Epithelia Flashcards
Describe the function of epithelia Describe the specialisations of epithelial cells in relation to their function Describe basic histological terms
4 basic types of tissues classification
Four Basic Types:
A. Epithelium (epithelial tissue)
B. Connective tissue
C. Muscle tissue
D. Nerve tissue
Where are epithelia found?
in skin, internal cavities, lumen of bodies
Main functions = PASSEF
protection, exchange, filtration, absorption, sensation, secretion
Structure
Avascular. closely apposed to each other by:
- tight junctions (impermeability of cells, limit movement of substances)
- anchoring junctions (mechanical stability)
- channel forming junctions (fluid exchange.)
=CAT
basement membrane =
basal lamina + reticular lamina (composed of type 3 collagen)
epc’s are specialized for
absorption, secretion, or protection
basal lamina thickness
40-120 nm thick
basal lamina composed of:
strong flexible foundation.
meshwork formed by: 4 cans of lame intact pearls = perlecan, type 4 collagen, intactin, laminin.
also acts as a mechanical barrier + anchoring epc’s.
important in angiogenesis
Epithelial tissue calssification can be based on:
- Based on the number of cell layers
- Simple
- Stratified - Based on shape of surface cells
- Squamous
- Cuboidal
- Columnar - Special categories
- Pseudostratified epithelium
- Transitional epithelium
Note: Specialisation of apical cell surface domain can be added
( eg. simple columnar ciliated epithelium)
simple squamous function and location:
fried egg shaped
Function: Absorption, filtration, diffusion, barrier (CNS), exchange, lubrication
Location: Capillaries (endothelium), alveoli, abdominal & pleural cavities (mesothelium) and Bowman’s capsule (kidney)
simple cuboidal fl:
round nucleus, centrally located.
Function: Absorption, secretion and transportation
Location: Glands and ducts, kidney tubules, surface of ovary (germinal epithelium), thyroid follicles
**triangular cells are still classifed as simple cuboidal.
**nuclei form rows or circles.
stratified squamous (keratinized/non-keratinized) fl:
Function: Barrier and protection
Location: Skin, oral cavity, upper throat, oesophagus, vagina
keratinized: resists abrasion. looks like a highlighter brush border. darkly stained. can prevent sun damage and dehydration.
non-keratinized: eg inside cheeks. exposed to friction but not outer environment.
Stratified Cuboidal fl:
**lumen is not always round
Function: Barrier and transport
Location: Sweat gland ducts, large ducts of exocrine glands, anorectal junction
Pseudostratified Columnar
**appears to have many layers but only has one. ciliated apical surface. tall+thin, nuclei squashed together. have goblet cells
Function: Secretion, absorption and protection
Location: Upper Respiratory tract, trachea and bronchial tree, ductus deferens, efferent ductules of epididymis
**ciliated apical surface. tall+thin, nuclei squashed together. have goblet cells. all cells are connected to the basement membrane.
Transitional Epithelium
**look like bubbles of soap stacked on top of each other.
Function: Barrier, distensible property
Location: Bladder, renal calyces, ureters, urethra
**number of layers and shapes of cells change depending on stretching of the organ.
allows for distension without damage.
microvilli - surface specialization
**actin, cytoplasmic processes
Surface specialisation of GI tract
Cytoplasmic process containing a core of network of cytoskeletal proteins (actin filaments)
Massively increases surface area for absorption
cilia - surface specialization
**microtubules
Surface specialisation of respiratory tract and fallopian tube
Cytoplasmic process containing microtubules (central and peripheral)
Transport secretions and foreign bodies
Transport cells on the surface (oviduct/fallopian tube)
found in cells which have to move fluids, to confer cell motility
in keratinised squamous epithelium, there are desmosomes. what if desmosomes were not working?
it gives mechanical strength to tissues, found in tissues which experience high mechanical force.
