Epithelial Tissue pt II

types of cell junctions

• tight/occluding junctions

• zonular adherens

• desmosome

• hemidesmosome

• communication junctions

function of tight junctions

• tightly adhere cells together along apical/luminal border

• forms selective barrier

• controls paracellular diffusion

• enables epithelium to protect proteins underlying tissues

• prevents diffusion of membrane proteins/lipids between apical and basolateral membrane necessary for polarity

what is the effect of fluorescein

• will wash away in healthy ocular surface

• will stain in damaged ocular surface since tight junctions are leaky

what is the function of adherens and adhering belt

• connect epithelial cells to each other to create another barrier below tight junctions

• connects cell-cell junction to actin cytoskeleton

• multiple zonula adherens for continuous belt around cell

• epithelial cells with high content of adheren junctions form strong cohesive epithelium

strong mechanical adhesion between neighboring cells

function of desmosomes

• desmosomes connect neighboring epithelial cells to each other forming plaques between cells

• anchor epithelial cells to intermediate filamentous cytoskeleton

function of hemidesmosomes

• anchor epithelia to basal lamina of basement membrane

• linked to intermediate filaments (keratin) within the cytoplasm

function of communicating junctions

• gap junctions are made of connexins form a channel between adjacent cells

• cell-cell communication, permit the passage of small molecules between cells

location of tight junctions

more superior region between cells

anchor/cytoskeleton of tight junctions

actin filaments

function of tight junctions

• prevent/limit leakage between epithelial cells

• maintains polarity of epithelial cells by limiting apicobasal diffusion

location of zonular adherens

inferior to tight junctions

anchor/cytoskeleton of zonular adherens

actin cytoskeleton

function of zonular adherens

• form cell-cell and cell-basement membrane adhesion complexes

• can form bands encircling the cell

• allows for a cohesive epithelium

location of desmosomes

more inferior region between cells

anchor/cytoskeleton for desmosomes

keratin intermediate filaments

function of desmosomes

• strong cell-to-basement membrane adhesion

• resistance to intense mechanical stress

location of hemidesmosomes

basal side of cell

anchor/cytoskeleton

keratin intermediate filaments

function of hemidesmosomes

• strong cell-to-basement membrane adhesion

• resistance to intense mechanical stress

location of gap junctions

between epithelial cells

function of gap junctions

directly connects the cytoplasm of cells allowing the exchange of small molecules, ion, and electrical impulses

what does the loss of cell-cell adhesion lead to

sloughing off of epithelial cells

what is epithelial basement membrane dystrophy

• defective corneal epithelial basement membrane

• redundant basement membrane

• leads to poor epithelial adhesion and epithelial inclusion cysts

what is recurrent corneal erosion

condition caused by abnormal epithelial adhesion to underlying basal lamina leading to repeated breaks in the corneal epithelium

symptoms of recurrent corneal erosion

ocular pain, blurred vision, tearing, and photophobia

etiology of recurrent corneal erosion

• trauma around 60% of the time

• genetics around 20-30% of the time

• epithelial basement membrane dystrophies, fuchs endothelial corneal dystrophy, previous cornel infections, dry eye disease, diabetes mellitus

treatment objectives for recurrent corneal erosion

• relief of symptoms

• epithelial integrity

• prevent infection

• reduce recurrence by lubricating epithelium

treatment options for recurrent corneal erosions

• hyperosmotics

• lubricants

• bandage contact lens

• anterior stromal micropuncture

• photoablation

• debridement

what are microvilli

• small finger like projections on the luminal side of epithelia

• not typically visible on light microscope

• shorter and narrower than cilia

• core contains actin filaments

what is the function of microvilli

• increase surface area by 30x

• increase absorption like in the brush border of the small intestine

function of microvilli in the corneal epithelium

• increases surface area for anchoring of the tear film via rich mucin glycocalyx

• corneal hydration

• barrier protection from pathogens and friction

what are cilia

• long motile structures

• visible by light microscope

• beat in rhythmic pattern allowing them to propel surface mucus and fluids for unidirectional movement

where are cilia found

• respiratory tract

• female reproductive tract

how do glands form

from epithelial cells after invagination into the underlying tissue

characteristics of endocrine glands

• no duct system

• secretions are released into the bloodstream

• may have multiple types of secretion

• act on distant targets

what type of gland are the thyroid, parathyroid, adrenal, pituitary, gonads, and pancreas

endocrine

how does exocrine secretion work

release their secretions into a duct and then onto an epithelial surface

what are the three types of exocrine secretion

• merocrine

• apocrine

• holocrine

characteristics of merocrine secretion

• most common

• involves exocytosis

• only secretory component is released

• mostly protein products

characteristics of apocrine secretion

• membrane bound vesicles released (apical)

• usually lipid products

• breast and some sweat glands

what type of secretion is this

merocrine

what type of secretion is this

apocrine

what type of secretion is this

holocrine

characteristics of holocrine secretion

• disintegration of cells to release lipid products

• sebaceous glands mainly

classification of merocrine/eccrine sweat glands

• secretory or acinar cells

• ductal cells

• myoepithelial cells

what type of glands are sweat, salivary, and lacrimal glands

merocrine/eccrine

classification of apocrine glands

• secretory or acinar cells

• ductal cells

• myoepithelial cells

what are merocrine glands associated with

thermoregulation

what are apocrine glands associated with

• thermoregulation (sweat surface tension)

• scent production

• territory marking

• sexual attractant

what are axillary/groin regions and mammary glands an example of

apocrine glands

what are meibomian glands, aerola, labia, and vulva examples of

holocrine sebaceous glands

characteristics of holocrine sebaceous glands

• usually associated with hair follicle (at about 1/3 depth)

• sebum - waterproofing and lubrication

• may be independent of follicle

characteristics of goblet cells

• modified columnar epithelial cells

• unicellular

• synthesize and secrete mucous

• scattered throughout many epithelial tissue linings

• protective function

where can goblet cells be found

epithelial lining of

• respiratory tract

• ocular conjunctiva

• digestive tract