Epithelium Flashcards
Parenchyma-active portion
fxnal
epithelial portion of organs
cells of an organ that provide fxn (hepatocyte)
Stroma-organization aspect
supporting CT of organ
CT serves as support, structure and protection of epithelial cells of the organ
Fxns of Epithelium
Covering/lining surfaces-skin, mucus membranes, respiratory tract, blood vessels
Absorption-intestines
Secretion-glands (salivary, intestinal, endocrine)
Sensation- neuroepithelium
Contractility- myoepithelium of sweat, salivary, mammary glands
Types of Epithelium: Shape
Squamous
Cuboidal
Columnar
Types of Epithelium: Number of layers
Simple
Stratified
Pseudostratified
Types of Epithelium: Specializations
Cilia
Microvilli
Goblet cells
Kertinization
Types of Epithelium: Fxn
Covering epithelia
Glandular epithelia
Secretory cells
Structure of Epithelium
All epithelial cells rest on a ECM called basal lamina (basement membrane)
Basal Lamina
Separates epithelium from support tissues (CT beneath)
Identifies orientation of cells above
Fxn of basal lamina
- Supports the epithelial cells above
- Acts as a diffusion barrier w/pores that are semi-permeable
- Controls cell organization and differentiation
- Pathway for cell migration during development and healing
Basal Lamina Components
Type IV collagen, laminin, heparan sulfate, fibronectin, CHO
—Composition of the basal lamina varies among tissue types based on the fxn of the particular tissues
Simple Squamous
Lungs
Lining of vessels
Serous lining of cavities
Facilitate mvmt of viscera; Active & Passive transport of substances
Simple Cuboidal
Covering of ovary, thyroid gland, kidney
Covering, secretion
Molecule Transport: active & passive
Simple Columnar
Lining of intestine, gall bladder
Protection, lubrication, absorption, secretion
Pseudo-stratified Columnar/Cuboidal
Lining of trachea, bronchi, nasal cavity, ducts of male repro.
Protection, secretion,absorption, cilia-mediated transport (trap air-borne particles)
Nuceli are at different levels–cilia;goblet cells
Keratinized: stratified squamous
Epidermis-multiple layers of squamous cells
Protection against friction, prevents water loss (dehydration)
no nuclei–deepest layer cuboidal shaped
Non-keratinized: stratified
Mouth, esophagus, vagina, anal canal
Protection-areas of repeated forces/friction, secretion, prevents water loss
nuceli present
Cuboidal: stratified
Sweat glands, ovarian follicles
Protection, secretion
Transitional: stratified
Bladder, ureters
Protection, distensibility
Columnar: stratified
Conjunctiva of eyes
Protection–mucus secreting
Goblet Cells
- Mucus secreting cells of epithelial tissues
- Found in intestinal and respiratory tracts
Facet cells
change shape according to degree of bladder distention (cuboidal to squamous (closer to surface))
Epithelial Cells: Innervation
Rich supply of capillary blood and sensory nerve endings from nerve plexuses in the CT (lamina propria-basement membrane)
Renewal of Epithelial Cells
renewed continuously by means of mitotic activity
Rate of renewal is variable
Rate of renewal rapid vs slow
Rapid: intestinal epithelial cells replaced each week; skin replaced in a month
Slow: liver and pancreas (monthS)
Communicating Jxns= Gap Jxns
control passage of chemical and electrical signals from cell to cell
allow easy exchange of ions and small molecules–and pass b/w ells w/o reaching the extracellular fluid
IMPORTANT FOR APs to be coordinated, synchronized
Occluding Jxns=tight jxns
seals cells together in a sheet-like formation
prevents mvmt of molecules b/w cells
Anchoring Jxns
Desmosomes; Hemidesmosomes
-Attach cells to other cells or to extracellular matrix
Gap Jxns Characteristics
Connexon
Permeability of the gap is controlled by individual connexins
Cells are able to control permeability of these jxns
Most wide spread cell jxns
Connexon
pair of 6-protein connexons span lipid bilayer of adjacent cells
each protein of connexon is called CONNEXIN
Tight Jxns-Occulding Jxns Structure and Fxn
Jxn forms a “band” completely encircling adjacent cells
Membranes “fuse” preventing material from moving b/w cells
Main fxn is to prevent diffusion b/w cells
Why are tight jxns important in epithelial tissues
Skin-provides waterproof barrier
GI tract-prevents molecules from moving out of the gut lumen b/w nutrient absorbing cells
Anchoring Jxns-Desmosomes
Serve as anchoring jxn to bind cells together
Widely distributed in animal tissues
Attachment sites for intermediate filaments
Make-up of Desmosomes
- intracellular attachment protein that connects desmosome to intermediate filament in cytoplasm
- transmembrane linker protein (cadherin)
Hemidesmosomes
bind cells to basal lamina
