Epithelial Tissues

basla lamina

connective tissue

cell-matrix

cell-cell

bring close together

Intestinal lining; skin epidermis

cells closely associated

limited ECM

cytoskeleton (mechanical stress)

cells attached to each other via proteins

bones, tendons

cells are rarely connected

plenty ECM

ECM handles stress

cells attach to matrix

- occluding junctions

- prevent mixing of extracellular matrix

- acts as fences in the membrane

-revents mixing of membrane proteins (apical and basal) 

- located in epithelial tissue

- dependent on adherins junction

if you block formation of adherin junctions, tight junctions do not form properly 

- interact homogenously 

- transmembrane proteins:

Extra cellular domains: interact with extracellular domains of proteins in neghbouring cell

- Claudin/Claudin Occludin/Occludin  (NEVER HETEROGENOUS)

Claudin: required for tight junction seals; functional proteins are required in both cells, but claudin most important

tight junctions

adherin junctions

desmosomal junctions

adherin + desmosomal junctions = cadherin

cell-cell anchoring juntions

cell-matrix anchoring junctions

links cytoskeletons of neighbouring cells

different proteins invovled in different types of interactions

adhesion belt: encircles the isnide of plasma membrane

at adherin junctions:

- cadherin proteins from neighbouring cells interact homotypically

- actin is tethered to cadherin by anchor proteins

tight junctions form sealing strand, adherins form an adhesion belt

- cadherins

transmembrane proteins

extracellular domain intreact with: adhesion proteins - i/a neighbour ECM

intracellular domains interact with anchor proteins

- link adhesion proteins to cytoskeletal filaments

- cytosolic proteins

link intermediate filaments

Eg. Keratin

Intermediate filaments provide the most structural strength

desmosome links neighbouring cells

hemidesmosome link to basal lamina

specific cadheren family members are adhesion proteins

desmoglobin

desmocolin

anchor proteins link the adhesion proteins to intermediate filaments

spot-welled epithelial cells to the basal lamina

- keratin filaments: inside cell

- linked to laminin in ECM

through integrin: transmembrane protein in hemidesmosome and it will link anchoring proteins to laminin

communication between cells

composed of connexin proteins

channel-forming junctions

It is a hemichannel

6 connexions make one connexon 

- usually closed, not open, however, gap junctions, which are composed of hemichannels usually remain open 

- allows two cells to communicate with each other; couple cells synchronization

- homomeric connexons mix with heteromeric connexons to make intracellular connections 

Electrically and metabolically: allow passages of ions an dmetabolites

passes through cAMP, nucleotides, glucose, AA

Does not pass: macromolecules, proteins, nucleic acids

Gap junctions open: a lot of Ca2+ flows in 

Gap junction closes when there is a saturation of Ca 2+ because Ca2+ damages the cell membrane

Closes to prevent losing metabolates from adjacent cells 

- special type of ECM

- underlies all epithelia, but not ALL cells

- thin

- ECM is secreted by the cells in the tissue

there is polarity (basal side vs apical side)

Surrounds: muscles, fat cells, schwann cells, structural role

- divides two sheets

- acts as a selective filter

- can also influence polarity: there are proteins that are associated with absal lamina that help localize their domains

Laminin

Composed of trimers: alpha, beta, gamma lamin

Binds to:

- integrins

0 many other components of ECM including other laminin molecules

- provides strength

- forms a strong flexible network

- many protein-protein interaction sbetween diferent components of the basal lamina

- refer to diagram 

- attachment site for epithelial cells

- prevents fibroblasts in the underlying connective tissue from interacting with epithelial cells

- yet allows passage of macrophages and lymphocytes

made up of connective tissue

different composition of ECM, which gives tissue different properties

not a static structure, can remodel over time

laminin, type IV collagen, nidogen, fibrillar collagen, fibronectin

- long linear polysaccheride chains composed of a repeating dysaccheride

pair of sugars, one is an amino sugar

- highly negatively charged (attracs Na2+ and water) 

form voluminous hydrated gel

 - simple GAG

- long chain of repeating disaccharide subunits

- not linked to a protein 

- most GAG are synthesized inside cell on proteins and exocytosed 

- all proteoglycans are glycoproteins (but not all glycoproteins are proteoglycans)

- proteoglycans have one sugar side chain and it MUST BE A GAG. They are extensive

Glycoproteins are proteins with any sugar side chain 

- plants produce and deposit their cell wall

- more rigid than ECM of animal tissues

- composed of cellulose and pectin