: Single layer of tall cells. Function: Protection, secretion, and absorption. Example: Ciliated (fallopian tubes) or microvilli-lined (small intestine).
• Pseudostratified Columnar: Appear layered but are not. Usually ciliated with goblet cells. Example: Respiratory passages.

Stratified Epithelium

• Stratified Squamous: Many-layered flat cells. Function: Protection. Example: Skin, esophagus.
• Stratified Cuboidal: 2 to 3 layers of cube-shaped cells. Function: Protection. Example: Sweat glands, salivary glands.
• Stratified Columnar: Several layers of tall cells. Function: Protection. Example: Pharynx.
• Transitional: Stretches. Function: Protection. Example: Lines bladder and uterus.

Glandular Tissue

• Glandular: Produces and secretes substances.
• Exocrine Glands: Secrete onto surfaces or into cavities. Examples: Salivary, sweat, ceruminous (ear), sebaceous (skin oils), and pancreas.
• Endocrine Glands: Secrete into the blood. Examples: Thyroid, pituitary.

Key Definitions

• Secretion: Substances produced and needed by the body.
• Excretion: Waste leaving the body.