Epithelium Flashcards
(18 cards)
Functions of Epithelium
- secretion
- selective permeability
- transport
- sensory perception
- protection
- absorption
Simple Squamous
- Single layer of flattened cells
- Facilitates passive diffusion of gases or fluids
- Examples – lungs and kidney
Simple Cuboidal
- Single layer of cells where height and width are
approximately equal - Examples - usually lines small ducts and tubules
- May have excretory, secretory or absorptive functions
Simple Columnar
- Single layer of tall cells; nucleus usually located basally
- Most frequently associated with absorption and
secretion - Examples – gastrointestinal tract and large ducts
Pseudostratified Columnar Ciliated
- Variant of simple columnar
- Appears as many layers as nuclei are at different levels,
but all cells make contact with the basement
membrane - Examples - trachea and bronchus
Stratified Squamous Non-Keratinising
- Many layers of cells with most superficial cells squamous
in shape - Microridges on apical surface
- Protective function
- Well adapted to withstand abrasion since loss of cells
does not compromise underlying tissue - Examples – entry and exit points of the body i.e. oral
cavity, oesophagus, vagina, anal canal
Stratified Squamous Keratinising
- As SSNK, but layers of anucleate keratin
- Adapted to withstand constant abrasion and desiccation
- Examples – epidermis of skin, gingiva, dorsum of tongue
Transitional
- So named as it is a transition between stratified squamous
and stratified columnar - Adapted to withstand stretch and toxicity of urine
- Examples – renal calyces, ureters and urinary bladder
Exocrine
Secretes product onto a surface via ducts
Endocrine
Secrete product into the blood stream, no ducts
Development of glands
- All glands begin as secretory cells on a surface epithelium
- Unicellular glands (goblet cells) – stay on surface
- Multicellular glands begin as
down-growing buds of cells - Exocrine glands develop a duct with secretory cells at the bottom in a secretory unit
- Endocrine glands develop by the isolation of the bud of cells from the surface epithelium. This isolated mass then acquires its own blood supply
Classification of gland - STRUCTURE
DUCTS
- Simple - unbranched ducts
- Compound - branched ducts
SECRETORY UNIT
- acinar - shaped like a hollow
berry; cells form a spherical
mass called an acinus with
central lumen extending into
a duct
- tubular - test-tube shaped
Classification of gland - SECRETION
- mucous secreting:
- Viscous fluid
- Rich in
mucopolysaccharides
to lubricate and
protect - pale staining
- serous secreting:
- Watery fluid
- Rich in enzymes
- dark staining
- seromucous (mixed) secreting:
- Contain both serous
and mucous cells
Gland Classification - methods of discharge
Merocrine/ Eccrine:
- Most common method – sweat glands, pancreas, salivary glands
- vesicle releasing contents into duct, secretion in duct
Apocrine:
- mammary gland
- secretory products stored in cell, pinched-off portion of cell in the secretion
Holocrine:
- sebaceous glands
- cell shed into duct, dying cell releases secretory products
Tight junction (Zonula Occludens)
- Membranes of adjacent cells are sealed
together at points to prevent transport of
substances between the cells - Maintains apical and lateral domains
Intermediate Junction (Zona Adherens)
- Ribbon-like adhering junction – anchors to
terminal web (TW) underlying apical membrane
Desmosome (Macula Adherens)
- Spot-like adhering junction – anchors to cell
cytoskeleton (intermediate filaments (IF)
Gap Junction
- allows the passage of small water-soluble molecules from cell to cell
