Epithelial Cells Flashcards
Adhering Junctions
zona adherenes; strength to epithelium by linking to actin cytoskeleton of adjacent cells; made of transcellular cadherin proteins; located beneath the tight junctions and form a contractile ring around the cell
Tight junctions
lateral side of epithelial cells, made of claudins and occuldins; block movement of molecules and help maintain polarity
Gap Junctions
Made from connexion ; allow passage of small molecules and nutrients between cells
Basement membrane
thin, non cellular membrane between the epithelium and the connective tissue; made of glycoproteins and proteoglycans; structural support and selective barrier
Gap Junctions
Made from connexin- 6 connexins form a unit and interact with connexins unit in opposite cell to form a connexon ; allow passage of small molecules and nutrients between cells (up to 1000 daltons in diameter);
Hemidesmosomes
connect cell to basement membrane, transmembrane proteins integrin binds to lamins in extracellular space
Extracellular matrix
ECM, made of protein fibers (collagen) and glycoprtoeins that makes a meshwork that surround the cells in the body; a common framework to support a group of cells; cells can change behavior based on the composition of the ECM
Cadherin
family of proteins that interact homotypically, i.e. E-cadherin only binds with E-cadherin (epithelial); N with N (neuron); and VE-VE (vascular endotheial- blood vessels); desmosomal cadherin found in desmosomes; cells can be sorted by the type of cadherin they express and how much cadherin they express (stronger binding cadherins localize to center) ; eg how the neural tube is formed (express N cadherin) ; interactions dependant on high calcium to bind to other cadherins ; need clusters to bind (1-1 cadherin too weak to hold cells together)
How do cadherins link to actin?
via proteins beta-catenin and alpha catenin
How do cadherins link to intermediate filaments?
Proteins plakophilin, plakoglobin, and desmoplakin
What is contact inhibition?
when cells make contact they arrest the cell cycle so that organs and tissues won’t be overproliferated with cells; strong interactions between cadherins arrest the cell cycle (cancer cells less tightly attached)
How does contact inhibition work?
down regulates Mitogen and Wnt pathways; cadhedrin binds beta catenin to attach to actin in adhering junctions so reduces catenin that would otherwise be used as a transcription factor to express cyclin D
What is the Wnt pathway?
normally APC (NOT anaphase promoting complex) phosphorylzes beta catenin and degrades it, but Wnt keeps APC from phos. b catenin and lets cyclin D be transcribed
How does Ca2+ effect gap junctions?
gap junctions make it possible to move damage across cells; when calcium enters one cell, it causes connexins to undergo a conformational change and close to prevent damage in other cells
What are the most common protein fibers in the ECM?
collagen
How do cells bind to the ECM?
Actin in the cell binds to the protein Talin which binds to integrins (a and b subunits) which bind to an ECM fiber
How do cells regulate binding to ECM?
integrin is not in correct conformation to bind unless attached to Talin so use expression of talin to regulate when integrin binds or doesn’t bind to ECM; used in immune cells that travel through the body to certain sites
Focal Adhesion
cluster of integrin where actin filaments can pull and test fibers to determine how tightly integrin is bound to the ECM and can make decisions according - attract signaling proteins
How does ECM stiffness relate to cell survival and proliferation?
Soft ECM triggers apoptosis, growth arrest
Medium ECM triggers migration
Stiff ECM triggers proliferation, spreading, and increases adhesion
What types of cells are there?
Epithelial; connective; nervous; and muscle
What are the functions of epithelial cells?
Protection, Diffusion, Absorption, Secretion
Types of epithelial cells and where they are found
squamous (blood vessels, air sacs of lungs, heart lining, lymphatic vessles)
stratified squamous: (esophagus, mouth, vagina)
cubital (glands and kidney secretary portions)
columnar (usually cilliated, in bronchi and uterus; smooth in intestine and and bladder)
stratified cuboidal : sweat salavary and mamary glands
pseudostratified columnar : ( trachea and upper respitory tract)
Stratified columnar : male urethra and some glands
transitional : (bladder)
Claudins
make up tight junctions; span membrane 4 times; linked to actin in cytoskeleton that keeps claudin in place; interactions between claudins generate size restrictive pores; relative “leakiness” of tight junctions depends on what type of claudin is expressed in what cells
Relative restrictiveness of claudins
Claudin 5 found in stomach, blood vessels in brain very restrictive bc don’t want acid from stomach lumen to get in ECF or things from body to get in brain
Less restrictive claudins in large intestines, bladder too
