Exam 1: Epithelial Tissue Flashcards
Four main tissue types
Epithelial
Musculoskeletal
Connective
Nervous
Where do the 4 main tissues come from
Epithelial - endoderm, ectoderm, mesoderm
Musculoskeletal - mesoderm
Connective - mesoderm
Nervous - ectoderm
Main characteristics of epithelial cells
Regenerative
Built on basement membrane
Avascular - dependent on underlying connective tissue
Apical border may have cilia, microvilli, or stereocilia
Little intercellular matrix, joint by intercellular links
Basement membrane
Glycogen fibers
•Basal lamina (EM) - from epithelial cells
•Reticular lamina (EM) - from connective tissue cells
Secreted by epithelial cells
Anchor the basal layer of the epithelium
Vascularization
Not in epithelium - avascular
In connective tissue below - dermis and sub dermis
Cilia
Ciliated epithelium are motile, carrying materials across surface
•ex, nasal epithelium
Microtubules allow cilia to move
Microvilli
Form brush border to enhance surface of absorptive and excretory epithelia
•ex, intestinal mucosa and renal tubule
Extensions of cell membrane with inner flexible scaffold of actin filaments
•no tubulin
No microtubules
Stereocilia
Long microvilli
Non motile and lack filamentous core
•Long finger like projections of membrane
Ex, epidydimal vas deferens epithelia
Found in reproductive tract
Keratinization
Epithelial cells covering dry surfaces (eg skin)
•Upper layer of dead cells, firmly attached, provide impermeable flexibility to minimize dehydration
Epithelial cells covering wet surfaces subject to abrasion (eg esophagus)
Types of intercellular links (junctions)
Tight junctions
Terminal bars
Desmosomes
Gap junctions
Most cells have at least 2 types of junctions
Tight junctions (zona occludens)
Fusion of intramembranous particles from adjacent cells
Contiguous membranes become indistinguishable even with EM
Columnar cells, apical border, to block small microorganisms from passing in between cells
ex - intestinal mucosa
Terminal bars (zona adhaerens)
Less tight of a union
Membranes are distinguishable with EM
Cuboidal and columnar epithelia, various tissues
Desmosomes (macula adhaerens, intercellular bridges)
Discontinuous junctions
May give epithelium a spiny appearance when cells shrink during histological processing
Composed of 2 hemidesmosomes anchored to their corresponding cells by tonofilaments
Squamous epithelium of epidermis, mostly
Gap junctions
Conduits between adjacent cells
Allows passage of ions and small molecules
Cuboidal epithelium
Ex - renal tube
Types of epithelium from the 3 germ layers
Endoderm - endothelium –> mucosa
Ectoderm - skin
Mesoderm - endothelium
Epithelia with their own names
Endothelium
Mesothelium
Classifications of epithelium - number of layers
Simple
Pseudostratified
Stratified
Classification of epithelium - cellular morphology
Squamous
Cuboidal
Columnar
Transitional
Squamous
Can be keratinized or non keratinized
Flat, scaly looking
Cuboidal
Cube shaped
Columnar
Column shaped
Transitional
Can be stretched or un-stretched
Morphology depends on what the organ is doing
In urinary bladder
•Need it stretched when full of urine
•Need it un-stretched when not full of urine
Simple
Single layer of cells
Simple squamous
Simple cuboidal
Simple columnar
Pseudostratified
Looks like it might be stratified but not
Pseudostratified columnar
Stratified
At least 2 layers
Stratified squamous
Stratified cuboidal
Stratified columnar
Naming epithelium
Go by top layer of cells for naming
•If top layer is columnar but other layers look cuboidal it would be stratified columnar
Pseudostratified columnar
Only type of pseudostratified you can have
Some columnar cells at top are touching the basement membrane
Real stratified - top layer doesn’t touch basement membrane, it rests on top of other cells
Classification of transitional by number of layers
Don’t do because not in definitive layers
Main functions of epithelium
Protection - epidermis
Delineation from environment - intestinal mucosa
Substance exchange - endothelium
Secretion - sebaceous glands
Types of glandular epithelium
Endocrine
Exocrine
Types of endocrine glandular epithelium
Follicle
Ribbon
Types of Exocrine glandular epithelium classifications
Morphology
Secretion mode
Secretion type
Endocrine glandular epithelium
Ribbon - capillaries go through secretory portion like ribbon of endocrine gland (kinda looks like a river)
Follicle - capillaries go around secretory portion of endocrine gland
Exocrine - morphology
Unicellular - 1 cell
Alveolar - round and sac shaped
Tubular - tube shaped
Can have simple and complex alveolar and tubular
Simple vs complex Alveolar and tubular exocrine glandular epithelium
Simple - just one sac/tube
Complex - branching sacs/tubes
Exocrine - secretion mode
Merocrine - release by exocytosis, cytoplasm intact
Holocrine - secretion is terminal, cells disintegrate after secretion
Apocrine - membrane bound blebs of cytoplasm
exocrine - secretion product
Mucus secretion - mucins hydrated into mucus, lubrication and protection
•ex - goblet cells
Serous secretion - proteins (digestive enzymes)
•ex - pancreas (exocrine portion)
Seromucous glands (complex) - combination of digestive enzyme and mucus •ex - salivary glands
