Histology and Epithelial Tissues

Study Notes

Histology and Tissue Structure

Histology is the study of tissue structure and organization within organisms.
Understanding tissue structure is critical to grasping how cells form tissues, which combine to create organs and systems.
Tissue changes may occur due to development, aging, trauma, or diseases, such as cancer.
The arrangement of cells in a tissue is specialized to perform specific functions.
Tissues are classified into four major types, each with diverse functions.

Epithelial Tissues

Epithelial tissue covers organs and body surfaces, and is anchored to a basement membrane.
Composed of tightly packed cells, epithelial tissues contain minimal intercellular materials and generally lack blood vessels.
Epithelial tissues renew frequently, undergoing constant replacement.

Types of Epithelial Cells

Simple Squamous Epithelium
- Comprised of a single layer of flattened cells.
- Facilitates diffusion and gas exchange in lungs; lines blood and lymph vessels, and body cavities.
Simple Cuboidal Epithelium
- Made up of a single layer of cube-shaped cells with central nuclei.
- Functions in secretion and absorption, particularly in kidneys and glands.
Simple Columnar Epithelium
- Formed by elongated cells with nuclei near the basement membrane; may have cilia.
- Lines the uterus, stomach, and intestines; involved in protection, secretion of digestive fluids, and nutrient absorption.
- Contains microvilli in intestines to increase absorption surface area; includes mucus-secreting goblet cells.
Pseudostratified Columnar Epithelium
- Appears layered due to varied nuclear positioning but is a single layer of cells.
- May have cilia and goblet cells; lines respiratory tubes to sweep away debris.
Stratified Squamous Epithelium
- Composed of layers of flattened cells to provide protection.
- Found in the outer skin, mouth, throat, vagina, and anal canal.
- The outer skin cells undergo keratinization, a process absent in moist areas like the throat and vagina.
Stratified Cuboidal Epithelium
- Made up of 2-3 layers of cuboidal cells lining lumens in mammary, sweat, salivary glands, and pancreas.
- This multilayer configuration offers greater protection.
Stratified Columnar Epithelium
- Consists of several cell layers and is located in the vas deferens, part of the male urethra, and parts of the pharynx.
Transitional Epithelium
- Designed for distension, it allows the urinary bladder to expand and contract while preventing urine diffusion.
Glandular Epithelium
- Comprises cells that produce and secrete substances into ducts or fluids.
- Exocrine glands secrete products into ducts, while endocrine glands secrete directly into body fluids and blood.