Epithelia Flashcards
Semester 1 year 1
What do epithelial cells generally do?
Form the boundary between a controlled internal environment + uncontrolled external environment
What can epithelial tissues develop from?
All 3 germ layers:
-endoderm e.g GI
-mesoderm e.g lining of DV system
-ectoderm e.g epidermis
Where are epithelial tissues found?
In every organ
What are the functions of epithelial tissues?
-protection e.g skin
-barrier e/g blood brain barrier (BBB)
-diffusion
-absorption
-secretion
Where is the basolateral membrane?
-at the bottom and sides
-is fixed
Where is the apical membrane?
Free membrane
What properties allow epithelial tissue to import and export substances?
-connected via tight junction, which decreases free diffusion
-distinct apical + basolateral domains with differing membrane properties and functions makes it polarised
What are tight junction?
What connects epithelial cells and tissues
What does it mean to say that epithelial cells are entirely cellular?
-avascular - no blood vessels
-lack extracellular fibres
-minimal extracellular space
Which of the basolateral and apical membrane are specialised?
Both
What is the basolateral membrane in contact with?
Extracellular fluid compartment
What is the basement membrane made up of?
-basal lamina (BL)
-reticular lamina –> reticular fibres anchor BL to underlying connective tissue
What do tight junctions stop?
Paracellular movement between cells
What are the 2 types of tightness that tight junctions can have?
-high barrier function –> stops most ions + water e.g renal thick ascending limb
-leaky –> allows transepithelial movement e.g renal proximal tubule
What determines the tightness of tight junctions?
-protein strands (claudins)
-different combinations of claudins determine the permeability
What do adherin junctions do and what happens if they’re disrupted?
-form belts around the cell under the tight junction
-if their organisation is disrupted, it can cause them to separate, leading to metastasis
What are cadherins?
Adhesion molecules
What do desmosomes do?
-form strong adhesion points between cells
-have extracellular domains (part of cadherin family)
What do anchor proteins (plaques) do?
Link cadherin cytosolic domains to intermediate filaments
What are the 2 main types of epithelia?
-simple –> single layer of cells
-stratified –> many layers of cells
What are 2 other types of epithelia for those that don’t fit the main ones?
-pseudo-stratified –> 1 layer of cells but appear to be more
-transitional –> cells change as you move up through the layers
What are the basic types of epithelia?
-simple squamous
-simple cuboidal
-simple columnar
-pseudostratified columnar
-stratified squamous
-stratified cuboidal
-stratified columnar
-transitional epithelia
Describe simple squamous epithelia
-appear like thin ‘scales’
-facilitate rapid passage of molecules
-secretion/absorption of molecules via active transport
Describe simple cuboidal epithelia
-secretion/absorption of molecules via active transport
-many have single non-motile cilia on apical membrane –> deformation ‘senses’ fluid flow
Describe simple columnar epithelia
-with or without microvilli or cilia
-secretion/absorption of molecules via active transport
-majority in GI tract
-ciliated surfaces move egg in fallopian tube + remove particulates in respiratory system
Describe pseudostratified columnar epithelia
-single cell layer but appear multi-layer as nuclei at different levels
-all in touch with basolateral membrane
-ciliated or nonciliated
-ciliated cells often interspersed with goblet cells
Describe stratified squamous epithelia
-most common type
-apical cells appear squamous, basal cells cuboidal or columnar
-areas of high abrasion
Describe stratified columnar epithelia
-rare
-allows tissue to stretch + contract
Describe transitional epithelia
-cells round when relaxed
-facilitates shape change in distension without damaging epithelial lining
Are stratified cuboidal common or not?
less common –> e.g glands
What do multicellular glands have?
complex ducts - secrete directly onto the epithelial surface
Where do single or different cell types secrete?
Directly into blood
If secretion is via ducts, what is it called?
Exocrine
If secretion is ductless, what is it called?
Endocrine
