General Histology – Epithelial and Connective Tissue Flashcards
Study of tissues under a microscope, usually after the tissues have been prepared in some way
histology
can visualize structures as small as 0.2 microns (µm, 1/1,000,000 of a metre)
Light microscopy
Anything smaller than 0.2 microns needs to use a ____________ as the radiation source
beam of electrons
Types of light microscopy include _________ microscopy and ________ microscopy
fluorescence and confocal
can view a cell or tissue in a particular
plane (i.e. doesn’t see the plane above or the plane below, so it’s a thin, almost “2-D” image)
Confocal microscopy
involves loading a cell with a fluorescent probe
Fluorescence microscopy
can visualize structures that are as small as 3 nm (i.e. molecular level of resolution)
Electron microscopy
Electron microscopy: Tissue sections are often frozen in ____________ and sliced into thin sections
liquid nitrogen
The tissue or cell being imaged can also be coated in a thin ___________ (scanning electron microscope)
layer of gold
What type of microscope always uses dead tissues/cells and is the only method that allows good visualization of organelles and large
Electron microscopy
In general, tissues are prepared for examination by:
- fixation
- dehydration and clearing
- infiltration and embedding
- trimming
preparation method: chemicals cross-link proteins and inactivate enzymes that degrade cells/cellular components
fixation
preparation method: tissues are passed through alcohol solutions (replaces the water) and then the alcohol is removed
Dehydration & clearing
preparation method: the tissue is infiltrated with a substance (i.e. paraffin wax) and then allowed to harden
Infiltration and embedding
preparation method: tissue is sliced into thin, almost transparent slices using a microtome
Trimming
The process of exposing a cell to a dye or molecule that improves visualization is known as
staining
______ is usually done with dead, fixed cells, but some stains can be done with viable cells
staining
immunohistochemistry
Cells can also be stained with fluorescent antibodies that bind to a very specific molecular structure
is a dark blue basic dye, and will bind to
negatively-charged molecules (DNA in particular)
Hematoxylin
Molecules that bind to basic dyes are known as what type of molecules?
basophilic molecules
molecules that bind to acidic dyes are known as
acidophilic
is a pink acidic dye – it binds to positively charged molecules (i.e. cytosolic proteins).
Eosin
great at showing glycogen and many glycoproteins
Periodic acid-Schiff stain
what two stains are usually done together in. tissue preparation
Hematoxylin and eosin
What stain highlights DNA and the Nucleus
DAPI
What stain highlights DNA, cell membranes and Apoptotic cells (programmed cell death)
AO/EB stain
what stain highlights keratin, collagen, DNA,
cytoplasmic proteins and muscle fibres, nuclei, collagen – complicated stain
Masson’s trichrome
What stain highlights glycoproteins, glycogen as well as cytosol, mucous and some ECM
PAS - Periodic acid-Schiff stain
what stain highlights collagen, mitochondrial elements and the mitochondria
Acid Fuchsin
Why is histology useful?
Much of the function of a cell or tissue can be deduced by its microscopic structure
what protective function does the epithelial have
- Function of all mucous membranes and the skin
- Bladder is an interesting case – chemical protection from urine and can stretch for storage
what transportive function does the epithelial have
Absorption - water, nutrients, electrolytes… almost anything your GI tract chooses
Secretion or removal of wastes – GI tract, kidney, lung
Exchange epithelium - Optimizes diffusion
* thin cells that reduce diffusion distanced
* endothelial cells, alveolar cells
what secretive function does the epithelial have
Glands that secrete substances into ducts (exocrine) or hormones into the blood (endocrine)
True or false: Epithelium is
avascular
True! No blood vessels
which epithelial form functions as an exchange epithelium
simple squamous epithelium
where would you find simple squamous epithelium?
air sacs of the lungs, lining of the heart, blood vessels and lymphatic vessels
which type of epithelial form functions as transport epithelium
simple cuboidal epithelium
where would you find simple cuboidal epithelium?
In ducts and secretory portions of small glands and in the kidney tubules
the primary function is motility
Cilia
where would you find simple columnar epithelium? What does this epithelium usually have on its structure?
usually have microvilli or cilia
ciliated tissues are in larger bronchioles, uterine tubules
what form of epithelium protects against abrasion? Where is it found?
stratified squamous epithelium and it lines the esophagus, mouth, vagina and found in the skin - provides extra layers for when top layer falls off
what form of epithelium allows the urinary organs to expand and stretch? This form acts a chemical protection from urine
transitional epithelium
where is transitional epithelium found?
lines the bladder, urethra and the uterus
describe paracellular transportation
a form of transportation for nutrients, gases etc through the epithelial linings. It occurs between epithelial cells, movement is across junctions
describe transcellular transportation
a form of transportation for nutrients, gases etc through the epithelial linings through
epithelial cells, movement across apical and basolateral cell membranes
the primary function is increasing the surface area
Microvilli
what part of the cytoskeleton is responsible for the shape and motility of the cell
Actin filaments
what part of the cytoskeleton is responsible for the structural “strength” of the cell.
Intermediate filaments
Desmin, keratin are examples of
Intermediate filaments
what part of the cytoskeleton determines polarity, cell division, and movement of cilia (if present)
Microtubules
Located at the apical aspect of almost all epithelial cells. Found in the gut, brain, skin and respiratory tract. Closest to the lumen.
