Epithelial tissue Flashcards
What are the types of epithelium?
Covering
Glandular
What is covering epithelium?
Lines cavities and cover surfaces
A continuous layer of cells which line externals surfaces e.g. skin
Internal - lines tracts e.g. reproductive, respiratory and digestive tracts.
What is glandular epithelium?
Secretory epithelial cells.
Arises from covering epithelium, forms when covering epithelium invaginates.
What is the differentiation of epithelial cells?
Differentiate into secretory cells, can maintain contact with covering or lose it.
Exocrine glands maintain contact via duct - have secretion of product into lumen of the gland, which then rises up and covers the surface of the covering epithelium.
Endocrine glands lose contact with covering epithelium, secrete products into bloodstream.
How do epithelial cells join?
Cell to cell contact between each epithelial cell via cell junctions.
These can form a continuous sheet, which sits on the basement membrane.
What are the sides of the basement membrane?
Side next to basement membrane is basal.
Side that is exposed (forms lumen), is the luminal surface or apical surface.
What is the basement membrane?
Extracellular matrix scaffold which epithelial cells adhere to - provides structural support to epithelial cells.
Forms a barrier to connect epithelium above to tissues below, only lets water and small molecules through.
What is the basal lamina?
It can be the basement membrane, but is actually part of the basement membrane.
Made from connective tissue below and some from epithelial cells above.
How is the basement membrane observed?
Basement membrane not seen by H&E, but can be made visible by PAS stain - stains carbohydrates.
Or electron microscopy.
What is simple epithelial tissue?
One cell thick
see image
What is stratified epithelium?
Multiple layers of cells.
image
How are epithelial cells classified through layers?
Simple or stratified
How are epithelial tissues classified through shape?
Cuboidal
Columnar
Squamous
What is cuboidal epithelium?
Round, cube shaped
image
What is columnar epithelium?
Taller than wider
Nuclei is towards the basal surface.
image
What is squamous epithelium?
Flattened cells
image
How are epithelial tissues classified through specialisations?
Cilia or keratinisation (keratin on apical surface)
What is the name order of epithelial tissue?
Specialisation, number, shape, Epithelium
Can have various shapes of cells but it is classified by the most superficial and uppermost cell seen.
What are the applications of stratified epithelium?
Stratified - Presence of many layers gives functional advantage of protection.
Found in areas where you find abrasion - anal canal, oesophagus and skin - in contact with external environment.
What are the applications of simple epithelium?
Simple line ducts and tubes and is in areas with secretory or absorptive functions.
e.g. found in digestive tract - easier to absorb nutrients through one layer of cells than many.
What is the application of cuboidal epithelium?
Secretory or absorptive functions - collecting ducts at kidneys, salivary glands, but not where there is physical abrasion or stress.
What is the application of columnar epithelium?
Columnar - highly absorptive areas - digestive tract, stomach, small intestine, large, and in the ducts of many glands.
What is the application of squamous epithelium?
Squamous - highly specialised, flat, little metabolic activity.
Involved in diffusion of material - found in capillaries, or alveoli, or lining surfaces not in contact with exterior environment.
What are the applications of cilia?
Cilia on apical surface, motile and help to waft and move cell debris over top of epithelial tissue.
Found in respiratory tract - clear mucus and protect your lungs.
What do ciliated epithelium look like?
ciliated simple columnar epithelium
found in fallopian tubes
image
What is the application of keratinised epithelium?
Keratinisation - excessive production of keratin, found on skin - waterproofs and strong, flexible outer coating, protection.
What does keratinised epithelium look like?
Keratinised stratified squamous epithelium on skin.
Various shapes of cells but it is classified squamous as it is the most superficial and uppermost cell seen.
image
What is pseudostratified epithelium?
Each cell is sat on the basement membrane so is a simple epithelium, but the nuclei are at different levels, so appears stratified.
image
e.g. ciliated pseudostratified columnar epithelium, found in the respiratory tract.
What is transitional epithelium?
Found in the ureter and bladder.
When the bladder is empty, see umbrella-shaped cells.
When bladder is full, the superficial cells flatten and allows lots of stretch, transition to a more squamous cell shape.
What is cell polarity?
The asymmetrical organisation of cellular context to allow functional difference at different poles of the cell.
What is the apical side?
Or luminal.
Has keratinisation, cilia, microvilli.
This is because it is the side in contact with the lumen.
What is the basal surface?
Has specialised cell junctions which help to anchor the base to the basement membrane.
Epithelium tissues receive nutrients from connective tissue below and receive nervous innervation.
What are tight junctions?
Tight junction / occluding junction - is very important for setting up differences between basal and apical surfaces.
So the apical cell surface can have relevant receptors and enable epithelium to be selective in which nutrients it takes up into epithelial cells.
Also prevent paracellular diffusion.
What is the lateral side?
Has specialised cell junctions which help connect the epithelial cells to neighbouring cells and help the cells form coherent epithelial layer.
What is paracellular diffusion?
Diffusion of nutrients between lumen and tissues beneath, and between the cells rather than through the cell.
Tight junctions prevents leakage into surrounding tissue.
What are zonular adhesions?
Or adheren junctions
Tightly bind adjacent cells together, and anchor sites for cytoskeleton within epithelial cells.
This ensures epithelium is cohesive and can withstand
movement.
What are gap junctions?
Or communicating junctions - formed by a ring of proteins which forms a channel where small ions can be directly transferred between cells, forms a functional bridge.
What are macular adherins?
Desmosomes - connect cytoskeleton together.
Macular means they are dotted around the cell, not banded.
These also rivet the cytoskeleton of neigbouring cells together.
What are hemidesmosomes?
Like desmosomes but only interact with extracellular matrix, adhere cells to basement membrane.
What is the structure of cilia compared to microvilli?
Made from microtubules, 10um, motile, present only in respiratory and reproductive tracts.
Microvilli - made from actin, 1um, less motile, more widespread - mainly in kidney and digestive tract.
What is the order of cell junctions?
Tight junction
Adhering junction
Desmosome
What is keratin?
A cytoskeletal protein.
At the top, cells die and leave behind keratin which acts as a protective, impermeable to water, layer.
What are secretory epithelial cells?
Scattered - goblet cells, found in respiratory epithelium.
Have many secretory granules
Do not stain well as produces mucus.
What is glandular epithelia?
Specialised epithelial tissue secreting a particular protein, lipid or carbohydrate.
Can be endocrine - produce hormones or exocrine e.g. salivary glands, the pancreas is both.
Glands can be straight or coiled or branched.
