Epithelial Tissue Overview

Study Notes

Defining Epithelial Tissue

Epithelial tissue is a sheet-like tissue that covers body surfaces, lines body cavities and forms glands.
It is characterized by closely packed cells with minimal extracellular matrix.
It acts as a barrier, protecting underlying tissues from mechanical injury, dehydration, and harmful substances.

Functions of Epithelial Tissues

Protection: Forms a barrier against pathogens, abrasion, and dehydration.
Secretion: Specialized epithelial cells produce and release substances such as hormones, mucus, and enzymes.
Absorption: Epithelial cells lining the digestive tract absorb nutrients.
Excretion: Removal of waste products.
Filtration: Selective passage of substances across the epithelium.
Diffusion: Movement of substances across the epithelium.
Sensory reception: Specialized epithelial cells detect stimuli, such as taste, smell, and touch.

Characteristics of Epithelial Tissues

Cellularity: Composed primarily of cells with minimal extracellular material.
Specialized contacts: Cells are closely joined by specialized junctions (tight junctions, adherens junctions, desmosomes, and gap junctions) to form continuous sheets.
Polarity: Apical (free) and basal (attached) surfaces with distinct structures and functions.
Supported by connective tissue: Attached to a basement membrane, a specialized layer of extracellular matrix.
Avascular: Lacks blood vessels, relying on diffusion from underlying connective tissue for nutrients and waste removal.
Regeneration: High capacity for renewal and repair due to rapid cell division.

Classification of Epithelial Tissues

Based on cell shape and arrangement in layers, epithelial tissues are categorized into different types:
- Squamous (flattened)
- Cuboidal (cube-shaped)
- Columnar (column-shaped)
Based on the number of layers:
- Simple (single layer) e.g., simple squamous epithelium
- Stratified (multiple layers) e.g., stratified squamous epithelium
Some special types:
- Pseudostratified columnar: Appears layered but all cells contact the basement membrane.

Example Tissues and their functions

Simple squamous epithelium: Lines blood vessels and air sacs of lungs, facilitating diffusion.
Stratified squamous epithelium: Forms the epidermis of the skin (protects against abrasion/drying).
Simple cuboidal epithelium: Lines kidney tubules, involved in secretion and absorption.
Stratified cuboidal epithelium: Found in sweat glands.
Simple columnar epithelium: Lines the digestive tract, involved in absorption and secretion.
Pseudostratified columnar epithelium: Found in respiratory tract, involved in secretion and movement of mucus.

Glands

Glands are derived from epithelial tissue specialized for secretion.
Classified as either exocrine (secrete products into ducts; e.g., sweat glands, salivary glands) or endocrine (secrete products directly into the bloodstream; e.g., thyroid gland).

Epithelial Tissue and Disease

Aberrant proliferation and differentiation of epithelial cells contribute to a variety of diseases including cancers such as skin cancer, lung cancer, and colon cancer.

Summary

Epithelial tissues perform essential functions in covering surfaces, lining cavities, and forming glands.
The structure, consisting of tightly packed cells attached to a basement membrane, dictates the diverse roles played by this essential tissue type.
Their highly regenerative nature is crucial for repairing damaged tissues and maintaining overall health.

Description

Explore the defining features and functions of epithelial tissue in this quiz. From its protective roles to its functions in secretion and absorption, gain a better understanding of this crucial body tissue. Test your knowledge on the characteristics and importance of epithelial tissues.