Epithelium Flashcards
Name the four basic tissues
epithelium, connective, muscle, nerve
Name 5 characteristics of epithelial cells
- cover exterior body surface
- avascular
- line internal cavities
- forms secretory portion of glands
- receptors for special sense
Where is the basement membrane?
between the epithelium and the connective tissue
What is the name of the connective tissue below the basement membrane?
Lamina propria
Does the basement membrane contain cells?
No it is acellular
Name 4 functions of the epithelium
1) Receptors for senses
2) Absorption
3) Secretion
4) Protection/Barrier
RASP
How many domains do epithelial cells have?
3
What are the domains of the epithelium?
Apical domain - exposed to lumen
Lateral domain - in contact with neighboring cells by junctional complexes and adhesion molecules
Basal domain - attached to basement membrane
What creates polarity in the epithelial cells?
Proteins that line the plasma membrane determine polarity (i.e. transmembrane proteins in apical and basal domain)
Name 4 major types of epithelium
Simple
Transitional
Stratified
Pseudostratified
Name 3 shapes that epithelial cells come in
Squamous
Cuboidal
Columnar
Describe simple squamous epithelia and where it is found
- one layer of cells that are wider than they are tall
- thinnest tissue in body
- lines blood and lymphatic vessels
- Nucleus always bulges into lumen
Where are simple squamous epithelia found?
Blood and lymphatic vessels (ex. bowman’s capsule in kidney, respiratory spaces in lungs)
Why is simple squamous epithelia ideal as a thin tissue?
Allows for transfer of material from lumen across epithelium and facilitates diffusion of gases and small molecules
Simple squamous epithelia that covers the closed cavities in the body is called what?
Mesothelium
Simple squamous epithelia that lines the atria and ventricles of the heart is called what?
Endocardium
Simple squamous epithelia that lines the blood vessels is called what?
Endothelium
Why is it important for the simple squamous epithelium to be the same direction as flow of blood?
To maintain health of blood vessels because points where blood vessels are going to branch
Describe simple cuboidal epithelia
- Width of cell similar to height
- Eosinophilic
- they are basic
Where are simple cuboidal epithelia found?
Ducts and Tubules (Kidney tubules, small ducts of exocrine and endocrine glands etc. )
What is the function of simple cuboidal epithelium?
Absorbing and secreting material into ducts
Describe simple columnar epithelium.
- shaped like a column
- nuclei are lined up in the basal portion of the cells
- sometimes apical domain contains specializations (microvillus/cilia)
Where are simple columnar epithelium found?
All through out GI tract such as small intestine, stomach lining, etc.
What is the function of simple columnar epithelium?
- Absorbs nutrients
- Protection
- Impermeable barrier to bacteria
What is a Goblet Cell?
secretory cell or “unicellular gland” which secretes mucus
stain magenta in PAS
Describe stratified squamous epithelia.
- Multiple layers of squamous epithelial cells (shape based on top most layer)
- can be separated visually
Keratinized/Cornified/Wet
Cells at surface are dead and have lost their nuclei (tend to peel off and shed very 10 days)
Non-Keratinized/Non-Cornified/Wet
Cells on surface are nucleated
Where is stratified epithelium found?
Oral cavity, esophagus, and vagina
Which type of epithelium can be keratinized?
Only Stratified Squamous Epithelium
Keratinized epithelium is located on places where there is more…
Abrasion (ex. feet and hands)
Where is stratified cuboidal epithelium found?
in large ducts of exocrine glands (aka sweat glands)
Define exocrine
glands that secrete into ducts
Define endocrine
glands that secrete into nearby capillaries (no ducts) (ex: pituitary)
Where is stratified columnar epithelium found?
largest ducts of exocrine glands (ex. rectum, anus)
Describe pseudo-stratified epithelium.
- all cells touch the basement membrane
- not all cells reach the surface
- nuclei are everywhere/no layer differentiation
Where is pseudostratified epithelium found?
Trachea (respiratory tract)
What type of epithelia is found in the respiratory tract? Why is this type important for its function?
Pseudostratified
- need to move material/mucus secretions up tract with cilia (dyenin motors)
Describe transitional epithelium.
- specialized stratified epithelia that is able to stretch
- can be multi-nucleated
- impermeable to salts and water
- surface looks like cobble stone streets
What is another name for transitional epithelium?
Urothelium
Where is transitional epithelium found?
Bladder, ureter, and urethra
What type of epithelia is found in the urinary system? Why is this type important for its function?
Transitional epithelium
- is able to stretch (bladder stretches)
How are transitional epithelium able to stretch?
storage membrane as little vesicles is able to expand by joining plasma
What is derived from epithelia?
