2 Epithelial Tissues Flashcards
Q: What is key to the formation and maintenance of epithelial layers? Describe these layers.
A: cell-cell junctions
formed from: epithelial cells make organised, stable cell-cell junctions to form continuous, cohesive layers
Q: What do epithelial layers line? position? List 4 functions.
A: internal and external body surface // Layer of epithelia lies on the basal lamina // Under the lamina you have interstitial connective tissue and extracellular matrix.
- transport
- absorption
- secretion
- protection
Q: How is epithelia classified? Why is this way of doing it useful?
A: -SHAPE - squamous or columnar or cuboidal
-LAYERING - single layer = simple; multi-layered = stratified
related to function and properties
Q: What are the classifications of epithelia? (5)
A: -simple squamous
- simple cuboidal
- simple columnar
- stratified squamous
- pseudostratified
Q: Describe simple squamous epithelia. Property? Nuclei? Examples? (3)
A: simple= single cell layer, squamous= flattened plate shape-> wider than tall
form thin epithelium that allows exchanges to occur (eg gas)
nuclei tend to be oval to accommodate flatted shape
- lung alveolar
- mesothelium (lining major cavities)
- endothelium (lining blood vessels and other blood spaces)
Q: Describe simple cuboidal epithelia. Examples? (2)
A: simple= single cell layer, cuboidal= approx. cube shaped-> width similar to height
- lining kidney collecting duct
- other ducts
Q: Describe simple columnar epithelia. Examples? (2)
A: simple= single cell layer, columnar= pillar-shaped-> taller than wide
- enterocytes (intestinal absorption)
- other absorptive and secretory epithelia
Q: Describe stratified squamous epithelia. Shape? Main types? (2) examples (1,5)
A: stratified= multiple cell layers , squamous= flattened plate shape-> cells have a variety of shapes - they are quite cuboidal near the basal lamina and quite flat at the surface
- Keratinising - epidermis (nuclei NOT VISIBLE in the surface cells)
- Non-Keratinising - linings of mouth, oesophagus, anus, cervix, vagina (exactly the same but the nuclei are visible in surface layer cells)
Q: Describe pseudostratified columnar epithelium. Nuclei? Examples? (2)
A: pseudostratified= falsely stratified, columnar= pillar-shaped-> taller than wide
- looks multilayered but the surface cells have contact with basal lamina
- nuclei are at different levels
- airway (trachea and bronchi)
- various ducts in urinary and reproductive tracts
Q: What does epithelia function require? Why? Key?
A: -polarity (either side is different)
- most epithelial functions must be directional eg. secretion, fluid and solute transport, absorption
- plasma membrane polarity is key to epithelial polarity
Q: How are many epithelial membranes separated? Into what? How do they differ? Draw diagram to show this.
A: cell-cell junctions separate
2 biochemically (different lipid and protein compositions) and functionally distinct membranes
- apical domain (lumenal (open) surface)
- basalateral domain (basal and lateral are usually grouped)
REFER
- forms a cohesive layer due to the junctions
- basolateral domain is attached to basal lamina, extracellular matrix
Q: Describe epithelial polarity in terms of transport. Composition? Example. Without directionality?
A: in ion and fluid transporting epithelia, ion pumps and channels have apical-basolateral polarisation in the plasma membrane ie activity is restricted to only some parts of the plasma membrane
- have high concentration of ion transporters
- mitochondria closely associated with extensive basal membrane infoldings (on that side), providing energy for active transport across membrane
- infoldings increase the amount of basal membrane that can pump ions and water
eg. on top: passive ion and fluid flow, bottom: “ and active Na+/K+ exchanger
Without directionality, there would be an even distribution of transporters so there would be no net directional flow. No directionality.
Q: Describe epithelial polarity in terms of secretion. Without?
A: secretion is polarised to ensure that the secreted products are delivered to the correct tissue compartment
could destroy yourself by having digestive E flowing the wrong way
Q: In many epithelia, where are junctions found? In what form?
A: apical region of cell-cell contact as junctional complex
generally come in 2 forms
- zonulae (continuous belts)
- maculae (discrete spots)
Q: What makes an apical junctional complex? (4) Which junction is key for epithelial polarity and function?
A: -tight junction nearest the apex
- adherens junction just below
- desmosomes (spot adhering junctions) are often scattered throughout the lateral membrane
- gap junctions are also important = act as regions of direct communication between adjacent cells
tight junctions
Q: What are tight junctions composed of? What do they seal? Another function? Specific to? Outcomes? (2)
A: -network of proteins on adjacent membranes that closely interact -> form the sealing strands
- seal the paracellular pathway (lengthways/ side/ between cells) = SEAL FUNCTION
- FENCE function that segregates apical and basolateral membrane polarity
- specific to the apical lateral membrane
- concentration differences across cell layers can be maintained
- any solutes crossing the cell layer need to pass through the cells, meaning that the cell control the passage. (strong barriers are specially needed when tissues need to transport against a large concentration gradient)
Q: Why are cell-cell junctions described as dynamic?
A: although they provide coherence and mechanical stability to cells in tissue, they are highly dynamic as they can be assembled and disassembled rapidly in response to extracellular and intracellular stimuli
Q: How do tubular tissues increase the surface area of their lining?
A: make tube longer // fold the lining to form structures like villi in the small intestine -> increase SA of the apical plasma membrane by creating tubular protrusions: microvilli
Q: Absorption of specific materials from the interior of a tissue tube is a key epithelial function. 2 places where this occurs? How is it maximised? Example where this happens?
A: intestine and kidney nephron,
- increasing the surface areas of absorbing tissue
- increasing the surface area of the plasma membrane that carries the specific membrane transporters
small intestine, which absorbs digested nutrients
Q: What makes a brush border? 1 example?
A: microvilli (striated border)
kidney proximal tubule cells
Q: How is the small intestine structured to maximise absorption? Histology?
A: -the small intestine surface area is increased by the interior surface of the wall being folded into numerous finer-like processes that point into the interior: villi.
-villi are covered with intestinal epithelial cells
- intestinal epithelium is simple columnar, with both absorptive and secretory cells
- with standard stains: Darker cells are the enterocytes (absorptive) and the cells with pale apical cytoplasm are Goblet cells (secrete mucus)
Q: What are the roles of the pancreas? Structure?
A: exocrine (into duct/lumen) and endocrine (into bloodstream) secretory functions
2 separate tissues
- islets of Langerhans are the endocrine (hormones into the bloodstream)
- Acinar cells belong to the exocrine pancreas (secrete digestive enzymes into the gut via a system of ducts- pancreatic ducts joins duodenum)
Q: What’s the usual arrangement of an exocrine cell? Example other than acinar cells in pancreas?
A: direction/polarity of secretion is: Basal -> Apical
- APICAL SIDE
- secretory granules (apical cytoplasm)
- golgi apparatus (packages and processes the proteins produced)
- extensive rough ER and nucleus (basal cytoplasm)
- BASAL SIDE
goblet cells that secrete mucous
Q: What’s the usual arrangement of an endocrine cell?
A: direction/polarity of secretion is: Apical -> Basal
- APICAL SIDE
- extensive rough ER and nucleus (basal cytoplasm)
- golgi apparatus (packages and processes the proteins produced)
- secretory granules (apical cytoplasm)
- BASAL SIDE
