Epithelial Tissue Flashcards
Epithelia
- Covers body surfaces, lines body cavities, & forms glands
- Contains surface epithelium of ectoderm (or endoderm), basement membrane, supporting connective tissue (lamina propria), & sometimes layers of smooth Mm (muscularis mucosae)
- Epithithelial cells are characterized by production of keratin intermediate filaments
- Produce different keratin (~54 types in humans); can be useful in tumor ID
Where is epithelia derived from?
ecto-, endo-, or mesoderm
Histogenesis of Mesoderm
- Epithelium of kidneys & gonads
- Mesothelium (lining pleura, peritoneal, & pericardial cavities)
- Endothelium (blood & lymph vessels)
- Adrenal cortex
Histogenesis of Endoderm
- Respiratory epithelium
- Alimentary epithelium (exceptoral & anal cavity)
- Liver, pancreas, gallbladder, thyroid, parathyroid, & thymus
- Epithelial lining of tympanic cavity & Eustaciantubes
- Transitional epithelium of bladder
Epithelia functions
- Barrier (e.g., skin)
- Absorption (e.g., intestines)
- SPM
- Transport (e.g., cilia in trachea)
- Secretion (e.g., stomach)
- Sensation (e.g., taste buds)
Epithelia avascular
neverpenetrated by blood vessels
Epithelium cells rely on what?
on diffusion of O2 & nutrients from underlying tissue
how is epithelia supported?
Supported by basement membrane, separates epithelium from underlying connective tissue & blood vessels
mucous membrane(= mucosa)
Epithelium that lines cavities that connect with outside world, (e.g., alimentary, respiratory, or urogenital tracts)
lamina propria
supporting connect tissue
muscularis mucosae
layers of smooth muscle
serous membrane(= serosa)
Epithelium that lines closed body cavities (e.g., peritoneal, pleural, or pericardial cavities)
what does serous membrane consists of?
- epithelial lining, the mesothelium, (mesodermally derived)
- basement membrane, & supporting connective tissue
- Lacks muscularis mucosae
endothelium (mesodermally derived)
- Epithelium that lines blood & lymph vessels
- Associated with variable #’s of Mm & connective tissue layers, or tunics
- Most epithelial cells have finite lifespan
basement membrane
- Basal surface of epithelial cells attached
- Provides structural support, scaffolding for growth, differentiation, & migration of cells during embryonic growth & regeneration
- Non-cellular, protein & polysaccharide-rich layer; acts as filter between epithelium & underlying connective tissue
external lamina
extracellular matrix proteins
how is the negative charge maintained in the basement membrane?
SPM for nutrients & metabolites to & from epithelium
how does the glomerular BM act in kidneys?
acts as highly selective filter for urine formation
Whare the the major components of BM?
- GAG’s(heparan sulfate)
- Type IV collagen
- structural glycoproteins (laminin, fibronectin, & entactin)
On EM, basement membrane has….
electron dense layer (lamina densa) sandwiched between electron-lucent layers, (lamina lucida& lamina reticularis)
Lamina lucida
contact with basal cell membrane
Lamina reticularis
merges with surrounding tissue
lamina densa
anchored to underlying connective tissue by microfibrils of Type IV collagen
Anchoring filaments
Type IV collagen anchored to microfibrils of connective tissue
cell junctions
- Epithelial cells adhere to one another
- intercellular epithelial attachment sites
- communication between cells
types of cell junctions (3)
- occluding
- adhering
- communicating
Occluding (=tight junctions)
- Located beneath luminal surface of simple columnar epithelia
- Act as gaskets
zonula occludens
Portions of opposing cell membranes fuse together, forming continuous, circumferential band around cell (seen in occluding junctions)
Fascia occludens
present between endothelial cells in wall of blood vessels
Adhering junctions (=anchoring junctions)
- Bind cells together, act as anchoring points for cell cytoskeleton
- Two basic morphological types & two specialized types
Zonula adherens
a continuous band characterized by transmembrane glycoproteins called cadherins
cadherins
class of cell adhesion molecules, or integrins
Are adjacent cell membranes fused?
NO
Macula adherens (= desmosomes)
- Small, circular patches; most common type of cell junction
- Located on lateral surface of cell
Desmosomes associated with what attachments?
with attachment plaques containing attachment proteins:
- desmoplakins
- desmogleins
- tonofilaments
Hemidesmosomes
(“half desmosomes”, adhering junctions)
•Found on basal surface only, anchoring it to basement membrane via integrins (transmembrane receptor proteins)
•Associated with high mechanical abrasion/ shearing forces (e.g., skin)
Junctional complex(= terminal bar)
(adhering junctions)
•Specialized, circumferential, intercellular connection
•Hybrid between adhering & occluding junctions—forms diffusion barrier between cells
how is the junctional complex arranged by (3 zonula)?
