HistologyLecture 2 Epithelia

What is a tissue? • A collection of cells that have similar

functions and morphologies

Vertebrate Tissue Types

• Epithelial• Connective• Muscle• Nerve

– Many organs/structures are combinations of these basic types

Features of Epithelial Tissues• Closely attached cells with very little

extracellular matrix• Cell to cell attachments strong• Flat/curved sheets lining sufaces (G.I. Tract

and vasculature)

Functions of Epithelia

• Covering and lining surfaces (skin)• Absorption (intestine)• Secretion (glands of skin & GI tract)• Sensation (taste buds, olfactory epith.)• Contractility (myoepithelium of glands)

Epithelial Cell Shapes• Squamous (flattened)• Cuboidal• Columnar• Nuclear Shape

– spherical– irregular– flattened

All Epithelia Have A Basal Lamina

• 20-100 nm thick• type 4 collagen, laminin, proteoglycans

2 main types of basement membraneA: 2 adjacent epithelial layersB: epithelium adjacent to connective tissue matrix

Basement Membrane Is Specialized and Thicker Than A

Simple Basal Lamina• Kidney glomeruli and some tubules• Lung alveoli and trachea

Epithelial Cells are Linked by Cell to Cell Junctions

• Tight junction (zonula occludens)• Belt desmosome (zonula adherens)• Gap junction• Desmosome• Hemidesmosome

Apical Specializations of Epithelial Cells

• Microvilli – brush border in kidney and small intestine

• Stereocilia– epididymis, hair cells of organ of Corti

• Cilia and Flagella– respiratory tract, oviduct, sperm

Types of Epithelia

• Covering epithelia• Glandular epithelia

Types of Covering Epithelia

• Simple – one layer of cells

• Stratified– more than one layer of cells

Types of Simple Epithelium

• Simple squamous– endothelium of vessels; mesothelium

• Simple cuboidal– kidney tubules, thyroid follicle, serosa of

some organs• Simple columnar

– small intestine, colon, stomach

Types of Simple Epithelium

Simple squamous

Simple cuboidalSimple columnar

Types of Stratified Epithelium

Types of Stratified Epithelium• Classified by the shape of the most

surface layer• Stratified squamous keratinized - skin

Stratified squamous nonkeratinized• Oral cavity, esophagus, vagina

Stratified cuboidal• Sweat gland duct

Stratified columnar• Conjunctiva, duct of pancreas

Transitional epithelium• Urinary bladder

Pseudostratified epithelium• Respiratory tract, nasal/olfactory epithelia

Specialized Epithelia

• Neuroepithelium - taste buds, organ of Corti, olfactory epithelium

• Myoepithelium - secretory glands such as salivary glands, sweat glands and mammary gland

Glandular Epithelia

• Pancreas, adrenal medulla, sebaceous glands, salivary glands, mammary glands

• Sweat glands (little synthetic activity; transfer of molecules and ions from blood)

Types of Glandular Epithelia

• Unicellular glands - goblet cells• Multicellular glands

– Endocrine glands: no ducts• cords of cells with vessels (adrenal cortex,

parathyroid, anterior pituitary)• follicular (thyroid)

– Exocrine glands: ducts (salivary glands, pancreas, mammary glands, etc.)

Types of Exocrine Glands

• Simple: secretory cells and one unbranched duct– tubular, coiled tubular, branched tubular, or acinar

• Compound: secretory cells and branched ducts– tubular, acinar, or tubuloacinar

Examples of Glands

Individual glandular cells = respiratory tract and digestive tract goblet cells; endocrine cells of gutSimple tubular = stomach epitheliumSimple coiled tubular = merocrine sweat glandSimple branched tubular = stomach epitheliumSimple branched acinar = sebaceous gland Compound tubuloacinar = submandibular gland, sublingual glandCompound acinar gland = exocrine pancreas, parotid glandCompound tubular gland = some types of salivary glands

Simple glands = one, unbranched ductCompound glands = branched ducts

Types of Secretion

• Merocrine: membrane-bound granules by exocytosis; pancreas, salivary glands

• Holocrine: secretions released by bursting of whole cell; sebaceous glands

• Apocrine: secretions released as droplet with cytoplasm from apical surface; mammary glands and apocrine sweat glands

Lamina Propria

• Area of connective tissue and vasculature underlying epithelium

• Separated from epithelium by basal lamina

Mucous Secreting Cells

• Goblet cell of intestine: large apical mucin granules, flattened basal nucleus, RER basal, Golgi apical

• Digestive tract, salivary glands, respiratory tract, reproductive system

Myoepithelial Cell• Stellate/spindle shaped• Base of acinar and duct cells in glands• Contain actin/myosin; contractile