All glands
Define mesenchyme
connective tissue that forms during embryogenesis
What do endocrine glands do?
makes hormones that are dumped into neighbor blood vessels that brings to other parts of the body
Name three modes of secretion
Merocrine, apocrine, holocrine
Define apocrine secretion
Some of the apical cytoplasm is pinched off with the contained secretions
Define merocrine secretion
Vesicular membrane fuses with plasma membrane to release its contents into the extracellular space (membrane can be taken back by endocytosis)
Define holocrine secretion
Cell produces and accumulates secretory product then cell disintegrates to release it (ex. sebaceous glands)
How are cells replaced when undergo holocrine secretion?
Replaced by adult stem cells
What mechanisms of secretion do mammary glands use?
- merocrine secretion for milk protein casein
- apocrine secretion for milk lipids
Transmembrane proteins in the plasma membrane create polarity to help ______ line up correctly.
Glycocalyx
What is the function of tight junctions?
To guide food/nutrients into cells and not between them
Where are tight junctions located?
Apical domain
Describe concept of maintaining polarity.
Lateral junctions (ex. symport protein and ATPase) in the apical end hold proteins in place which maintain biochemical properties of the membrane
If you see lots of mitochondria between plasma membrane and basement membrane, what does it mean?
Increasing surface area of plasma membrane causes an increase in the number of sodium potassium pumps at the base –> this is an energy requiring process so we see lots of mitochondria between plasma membrane and basement membrane
What determines the polarity of the cell domains? What maintains polarity?
The biochemical characteristics and geometric arrangement of the cells determine polarity, while the junctions between cells maintain it
What are examples of apical specializations?
microvilli and cilia
Describe microvilli and its characteristics.
- cells that transport fluid and absorb metabolites
- nonmotile
- closely packed, finger-like projections of plasma membrane that increase surface area of the cell
- number and shape on the cell surface correlate with absorptive capacity
What structurally supports microvilli?
a core of actin filaments which are cross-linked by several actin binding proteins (ex. Villin) in the cytoplasm
What is the name of the site of where actin bundles binds to the cytoskeleton?
Terminal Web
Describe stereocilia
- long nonmotile processes
- structurally similar to microvilli
- facilitates absorption
- in the ear, sensitive to mechanical vibration
What is the function of motile cilia?
to move fluid or particles along an epithelial surface
Describe cilia and its characteristics.
- beat in synchronous pattern
- arranged in orderly rows
- appear like hair-like structures at apical surface
Where are microvilli normally found?
Small intestine and kidney (needed for absorption)
Where are cilia normally found?
Respiratory tract
Why are cilia important for the respiratory tract?
they move mucus from the epithelial surface which prevents bronchitis (example)
What attaches cilia to the epithelium?
Basal body
Where does cilia grow from?
Basal body
What is the basal body?
core fo 9 microtubule triplets where assembly of cilia is initiated
What are cilia made of?
microtubules arranged in a 9 microtubule doublet pattern with each doublet containing dynein arms
Does the basal body contain motor proteins?
No motors proteins present in BB
What are the motor proteins in cilia?
Dynein arms
What is Kartagener’s syndrome?
a structural abnormality that results from the absence of dynein arms thus altering cilia function»_space; results in respiratory diseases such as bronchitis
What are nonmotile primary cilia called?
Monocilia
What is monocilia?
- nonmotile cilia
- microtubule-based cellular organelles that protrude from surface of cells to act as cellular antenna
- function: transduce/regulate signaling pathways
- important for normal tissue morphogenesis during embryogenesis
What type of receptors are monocilia?
Chemosensors, osmosensors, mechanosensors
What apical specialization is important during embryogenesis?
Monocilia because their signaling dictates where organs end up.
Example - Situs Inversus (L+R asymmetry)
What are the four functions of intercellular junctions?
1) generate functional barrier and maintain cohesive nature of epithelium
2) regulate movement of molecules between and through cells
3) restrict movement of plasma membrane proteins along domains
4) recruit signaling proteins to the cell surface or cytoskeleton
Define intercellular vs. intracellular
Intercellular - between two cells
Intracellular - within the cell
Junctional complexes are made up of proteins called ______
cell adhesion molecules (CAMs)
Name the lateral specializations.
Zonula occludens (tight junctions)
Zonula adherens (Adhesion belt)
Macula Adherens (Desmosomes)
Name the lateral specializations from location apically to basal.
Tight Junctions –> Adhesion Belt –> desmosomes
What is pemphigus vulgaris?
immune disease in the oral cavity that causes patient to make antibodies against desmosomal junctions
What are tight junctions?
junctions where the plasma membranes of adjacent cells come in contact to seal off intercellular space (not a continuous seal but a series of focal fusions)
What are focal fusions?
junctional proteins of adjacent cells traverse the plasma membrane and come in contact to occlude the intercellular space
What transmembrane proteins make up tight junctions?
