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91 Cards in this Set

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What are the functions of epithelial tissue?
Selective diffusion
Absorption
Secretion
Physical protection
Containment
Describe the polarity in epithelial cells:
In simple epithelia, intracellular organelles, membrane proteins and cell surface specializations are spatially arranged.
In stratified epithelia, the cells differentiate as they move from the basal layer to the surface layer.
All epithelia are supported by a __________________
Basement Membrane
Epithelium has lots of extracellular stuff. T/F
F, very little extra cellular things.
Define simple epethelia:
One layer of cells
What are the subclasses of simple epithelia?
Simple squamous (flattened or plate-like)
Simple cuboidal
Simple columnar
Pseudostratified columnar (all cells contact the basement membrane, but not all reach the surface)
Define stratified epithelia:
Cell type changes. Tissue XtoTHEz exhibits polarity.
What are the subclasses of stratified epithelia?
Stratified squamous
Stratified cuboidal
Transitional (found only in the urinary tract)
What type of tissue is in glands?
Epithelial cells
Holocrine Glands
The entire cell and its contents are released into the lumen.

e.g. sebaceous glands.

"holy" self sacrifice
Apocrine Glands
A portion of the cell is pinched off,

e.g. lactating mammary glands.

"a piece"
Merocrine Glands
Secretory granules fuse with the apical plasma membrane and the contents are released (exocytosis),

e.g. salivary glands.
What are the functions of epithelia?
Selective permeability barrier
Protection from mechanical and chemical insult
Transcellular transport
Absorption
Secretion
Describe epithelial cell polarity:
Most epithelial cells have distinct biochemical and functional domains, i.e. they demonstrate polarity. For instance, an apical domain faces a lumen and a basolateral domain is oriented toward the basement membrane and the extracellular milieu. As a result of the functional specialization, the cell surface may demonstrate structural specializations that are related to specific functions.
What are the (3) junctional complexes between cells?
1) the zonula occludens or tight junction,

2) the zonula adherens or adhering junction and the

3) macula adherens or desmosome.

Gap junctions, which allow electrical coupling of cells, may also be present, .
Describe the Tight Junction:
The tight junction is the uppermost (closest to the surface) component of the complex. At the tight junction, the apposed plasma membranes of neighboring epithelial cells are fused together, obliterating the intercellular space. The lines of fusion form an efficient seal that can block the passage of ions, water, and molecules of all sizes from passing between the cells. The tight junction also act as a barrier to prevent diffusion of plasma membrane components (e.g. ion channels) between the apical and basolateral surfaces of the cell.
Describe the adhereing junction:
The adhering junction is also continuous around the apex of the cell, but it is permeable.

It provides a strong adhesion between cells. The adherens junction contains cadherins, which are integral membrane proteins that span the membrane and have a large domain that projects out from the cell that binds tightly to an identical domain from an adjacent cell.

The intracellular domain links to several proteins that interact with actin microfilaments inside the cell. Thus, mechanical stress can transmitted across the epithelial monolayer.
Describe desmosomes:
Desmosomes are "spot welds" between cells.

Unlike tight junctions and adhering junctions, they are not arranged as a continuous seal around the cell, but like adherens junctions, they consist of specialized protein plaques connected to the intermediate filaments of the cytoskeleton, transmembrane linking protein of the cadherin family.

As a result, desmosomes are particularly important in providing mechanical strength to epithelial sheets.
Describe a gap junction:
Within a gap (communicating) junction, apposed plasma membranes are closely parallel, but not fused, and there is a plaque of closely packed intramembrane particles. Each particle, called a connexon, has a central aqueous channel through the membrane. Connexons of adjacent cell membranes are lined up with one another, forming a channel of communication between the adjacent cells (molecules up to 1,500 daltons in size can pass from one cell to the next). Gap junctions are not limited to epithelial tissues. In the heart, gap junctions couple cardiac muscle cells together electrically so contractions of individual cardiac muscle cells are coordinated.
Name (4) types of cell-surface specializations:
Microvilli
Cilia
Steriocillia
Flagella
Describe microvilli:
On adsorptive cells (e.g. intestinal epithelium and proximal tubules of the kidney), these extension of the cell surface vastly increase the surface of the cell.
Describe Cilia:
These hair-like projection are specialized to function in propelling substances across an epithelium. At the electron microscopic level there is a characteristic 9 + 2 organization of microtubulues present in the core of each cilium.
Describe sterocilia:
Not to be confused with true cilia, these structures are actually long microvilli.

In the ear, they function in signal generation.
Describe flagella:
Flagella - In humans, the only cells that have flagella are spermatozoa (to be discussed later).
Describe the subdivisions of the basolateral domain:
The basolateral domain may be subdivided into two regions; a lateral and a basal plasma membrane.

