Epithelia Flashcards
Identifying features of epithelia
Forms dense cellular sheets
Has no blood vessels
Rests on a basal lamina complex
Polarised cells
Stains well with haematoxylin and eosin
How are epithelial cells attached to each other?
Via desmosomes and adherens junctions
Different epithelial cell shapes
Squamous
Cuboidal
Columnar
How are nutrients delivered to epithelial cells?
Diffuse from blood vessels in adjacent connective tissue
Different types of cell arrangement
Simple - single layer
Pseudostratified - all cells in contact with basal lamina
Stratified - multiple layers
Simple squamous epithelium
Location - Lining surfaces involved in passive transport of gases or fluids
Function - Allows material to pass through by diffusion and filtration, secretes lubricating surfaces
Simple cuboidal epithelium
Location - Lines small ducts and tubules eg - collecting tubules of kidney, small excretory ducts of salivary glands and pancreas
Function - Secretes and absorbs
Cell specialisation types
Cilia - movement
Microvilli - absorption
Keratinisation - protection
Function of microvilli
Increase surface area for absorption, with a brush border
Structure of microvilli
Shape maintained by actin filaments anchored to the cell membrane
Base of actin filaments form part of the terminal web which is linked to intermediate filaments of the cell
Simple columnar epithelium
Location - Absorptive surfaces such as small intestine and secretory surfaces such as the stomach
Function - Absorbs - also secretes mucus and enzymes
Why do goblet cells appear empty under the micrscope?
Mucus is lipid based
Goblet cell
Modified columnar epithelial cell that produces and secretes mucus
Found in many simple epithelial linings
Stains poorly with Hematoxylin and eosin
Pseudostratified columnar epithelium
Location - In the airways of respiratory system - all cells are still attached to the basal lamina but not all reach the apical surface
Function - Secretes mucus - ciliated tissue moves the mucus
Cilia function
Motile structures that move fluid and particles along the epithelia surface
Structure of cilia
Core of 20 microtubules arranged as 9 doublets around a central pair (9+2 arrangement)
Which is larger - microvilli or cilia?
Cilia
Squamous stratified epithelium
Location - Physical protection in oral cavity, pharynx, oesophagus, anal canal, uterine cervix and vagina
Function - Protects against abrasion
Replication of squamous stratified epithelial cells?
Only cells along the basement membrane replicate
The replicated cells move from the base to the apical side
Where are keratinised stratified epithelium found?
On surface layers of keratinised dead cells
Water cannot pass through
Where is transitional epithelium found?
Location - In the ureter and bladder only
Function - Allows urinary organs to expand and stretch
Features of transitional epithelium
Able to change shape
Tight junctions between cells to prevent material flowing
Distension - allow bladder to stretch
Protection - from toxic urine
Waterproof - prevents water leaking into concentrated urine
Functions of cell junctions in epithelial cells
Keep epithelial cells tightly bound
Allow functional integrity of cells
Examples of junctions
Desmosomes
Hemidesmosomes
Adherens junctions
Tight junctions
Gap junctions
Tight junction
Seals neighbouring cells together in an epithelial sheet to prevent leakage of molecules between them
Found where movement along concentration gradient is prevented
Adherens junction
Joins an actin bundle in one cell to a similar bundle in a neighbouring cell
Provide some mechanical support
Desmosome
Joins intermediate filaments in one cell to those in a neighbour
Gap junction
Allows the passage of small water soluble ions and molecules
Channels are closed until connection is established between 2 adjacent cells
Hemidesmosomes
Anchors intermediate filaments in a cell to the basal lamina
Protein components of desmosomes
Desmoglein and desmocolin cross the cell membrane
Outside they bind homophobically - to their same kind
Inside the cell, plaque (a dense protein) bind to intermediate filaments and link them to desmoglein and desmocolin
