Lecture B1 Flashcards
epithelial cells make up a large component of the body (less than erythrocytes) because _____
they forms the inside & outside layers
epithelial cells are the building ____
blocks of tissues
3 main functions of epithelial cells
-covering, lining surfaces
-absorption
-secretion of enzymes, sweat, mucous etc.
5 common features of epithelial cells
-Layer(s) of tightly adhering cells to prevent leakage
-Show a polarity (apical & basolateral)
-Can have specialized apical surfaces
-Lipid rich
-Largely avascular
Epithelial cells sits on ___ which is ____
-basement membrane
-the interface of epithelial cells and connective tissue
since epithelial cells are avascular, they get their blood supply from ____
the surrounding connective tissue which has capillaries
epithelial cells come from _____ (embryonic layer)
all layers (ectoderm, endoderm, mesoderm)
epithelial cells from ectoderm form _____ (4)
skin, lining of mouth, nose, anus
epithelial cells from endoderm form _____ (2)
lining of airways, digestive system
epithelial cells from mesoderm form _____ (2)
lining of vessels of lymphatic and cardiovascular
(endothelium)
Epithelial cells were histologically classified by _____ (3) because _______
-cell shape, cell layers, nuclei shape
-epithelial cells are lipid rich and hard to see with light microscopy
epithelial cells are characterized by ___ (2)
-number of layers
-shape of top layer of cell
simple epithelial cell means ____
one layer
stratified epithelial cell means ____
two or more layer
squamous epithelial cell means ____
flat cell
cubiodal epithelial cell means ____
cubed shaped cell
columnar epithelial cell means ____
columned shaped cell
columnar epithelium is often ____
ciliated on the apical surface (have modified apical surface)
pseudo stratified epithelial cell (descr.)
-cells look stratified (nucleus at different levels) but all the cells touch the basement membrane
-not all the cells with reach apical surface
simple squamous epithelium location
-air sacs of lungs
-lining of the heart, blood vessels, lymphatic vessels
simple squamous epithelium function
-allows materials to pass through by diffusion
-filtration
-secretes lubricants
simple cuboidal epithelium location
-ducts
-secretory portions of small glands
-kidney tubules
-ovary and thyroid
simple cuboidal epithelium function
-secretion and absorption
-covering
-high level of active transport
simple columnar epithelium location
-ciliated tissues in bronchi, uterine tubes, uterus
-non-ciliated tissues/smooth are in digestive tract, bladder
simple columnar epithelium function
-absorption
-secretions mucous & enzymes
-protection, lubrication
pseudo stratified columnar epithelium location
-ciliated tissue in the trachea & upper respiratory tract
-bronchi and nasal cavity
pseudo stratified columnar epithelium function
-secretes mucous, ciliated tissue moves particles trapped in mucus
-protection
stratified squamous epithelium location
-lines the esophagus, mouth, vagina
-(keratinized/dry) = skin/epidermis
stratified squamous epithelium function
-protects against abrasion
-secretion, prevents water loss
-(keratinized/dry) = protection, prevents water loss
stratified cuboidal epithelium location
-sweat glands
-salivary glands
-mammary glands
stratified cuboidal epithelium function
-protective tissue
-secretion
stratified columnar epithelium location
-male urethra
-ducts of some glands
stratified columnar epithelium function
-secretes and protects
transitional epithelium (descr.)
-type of stratified epithelium
-changes shape when stretched
-relaxed: looks cuboidal
-stretched: looks squamous
transitional epithelium location
-lines bladder, urethra, ureters
transitional epithelium function
-allows the urinary organs to expand and stretch
-protection
All epithelial tissue, regardless of functions, have _____
-apical junctions to maintain the tight separation of apical and basolateral compartments (creates polarity)
apical junctions prevents ____
the paracellular movement of solutes
Absorption (def.)
process of transport from an organ or duct’s lumen to capillaries near the epithelial basement membrane and involves movement from the apical to the basolateral cell membrane domains
Secretion (def.)
involves transport in the other direction from the capillaries into a lumen
Features of typical epithelial absorptive cells
-apical membrane has a brush border/microvilli to increase surface for transport/absorption
-endocytosis, pinocytosis, transcytosis
-basal membrane has invaginations which associate with mitochondria
endocytosis (def.)
pinocytosis (def.)
transcytosis (def.)
- uptake of things outside the cell (general classification)
-uptake of dissolved solutes
-vesicular transport of macromolecules from one side of a cell to the other
glands (def.)
specialized secreting tissues formed from epithelial tissue in the fetal stage
glands are formed by the ____
invaginations of epithelial cells in to CT due to TF, signals
exocrine gland (def.)
-maintain the connection to the overlying epithelium via a duct
endocrine gland (def.)
-lose the connection to the overlying epithelium
exocrine gland function
Secrete specific substances to other organs or body surface via the duct
endocrine gland function
-Produce hormones
-Are rich in capillaries that absorb secreted hormones
secretory cells of endocrine gland are arranged in _____
irregular cords or rounded follicles
exocrine glands can come in different structures: _____
-simple (ducts don’t branch)
-compound (ducts from different secretory unit converge to form a large duct)
parts of exocrine gland
-duct
-secretory portion/acinus
exocrine secretory portion can also be ____
branched
3 types of secretion by exocrine glands
-merocrine gland: exocytosis of vesicles/granules on apical side; most common
-holocrine gland: secretion of the entire terminally differentiated cells
-apocrine gland: secretion of apical membrane (pinched off(
merocrine gland typically secrete ____ & gland example? holocrine? apocrine?
