EPITHELIUMDR. SWATI PATIL

INTRODUCTIONEpi= upon; Thelia= nipple

DEVELOPMENTEctoderm- skin, mouth, nose and anal canal.

Endoderm- GIT, glands, resp tract Mesoderm-body cavities

(Mesothelium), endothelium.

Function of Epithelial Tissue

• Protection

• Absorption

• Filtration

• Secretion

Characteristics of Epithelial Tissue• Form continuous sheets

(fit like tiles)

• Apical Surface– All epithelial cells

have a top surface that borders an open space (lumen)

• Basement Membrane – anchors

epithelial cells to underlying connective tissue

BASEMENT MEMBRANE

- visible under LM- PAS +- comprises of basal lamina & reticular lamina

BASAL LAMINA- visible in EM- 20-100 nm thick- consists of dense and clear layers- composed of macromolecules

1. Laminin2. Type IV collagen3. Entactin (Nidogen)4. Proteoglycans

• Avascularity – Lacks blood

vessels– Nourished by

connective tissue• Regenerate & repair

quickly

Classification of Epithelial Tissue

Classification of Epithelial Tissue - Criteria

• Cell Shape– Squamous – flattened– Cuboidal - cubes– Columnar - columns

• Cell Layers– Simple (one layer)– Stratified (many layers)

• Named after type of cell at apical surface

Simple Squamous Epithelium• Structure

– Single Layer of flattened cells

• Function– Absorption, and filtration– Not effective protection –

single layer of cells.• Location

– Walls of capillaries, air sacs in lungs

– Form serous membranes in body cavity

Simple Cuboidal Epithelium

• Structure– Single layer of cube

shaped cells• Function

– Secretion and transportation in glands, filtration in kidneys

• Location– Glands and ducts

(pancreas & salivary), kidney tubules, covers ovaries

Simple Columnar Epithelium• Structure

– Elongated layer of cells with nuclei at same level

• Function– Absorption, Protection

& Secretion– When open to body

cavities – called mucous membranes

• Special Features– Microvilli, bumpy

extension of apical surface, increase surface area and absorption rate.

– Goblet cells, single cell glands, produce protective mucus.

• Location– Linings of entire digestive

tract

Simple Columnar Epithelium

Features of Apical Surface of Epithelium

Finger-like extensions of plasma membrane of apical epithelial cell

Increase surface area for absorption

Temporary or permanent 1 µm : height, 0.8 µm : width BRUSH/STRIATED BORDER:

seen in LM Terminal web : supports

microvilli composed of actin filaments w/

fimbrin & villin(eg.) in small intestine

Microvilli

Features of Apical Surface of Epithelium

Cilia: (eg.) respiratory tubes Whip-like, motile extensions Moves mucus, etc. over epithelial surface 1-way 5-10 µm : length 0.2 µm : diameter

* Flagella: (eg.) spermatozoa Extra long cilia Moves cell

Stereocilia (eg.) epididymis & ductus deferens Longer but non motile, compared to microvilli Branched

Pseudostratified Epithelium• Structure

– Irregularly shaped cells with nuclei at different levels – appear stratified, but aren’t.

– All cells reach basement membrane

• Function– Absorption and Secretion– Goblet cells produce mucus– Cilia (larger than microvilli)

sweep mucus • Location

– Respiratory Linings & Reproductive tract

Myoepithelial cells

Stratified Squamous Epithelium• Structure

Many layers (usually cubodial/columnar at bottom and squamous at top)

Function– Protection– Keratin (protein) accumulates in older cells near

the surface • waterproofs and toughens skin.

• Location Nonkeratinised

Keratinised

Stratified squmous keratinised

Stratified squamous non-keratinised

Stratified cuboidal epithelium

Stratified columnar epithelium

Transitional Epithelium • Structure

– Many layers– Very specialized

• cells at base are cuboidal or columnar, at surface will vary.

– Change between stratified & simple as tissue is stretched out.

• Function– Allows stretching (change size)

• Location– Urinary bladder, ureters &

urethra

GLANDS• One or more cells that make and secrete a product.• Secretion = protein in aqueous solution: hormones, acids, oils.• Endocrine glands

– No duct, release secretion into blood vessels – Often hormones– Thyroid, adrenal and pituitary glands

• Exocrine glands– Contain ducts, empty onto epithelial surface– Sweat, Oil glands, Salivary glands, Mammary glands.

Modes of Secretion

• (How the gland’s product is released)

• Merocrine - secretory products are released by

exocytosis– Ex: Sweat glands and salivary glands

• Apocrine-apical part is shed off to discharge –

secretion- Ex:mammary glands

Modes of Secretion

• Holocrine– Entire cell disintegrates

while discharging its secretion

– Sebaceous (oil glands on the face) only example

Classification of Exocrine glands

Branching

Simple – single, unbranched duct

Compound – branched.

• Shape:– tubular or alveolar– Tubular – shaped like a tube– Alveolar – shaped like flasks or sacs– Tubuloalveolar – has both tubes and sacs in

gland

Cell Junctions & Cell-Cell Adhesion

Classification of cell contacts

• Unspecialised contacts -cell adhesion molecule -intermediate protein

Cell-cell adherence junctions

1. Calcium-dependent

Cadherins

Selectins

Integrins

2. Calcium-independent

Neural cell adhesion molecule

Intercellular adhesion molecule

Actin cytoskeleton dependent cell-cell and cell-ECM adhesions

• Specialized contacts -Anchoring junctions 1.Adhesive spots or desmosomes or macula

adherens 2.Adhesive belts or zona adherens 3.Adhesive strips or fascia adherens - Occluding junction or zonula occludens or tight

junction -Communicating junctions or gap junctions

Desmosomes

Zonula adherens

Fascia adherens

Desmosomes

&

hemidesmosomes

Focal adhesion plaques

Tight Junctions

Types of Cell Junctions

Summary of cell junctions

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