Epithelial Tissues Flashcards
What type of tissues are epithelia?
- line body surfaces
- line body cavities
- surface of internal tubes/ ducts
- functional units of glands
What are 5 common properties of epithelial cells?
- Adherent to one another
- Arranged in 1 to several layers/ sheets
- Polarized (apical and basal/basolateral surfaces)
- Basal lamina attaches basal surface to connective tisue
- Undergo turnover/ renewal (driven by Epithelial stem cells)
- Avascular -> nutrients and oxygen through diffusion
- Divers: many types and within single epithelium may be several types
What are some functions of epithelia?
- Barrier
- Selective absorption & transport
- Selective secretion
- Movement of particles & mucous
- Biochemical modification (liver)
- Communication from other tissues/ organs
- Reception of sensor stimuli
What are cells that face blood and lymph called?
endothelium
Blood and lymph vessels
What are cells that line the enclosed internal spaces of body cavities called?
mesothelium
Abdominal cavity and internal reproductive organs
What are mucosa (mucus membranes?
epithelia lining mouth, nose, GI and reproductive organs
What organs are composed of mainly epithelial cells?
liver
kidney
pancreas
From which germ layers are epithelia derived?
all 3:
ectoderm
endoderm
mesoderm
What is the epithelial to mesenchyme transition?
embryonic epithelia disassemble -> move into mesenchyme (connective tissue) ->
- migrate to form new epithelim
- transforms into non-epithelial cells
What do epithelia attach directly to?
basal lamina/ connective tissue
- separated from blood vessels
- muscle
- nerve endings
What is the lamina propria?
Connective tissue below epithelial mucosa
- usually contain lots of immune cells
What is the submucosa?
Deeper than lamina propria
- different properties- bigger vessels and muscles
- nerve axon bundles
- deep to lp, but continuous with
What are epithelia where all cells are arranged in a single layer/ sheet called?
Simple
What are epithelia with more than one layer, or where the outer layers do not touch basal lamina called?
Stratified
What is pseudo stratified epithelia?
special case
- some cells don’t reach free surface
BUT
- all cells rest on basal lamina
What are flattened epithelia called?
Squamous
What do cuboidal epithelia look like?
cube shape
What dos columnar cells look like?
Taller than they are wide
What is transitional epithelia and where is it found?
at rest they are stratified
-> stretched and change from cuboidal to squamous
=> tightly adherent, resilient, stretchable epithelium
**found in bladder **
What are tight junctions?
aka zona occludens
- highly selective barrier
- limit/ prevent diffusion of substances/ membrane proteins
- forces excretions to pass through specific transport pathways
Key proteins: occludins & claudins
What are adherence junctions?
AKA zonula adherens
- promote attachment and polarity
- specific cadherins link actin filaments & other signaling proteins to cytoplasm
What are desmosomes?
aka macula adherens
- promote mechanical strength
- structure and organization of epithelial sheet
Cadherins link intermediate filaments and adapter proteins
What type of junctions promote rapid communication through ion and small molecule diffusion?
Gap junctions
What are 2 important aspects of polarity?
- plasma membrane locally segregated into domains
- different membrane proteins, lipids, ion channels, receptors
- basal-lateral usually more similar - cytoplasm polarized
- organelles have patterns
- secretory vesicles vary by location, move in certain directions
Where are tight junctions typically located?
apical side
What are the functions of polarity?
- allow unidirectional secretion and absorption (apical to basal or basal to apical)
- localizes/ orient intracellular signaling (among epithelia and between epithelia and other cell types)
What is transcytosis?
endocytosis of a substance at one membrane -> trans-cellular transport -> exocytosis from another membrane
What are microvilli?
type of specialization of apical side of epithelial cells
- contain actin bundles connected to cytoskeleton
- increase surface area -> increase rate or efficiency of membrane transport/ secretion
Where are stereo-cilia located?
epididymus and sensory cells of ear
- reception of sound
NOT RELATED TO CILIA
What are cilia?
