Are epithelial cells vascular or avascular?

avascular, receive nutrients, oxygen etc via blood vessels in underlying connective tissue

4 functions of epithelial tissue

1. cover/protection

2. absorption/secretion

3. barrier

4. sensory

Epithelial cell classification by number of cell layers

1. Simple (1 layer)

2. Stratified (2 layers +)

Epithelial classification by cell shape

1. Squamous

2. Cuboidal

3. Columnar

*classified by morphology of most apical layer

Pseudostratified columnar epithelium

all cells are in contact with basal lamina, but don't all reacha apical surface

appearance of multiple layers of nuclei

most are ciliated

Transitional epithelia

stratified epithelia with relaxed and distended configurations

relaxed: dome shapes

distended: flattened

found in urinary tract

Keratinized layers

non-nucleated, keratin-filled cells in stratified, squamous epithelia

Polarization of epithelial cells

apical, basal, lateral (2) surfaces

Microvilli

found on apical surface

1 micron long, .08 in diameter

core of actin filaments

non-motile

function: increase surface area

terminal web

apical cytoskeletal filaments (actin and spectrin) to which microvilli anchor

Stereocilia

large microvilli (10-25 microns)

may be branched

actin core

found in epididymis (inc. surface area) and hair cells of inner ear (signal generation)

Cilia

much larger than microvilli (10 microns long)

MOTILE (dynein)

MICROTUBULE core (called axoneme), 9+2 arrangement

function: move substances across epithelial layer

flagella, structurally similar, found only in sperm

axoneme

9+2 microtubule core in cilia and flagella

basal bodies

anchor cilia (each has its own basal body)

composed of 9 microtubule triplets

immotile cilia syndrome

Kartagener's syndrome and Young's syndrome

cilia lack/have malformed dynein arms

male sterility

thick mucus secretions, resp distress, sinus infections

Young's disease

immotile cilia syndrome

Kartagener's syndrome

immotile cilia syndrome

Zonula Occludens

most apically-located lateral specialization

tight junction

belt-like structure

occludins/claudins in assoc. with cadherins bring memb. of adjacent cells very close together

no free flow of water-sol molecs between cells, compartmentalizes integral memb proteins into apical/basolateral domains

Zonula Adherens

aka adhering junction

adjacent and basal to zonula occludens

belt-like

uniform distance between adjacent plasma membs

adhesion via integral memb proteins--cadherins interacting with catenins (linked to actin)

anchor pt for actin filaments

cell adhesion/link cytoskeleton of adj cells--structural

assoc'd w/ Ca²⁺ ions

Macula Adherens

aka desmosome

basal to belt junctions

distributed RANDOMLY along lat memb domain

spot adhesions

attachment plaques (desmoplakins/pakoglobins)

assoc'n with intermed filaments of cytokeratin

fn=strong adhesions

disperse shearing forces

Gap junctions

packed plaques of connexons (formed by integral memb proteins called connexins) on adj cell membs form aqueous pore thru which small molecules (sugars, ions, aas, cAMP, some hormones) pass

channels regulated by Ca²⁺ and pH

clostridium perfringens

toxin binds claudin proteins of tight junctions--junctions break down-->diarrhea and abdominal pain

heliobacter pylori

binds to extracellular domains of zonula occludins-->cytoskeletal rearrangements and junction failure-->gastric ulcers

dust mites

fecal pellets contain peptidases -->attack tight junctions of resp epithelium-->lungs exposed to inhaled allergens-->asthma attacks

Hemidesmosome

basal specialization

instead of linking cell to cell like desmosome, links cell to basal lamina

site of keratin tonofilament (intermed. fil) attachment

integrin proteins link cytoskeleton to extracellular matrix (adhesion/traction/bidirectional signaling)

basal membrane infoldings

invaginations of basal memb

increase surface area for transport

found in mitochondria

basal lamina

extracellular matrix upon which epithelial sheet rests

2 layers: lamina lucida (rara)--electron lucent layer, lamina densa--electron dense layer, most basal

support/attachment, sieve functions

basement membrane

basal lamina (lamina rara + lamina densa) + lamina reticularis (produced by connective tissue)

Exocrine glands

as with endocrine glands, developed from epithelial sheets, but maintains connection to surface of origination via ducts

unicellular exocrine glands

goblet cells of resp and GI tracts

(secrete mucus)

simple exocrine gland

one duct

compound exocrine gland

complex, branched, differentiated duct system

tubular exocrine gland

simple, simple branced, simple coiled

acinar (aka alveolar) exocrine glands

acinus=cluster of cells organized around a lumen

simple branced acinar or compound tubuloacinar

compound exocrine glands

usually organs, divided into lobes/lobules with complex differentiated duct system

ex: mammary gland

parenchyma

functional part of organ

stroma

supports parenchyma, connective tissue component of organs

mucous vs serous

secretes mucinogens (lg glycosylated proteins--mucus) vs secretes solution of proteins

mixed, serous-mucous glands produce both (ex: submandibular salivary gland)

myoepithelial cells

contractile function--move secretoins out of gland and into ducts

metastasis

moves through basal lamina, attacks adjacent tissues