Epithelium Histology Flashcards
what is one of the 4 fundemental tissue types?
what are epithelia?
give 2 examples of epithelia found in the body.
Where do glands originate from?
what are some of the functions of epithelial tissue?
Epithelia are one of the four fundamental tissue types in the body.
Epithelia are contiguous sheets of cells that line the internal and external surfaces of the body.
For example, the skin is an epithelium that lines or covers the outside of the body, and the GI tube is lined (at its inner surface) by an epithelial mucosa.
Glands also originate from invaginated epithelial tissues.
Some of the functions of epithelial tissue are protection, secretion and absorption of molecules, and detection of sensations via specialized epithelial cells
what kind of surface do epithelial tissues have?
what is the opposite surface called?
what is the basal surface underlain by? what is it?
how are epithelial cells bound?
How do epithelial tissue obtain nutrients? what is their function?
Epithelial cells have a free surface- this is the apical surface. The opposite surface is called the basal surface and is underlain by a basal lamina- a protein matrix that is synthesized in part by the epithelial cells. Cells in epithelia are tightly bound to one other and to the underlying matrix by junctional molecular complexes. Epithelial tissues are avascular; they obtain nutrients by diffusion from blood vessels located in the connective tissue that is basal to the basal lamina
how are epithelial tissue classified?
what are tissues with a single layer of epithelial cells called?
what about tissues with more than one layer of these cells?
At what angle can you see the various shapes of the cells? what other types of epithelial shapes exist?
Epithelial tissues are classified by the number of cell layers between the basal lamina and the free surface, and by the morphology of the cells located on the free surface of the tissue. Epithelial tissues with a single layer of cells are called simple epithelia. If the tissue has more than one layer of cells (even just two) it is called a stratified epithelia. The shape of the cells when viewed in sections taken perpendicular to the basal lamina can be squamous (flattened), cuboidal, or columnar.
how is simple squamous epithelial composed?
can you see every nucleus in this epithelia when cross sectioned? why or why not?
where are 3 locations where simple squamous epithelia is found?
Simple squamous epithelia is composed of a single layer of tightly packed cells that in perpendicular sections appear flattened or low polygonal with flattened nuclei. When viewed in section only some of the cells will contain nuclei because the plane of section does not always cut through the nucleus. Simple squamous epithelia are found most often lining blood vessels in the body where they present a frictionless surface along which blood can flow. Simple squamous epithelia are also found lining the alveoli (sacs) in the lung, and in parts of the kidney tubules
how are simple cuboidal epithelia comprised?what do they look like when viewed in cross section?Where are simple cuboidal epithelia found?
Simple cuboidal epithelia are comprised of a single layer of polygonal shaped cells. When viewed in cross section the cells appear to look like cubes with a round centrally placed nucleus. Simple cuboidal epithelia are found in ducts of many glands in the body and in some kidney tubules
how are simple columnar epithelia composed?
Where are the nuclei usually located?
Where are simple columnar epithelia are found?
what is unique about what simple columnar epithelia contain?
what is the brush border composed of?
What do microvilli serve to do?what covers the microvilli?
where are actin filaments found within simple columnar epithelia?
Where are striated and simple brush borders also found?
Simple columnar epithelia are composed of a single layer of tall, rectangular shaped cells. Their nuclei are usually located in the basal half of the cells. Simple columnar epithelia are found in the lining of much of the digestive tract, gallbladder and large ducts of glands. Simple columnar epithelia often contain a specialization at their apical surface called a brush border. The brush border is composed of many small infoldings of the plasma membrane called microvilli covered by a sugar or carbohydrate coat called the glycocalyx. Microvilli serve to increase the apical surface area available to the epithelial cell for absorption or secretion. Actin filaments are found within, and extend out to the apical most ends of, the microvilli. Striated or brush borders are also found in simple cuboidal epithelia lining the kidney tubules, another absorptive tissue.
what is stratified squamous epithelium composed of?
Which layer is in contact with the basal lamina?
what is the shape like in stratified squamous epithelium?
What is the apical most layer like?
where is stratified squamous epithelium found?
what can sometimes be found on the apical most layer of these cells? what is this called?
what is keratin? what is skin a good example?
