Wk 2: Surface Epithelium Flashcards
6 Functions of Epithelial Tissue
- Protection
- Transcellular transport via selective permeability of intracellular junctions between epithelial cells
- Secretion - hormones, enzymes, other molecules
- Absorption of material from lumen
- Sensation via tastebuds
- Immune defense - physical barrier prevents invasion & epithelial cells house cells of immune system
What is the epithelium separated from the underlying CT by?
By an extracellular matrix referred to as the basement membrane
since epithelium is avascular, how is nourishment supplied?
Nourishment & O2 supplied by adjacent connective tissue through capillary beds via diffusion through basement membrane.
What kind of regenerative capacity do epithelium have
High regenerative capacity & can reproduce rapidly as long as they have adequate nutrition
What are the 2 constituents of the basement membrane
- Basal Lamina
- Lamina Reticularis
Functions of basal lamina (of basement membrane)
Molecular filter & support for overlying epithelium
2 components of the basal lamina
- Lamina Lucinda
- Lamina Densa
Where is simple epithelium found
Adapted for transport of substances between tissues.
Found in areas where absorption, secretion & filtration occur.
Where is stratified epithelium found
In high abrasion areas where protection is needed
What do polarised cells possess
An apical domain that faces lumen.
A basolateral domain whose basal component is in contact w basal lamina.
What is simple squamous epithelium adapted for
- Rapid diffusion (one cell thick) of substances - O2, CO2, fluids, ions
Where is simple squamous epithelium found
- Lining air sacs of lungs
- Lining segments of kidney tubules
- Lining blood vessels
What are simple cuboidal epithelium thin enough for
Rapid diffusion of substances
Where are simple cuboidal epithelium found
- Renal tubules
- Respiratory passages
- Ducts of many glands
- Thyroid gland
Where are the nuclei located in simple columnar epithelium
Nuclei located in basal portion of cell
What do simple columnar epithelium often have on them and for what purpose
- Microvilli on apical membrane - increases surface area for absorption of substances
- Cilia - propel substances through hollow organs
Where are simple columnar epithelium with microvilli found
- Small intestine
Where are simple columnar epithelium with cilia found
- Uterine tubes
- Segments of respiratory tract
Function of stratified epithelium
Protective barriers in locations w high degrees of stress
In stratified epithelium what kind of epithelium make up the apical membrane and what kind make up the basal cells (deepest cells)
- Cells in the apical membrane of the epithelium are squamous in shape
- Basal cells are cuboidal in shape
Features of keratinised stratified squamous epithelium (5)
- Cells in apical layers are dead
- Cells in apical layers lack nuclei
- Cells in apical layers are filled with keratin
- The tissue is tough & resistant to friction
- The tissue is adapted for outer layers of skin
Features of non keratinised stratified squamous epithelium (3)
- Cells in apical layers retain nuclei
- Cells in apical layers are still alive
- Found in regions of mechanical stress where surface must remain moist
Where would non keratinised stratified squamous epithelium be found
- Mouth
- Throat
- Esophagus
- Anus
- Vagina
Where is lined by stratified cuboidal epithelium
Lines ducts of sweat glands
What shape of epithelial cell is in the apical cell layer and basal cell layer of stratified columnar epithelium
- Apical cell layer is columnar
- Basal cell layer is cuboidal
Where is stratified columnar epithelium found
- Male urethra
- Cornea of eye
- Ducts of salivary glands
Which system is transitional epithelium found in
Only found in urinary system
Transitional epithelium; what kind of epithelium on apical membrane vs basal layer
- Basal cell layers are cuboidal
- Apical cell layers are dome shaped when tissue is relaxed
What is pseudostratified columnar epithelium
Epithelium that appears to be layered as nuclei are found at various heights, but the epithelium is actually one cell thick.
Where is pseudostratified columnar epithelium found
- Segments of respiratory tract
- Nasal cavity
What is usually found on pseudostratified columnar epithelium
Cilia
Describe tight junctions
- They hold cells tight together so the space between cells is impermeable to movement of macromolecules
What are desmosomes composed of
Linking integral proteins
What do desmosomes do
- Allow materials in extracellular fluid pass through space between cells
- Increase strength of tissue by holding cells together
What are gap junctions
Small pores formed by protein channels between adjacent cells
Function of gap junctions
Allow ions & small substances to flow freely between each cells cytoplasm
What kind of cells are gap junctions found in
Cells that communicate with electrical signals such as cardiac muscle cells
What happens in paracellular transport
Substances leak between cells in an epithelial membrane
Why is paracellular transport limited
Due to tight junctions as they make spaces between cells nearly impermeable
What happens during transcellular transport
Substances enter cell by crossing plasma membrane
, diffusing across cytosol and exiting cell through plasma membrane at opposite side
