Epithelial Tissue

discribing the epithelial tissue

Epithelial Tissue

Covers a body surface or lines of body cavity, Forms parts of most glands

Function of epithelial tissue

Protection, secretion, absorption, diffusion, filtration, sensory receptions

Cellularity

Cell separated by minimal extra cellular material

specializes contacts

Cells joined by special junctions

Polarity

Cell regions of the epical surface differ from the basal surface

Special characteristic of epithelial

1- Support by connective tissue

2- Avascular but innervated

3- epithelial receives nutrients from underlying connective tissue

4- Regeneration: lost cells are quickly replaced by cell division.

Classification of epithelial first name of epithelial cells

Simple epithelial: single layer of cells attached to basement membrane

Stratified epithelial: Multiple layers of cells, Basal layer of cells attached to basement membrane

Classification of epithelial last name of epithelial cells

Squamous: cell are wider than tall, disc form

Cuboidal: cell are as wide as tall, like cubes

Columnar: cell are taller than they are wide, like columns

Function of simple squamous epithelial tissue

Diffusion and protection; Passages of material by passive diffusion and filtration,

Secretes lubricating substances in serosae

Location of simple squamous epithelial tissue

Renal corpuscles,

alveoli of lungs,

Lining of heart and blood and lymphatic vessels

Lining of ventral body cavity (serosae)

Location of simple cuboidal epithelial tissue

Kidneys tubules,

Secretory portions of small glands, ovary surface.

Description Simple columnar epithelium

Single layer of column shaped (rectangular) cells with oval nuclei

Some bear cilia at their apical surface

May contain gobbet cellls

Function of simple columnar epithelium

Absorption secretion of mucus, enzymes and other substances

Ciliated type propels muscles or reproductive cells by ciliary action

Location Simple columnar epithelium

Nonciiliated form: Lines digestive tract, gallbladder, ducts of some glands

Ciliated form: Lines small bronchi, uterine tubes, and uterus.

Description Pseudostratified Columnar Epithelium

• All cells originate at basement membrane

• Only tall cells reach the apical surface

• May contain goblet cells and bear cilia

• Nuclei lie at varying heights within cells

• Gives false impression of stratification

Stratified Epithelia properties

Contain two or more layers of cells

• Regenerate from below (basal layer)

• Major role is protection

• Named according to shape of cells at apical

layer

Description Stratified Squamous Epithelium

Many layers of cells are squamous in shape

• Deeper layers of cells appear cuboidal or

columnar

• Thickest epithelial tissue

• Adapted for protection from abrasion

Two Types of Stratified Squamous Epithelium

1- Keratinized

• Location—epidermis

• Contains the protective protein keratin

• Waterproof

• Surface cells are dead and full of keratin

2- Nonkeratinized

• Forms moist lining of body openings

Function of stratified squamous epithelium

Function Protects underlying tissues in areas

subject to abrasion

Description of stratified Cuboidal Epithelium

generally two layers of cube-shaped cells

Function Stratified Cuboidal Epithelium

Protection

Location of stratified cuboidal epithelium

Location

• Forms ducts of

• Mammary glands

• Salivary glands

• Largest sweat glands

Description Stratified Columnar Epithelium

several layers; basal cells usually cuboidal; superficial cells elongated

Function of stratified columnar epithelium

protection and secretion

Location of stratified squamous epithelium

• Keratinized forms epidermis

• Nonkeratinized forms lining of mucous

membranes

• Esophagus

• Mouth

• Anus

• Vagina

• Urethra

Location of stratified columnar epithelium

Rare tissue type

Found in male urethra and large ducts of some

glands

Description Transitional Epithelium

• Has characteristics of stratified cuboidal and

stratified squamous

• Superficial cells dome-shaped when bladder is

relaxed, squamous when full

Location of transitional epithelium

epithelium of urinary bladder, ureters, proximal urethra

Function of transitional epithelium

permits distension of urinary organs when they are filled with urine

Description of simple cuboidal epithelium

Single layer of cubelike cells with large,spherical central nuclei

Function of simple columnar epithelium

Secretion and absorption

Description of simple squamous epithelium

single layer; flat cells with disc-shaped nuclei

The Basal Lamina

Located at the boundary between the

epithelium and connective tissue

• Noncellular supporting sheet between the

epithelial tissue and the connective tissue

deep to it

• Consists of proteins secreted by epithelial cell

The Function of Basal Lamina

Functions

• Acts as a selective filter, determining which

molecules from capillaries enter the epithelium

• Acts as scaffolding along which regenerating

epithelial tissue cells can migrate

• Basal lamina and reticular layers of the

underlying connective tissue deep to it form the

basement membrane

Microvilli Fingerlike extensions of plasma membrane

• Have a core of actin filaments that stiffen the

microvillus

• Abundant in kidney tubules and small intestine

• Maximize surface across which small molecules

enter or leave cells

Cilia—whiplike, highly motile extensions of apical surface membranes

• Contain a core of microtubules held together by

cross-linking and radial “motor proteins”

• Cilia originate as microtubules assemble around

centrioles