Epithelial cell specializations Flashcards
What are apical cell surface specializations?
Microvilli
Sterocilia
Cilia
What are lateral cell surface specializations?
Occluding junctions
Adhering junctions
Communicating junctions
Membrane plicae
What are basal cell surface specializations?
Basal lamina
Basal striations
What is the function of microvilli?
Increase the surface area of the cell.
What is the terminal web?
A web of actin below microvilli that can translate movement inside the cell to the microvilli
The _____ and _____ of the cell’s microvilli reflect the cell’s absorptive capacity.
Number and shape
What is the core of the microtubule called?
Axoneme
What is the morphology of a microtubule?
“9 + 2” - 9 peripheral pairs of microtubules and one central one.
Each pair = A and B component with dynein arms
From where does the axoneme grow?
The basal body, a short cylinder of 9 microtubule triplets
What are stereocilia and what is their functin?
Very long microvilli
Stereocilia in the ductus epididymis function to absorb luminal fluids.
Is cilia beating coordinated between cells?
Yes!
What is the function of beating cilia?
To move material parallel to the surface
What are the functions of intercellular junctions?
Occluding
Adhering
Communicating
What is the occluding junction and what is its function?
Zonula occludens/tight junction
Prevents the passage of material between adjacent cells and keeps the apical membrane domain separate from the basolateral domain.
What are macula adhering junctions/desmosomes?
Spot adherens
What are fascia adherens?
A sheat of adhesion (found in heart)
What are zonula adherens?
A belt of adhesion
What is the communicating junction?
Gap junction
What is the structure of tight junctions?
Rows to tight junctions serve to stitch the membrane together, sealing adjacent cells.
The leakiness of tight junctions will depend on what ratio?
Occludins to claudins. Claudins = leaky/allow water
To give the stability/strength, the actin cytoskeleton is linked into ________ junctions.
Intermediate adhering
The integrity of intermediate adhering junctions is _____-dependent.
Ca2+ binding to extracellular domain for reinforcement
How big is the space between cells (plasmolemma)?
10-15 nm
What is the structure of a desmosome/macula adherens?
Intermediate filaments (keratin) loop in bundles to link the plaques for very tight binds. Also Ca2+ dependent
Which is stronger: macula adherens or zonula adherens?
Macula adherens!!
What makes up the junctional complex? What is it called?
Zonula occludens (tight), and adherens (intermediate). macula adherens (desmosome). Called the terminal bar.
What are plicae?
Lateral membrane infoldings to increase the membrane area for protein transport.
What does the hemidesmosome do?
Links cytoskeletal intermediate filaments to transmembrane integrins which link the epithelium to the basement membrane,
What is the structure of gap junctions (nexuses)?
6 connexins make 1 cylindrical connexon channel to transport water, AAs, small signaling molecules, ions, etc.
Are gap junctions able to close?
Yes, in response to changing voltage.
What cell organelle will be adjacent to basal enfoldings and why?
Mitochondria to provide ATP for the ion pumps all over the enfoldings.
How does the basal lamina/basement membrane appear on EM?
Dark line (lamina densa) + light line (lamina lucida)
What are the functions of the basal lamina?
Attachment (flexible and firm)
Filtration barrier (physical and anionic)
Compartmentalization
Tissue scaffolding
Regulation and signaling (in development, wound healing, etc.)
What type of collagen makes up the basal lamina?
Type IV
What is the basal body?
The insertion/anchor of the cilia in the apical cytoplasm.
What is the striated border? What is a nickname?
Brush border. Tightly packed uniform microvilli in large and small intestine.
Compare terminal web and terminal bar.
The terminal web is the concentrated mesh of INTRAcellular cytoskeletal elements, mostly actin WITHIN the apical portion of the cell.
The terminal bar refers to the junctional complexes (3 jcts)
What transduces signals in the inner ear?
Stereocilia
Where is the striated border located?
Alimentary tract and gall bladder
Where is the brush border located?
Proximal convoluted tubules of the kidneys
Where are stereocilia located?
Ductus epididymis and inner ear
Where are cilia located?
Respiratory system, oviduct, ependymal lining of brain ventricles
Which junctions have the least intercellular space?
Gap junctions: ~2nm
Which junctions have the greatest intercellular space?
Macula adherens/Desmosomes: ~30 nm
