EPITHELIUM

CAPT DR POONAM SINGHDEPT OF ANATOMY

SEQUENCE OF PPT

1. INTRODUCTION2. DEVELOPMENT3. CLASSIFICATION4. HISTOLOGICAL APPEARANCE5. APICAL DOMAIN & ITS MODIFICATIONS6. LATERAL DOMAIN & ITS SPECIALIZATIONS7. BASAL DOMAIN8. GLANDS & ITS TYPES

TISSUES4 Basic types

DEVELOPMENT

5 – 6 DAY

Implantation of the Blastocyst6th DAY

9TH DAY

DEVELOPMENT

DEVELOPMENT OF EPITHELIUM

1. Ectoderm:- skin, hair follicles, mammary glands, cornea, conjunctiva, some parts of mouth & anal canal.

2. Endoderm:- GIT ( except part of mouth &anal canal), resp tract, glands.

3. Mesoderm:-body cavities (Mesothelium), endothelium.

EPITHELIUM

• Avascular tissue composed of cells,1. Covers the exterior of body surfaces2. Lines internal body cavities & body tubes3. Forms parenchyma of glands their ducts4. Specialized epi cells fxn as receptors for the

special senses.

• Nourished by connective tissue• Regenerate & repair quickly

FUNCTIONS

1. Protection2. Absorption3. Secretion4. lubrication5. Transportation6. Receptor fxn ( sensory)

Characteristics

1. Cell junctions:- specific cell-to-cell adhesion molecules.

2. Exhibit functional & morphological polarity a) Apical domain

b) lateral domainc) basal domain

3. Rest on basement membrane- anchors epithelial cells to underlying connective tissue

CLASSIFICATION

• Based on 2 factors:-

1. Simple / Unilaminar

2. Compound / Stratified / Multilaminar

Based on the shape of surface cells:-

W > H

W = H H>W

EPITHELIUM

UNILAMINAR/ SIMPLE MULTILAMINAR/ SRTATIFIED

STRATIFIED SQUAMOUS

KERATINIZED

NON-KERATINIZED

STRATIFIED CUBOIDAL

STRATIFIED COLUMNAR

TRANSITIONAL

SQUAMOUS

CUBOIDAL

COLUMNAR WITHOUT SPECIALIZATION

WITH SPECIALIZATIONS

MICROVILLI CILIA

GLANDULAR CELLSPSEUDOSTRATIFIED

MYOEPITHELIAL CILIA

SENSORY CELLS

NONCILIATED CILIATED STEREOCILIA

Classification of Epithelial Tissue

Simple Squamous Epithelium• Structure

– Single Layer of flattened cells• Function

– Diffusion and filtration– Not effective protection – single

layer of cells.• Location

– Endothelium– Mesothelium– Lung alveolus

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, germinal layer ofovaries

Simple Columnar Epithelium• Structure

– Elongated layer of cells with nuclei at same level

• Function-- Absorption, Protection

& Secretion

• Location-- GIT

Simple Columnar Epithelium with specializations

1. Ciliated columnar epithelium:--cell surface bears cilia.-lines the resp tract, uterus, uterine tubes.

2. Simple columnar epithelium with microvilli:--visible only under EM.-striated border:- small intestine- brush border:- GB- increase surface area & absorption rate

Simple Columnar Epithelium with specializations

3. With secretory function: Goblet cells- scattered in the mucosa of stomach & small intestines- single cell glands, produce protective mucus.

Stratified Squamous Epithelium

• StructureMany layers (usually Cuboidal/columnar at base & squamous at

surface) Found in those surfaces subject to friction.

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

• waterproofs and toughens skin

• Keratinized/ Non-keratinized

Stratified squamous keratinized • Loc:- skin

• Superficial cell die & lose their nuclei

• Keratin (+)

Stratified squamous non-keratinised• Loc:-

Mouth, tongue, pharynx, esophagus, vagina & cornea.

Stratified squamous epithelium

• Eg..vagina

Stratified Cuboidal epithelium

• Loc:-large ducts of sweat glands, salivary glands, pancreas.

Stratified columnar epithelium

• Loc:- palpebral conjunctiva

Special classification of epithelium1. 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

2. TRANSITIONAL EPITHELIUM

• Structure– Many layers / Stratified epithelium– 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)– Impermeable to salts

• Location– Urinary bladder, ureters & urethra

URINARY BLADDER

-exhibits special structural surface modifications to carry out specific fxns.

