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
Q: How is secretory epithelia in glandular tissues arranged? .
A: into tubules and ducts of varying complexity (simple or compound)
Q: The way in which cells secrete materials can be classified as? (2)
A: CONSTITUTIVE - secretory vesicles, as they are formed, move directly to the plasma membrane and release their contents
STIMULATED - secretory vesicles are stored in the cytoplasm and only fuse with the plasma membrane to release their contents when stimulated
Q: Example of constitutive secretion?
A: production of plasma proteins by hepatocytes (constitutive endocrine secretion)
Q: 2 examples of stimulated secretion?
A: release of adrenaline from cells of the adrenal medulla after a fight-or-flight stimulus (stimulated endocrine secretion)
when stomach contents enter duodenum, pancreatic acinar cells are stimulated to release their digestive enzymes into ducts (stimulated exocrine secretion)
Q: What type of epithelia is usually involved in protection? Describe. How does it perform this function? From which insults? (4) 2 example locations?
A: STRATIFIED SQUAMOUS EPITHELIA (both keratinising and non-keratinising)
- Keratinising - no nuclei visible in surface layer cells - they are dead cells and are made very tough by the production of several keratin proteins and lipids - this gives a dry protective quality.
- Non-Keratinising - nuclei are visible in the surface layer cells (e.g. oesophagus) - this is a wet epithelium. projects surfaces subject to chemical and physical damage
can form thick layers that protect underlying tissue from various insults eg heat, cold, solvents (alcohol), abrasion
- skin epidermis
- lining of oesophagus
Q: Describe skin protective epithelia. Acts as? Growth/ stimulation?
A: - consists of three main layers: epidermis, dermis and hypodermis
- The epidermis is the keratinising stratified squamous epithelial layer -> acts as an important BARRIER to the environment and to mechanical damage.
- The cells in the skin go through a programme of differentiation as they move up towards the surface (constantly replacing layers that fall out)
- When subject to mechanical irritation the stem cells are stimulated to proliferate to replace the lost cells.
Q: What can cause blistering?
A: Defects in cytokeratins or cell-cell junctions lead to BLISTERING DISEASES as a result of EPIDERMAL cells DAMAGE
if intermediate filaments that provide stability for epithelia are compromised, manifests itself as blistering of skin
Q: What is the role of desmosomes and where are they abundant? What happens when desmosomes are damaged?
A: role is to mechanically link cells to each other and the ECM and intermediate filaments (maintain continuity between cells) // between cells in stratified squamous epithelia
loss of desmosome function (less adhesion) -> severe blistering
Q: What do cervical smear tests sample?
A: surface cells of non-keratising stratified squamous epithelium of uterine cervix
(mild scraping->microscope slide and stained-> abnormal cells indicate serious pathology)
Q: What is a skin callus?
A: hard skin, formed as a normal response to environmental stimuli (that affect normal turnover in that particular cell)
Q: How often are cells replaced in the:
gut lining?
fat, heart, bone tissue?
cells of nervous system?
epithelia: small intestine, colon, epidermis (skin)?
A: -every 3-10 days depending on region
- every 8-10 yrs
- most are not replaced -> if they die, they are lost
consistently: 3-5 days, 5-7 days, 48 days (depend on region)
Q: How does cell division occur in the small intestine?
A: -Cells are lost at the tip and are produced in the crypt // constant turnover of cells
- crypt of leiberkhun contains ISC - Intestinal Stem Cells
- It acts like an escalator - as the cells mature they move up towards the tip of the villus
Q: What happens when cell-turnover becomes unbalanced?
A: can increase or decrease cell proliferation
decrease: cells are lost from villus tip but not replaced -> loss of tissue -> villi shorten
increase: eg in colon -> too much tissue forms -> called benign tumour: adenoma (polyp) -> can become malignant as more cells = higher risk of acquiring more mutations that switch it to cancer
Q: Why can chemotherapy cause strong gut side-effects?
A: loss of turnover (shortens villi)
Q: What causes warts?
A: result of infection of epidermal keratinocytes by one of the family of human papilloma viruses
virus hijacks cell proliferation machinery and increases cell proliferation
Q: Provide 2 examples or normal physiological responses involved in cell turnover.
A: cyclic production and loss of endometrial epithelial lining of uterus in menstrual cycle
large increase, during pregnancy, in the number and size of the epithelial glands of the breast and their loss after weaning (stopping breast feeding)