Each region posses its own junctional specializations, such as tight junctions on the lateral membrane and hemidesmosomes on the basal membrane.

These surfaces are also rich in ion channels and Na+-K+-ATPase.
Describe the polarity of stratified epithelium:
Within stratified epithelia, the different cells also demostrate differences in fiunction and differentiation. Cells in the basal layer form the basement membrane and are capable of mitotic activity. As cells leave the basal layer they actually differentiate, and this differention continues as the cells move toward the surface. Keratinization of surface layer of skin or gingiva and the desquamation of dead cells, for example, represent terminal differentiation of the epithelial cells in a stratified squamous keratinizing epithelium.
What are the different names of the basement membrane?
basement membrane (light microscope)

or

basal lamina (electron microscope)
Describe the basement membrane:
fibrillar layer that underlies all epithelia, and is formed by epithelial cells. It has three major protein components.
What are the (3) major protein components of the basement membrane?
Type IV collagen

Laminin, a large glycoprotein of 850 kiloDaltons (kD).

Heparan sulfate proteoglycan (HSPG)
How do the type IV molecules work in the basement membrane?
Type IV collagen molecules bind to one another, end to end, to form a fine mesh.
How does the laminin in the basement membrane work?
Laminin binds to Type IV collagen, and may cross-link the collagen molecule network and attach it to the base of the epithelium.
How do the HSPG molecules in the basement membrane work?
The HSPG molecules coat the two surfaces of the basement membrane, giving each surface a strong negative charge due to the sulfate groups.
Besides collagin type IV, laminin, and HSPG, what other components are in the basement membrane?
Other components of the basement membrane include fibronectin, entactin and collagen Type VII (anchoring fibrils). The anchoring fibrils are formed by fibroblasts in the underlying connective tissue.
How do epithelial cells anchor themselves to the basement membrane and other ECM items?
hemidesmosomes

integrins

The epithelial cells have specialized anchoring junctions (hemidesmosomes and integrins) that link the intracellular cytoskeleton with the components of the basement membrane and other extracellular matrix macromolecules.
In addition to anchoring the epithelial tissue, what are some functions of the basement membrane?
It acts as a semi-permeable membrane for the passage of nutrients, etc.
It influences cell polarity and metabolism.
It regulates cell proliferation and differentiation by binding growth factors.
It guides cell migration, and acts as a barrier to tumor cells.
What is cystic fibrosis?
Genetic defect in the chloride transport.