Stratified squamous epithelium is composed of several cell layers and therefore is thick. Only the deepest layer is in contact with the basal lamina. The shape of the cells in stratified squamous epithelium varies with the position of the cells. The apical most layer- the layer of cells on the free surface- are squamous or flattened in shape, and give the tissue its name. Stratified squamous epithlelium is found in regions of the body subject to mechanical stress- such as the vagina and cervix of the uterus, and the mouth and esophagus. Some stratified squamous epithelia may be keratinized – the apical most layer of cells is covered by a thin or thick layer of keratin. Keratin is composed of dead cells whose cytoplasm and nuclei have been replaced by keratin (a cross-linked intermediate filament protein). Skin is an example of keratinized stratified squamous epithelium
which type of epithelium is rare?how many layers it is composed of and where is found?
where is transitional epithelium found? what is an also known as?
how many layer is transitional epithelium compsed of?
what is the shape of thetop most layer of cells in bladder when it is empty? what about when the bladder is full or distended?
Is transitional epithelium keratinized? Y/N?
Stratified cuboidal/columnar epithelium is rare. It consists of only two layers of cuboidal/columnar cells and is found in the lining of sweat gland ducts. You will see this in the skin lab.
Transitional epithelium is a unique type of epithelium found only in the lining of the urinary tract and the urinary bladder. It is sometimes called the urinary epithelium. Transitional epithelium is composed of many layers of cells. When the bladder is empty the top most layer of cells are dome shaped. When the bladder is full or distended the top-most layer of cells in the transitional epithelial tissue become squamous. Transitional epithelium is NOT keratinized
what do pseudostratified columnar epithelium appear to look like?
where do all of the cells in a pseudostratified columnar epithelium sit ? so all of them reach the apical or free surface of the tissues? Y/N?
what do the cells look like that do not reach the apical surface ? what about cells that extend all the way from bottom to the top?
What gives these types of epithelium(pseudostratified) to look like being stratified?
Where is the most widespread type of pseudostratified columnar epithelium found? what would it be called?
what do respiratory epithelium have?
what do cilia look like? what is their function?
what is the core of cilia called?
how many peripheral microtubule doublets do cilia contain? how are they arranged?
how are the peripheral microtubules linked together?what are they connected to?
Explain what occurs when bending on cilia happens?
what is the base of the cilia called? how many peripheral microtubules triplets does the basal body contain? they are found surrounding what?
Pseudostratified columnar epithelium appears to be stratified but is actually composed of a single layer of columnar cells. All of the cells in a pseudostratifed columnar epithelium sit on the basal surface (the basal lamina) of the tissue but only some of them reach the apical or free surface of the tissue. Cells that do not reach the apical surface tend to be more pyramidal shaped, with broad bases and pointed apices, while cells that extend all the way from bottom to top tend to be more columnar. Because the cells of this epithelium are of different heights, their nuclei are located at different levels, and thus give the appearance of being stratified.
The most widespread type of pseudostratified columnar epithelium is found in the respiratory system and is called the respiratory epithelium. The respiratory epithelium is also ciliated. Cilia are long, motile hair-like structures emanating from the apical cell surface. They function to help propel air or mucous past the tissue. The core of cilia is called the axoneme, and is composed of a complex arrangement of microtubules. Cilia contain 9 peripheral microtubule doublets arranged around a central microtubule pair (a 9+2 arrangement). The peripheral microtubules are linked to one another by Nexin and connected to the central microtubule pair by Radial Spoke like Proteins. Bending of cilia occurs when the peripheral microtubule pairs try to slide past one another via the action of a motor protein called Dynein but are restrained by the nexin and radial spoke cross links. The base of the cilia is called a basal body and contains 9 peripheral microtubule triplets around a central lumen.
what is the basal surface of all epithelial underlain by?
what are the 2 protein components of the extracelular matrix (ECM)?
what type of molecular junctions do epithelial cells have? what are these types of molecular junctions and what are they called?
what do hemidesmosomes attach to?
what do hemidesmosomes contain? and what does it do?
what are hemidesmosomes critical for?
what is wrong with epidermolysis bullosa disease? what does this result in? what does this cause in skin.