- zonula occludens (tight junction)
- zonula adherens (adherent junction)
- macula adherens (desmosomes)
Communicating junctions (= gap junctions or nexus junctions)
- Focal, or regional adherent zones located on lateral border of cell
- connexons-> connexins
- Permit passage of small molecules between adjacent cells
- allow transport of information & metabolites between cells
connexons
Roughly circular, intercellular contact areas containing hundreds of individual channels
connexins
connexons, formed by ring of 6 integral proteins called connexins surrounding 2 nm diameter pores
Types of cell surface modifications (3)
- Microvilli
- Stereocillia
- Cilla
Microvilli
- finger-like cytoplasmic projections, extend from cell surface
- Contain actin filaments
- ↑surface area for absorption or secretion
- supported by terminal web
location of striated border & brush border
striated border- intestine
brush border- renal tubules
terminal web
network of actin microfilaments at base of microvilli; provide support
Stereocilia
- long microvilli, not cilia;
- found only in epididymis of males & sensory cells of inner ear
- Non-motile, also contain actin filaments
Cilia
- long, motile, cytoplasmic extensions
- Possess axoneme
- Each cilium arises from individual basal body
- Cilia beat in synchronous, metachronal rhythm
- Cilia normally contain microtubule doublets with dynein arms
axoneme
9 + 2” arrangement of microtubules, seen in cilia
basal body
develop from centrioles
metachronal rhythm
cilia has rapid, rigid, effective stroke& slower, flexible recovery stroke
If microtubules lack dynein arms, ciliary mobility is impaired or absent… what can it cause (3)?
- Kartagener’s syndrome
- Dextrocardia or situs inverses
- Hydrocephalus
Kartagener’s syndrome
causes sterility in males due to non-functional flagella on sperm
Dextrocardia, or situs inversus
(LR)—due to absence of ciliary activity during embryonic development, heart is in opposite position from normal placement
Hydrocephalus
due to non-functional cilia on ependymal cells unable to circulate CSF
Epithelia classification (3)
- # of cell layers
- shape of cells (at epithelial surface)
- surface specializations (eg. cilia, keratin)
of layers (3)
- Simple—1 cell layer thick
- Stratified—2 or more cell layers
- Pseudostratified—looks stratified, but isn’t; all cells rest on basement membrane, but notall cells extend to epithelial surface
shape of cells (3)
- Squamous—flattened, width > height
- Cuboidal—width ~= depth ~= height
- Columnar—height > width
surface specializations can have what attached to it?
e.g. ciliated
types of specialized epithelia (3)
- transitional
- endothelium
- mesothelium
Transitional
- lines most of urinary tract (except for parts of urethra)
- Stratified epithelium, modified for distensibility
- Varies from squamous to cuboidal
- umbrella like
Endothelium
- epithelium lining blood vessels & lymphatics
- simple squamous
Mesothelium
- epithelium lining closed body cavities (i.e., thoracic, pericardial, & abdominal cavities)
- Simple squamous
Glands
composed of epithelial cells, specialized for synthesis & secretion
Gland classification (3)
- morphology
- type of secretory prod
- mode of discharge of secretory prod
Duct morphology (2)
- Simple gland—unbranched ducts (straight or coiled)
2. Compound gland—branched ducts
Shape of gland (3)
- Tubular—tube-like (straight or coiled)
- Acinar(= alveolar)—sac-like or flask-shaped; individual sac called acinus
- Tubuloacinar(~= alveolar)—intermediate; tube with dilated end
Type of secretory products (5)
- Serous
- Mucous
- Mixed (=seromucous)
- Sebaceous
- Ceruminous
Serous
watery; basophilic acini (e.g., parotid)
Mucous
thick, viscid secretion (mucus); clear on H&E (e.g., palatal)
Mixed (=seromucous)
- contain both mucous & serous acini
- include serous demilunes (e.g., sublingual, submandibular)
Sebaceous
glands of skin, secrete lipids in form of sebum
ceruminous
glands of external ear canal, secrete cerumen(ear wax)
What are the 2 major function groups of glands?
- endocrine gland
2. exocrine gland
endocrine gland
lack ducts; secrete products (hormones) directly into bloodstream
exocrine gland
- secrete product onto epithelial surface via ducts
- Contain myoepithelial cells
myoepithelial cells
specialized contractile cells in exocrine gland
myoepithelial cell location
- Lie between secretory cells & basement membrane, assist in secretion
- near Goblet cells
goblet cells
- specialized, unicellular exocrine glands, located in epithelium
- secrete mucus
Mode of discharge for glands(3)
- merocrine
- apocrine
- holocrine
merocrine (= eccrine)
- only secretory products released (generally proteins)
- Most common
- involves simple exocytosis
apocrine
- secrete membrane-bound vesicles
- product accompanied by some cytoplasm
- lipid products (e.g., sweat & mammary glands)
Holocrine
- entire cell-secreted (ruptures, releases contents)
- ex. sebaceous glands