Apical domain and its modifications

1. Microvilli- fingerlike cytoplasmic projections- increase surface area for absorption- length= 5 µm - varya) short, irregular, bleb-like (transepithelial transport is less).b) tall, closely-packed, uniform ( transport fluid & absorb metabolites).

2. STEREOCILIA

• Extremely long, immotile microvilli.

• length= 5-10 µmLimited to:-• Epididymis• Proximal part of ductus

deferens• Sensory cells of the

inner earIn EM:- hairs of a paint

brush

3. Cilia- hair like extensions of apical plasma membrane containing anoxeme.- motile extensions Moves mucus, etc. over epithelial surface 5-10 µm : length 0.2 µm : diameter

3 Types of cilia1. Motile:- large no. (+)nt on the apical domain of many epithelial cells.

2. Primary / Monocilia:- - solitary projections, Immotile- single cilium per cell (+)ntfxn:- Chemosensors mediate light sensation Osmosensors Odorant Mechanosensors sound perception in multiple organs in the body

3. Nodal cilia:- -Found in the embryo on the bilaminar germ disc -Concentrated in the area that surrounds the primitive node.

Lateral domain & its specializations

• Characterized by the presence of CAMs

Classification of cell contacts

• Unspecialized contacts

-Cell adhesion molecule - Each CAM is in contact with

intermediate protein.-Force is transmitted from

cytoskeleton of one cell to another.

-TEM:- bead-like

Specialized junctional structures• Forms the barrier & attachment device junctional complex

responsible for joining cell together.• Three types:-1. Anchoring jxns 2. Occluding jxns/ tight cell to cell contact: jxns / Zonula occludens(a). Macula adherens

(Desmosomes)(b). Zonula adherens 3. communicating jxns/ Gap

(Adhesive belts) jxns

Cell to extracellular matrix :(a) Focal adhesions / Adhesive strips(b) Hemidesmosomes / Focal spots

Desmosomes

Zonula adherens

ANCHORING JUNCTIONS

DESMOSOME ZONULA ADHERENS

Fascia adherens

Hemidesmosomes

Occluding junctions

Gap junctions

TYPES OF CELL JUNCTIONS

TYPES OF CELL JUNCTIONS

Basal domainBASEMENT MEMBRANE• Amorphous, dense layer of

variable thickness at the basal surfaces of epithelia.

• Consists of:1. Basal lamina

a). Lamina densa b). Lamina Lucida2. Reticular lamina• Visible under LM

BASEMENT MEMBRANE

• Functions:1. Adhesion 2. Act as barriers3. Cell organization4. Regeneration of

peripheral nerves after injury

GLANDS

EXOCRINE GLANDS ENDOCRINE GLANDS-Consists of duct - Lacks duct system-Secretes their product into the surface directly / thru the duct

- Secrete their product into the CT enter bloodstream reach target cells

-Secretion: Unaltered, concentrated -product called as HORMONES

- Sweat, Oil glands, Salivary glands, Mammary glands.

- Thyroid, adrenal and pituitary glands

Classification of Exocrine glands

1. Unicellular- simplest, single cell- Unbranched duct

2. Multicellular / compound- > one cell- Branched duct

1. Tubular:- tube like2. Alveolar/ Acinar:- flask shaped3. Tubuloalveolar:- tube ends in sac like dilation

** Tubular secretory portions:- straight, branched, coiled

** Alveolar portions:- single / branched

Modes of Secretion

1. Merocrine Glands:-• secretory products

del in membrane bounded vesicles apical surface of cells extrude by exocytosis

• Eg.. Pancreatic acinar cells, sweat gland, salivary glands

Modes of Secretion

2. Apocrine Glands:-• Secretory product

released in apical portion of cell surrounded by a thin layer of cytoplasm within an envelope of plasma membrane.

• Eg.. Mammary gland, ceruminous gland of ext auditory meatus

Modes of Secretion

3. Holocrine Glands:-• Secretory product

accumulates within the cell programmed cell death

• Sec products & cell debris discharged into lumen

• Eg.. Sebaceous gland of skin, meibomian glands

PARACRINE GLANDS

• Secretory material reaches the target cells by diffusion through the extracellular space / subjacent CT.

ENDOCRINE GLANDS• Eg… Pituitary gland, ovaries, testes, pancreas

Thyroid gland, Adrenal gland

DISCUSSION