1. Epithelial tissue Functions Absorption Excretion Filtration Secretion
Protection
Sensory reception

2. Characteristics of epithelium
Cellularity
Tightly packed cells
Forms sheet
Little extracellular materials
Specialized contacts
Tight junction
Desmosomes

3. Characteristics of epithelium
Polarity
Apical surface
Upper surface exposed to the outer environment
Specialized structures
Microvilli
Basal surface
Lined with basal lamina
Thin membrane
Apical
Surface
Basal
Surface
Basal
Lamina

4. Characteristics of epithelium
Supported by connective tissue
Basement membrane
Basal lamina
Composed of glycoproteins
Reticular lamina
Composed of collagens
Tougher than basal lamina
Resists stretching
Define epithelial boundary

5. Characteristics of epithelium
Innervated
Nerve endings
Avascular
Utilizes nutrients diffused from blood vessels underlining connective tissue
Highly regenerative
Many epithelial cells are exposed to extreme external environment

6. Classification of epithelia
Based on the number of cell layers
Simple
Stratified
Simple epithelia
Absorption/filteration
Stratified epithelia
Extreme environment

7. Classification of epithelia
Based on the shape of cells
Squamous
Flat, scale-like cells
Cuboidal
Box-like cells
Height/width = 1
Columnar
Tall, column-like cells
Shape of the nucleus
Reflects cell shape

8. Simple epithelia Simple squamous epithelium Flat cells
Looks like tiled floor
Found in tissues involved in rapid exchange of materials
Lungs
Kidneys

9. Simple epithelia Special simple squamous epithelia Endothelium
Inner lining of blood vessels and lymphatic vessels
Extremely thin
Mesothelium
Membrane that covers chest and abdominal cavity and organs found in these cavities

10. Simple epithelia Simple cuboidal epithelium cube-like cells
Found in tissues involved in secretion and absorption
Kidneys

11. Simple epithelia Simple columnar epithelium Tall, column-like cells
Found in digestive tract
Absorption
Secretion
Goblet cells produce protective mucus
Ciliated

12. Psuedostratified columnar epithelium
Cells vary in their height
Tallest cells interact with external environment
Shorter cells serve as reserves
False appearance of stratification
Location of nuclei within the layer

13. Psuedostratified columnar epithelium
Involved in secretion and absorption
Ciliated
Removal of particles within the air

14. Stratified epithelia Multiple layers of cells More durable
cells in lower layers
Replacement
More durable
Protective covering

15. Stratified epithelia Stratified squamous epithelia Most wide spread
Cells on the apical surface
Squamous
Basal cells
Cuboidal or columnar
Different cell viability

16. Stratified epithelia Stratified squamous epithelia
The outer layer (epidermis)
Keratinized in skin because of protective protein called keratin

17. Stratified epithelia Stratified cuboidal epithelium
Very rare
Found in large glands (sweat, mammary)
Usually contains two layers of cells
Stratified columnar epithelium
Only its top layer contains columnar cells

18. Transition epithelium
Found in organs that stretches
Urinary bladder
Basal cells
Columnar or cuboidal
Apical cells
Vary in appearance depends on how much distention the organ undergoes

19. Transition epithelium
Changes the number of cell layers as the organ distends
6 to 3 when the bladder stretches with urine
Apical cells flatten and look like squamous cells

20. Glandular epithelia Glands
Composed of cells involved in production and secretion of product
Fluid-like
Proteins
Lipids
Secretion
Active process

21. Glandular epithelia Glands Location of secretion
Endocrine (within the body)
Exocrine (outside of the body)
Number of the cells that compose the gland
Unicellular
Multicellular
Ducts