-protein/glycoprotein (ex. salivary gland)
-lipids (ex. sebaceous gland)
-large secretions (ex. mammary gland)
How do epithelial cells stick together?
Intercellular adhesion and other junctions
Cell junctions in mammalian cells
-Tight junctions
-Adherens junctions
-Desmosomes
-Gap junctions
-Hemidesmosome
Tight junctions descr.
-most apical.
-Seals neighbouring cells together in an epithelial sheet to prevent leakage of molecules between them
-associated with actin filaments, microtubules
Adherens junction descr.
joins actin bundles in one cell to a similar bundle in another cell
Desmosomes descr.
joins the IFs in one cell to those in a neighbour
Gap junction descr.
allows passage of small water soluble ions and molecules between cells; “holes between cells”
Hemidesmosome descr.
anchors IFs in a cell to the basal lamina
Tight junctions (aka _____ )
occluding junctions
Tight junctions and Adherens junctions are composed of _____
protein complexes
anchoring junctions (3)
-adherens junction
-desmosome
-hemidesmosome
gap junctions (aka ____)
communicating junction
Tight junctions includes ______ and forms ______ and contains ridges to ______
-occludins, Claudins and ZO1 proteins
-a continuous band around the cell
-prevent passive flow of molecules between cells
Adherens junctions contains ______ which forms ______
-cadherins (ex. E-cadherins)
-homodimers in the plasma membrane of each interacting cell
Adherens junctions are ___-dependent
Ca++ (occurs in the presence of calcium)
Adherens junctions: The extracellular domain of one cadherin dimer binds to ______
-the extracellular domain of an identical cadherin dimer on the adjacent cell.
Adherens junctions: The intracellular tails of the cadherin proteins bind to ______
-anchor proteins (α-catenin, β-catenin) that tie them to actin filaments.
______ & ______ together of Adherens junction form a _____
-Cadherins
-a/B-Catenin
-stabilizing strong belt like structure that encircles the cell
Desmosomes are _____ points of intercellular contact that ______
-button–like
-rivet cells together
Desmosomes are anchoring points for _______ ( ______ in epithelial cells)
-intermediate filaments
-keratin filaments
Desmosomes forms a cytoplasmic plaque containing _____ & bound to ______ extracellularly
-plakoglobin and desmoplakin bind to IFs
-cadherin family proteins desmoglein and desmocollin
Hemidesmosomes (half desmosome) while
similar in appearance to desmosomes, they
include the adhesion proteins called ______
.
-integrins rather than cadherins
Gap junctions: A ______ gap between cells formed by channel forming proteins called _______. Gap is formed by _______
-2-4 nm
-connexons
-6 transmembrane connexin subunits
Similar to hemidesmosomes another adhesion complex, _______, anchor cells to the underlying basal lamina (basement membrane)
-Focal Adhesions (FAs)
Focal Adhesions are formed by ____________ of which extracellular domain bind to extracellular matrix (proteins) and the
cytoplasmic tail of ______ via several intracellular anchor proteins such as ________
-transmembrane integrin heterodimers (a and β subunits)
-β subunit binds indirectly to actin
-actinin, talin or filamin and vinculin.
Focal Adhesions vs Hemidesmosomes
-focal adhesion bind actin to ECM
-hemidesmosomes bind IF (keratin) to ECM
-both use integrins (transmembrane)
Changing in protein make up of tight junctions changes ____
permeability of epithelial tissue
tight junctions major function? adherens junction? desmosome? hemidesmosome? gap junction?
-seals cell together, prevents passage of molecules
-strengthens tight junctions
-strengthens tissues
-anchor to basal lamina
-allows movement between cells
tight junctions loss leads to _____ ? adherens junction? desmosome? hemidesmosome? gap junction?
-bad blood-brain barrier
-allows for metastasis of cancer cells
-loss of cohesion of cells
-skin blistering
-deafness & peripheral neuropathy
proteins that make up cytoskeleton
-actin (smallest)
-microtubules (biggest)
-intermediate filaments
actin cytoskeleton descr.
-determine shape of cell surface
-needed for cell movement
-needs binding to other accessory and motor proteins
-constantly changing (constant state of flux)
-temporary & permanent
microtubule cytoskeleton descr.
-determine position of membrane enclosed organelles
-direct intracellular transport
-stiffer than actin filaments
intermediate filament cytoskeleton descr.
-provide mechanical strength and resistance to shear and bending stress
-filaments composed of smaller subunits of elongated fibres (acidic and basic keratins in epithelial cells)
-highly resistant to bending/stretching forces
Actin assembly
-actin globular monomers (G-actin) spontaneously nucleated (unfavourable) or by nucleation-promoting factors (NPFs) (Formin/Arp 2/3) to form actin filament (F-actin)
actin filaments and microtubules are _____
polarized (+/- sides)
microtubule assembly
-tubulin dimers intrinsically self-assemble to form protofilaments which are arranged on NPFs like ɣ-TuRC to form microtubules
Junctions and the cytoskeleton are important for function of an epithelial cells in terms of ______
-targeting proteins to the proper location in a cell
To ensure selective targeting of proteins to establish apical/basal domains: ______
1) Selective targeting of a protein to specific cell surface domain
2) Selective stabilization of a protein at a specific cell surface domain
Apical /Basal polarity of plasma membrane is needed for _________
-vectorial trafficking or secretion of proteins, solutes,
ions.
Cytoplasmic polarity can generate ______ after division for tissue development
-different cell progeny
Apical and Basal surfaces have different ______
-proteins and lipid components