Microtubule containing extensions on apical surface of epithelia
What are primary cilium and where are they located?
- single cell
- involved in signal transduction systems (cell division, differentiation, function)
- many epithelial cell types
What are motile cilia, and where are they located?
microtubule extensions that move
- wave like wave or oar to move mucous and other materials
In respiratory tract
oviduct
What are sensory cilia and where are they found?
non motile, function in sensory reception
- variation of primary cilia?
hearing (vestibular hair cells of ear
taste
What type of surface modifications do the basal plasma membranes of epithelia have?
in-folds & out folds
- increase surface area
- less organized than cilia or microvilli
- found in epithelia that transport lots to/from basolateral surface
Where are basal lamina?
thin sheet of extracellular material at basal surface of epithelial tissue
- surround blood vessels, muscles, nerves
What are basal lamina made of?
Collagen- type IV (fibrous protein) interwoven with glycoproteins (laminins and enactin)
- diverse structure
fibroblast products bind and organize elements of basal lamina
What are some important functions of the basal lamina?
- mediate attachment of epithelia to connective tissue
- selective filtration of substances diffusing to or from epithelia
- establish and maintain epithelial polarity
- pathway for cells moving through connective tissue
- barrier to microbes/ cancerous cells
- control gene expression => affect proliferation & development
- tissue scaffolding => morphogenesis, development and organization of epithelial cells
- Repair of epithelia after injury/ disease
What directly attaches epithelial cells to the basal lamina?
hemidesmosomes
-> connect to intermediate fillaments -> provide strength to the attachment
focal adhesios
-> connect to actin filaments inside cell -> regulate polarity
What class of proteins forms the links between the epithelia and the basal lamina?
integrins
Why do stem cells reproduce?
- self renew
2. produce differentiated cell types specific to they type of epithelia
What are transit amplifying cells?
proliferating daughters of stem cells (often faster than parent) - produce differentiate cells directly OR through several steps of specification
What is a cell lineage?
specific stem cell type
intermediate progeny
AND
differentiated progeny
What are the parts of a typical signaling pathway?
extracellular ligand-> receptor binds and activates de-activates due to ligand -> down stream effector proteins in cytoplasm/nucleus -> modulator proteins that promote/ suppress pathway
What are 2 important principals of signaling pathwyas?
- each pathway used by multiple, distinct stem cell systems (different organs and tissues)
- stem cell and all its differentiated daughters - Signaling pathways trigger different responses in different stem cell lineages
Why do different lineages respond differently to the same signaling pathway?
- different cytoplasmic/ nuclear states
- environment of cell
- different levels of extracellular ligands, receptors and downstream components
What do exocrine glands do?
secrete materials onto epithelia-lined surfaces or outside world
- apical secretion
- multicellular
What do endocrine glands do?
secrete substances into bloodstream
How do glands secrete?
- exocytosis (merocrine/ apocrine)
2. total disintegration (holocrine)
What are the 2 parts of multicellular exocrine glands?
secretory unit
duct
What are the types of secretory units?
alveoli/ acini - bowl or flask shaped
tubular
How are simple and compound glands different?
Simple glands: 1 duct
compound glands: multiple ducts
How do substances secreted by endocrine glands enter the bloodstream?
cross basal surface of epithelia -> basal lamina -> basal lamina and epithelial layer of capillary -> capillary
How are the secretions of glands regulated?
autonomic nervous system & hormones -> or both
- exocrine constitutively active -> greatly increase production with signal (i.e. saliva)
- endocrine tightly regulated by hormones/ nerves
Give examples of diseases caused by epithelial malfunction
Cystic fibrosis
ulcerative colitis (ulceartion and destruction of absorptive epithelium)
pemphigus (blistering of skin due to antibodies to desmosomes)
Why are epithelia especially prone to disease/ cancer
essential roles
high turn over
exposure to damaging factors
What are epithelial cancers called?
carcinomas
adenocarcinomas (glands)
