Epithelial Cells

Where are simple squamous epithelium cells found?

Alveoli, kidney tubules, endothelium (vessels), and mesothelium (body cavities)

Where can stratified squamous epithelium cells be found?

Skin (Keratinized), mouth, esophagus, anus, and the vagina (nonkeratinized).

Where can cubodial epithelium cells be found?

Simple: Glands, ducts, thyroid, kidney tubules

Stratified: Sweat glands

Where can transitional epithelium cells be found?

Bladder, ureters, and parts of the urethra

Where can columnar epithelium cells be found?

Simple: Digestive tract, uterus, kidney ducts

Pseudo-stratified: Respiratory tract

Stratified: Salivary gland ducts

Tight junctions

-Prevent diffusion between adjacent epithelial cells

-Forms barriers separating the basolateral surface from the lumen

-Formed by fusion of the plasma membrane

Adhesion belts

-Dense protein bands that reinforce tight junctions

-Link actin cytoskeletons of adjacent cells

-Provide structural integrity during stretching or twisting

Gap junctions

-Permit passage of ions and small molecules between cells

-Allow electrical and chemical communication

Desmosomes

-Strongest cell junctions for mechanical stability

-Found in the skin, and heart

Hemidesmosomes

-Anchor epithelial cells to the basal lamina

-Essential for tissue cohesion and resisting mechanical stress

Lamina lucida

-Contains glycoproteins and fine filaments

-Clear layer

Lamina densa

-Dense layer

-Contains coarse collagen fibers

Function of the basement membrane (basal lamina)

Strength, filtration, anchoring epithelium to connective tissue

What are microvilli used for?

Absorption

What are cilia used for?

Movement

What does the apical surface of an epithelial cell usually include?

Microvilli and cilia

Endocrine

Secrete hormones into interstitial fluid and bloodstream

Exocrine

Secrete onto surfaces or ducts (ex. Sweat, salivary glands)

Merocrine

-Exocytosis

-Ex. Mucin-Mucus in respiratory cells

-Cell remains intact

Apocrine

-Loss of cytoplasm with secretion

-Ex. Mammary glands

-Cell remains living but not intact

Holocrine

-Entire cell disintegrates to release contents

-Ex. Sebaceous glands

-Cell is not living nor intact

What type of exocrine secretion method is goblet cells?

Merocrine

Goblet cells

-Single mucus (goblet) cells among columnar epithelium

-Secretes mucin

-Mucin + Water = mucus

-Lubricant, protective, traps pathogens