Lecture 34: Epithelia 1 Flashcards
(36 cards)
What are the 5 functions of epithelia?
- Protection (skin)
- Absorption (kidney, GIT)
- Secretion (glands)
- Filtration (kidney)
- Sensation (skin, eye)
What is the role of airway epithelium (lungs)?
Ciliated, cleaning lungs, gas exchange, moistens air, lavage to get rid of sticky mucus
What disease is associated with airway epithelium?
Cystic fibrosis
What is the role of the blood brain barrier?
Protect the brain, secretion of metabolites from the brain
What is the role of tubules in the kidney and GIT?
Absorption and secretion of ions, metabolites, solutes such as glucose, amino acids, urea
What are epithelial cells and epithelial tissue?
- Border between internal and external environment
- Varied shapes e.g. cuboidal, columnar, squamous or ciliated
What are the roles of epithelial cells and epithelial tissue?
- Protection
- Absorption and/or secretion of ions and organic molecules
What are 4 key structures of epithelial tissue?
- Basement membrane - barrier and anchor
- Basolateral membrane - closest to blood
- Apical membrane - facing the ‘outside world’/lumen
- Tight junctions - selective barriers
What movement does epithelia restrict?
Movement of ions and molecules between the internal and external environments
What are the 4 types of cellular junctions in epithelia?
- Tight
- Desmosome
- Gap
- Adhering
What is the basement membrane?
Thin, flexible but tough - prevents cell movement
Where are basement membrane proteins made and secreted from?
Epithelial cells
What is epidermolysis bullosa?
Collagen malfunctions so anchoring of basement membrane to skin epithelia fails and blistering occurs
What are tight junctions?
- Connects 2 adjacent plasma membrane of 2 different cells; does NOT connect cytosols
- Continuous band under apical surface that pulls cells close together so there’s no intercellular space between them
What type of barrier do tight junctions form?
Selective barrier: may allow selective movement of ions and/or organic substances between cells
What is the role of the cell polarity of tight junctions?
Separates apical and basolateral membrane
What side of the epithelial cell faces inside?
Serosal = basolateral = interstitial = blood side in kidney
What are the 3 main function of tight junctions in epithelia?
- Barrier: limits passage of ions and molecules between cells in the paracellular pathway
- Gate: allows certain solutes to flow through the paracellular pathway
- Fence: prevent movement of proteins between apical and basolateral domains
What side of the epithelial cell faces outside?
Mucosal = apical = luminal = urine side in kidney
Describe the role of a tight junction in determining the ‘tightness’ of epithelia:
Epithelia can be ‘leaky’ or ‘tight’ depending on how tight the tight junctions are
What properties does the ‘tightness’ of tight junctions define?
Properties of the paracellular pathway and constrains diffusion of solutes and fluids
- leaky: proximal tubule (PC), gate
- tight: collecting duct (CD), barrier
Describe the properties of the apical membrane:
- Faces lumen
- Variable depending on cell type (e.g. water permeability)
- Contains microvilli in highly re-absorptive or secretory epithelial cells
- Doesn’t contain Na+/K+-ATPase
Describe the properties of the basolateral membrane:
- Basal membrane and lateral intercellular membrane
- Faces ISF
- Similar between different BLMs (high water and K+ permeability)
- Doesn’t contain microvilli, but membrane infoldings
- Expresses Na+/K+-ATPase
What are the 5 key features of epithelia?
- Cells have polarity or asymmetry
- Proteins may be located in only the apical OR basolateral membrane
- Different epithelia = different functions
- Control movement of solutes and water in and out of body
- Regulated differently e.g. different hormones
