Epithelium

Histology

The study of tissues

Epithelium

Tissue that covers the outer body surface or lines a body cavity

One tissue cannot be

A component of another tissue

Cellularity

Epithelium is made almost entirely of cells

Cell junctions

Structures that connect epithelial cells to each other

Polarity

Epithelial cells have two different sides

Apical surface

Side facing open space

Basal surface

Side attached to the basement membrane

Goblet cell

Cell that secretes mucus

Basement membrane

Layer that anchors epithelium to connective tissue

Regeneration

Epithelial cells replace themselves quickly

Avascular

Has no blood vessels

Innervated

Associated with nerve cells

Absorption

Active uptake of molecules

Secretion

Active release of molecules

Diffusion

Movement of molecules down a concentration gradient

Filtration

Fluid leaking across capillary walls

Microvilli

Increase surface area

Cilia

Move fluid across the epithelial surface

Simple epithelium

One layer of cells

Stratified epithelium

Multiple layers of cells

Squamous

Flat cells

Cuboidal

Cube-shaped cells

Columnar

Tall cells

Simple squamous

Thin cells for diffusion and filtration

Simple squamous locations

Alveoli, blood vessels, kidney glomeruli, body cavities

Simple cuboidal

Cube-shaped cells for secretion and absorption

Simple cuboidal locations

Most glands and kidney tubules

Simple columnar

Tall cells for absorption and secretion

Non-ciliated simple columnar

Digestive tract

Ciliated simple columnar

Bronchi and uterine tubes

Pseudostratified columnar

Looks layered but all cells touch basement membrane

Pseudostratified columnar location

Trachea and upper respiratory tract

Stratified squamous

Thick protective epithelium

Keratinized stratified squamous

Skin

Non-keratinized stratified squamous

Digestive and reproductive tract openings

Stratified cuboidal

Large ducts of glands

Stratified columnar

Urethra

Transitional epithelium

Epithelium that stretches and changes shape

Transitional epithelium location

Urinary bladder

Gland

A structure specialized for secretion

Exocrine glands

Secrete through ducts onto surfaces or cavities

Endocrine glands

Secrete hormones directly into the blood