Epithelial Cell Function

where are epithelial cells found

cover external and internal surfaces of body organs

general function of epithelial cells

•Protection: form a protective barrier (skin)

•Selective barrier; only allows selective molecules to pass through

•Gland formation: cells group together to form glands, secretes products

•Regulation: regulate the exchange of molecules

•Absorption: e.g., epithelial lining of small intestine

epithelial cell diagram

-basal: left to right

-lateral: up and down

-basolateral region important for cell polarity

-apical regions have specific structures which are pointed towards lumen of particular organ

-basal region: has connective tissue underneath it to provide matrix for support and is in contact with blood supply

-basal lamina: helps entire cellular lining to be embedded/ connected with connective tissue

-basal lamina and region under it is rich in lots of dif proteins and enzymes and act as reservoir for lots of dif cellular activities

-extra cellular matrix (under basal lamina): rich in connective tissue, collagen proteins, fibroblast

-lateral regions: rich in junction proteins (green): maintain tissue integrity so cells don’t start floating around in extracellular fluid, function like a tissue

epithelial cell vs endothelial cell

-both line body surface

epi:

-internal and external surfaces of body

-squamous, cuboidal and columnar

-simple(single lining of cells) or stratified(layers)

endo:

-special type of epi

-line inner surface of blood and lymph vessels

-simple squamous epithelium

endothelial cell diagram

epithelial cell diagram

squamous, cuboidal, columnar and stratified

cell polarity

-epithelial cells all have polarity

-every surface has specific proteins/morphology: maintenance of cell polarity 

-cells remain in their domains

what happens when cell loses its polarity

cancer

domains in cell

-apical

-lateral

-basal

what is in apical surface and what do they look like

-glycocalyx

-cilia

-microvilli 

what is glycocalyx

-gel like substance present onto of cells

-carb coating (glycoproteins or glycolipids)

glycocalyx function in epithelial cells

-cell to cell recognition: helps differentiate between self and non self

-intercellular adhesion

-cell to cell communication

-embryonic development: attaches cells together and helps in movement of cells

glycocalyx function in endothelial cells

-regulates vascular(relates to rbc) permeability (exchange of molecules that happens)

-interactions between blood and endo cells

cilia sturcture

-motile cytoplasmic structure 

-appear as short fine hair like structures

-length: 1-10 pm

cilia function

-capable of moving particles an fluid along epithelial surfaces

where is cilia found

-trachea

-large bronchi

-uterine walls

microvilli structure

-irregular projections of cell membrane

-1pm

-closely packed cells that have absorptive function

microvilli location found

-small intestine

-kidney

lateral domain diagram

basal domain diagram

basal region: lamina lucida & densa

function of basal domain

-helps in adhesions between epithelial cells and ecm

-acts as permeability barrier which controls entry and exit from the cell

-may control cell organisation & specialisation: resevoir for many dif proteins

what protein does the extracellular matrix have?

-collagen fibres

why is the lungs different

-patient has cystic fibrosis 

-lots of mucus in lung

what is cystic fibrosis 

-multisystem disease: lots of dif organs r affected

-not possible to treat

-genetic disorder

-autosomal recessive; both genes mutated in order for a person to have symptoms 

-life shortening

-affects mostly lungs

cystic fibrosis symptoms 

-thick sticky mucous blocks airways

-difficult to breath

-cough up mucus

-freq lung infection

-elevated sweat chloride levels

-dif ppl have dif deegree of symptom

why do cf pateint get freq lung infections

-mucus stays for long time

-hard for clinician to aspirate mucus out

-mucus inhabits in that region

-promotes bacterial growth 

why do cf patient have elevated sweat chloride levels

-lots of NaCl accumulation on skin surface

cystic fibrosis transmembrane conductance regulator (cftr)

-trans membrane protein on apical region of cell

-expressed on epithelial cell lining of lungs, gut, exocrine glands

cftr diagram

-green balls rep movement of ions across cell membrane

function of cftr 

-allow movement of water molecules; as osmotic gradient is created

-helps maintain water salt balance on many surfaces

-transports ions across epithelial cell surfaces; pumps Cl- ions out with water mol

-allows water to flow into luminal space

why does water flow into luminal space

-goblet cells and submucosal glands are near luminal space 

-they secrete mucus; needs to be cleared

-when mixed with water is thin watery substance; easy for cilia to wipe out

-mucociliary clearance and airway defence in optimal

mutation in CTFR

-Mutations can reduce channel number/function

-Inability to establish osmotic gradient due to inhibited flow of ions

-Flow of water inhibited

-Result= Dehydration, decreased airway surface liquid, build-up of thick mucus layer on the outside of cells, static mucous

-Less airway surface liquid

-Decreased bicarbonate transport = acidic pH

cadherins diagram

what type of cells are cadherins

-transmembrane proteins

-major constituents of adherens junctions

cadherins function

-important for cell - cell binding

-cadherins mediate intercellular adhesion

what does e-cadherin do in normal cells

-helps joining cells together

-contact inhibition: proliferation/growth ceases when cell come in contact with each other

contact inhibition diagram

e-cadherin in cancer cells

-cells undergo malignant transformation

-loss of contact inhibition

-uncontrolled cell proliferation & tumour formation

-cells proliferate in a dysregulated fashion

-disrupted cell adhesion-multiple layers of cells formed

-some cell may detach: nothing for cells to be bound together with

what is the issue with cells detaching due to lack of e-cadherin

-float around: host into another house/organ

-causes secondary cancer

-loss of polarity

e-cadherin in cancel cells vs normal cells diagram

-yellow dashes: functional e-cadherin

-red dashes: non-functional e-cadherin

what epithelial cells provide barrier function

skin

what epithelial cells provide gas exchange

lungs/alveoli

what epithelial cells provide absorption

intestine

what epithelial cells provide reabsorption 

intestine 

what epithelial cells provide secretion

exocrine & endocrine glands

how does skin provide barrier function

-maintain physical barrier

-maintain communication between internal and external environments 

barrier against:

-environmental insults

-microbial invasion

-chemicals

-toxins and allergens

healthy skin barrier vs damaged skin barrier diagram

how do lungs provide gas exchange

type I pneumocytes:

-line 95% of alveoli

-united by tight junctions

type II pneumocytes:

-prod thin layer of surfactant: covers alveolar surface

how gastrointestinal system provides absorption

-absorptive cells

-tall cells forming single layer (simple) with microvilli on their apical surface

-tight junction prevent passing material between cells

-allows only selection of material to be absorbed 

-abnormal expression levels/activity of Na-K pump in diabetes, alzheimer’s disease, hypertension and tumours

how does kidney provide reabsorption

•Water/solutes transported into bloodstream

•Amino acids, glucose (100%), salts, and water (65%) reabsorbed

•Active transport- e.g. , glucose, amino acids

•Passive transport- water, chloride ions

•Concentrated urine formed

pancreas diagram

how does pancreas exocrine provide secretion 

pancreatic acinar cells:
-secrete digestive enzymes, ions and water into duodenum

-high conc of NaHCO_3whay

what effects acinar cells

-alcohol, high fat diet, smoking increase stress on acinar cells

what happens if acinar cell injury occurs

-loss of exocrine pancreatic function; reduced