The basal surface of all epithelia is underlain by the basal lamina- an extracellular protein (molecular) matrix. Two protein components of the extracellular matrix are collagen and laminin. Epithelial cells elaborate [contain] molecular junctions - concentrated, punctal areas of proteins in their BASAL plasma membranes- that are called hemidesmosomes. Hemidesmosomes mechanically attach epithelial cells to their underlying basal lamina. Hemidesmososmes contain transmembrane proteins called integrins that link intermediate filaments inside of the epithelial cell with the collagen and laminin proteins in the basal lamina outside of the epithelial cell. Hemidesmosomes are critical to the function of the epithelium. Epidermolysis Bullosa are diseases of the basal lamina in which a protein component of the hemidesmosome such as integrins or a protein component of the basal lamina such as collagen are mutated. This results in mechanical deattachment of the epithelium from the underlying basal lamina. In skin this leads to separation of the epidermis from the dermis and blistering
what does the lateral membrane between adjacent epithelial cells contain?
what are the apical most cell-cell tight junctions called?
what do tight junctions form?
what are occludins and claudins?
what are tight junctions further reinforced by?
what do tight junctions cause due to how tight they are?what does this allow?
what is the secondary function of tight junctions?what is the mechanism underlying this secondary function?
The lateral membrane between adjacent epithelial cells also contains several cell-cell adhesive junctions made up of densities (dense collections) of proteins. The apical most cell-cell junctions are called tight junctions or zonula occludens. Tight junctions form a belt of junctions around the entire circumference of a cell that ‘sews’ a cell to its neighboring cells. Occludins and claudins are transmembrane proteins found in tight junctions. The tight junction is further reinforced by other transmembrane proteins called cadherins as well as ZO-1, ZO2 and ZO-3. Tight junctions are so ‘tight’ they literally obliterate the extracellular space between two adjacent cells- making it impermeable to diffusion of water and other large molecules. Tight junctions also have a secondary function of dividing the membrane of an epithelial cell into two domains- the apical and basolateral domains. The mechanism underlying this is that tight junctions are fixed in position in the plasma membrane, and thus, prevent the diffusion of other transmembrane proteins freely within the plasma membrane, specifically through the tight junction
where are zonula adherns found?
what do zonula adherns circulate?
what do zonula adherns connect to?
what are cadherins?
On the other cytoplasmic face what do cadherins connect to?
The cell-cell junction found just basal to the tight junction in the lateral membrane of epithelial cells is the Zonula Adherens- an adhering junction. Zonula adherens junctions circle the entire circumference of an epithelial cell, similar to the distribution of tight junctions. However, zonula adherens connect to the actin cytoskeleton and support adhesion between neighboring cells. The transmembrane proteins found in zonula adherens are cadherins. On their cytoplasmic face, cadherins connect to catenins that link ultimately to the actin cytoskeleton.
what is a third type of cell to cell junction?
do desmosomes form belts? y/n?
how are desmosomes distributed?
extracellularly what do cadherins link to?
on the other side of cytoplasmic face what do cadherins connect to ? who are these proteins deposited? what do these proteins connect to?
what are desmosomes thought to distribute?
The third type of cell-cell junction in the lateral plasma membrane of epithelial cells are Desmosomes (Macula Adherens). Desmosomes do not form belts like ZOs and ZAs. Rather, Desmosomes are distributed sparsely and randomly throughout the lateral membrane of simple epithelia. A special type of Cadherin transmembrane protein is found in desmosomes; Extracellularly, these cadherins link to a filamentous protein called desmoglein. On their cytoplasmic face, Cadherins connect to cytoplasmic proteins such as plakoglobin and desmoplakins that are deposited in a heavy plaque-like configuration (visible by EM). The plaque-like proteins, in turn, connect to intermediate filaments called cytokeratin. Desmosomes are thought to distribute shearing forces encountered by neighboring epithelial cells
what happens to cell to cell junctions when metastasis occurs? what decreases and what increases?
what happens when metastatic cencer leaves the epithelial sheet? what does this allow them to physicall do?
what do these cancer cells increase their expression of?
what is required for the the attachment of cells ?
what does the increased expression of integrins allow for?
Metastasis of cancer cells from an epithelial sheet involves a decrease in the expression of proteins in cell-cell junctions and an increase in the expression of proteins in cell-matrix junctions. Specifically, when metastatic cancer cells leave the epithelial sheet they decrease the expression of Cadherin proteins (which form the basis of all three lateral cell-cell junctions). This allows them to physically deattach from their neighboring cells. Concomitantly, these cancer cells increase their expression of integrins (which form the basis of hemidesmosomes). Integrins are required for attachment of cells to collagen fibers found in the basal lamina and in the underlying connective tissue. The increased expression of integrins allows the metastatic cells to bind more sites on the collagen fibers and exert more traction on the matrix, thereby promoting efficient migration