Claudin and Occludin
What regulates what can travel through a junction?
tightness of a junction
Paracellular vs. Transcellular pathway
Paracellular - in between cells
transcellular - through cells
Occluding junctions are _____ and allow the epithelium to function as a barrier
impermeable
How do tight junctions relate to the blood brain barrier?
junctions regulate selective passage of substances between endothelial cells –> generating BBB
Glucose transport is a _____ pathway.
Transcellular
What proteins are a part of the Ig fam?
Junctional adhesion molecules (JAM) and Nectins –> both are CA2+ independent
What proteins are a part of the tetraspan family?
Claudin and occludin
What is the function of tight junctions?
seal the intercellular space, keep transmembrane proteins in place, and regulate paracellular diffusion
What are zonula adherens and their function?
- lateral adhesions using proteins that link into the cytoskeleton
- continuous belt that encircles cell
- provides cell to cell attachment
- important for maintaining the structural integrity of the epithelium
What are cadherins?
- transmembrane protein that is CA2+ dependent so need calcium to be attached- main component of Zonula adherens
What are the four families of CAMs?
cadherins, integrins, selectins, and immunoglobulin superfamily
What intracellular helper proteins does cadherin interact with to bind to actin filaments in cytoskeleton?
Catenin, vinculin, and alpha-actinin
What is catenin?
structural and helper protein that helps with signaling during embryonic development
Difference between cadherin and catenin
Cadherin - transmembrane protein
Catenin - helper protein that helps bind cadherin to actin in cytoskeleton
Describe what happens during epithelial-mesenchymal transitions (EMT) in human disease.
Epithelial cells are differentiated and don’‘t move, while mesenchymal (fibroblast-like) cells migrate and can differentiate
When epithelial cells switch to mesenchymal cell, cadherins are down regulated and other molecules like vimentin are up-regulated resulting in breaking attachments with enzymes
What is another name for desmosomes?
Macula adherens
What are desmosomes and their function?
- specialized structure for cell-to-cell adhesion
- randomly arranged on lateral sides of plasma membranes
- not a continuous structure
- super strong attachments
The protein components of desmosomes are attached to…
intermediate filaments
What are gap junctions and their function?
- accumulation of transmembrane channels
- composed of integral membrane proteins called connexins
- direct passage of electrical and chemical communication from one cell to another
- allow small molecules to pass but not large
when are gap junctions useful?
when adjacent cells need to be coordinated with one another (ex. cardiac muscle contraction)
What are connexins?
integral membrane proteins that make up gap junctions
How many connexins are needed for a gap junction passage?
6 connexin monomers to form a connexon
need 2 connexon (one from each cell) to make a passage
Connexon passages are regulated to open/close due to changes in…
- ion concentration (calcium)
- low pH
Mutation in Connexin 26 gene leads to…
Deafness
Mutation in connexin 32 leads to…
X-linked Charcot-Marie-Tooth Demyelinating neuropathy
What is X-linked Charcot-Marie-Tooth Demyelinating neuropathy?
- cx32 mutation
-symptoms include muscle degeneration and impairment of reflexes
What are hemi-desmosomes?
Desmosomes that only attach one cell’s plasma membrane to the lamina lucida of basal lamina
Name the three layers of the basement membrane.
- lamina lucida
- lamina densa
- reticular lamina
What two layers make up the basal lamina?
lamina lucida and lamina densa
What domain specialization are hemi-desmosomes?
Basal specializations
Mutation in Connexin 50 gene leads to…
Congenital cataracts that leads to blindness
Mutation in the deletion of Connexin 43 gene leads to…
skeletal defects and delays in mineralization
What is the basal lamina composed of?
meshwork of proteins including laminins, collagens, glycoproteins, and proteoglycans
What is the function of basal lamina?
- structural attachment of the epithelial cells
- compartmentalization of connective tissue
- filtration
- tissue scaffolding
- regulation and signaling
What are the stages of cancer malignancy?
- dysplasia
- carcinoma in situ
- microinvasion
- metastasis/invasion
What is dysplasia?
When cancer cells remain in epithelial layer but have not yet invaded basement membrane
What is carcinoma in situ?
When cancer cells cause the epithelial organization to be lost but have yet to invade the basement membrane
What is microinvasion?
when the cancer cells break down the basement membrane and invade the connective tissue
What is metastasis/invasion?
When the cancer cells can rapidly enter the blood vessels and invade distant tissues
What binds the basal lamina (lumina densa) to the reticular lamina?
Type 4 collagen and laminin 5 anchoring fibers as well as focal adhesions
What attaches and interacts with laminin 5 and collagen type 4 in the basal lamina?
Integrins which are structural and signaling proteins
Hemi-demosomes are most commonly found in the…
SKIN
blistering disease
when a person makes antibodies against proteins that attach cells, they end up with a blistering disease
What is the difference between helper protein and integrin attachment?
Helper proteins attach to actin in cytoskeleton
Integrin attaches to basement membrane
** need to check concept