Tight Junctions
Key functions of tight Junctions
barrier that prevents movement of undesirable substances to the tissues below
Regulates the movement of a variety of molecules between cells, through the barrier
Helps establish polarity – TJs seem to help direct membrane proteins to the apical vs. basolateral sides
Tight junction component: trans-membrane proteins that can act as channels for small molecules (paracellular)
Claudins
Some are permeable (Claudin2), some are relatively impermeable (Claudin-1)
Tight junction component: trans-membrane protein, function not clear
Occludin
Tight junction component: Trans-membrane protein that may mediate permeability to larger molecules
Junctional adhesion molecules (JAM)
Tight junction component: Important in tight junction formation, interacts with the cytoskeleton
ZO-proteins
What are the junctions that are found immediately below tight junctions?
Found immediately below tight junctions
The function of Adheren junctions
- Strengthens and stabilizes tight junctions
- Participates in cell-cell signaling that regulates cell division and proliferation
Both adherens junctions and tight junctions circle the entire _____ aspect of a columnar of cuboidal epithelial cell
apical
Desmosomes only attach to _______ of the epithelial cell membrane
certain spots
transmembrane protein that
interacts with other cadherins on the
neighbouring cell (similar to claudins)
Cadherin
linker molecules that connect the
the intracellular face of claudins to the actin
cytoskeleton
Catenins
When cadherins connect across cells,
beta-catenin remains associated with
cadherins. When they don’t connect, beta-catenin can …
dissociate and signal cell division
While adherens junctions and tight junctions circle the entire apical aspect of a columnar of cuboidal epithelial cell, what only attaches to certain spots of the epithelial cell membrane
Desmosomes
Similarities between desmosomes and adherens
- Strong adhesion between cells
- Desmosomes use cadherin-like molecules
- Both have intracellular “plaques” that interact with proteins that can act as “signalers” and “linkers” (i.e. beta-catenin)
differences between desmosomes and adherens
- Desmosomes connect to intracellular intermediate filaments (i.e. keratin)
- Desmosomes provide more structural stability to the cell
Transmembrane “linking” protein is an integrin, not a claudin-like molecule. An Integrin binds to a component of the basement membrane known as laminin
hemidesmosomes
______ do not bind to a molecule on an adjacent cell and do not seem to have important intracellular signalling functions
Hemidesmosomes
Hemidesmosomes do link to ________ filaments
intracellular intermediate
Transport of substances from the apical side to the basal side of the epithelium (paracellular transport)
tight junctions
Barrier that restricts movement of substances from the apical side to the basal side of the epithelium
Tight junctions
Strength of the epithelial lining
desmosomes
Determination of polarity (apical vs. basal) across the epithelial cell
tight junctions
Signaling and regulation of the activity of the epithelial cell
adherents: beta-catenin and gap junctions
Anchoring the epithelial cell to the underlying connective tissue
hemidesmosomes
Almost all cells – including epithelial cells - have one primary cilia
These are non-motile cilia that have a ring of 9
microtubular structures, but no ________
central doublet
when is primary cilia extremely important?
Extremely important in the development of the embryo, sensing fluid movements, and sensing the presence of
growth factor
what type of connective tissue is often found
beneath the epithelial lining of many tissues
loose CT
how is collagen organized in dense irregular connective tissue
Collagen is arrayed in bundles
that are not parallel, but
arranged in many different
directions
Resists stresses from multiple
different directions
what type of connective tissue has fewer cells, less ground substance than loose connective
tissue
Dense irregular connective tissue
what type of connective tissue has lots of collagen (type I) with less ground substance and cells than loose connective tissue
Dense regular connective tissue
how is collagen organized in dense regular connective tissue
Collagen is oriented in one particular
direction
Resists stresses along one line or plane
Typical examples of Dense regular connective tissue
tendons, ligaments,
aponeuroses
Synthesized by fibroblasts
Collagen
resists tension, multiple triple helices bound together to form fibrils, and fibrils are organized to form fibres. Major collagen type in dense CT and bone
type 1 collagen
smaller fibrils with less organized orientation
than dense regular tissue. Major component of cartilage – mainly resists pressure
and absorbs shock
type 2 collagen
reticular fibres - Major component of loose connective tissue
Type 3 collagen
Type I, II, and III collagens are known as ________ collagens
fibrillar
forms the basement membrane that
connects epithelial and connective tissue layers
Type IV collagen
Forms a sort of cross-linked “net” with laminin
(glycoprotein) and proteoglycans interspersed within it
The basement membrane is formed from an organized meshwork of type ___ collagen, proteoglycans, and laminin
IV
Note that integrins (hemidesmosomes) bind to the laminin in the basement membrane
Proteoglycans – 3-part structure:
- A very long, linear polymer of hyaluronic acid (a GAG)
- Linking proteins attached to the hyaluronic acid polymer
- Shorter GAG chains attached to the linking proteins
what are the two major components of the ground substance:
- multi-adhesive glycoproteins: § These bind to a wide variety of components of the
extracellular matrix - proteoglycans
_______ binds to type IV collagen and the integrins of hemidesmosomes
laminin
________ binds to collagen, glycosaminoglycans (GAGs) on proteoglycans, and some integrins
Fibronectin
Proteoglycan: Highly ________ – “collect” water in the ECM due to the OH-groups on
the carbohydrate GAGs
hydrated
Proteoglycan: Link between _______ and
__________ – help bring structural integrity to the ECM
collagens and glycoproteins
Proteoglycans: An ECM rich in proteoglycans is _______ for most bacteria to penetrate
difficult
Proteoglycans:
main intermediate filament in keratinocytes
kertin
_______ is strong and forms bundles – a barrier that prevents water loss from
deeper layers and microbe invasion
Keratin
Keratin complexes with another protein – __________ – that helps compact keratin
and attracts water, aiding in skin
moisturization
filaggrin
