Epithelium-Leture 9/13/21 Flashcards
Epithelium
Form continuous sheet lining free surface
Characteristics of epithelial (3)
- Polarized, free spiral surface and basal surface
- Express keratin intermediate filaments
- All avascular
Apical surface
Faces towards the lumen of the cell
Basal surface
Attached to basal lamina or basement membrane
Epithelial function (8)
- Protection
- Surface transport (cilia)
- Absorption
- Secretion
- transepithelial transport
- reproductive
- Special sensory
- Contraction
Epithelial cell types (6)
Simple squamous, simple cuboidal, simple columnar, stratified columnar, stratified squamous, pseudostratified, transitional
Simple squamous
One layer of thin cells flat irregular shape
Simple cuboidal
One layer of cubed epithelium
Simple columnar
One level of long, column like epithelium
Stratified columnar
Cells closest to the lumen have columnar shape, more than one layer
SSKE
Stratified squamous keratinizing epithelium, has dead protecting layer like skin
SSNKE
Stratified squamous non-karatinizing epithelium, cells go all the way to the lumen
Pseudostratified
Looks stratified, but all cells attach to basal lamina but don’t necessarily span the whole layer, typically have cilia
Transitional
Only found in urinary tract, umbrella cells large top layer (often bind cleave)
Characteristics of apical surface (4)
- Microvilli
- Glycocalyx
- Cilia
- Stereocilia
Characteristics of Basal Surface
- Hemidesmosomes
Basal lamina
Basal invaginations
Basal evaginations
Characteristics of the Lateral surface
- Zonula occludens
- Zona adherins
- Macula adherins (desmosomes)
- Gap junctions
Zonular junctional complexes
Unites epithelial cells and form apical barrier, includes zonula occludens and zonula adherins
Zonula Occludens
Aka tight junctions, regulate apical border seal and create apical and basso lateral domains
Proteins involved in tight junctions
Occludin, Claudin (transmembrane proteins)
Actin (anchors to cells)
Zonula adherens
Also called Cadherins, Ca2+ dependent intercellular linkages continuous with the actin cytoskeleton, resists mechanical stress and sends signals
Macula communicans
Gap junctions that form a channel for ions and other stuff to pass through
Proteins of gap junctions
Cluster of 6 connexins form one connexon
Structure of basal lamina
Mainly comprised of a chicken wire complex made of collagen type IV and laminitis connected by nidogen
Reticulum lamina
Under basal lamina, made up of collagen type III
Roles of basal lamina (5)
- Physical support for epithelial
- Roles in development, morphogenetic, and differentiation
- Role in cell migration following injury
- Filtration barrier
- May be discontinuous
Types of epithelial glands
- Unicellular
- Multicellular, simple (unbranched duct)
- Multicellular, compound (branched duct)
Exocrine glands
Maintain contract with surface epithelium, secretes into lumen
Endocrine glands
Lose contact with surface epithelium, secrete to interstitial space
Modes of secretion (3)
- Merocrine
- Apocrine
- Holocrine
Merocrine
Exocytosis, only the product is released
Typical secretion from Merocrine glands
- Zymogens
- Sweat
- Mucus
- Lysozyme
Apocrine
Aka decapitation secretion, a portion of the apical cytoplasm is released along with product
Holocrine
The entire cell and its contents (sebum) become the secretory product, cell borders disappeared, nucleus degenerates, cytoplasmic droplets coalesce
Serous glands
- Watery secretion
- Abundant RER
- Round nucleus
- Cells well stained
Mucous glands
- Thick secretion
- Clear cytoplasm
- Flat nucleus
- Cells poorly stained
Myoepithelial cells
Aka basket cells, contract in order to help expel secretory products
