Epithelium

Presented by: Dr M. ArianmaneshPhD in Reproductive and Developmental Biology

Dept. of Anatomical Sciences

Today we will discuss:

• Classification of Epithelium

• Special Characteristics of Epithelial Surfaces

• Glandular Epithelium

Tissue

• Definition: Collection of specialized cells & thesubstances between them

• Classification:

• Epithelial

• Connective

• Muscle

• Nervous

Epithelial Tissue

• Surface Epithelium:

• Covers body surfaces:• Skin

• Lines hollow organs:• Digestive system

• Respiratory system

• Urogenital system

• Body cavities

• Glandular Epithelium:

• Formation of glands

Apical Surface

Lateral Surface

Basal Surface

Classification of Epithelium

• Based on shape of cells:

• Squamous

• Cuboidal

• Columnar

• Based on number of layers of cells:

• Simple

• Stratified

Basal/Germinal

layer

Based on number of layers of cells + shape of cells

Simple Stratified

Squamous

Cuboidal

Columnar

Squamous

Cuboidal

Columnar

Pseudostratified

Transitional

Keratinized

Non Keratinized

Simple Squamous Epithelium

EndotheliumMesothelium

Simple Cuboidal Epithelium

Simple Columnar Epithelium

Stratified Squamous Epithelium

Keratinized Stratified SquamousEpithelium

Non keratinized/Mucosal Stratified Squamous Epithelium

Pseudostratified Columnar Epithelium

Ciliated

Transitional Epithelium/Urothelium

• Apical Surface (Luminal/Free Surface)

• Microvilli:

• 0.5-1 µm in length

• Two observation:

• Brush/Striated/Regular border: Small intestine & Proximalconvoluted tubules of kidney

• Irregular: Endometrium

• Actin filaments, Villin, Fimbrin

• Terminal Web: Actin filaments,

Myosin II & Tropomyosin

• Motile

Special Characteristics of Epithelial Surfaces

Microvilli

Special Characteristics of Epithelial Surfaces

• Cilia:

• 5-10 µm in length

• Axoneme:

• Nexin

• Outer & inner dynein

• Radial spoke

• Motile

Continued…

Immotile Cilia Syndrome

Cilia

Special Characteristics of Epithelial Surfaces

• Stereocilia:

• Structure is the same as microvilli

• Nonmotile, 100 µm in length

• Epididym & hair cells of the inner ear

Continued…

• Lateral Surface

• Intercellular junctions:• Tight junction/Zonula occludens:

• Located in apical of lateral surface

• Claudin transmembrane protein

Special Characteristics of Epithelial Surfaces

Continued…

Special Characteristics of Epithelial Surfaces

• Zonula adherens/Adherent:

• Intercellular space: 15-20 nm

• Proteins:

• Cadherins (E cadherin)

• Actin filaments inside the cells

Continued…

Fascia Adherence incardiac cells

Special Characteristics of Epithelial Surfaces

• Macula adherens/Desmosome:

• Intercellular space: 20-30 nm

• Subplasmalemmal dense plaque:

• Proteins:

• Dense plaque: Desmoplakin,Pakoglobin

• Intercellular space: Desmoglein,Desmocollin

• Hemidesmosome:

• Connection of basal surface of the cellto the basal lamina

Continued…

Desmosome

Hemidesmosome

Special Characteristics of Epithelial Surfaces

• Gap/Nexus:

• Intercellular space: 2-3 nm

• Connexon

• Hexagonal unit: 6 integral proteins

• Central pore:

• 1.5 nm

• Passing ions, cAMP, amino acids

• Abundant in epithelium, smooth & cardiacmuscles, bone cells and embryonic cells

Continued…

Gap junction

• Basal Surface:• Basal Lamina: (EM)

• Contains: Type IV Collagen, Nidogen/Entactin,Proteoglycans, Integrin & Laminin

• 2 layers:• Lamina Lucida/Rara: 40-50 nm• Lamina Densa: 40-50 nm

• Basement membrane: (LM)

• Lamina Lucida• Lamina Densa• Lamina reticularis:

• Anchoring Fibrils

(Type VII Collagen)

Special Characteristics of Epithelial Surfaces

Continued…

External lamina

Basement Membrane

Basal Lamina ReticularLaminaLamina

Lucida(Rara)

Lamina Densa

Anchoring fibrils (type VII collagen)

• Development of glands:

• Exocrine glands

• Endocrine glands

Glandular Epithelium

• Classification of exocrine glands:

Based on the number of cells:

• Unicellular:

• Goblet cells

• APUD cells (amine precursor uptake & decarboxylation)

• Multicellular:

• Alveolar/Acinar

• Tubular

Glandular Epithelium

Based on mode of secretion:

• Merocrine

• Apocrine

• Holocrine

Based on secretory materials:

• Mucous glands:• Tubular

• Mucigen granules

• Serous glands:• Alveolar

• Zymogen granules

Glandular EpitheliumContinued…