Characteristics of Epithelial Tissues

Basic Types of Tissues

• Four primary types of tissues: epithelial, connective, muscular, nervous.

Characteristics of Epithelial Tissue

• Covers and lines body surfaces.
• Cells are closely packed with little intercellular substance.
• Firm attachment through intercellular junctions.
• Rest on a basement membrane from underlying connective tissue.

Basement Membrane Functions

• Anchors epithelial tissue to connective tissue.
• Serves as a selective barrier for nutrient diffusion.

Nutrient Supply

• Epithelial tissue receives nutrients through diffusion from underlying connective tissue.

Nerve Supply and Vascularity

• Richly supplied with nerve fibers.
• Avascular, meaning it lacks its own blood supply.

Germ Layers and Epithelial Development

• Derived from ectoderm, mesoderm, and endoderm.
• Ectoderm forms the epidermis; endoderm forms the digestive tract epithelium; mesoderm forms the serous lining of cavities.

Classifications of Epithelial Tissue

• Covering/lining epithelium.
• Glandular epithelium (endocrine and exocrine).
• Neuroepithelium (taste buds).

Epithelial Classification Criteria

• Classified by the number of layers (simple or stratified) and shape of surface cells (squamous, cuboidal, columnar).

Simple Epithelial Tissues

• Composed of one cell layer.
• Functions include absorption, diffusion, secretion, and excretion.
• Types include simple squamous, cuboidal, columnar, and pseudostratified columnar.

Specific Functions and Locations

• Simple squamous: major function is diffusion; found in Bowman's capsule, blood vessels, alveoli.
• Simple cuboidal: involved in absorption, secretion; located in kidney tubules, thyroid gland.
• Simple columnar: aids in absorption, secretion; ciliated form found in uterine tubes; non-ciliated in stomach and intestines.
• Pseudostratified: appears layered but is one cell layer; varies in respiratory and male reproductive systems.

Stratified Epithelial Tissues

• Main function is protection against wear and tear.
• Types include stratified squamous, cuboidal, columnar, and transitional.

Stratified Epithelial Locations

• Stratified squamous: keratinized in skin, non-keratinized in oral cavity, vagina.
• Stratified cuboidal: rare, found in small ducts of sweat glands.
• Stratified columnar: rare, found in salivary glands and penile urethra.
• Transitional: changes shape, found in urinary system structures such as bladder.

Cell Junctions

• Types include tight junctions (prevent leakage), adherent junctions (strong adhesion), gap junctions (ion and small molecule transport), desmosomes (connect cells), and hemidesmosomes (attach to connective tissue).

Surface Specializations

• Cilia: propel substances; found in respiratory tract and fallopian tubes.
• Microvilli (brush border): increase surface area for absorption; found in small intestine.
• Stereocilia: long microvilli; located in male reproductive passages, absorb testicular fluid.

Goblet Cells and Myoepithelial Cells

• Goblet cells: modified cells that secrete mucus; found in GI tract and respiratory tract.
• Myoepithelial cells: contractile cells around glandular secretory units; found in lacrimal, salivary, mammary, and sweat glands.

Glandular Epithelium

• Organized collections from covering epithelial cells that synthesize and secrete substances.
• Vascularized.
• Classifications: exocrine (ducts) and endocrine (no ducts).

Exocrine Glands

• Release secretions into ducts.
• Classified based on duct branching (simple or compound), secretory unit shape (tubular or acinar), secretion type (serous, mucous, mixed), and mode (eccrine, apocrine, holocrine).

Endocrine Glands

• Classified by arrangement; include follicular (e.g., thyroid gland) and anastomosing cords (e.g., parathyroid gland).

Functions of Epithelial Tissue

• Protection: covers surfaces and lines organs.
• Absorption: occurs in intestines and kidneys.
• Secretion: performed by glandular epithelium.
• Excretion: conducted by kidneys.
• Sensation: neuroepithelium role in taste.
• Contractility: myoepithelial cells in glands.
• Reproduction: germinal epithelium in ovaries and testes.

Test your knowledge on the fundamental characteristics and types of epithelial tissues. This quiz will cover the basic types of tissues in the body and the major traits that define epithelial tissue. Ideal for students studying anatomy and physiology.