In airways, this leads to very thick mucous => loss of function.
Name a location in the body where selective diffusion in epithelial tissue takes place.
Lungs, Capillaries
Name a location in the body where absorption in epithelial tissue takes place.
Lining of gut
Name a location in the body where secretion in epithelial tissue takes place.
glands, cells that make things for export
Name a location in the body where physical protection in epithelial tissue takes place.
skin (thick and cornified)
Name a location in the body where containment in epithelial tissue takes place.
bladder, thyroid gland
What are the three general types of epithelial tissue?
Simple
Stratified
Glandular
What seperates epithelial cells from the connective tissue?
Basement membrane
What is endothelium?
simple squamous epithelium that lines inside of circulatory system
From the surface, what do simple cuboidal cells look like?
Polygon shaped
In simple cuboidal cells, where is the nucleus and how is it shaped?
It is in the center and spherical in general
Where are simple cuboidal cells found?
Simple cuboidal cells are found lining small ducts and tubes which may have excretory, secretory, or absorptive functions.
Within simple columnar cells, where is the nucleus and what shape does it form?
Nuclei are elongated and generally located near the base.
Where is simple columnar located?
. Simple columnar is most often found on highly absorptive surfaces such as in the small intestine, and often have specializations of the surface. Also located in gall bladder.
Within epithelial tissue, what type of single cell is capable of secretion as its main function?
Goblet cells. It secretes mucous
What do goblet cells secret?
Mucous
Why is pseudostratified unique in comparison to other epithelial tissues?
All cells are attached to the basement membrane yet not all of them reach the apical surface of the tissue.
Within pseudostratified tissue, where are the nuclei and in what shape are they?
The nuclei tend to be elongated like columnar, yet can be found at varying heights giving the impretion of stratified tissue.
What is pseudostratified epithelium commenly called?
Respiratory epithelium
Are cilia present on stratified epithelia?
No, never.
In stratified tissue, do cells exhibit polarity?
In general, the cells do not exhibit polarity themselves. The tissue however, does exhibit polarity.
Does pseudostratified epithelium have microvilli?
NO!! They only have cilia
How is stratified epithelia named?
According to the cell type on the most apical layer of the tissue
How are cells added to stratified epithelial tissue?
The basal cells divide continuously, and the daughter cells are pushed up towards the surface where they are shed
Where in the body can stratified epithelial tissue be found?
Lines the oral cavity, pharynx, esophagus, anal canal, uterine cervix, and vagina
Describe the concept of polarity of stratified epithelium.
Within stratified epithelia, the different cells also demonstrate differences in function and differentiation. Cells in the basal layer form the basement membrane and are capable of mitotic activity. As cells leave the basal layer they actually differentiate, and this differentiation continues as the cells move toward the surface. Keratinization of surface layer of skin or gingiva and the desquamation of dead cells, for example, represent terminal differentiation of the epithelial cells in a stratified squamous keratinizing epithelium.
When looking at histological slides, what is a characteristic difference between keratinized and non-keratinized stratified squamous epithelia?
Non-keratinized will retain their nucleus all the way to the apical surface.
What happens to the cell layer that becomes keratinized?
As the cells die and the nucleus is extruded, the cells develop strong cytoskeletal elements that link each other together and allow for dissapation of forces.
What is the most important characteristic to recognize in transitional epithelial tissue slides?
The apical surface looks like pillows or umbrellas.
Where in the body is transitional epithelial tissue located?
Confined to the urinary tract
Is simple epithelial tissue considered to exhibit polarity?
Yes, even in simple epithelial tissue such as glands exhibit polarity due to the segregation of certain organelles to specific regions.
When descibing the top of a cell (facing into the lumen for example) what is it called?
Apical surface
When referring to the bottom and lower side of the cells, what is it called?
Basolateral
What are some specializations of the apical domain on cells?
cilia
microvilli
stereocillia
What is a tight junction called?
Zonula occludens
What are adhering junctions called?
Zonula adherens
What are desmosomes called?
Macula adherens
Describe the tight junction:
The tight junction is the uppermost (closest to the surface) component of the complex. At the tight junction, the apposed plasma membranes of neighboring epithelial cells are fused together, obliterating the intercellular space. The lines of fusion form an efficient seal that can block the passage of ions, water, and molecules of all sizes from passing between the cells. The tight junction also act as a barrier to prevent diffusion of plasma membrane components (e.g. ion channels) between the apical and basolateral surfaces of the cell.
Describe the adhering junctions:
The adhering junction is also continuous around the apex of the cell, but it is permeable. It provides a strong adhesion between cells. The adherens junction contains cadherins, which are integral membrane proteins that span the membrane and have a large domain that projects out from the cell that binds tightly to an identical domain from an adjacent cell. The intracellular domain links to several proteins that interact with actin microfilaments inside the cell. Thus, mechanical stress can transmitted across the epithelial monolayer.
Describe the desmosomes:
Desmosomes are "spot welds" between cells. Unlike tight junctions and adhering junctions, they are not arranged as a continuous seal around the cell, but like adherens junctions, they consist of specialized protein plaques connected to the intermediate filaments of the cytoskeleton (cytokeratin in epithelium), transmembrane linking protein of the cadherin family. As a result, desmosomes are particularly important in providing mechanical strength to epithelial sheets.
What protein is involved in creating the channels in gap junctions between cells?
Connexon. Creates a central aqueous channel.
What are sterocillia?
- Not to be confused with true cilia, these structures are actually long microvilli. In the ear, they function in signal generation.
Where in humans are flagella present?
Spermatozoa.

Or a nasty case of vaginal infection.....
When the number of microvilli per cell is high, what is the descriptive term used for the surface?
Brush border
What is at the core of each microvillus?
Actin
What extends up the center of microvilli to give it support?
A core of actin filaments
What is a basal body?
Basal body, a microtubular arrangement identical to that of a centriole, at the base of cilia
What extends up the center of cilia?
Each cilia contains a central core called the axoneme consisting of 20 microtubules arranges as a central pair surrounded by nine doublets. At the base the axoneme inserts into a basal body which has a microtubular arrangement identical to that of a centriole
On the basal surface of epithelial cells, what type of attachment occurs to the basement membrane?
Hemidesmosomes and integrins
What is an integrin?
Two subunits, part of desmosome, but also found elsewhere along the basal surface of the cell, and interact with extracellular proteins and are linked to actin.
What is a selectin?
involved in homing mechanisms, such as inflammatory process. Tell neutrophill where to get off. Cells of capillary stick this protein out, and neutrophill sticks to it.
Name
America!....Fuck Yeah!!
Name
woot
Describe endocytosis and phagocytosis:
loot
What type of secretion is endocrine secretion?
merocrine
What are the two distinct layers of the basement membrane?
lamina lucida and the lamina densa.