Epithelium I pack Flashcards
What are the steps for preparing tissues for histology?
Fixation, Dehydration, Clearing, Infiltration, and Embedding
What is the first step in tissue preparation for histology?
Fixation: Preserve cell and tissue structure
What happens during the dehydration step in tissue preparation?
Removes all water and replaces it with alcohol
What is the purpose of the clearing step in tissue preparation?
Alcohol is removed and paraffin is made miscible
What occurs during the infiltration step in tissue preparation?
Tissue is placed in melted paraffin until it becomes completely infiltrated
Describe the embedding step in tissue preparation.
Melted paraffin is allowed to harden around the tissue
Why must tissue sections be stained before microscopic study?
Cells and extracellular material are colorless and need to be dyed for visibility
What does Hematoxylin stain?
DNA in the cell nucleus RNA-rich portions of the cytoplasm and the matrix of cartilage
What color does Hematoxylin produce?
Dark blue or purple
What does Eosin stain?
Other cytoplasmic structures and collagen
What color does Eosin produce?
Pink
How might a highly coiled tube appear in thin sections?
As several round and oval structures
Why is it important to develop interpretive skills in microscopy?
To understand tissue and cell morphology in microscopic preparations
What is resolution in microscopy?
The smallest distance between two structures at which they can be seen as separate objects
What is the maximal resolving power of a light microscope?
Approximately 0.2 μm
What magnification range permits clear images with the maximal resolving power of a light microscope?
1000-1500 times
What do objective lenses provide in microscopy?
Higher magnification and higher resolving power
What does the eyepiece lens do in microscopy?
It only enlarges the image obtained by the objective and does not improve resolution
How can images be scanned in virtual microscopy?
Using an automated slide scanner
What is done with the images after scanning in virtual microscopy?
They are saved and displayed virtually
Can phase-contrast microscopy be used with living cultured cells?
Yes
On what principle is phase-contrast microscopy based?
Light changes its speed when passing through cellular and extracellular structures with different refractive indices
How does the phase-contrast system cause structures to appear lighter or darker?
By using changes in light speed to create contrast between structures
What does fluorescence microscopy combine?
The magnifying properties of the light microscope with fluorescence technology
Where is epithelium found in the body?
It lines and covers all body surfaces except the articular cartilage the enamel of the tooth and the anterior surface of the iris
How does epithelium receive nutrients?
By diffusion as it lacks a direct blood and lymphatic supply
What is the extracellular matrix (ECM) like in epithelium?
It has very little ECM
How is the cohesive nature of epithelium maintained?
By cell adhesion molecules and junctional complexes
What anchors epithelium?
A basement membrane
What structural and functional feature does epithelium have?
Polarity
From which germ layers does epithelium derive?
Ectoderm mesoderm and endoderm
How do most epithelial cells renew?
By mitosis
What is another function of epithelial tissues?
Absorption (e.g. the intestinal lining)
What is another function of epithelial tissues?
Secretion (e.g. parenchymal cells of glands)
What is another function of epithelial tissues?
Excretion (e.g. kidney tubules)
What is another function of epithelial tissues?
Gas exchange (e.g. lungs)
What are the two primary parameters for classifying epithelial tissue?
The shapes of individual cells and the arrangement of the cells in one or more layers
What other aspect might be considered in the classification of epithelial tissue?
Other special features (to be discussed later)
What is the shape of cuboidal epithelial cells?
Have equal dimensions
What is the shape of columnar epithelial cells?
Taller than wider
How many cell layers are there in stratified epithelial tissue?
More than one layer
How is stratified epithelium classified?
According to the cell shape of the superficial outer layer (squamous cuboidal or columnar)
How do the cells of simple squamous epithelium appear when viewed from the side?
Flattened
How do the cells of simple squamous epithelium appear in a top-down view?
Round
What is the functional advantage of simple squamous epithelium?
It minimizes the distance between the apical and basal sides of the cell to maximize diffusion efficiency
Where is simple squamous epithelium typically found?
In tissues and organs that utilize diffusion for molecular movement like capillaries
What function are simple cuboidal and columnar epithelium involved in?
Active transport of molecules from one side of the epithelium to the other using pump and channel molecules
What energy source is required for the active transport in simple cuboidal and columnar epithelium?
ATP
Why do cells in simple cuboidal and columnar epithelium typically have large numbers of mitochondria?
Because active transport requires ATP
What gives pseudostratified columnar epithelium its stratified appearance?
The nuclei of the cells form two distinct rows
What surface specializations are typically found in pseudostratified columnar epithelium?
Cilia
What is the function of cilia in pseudostratified columnar epithelium?
To aid in the movement of mucus or absorption of other material
How is transitional epithelium different from other epithelia in terms of classification?
It is not classified by the shape of cells at the surface but by the presence of umbrella cells
Where is transitional epithelium typically found?
In parts of the urinary tract
How does the epithelium appear if viewed from the side?
Like a flat sheet of cells with some thickness
How does the epithelium appear if viewed from above?
Like a flat sheet of cells with a top-down view
What classification is given to epithelia with cilia on the apical surface?
Simple columnar or pseudostratified columnar ciliated
What is keratin in the context of stratified squamous epithelium?
A layer of anucleate cells at the surface of the stratified squamous epithelium
What is the term for epithelium with a surface layer of keratinized cells?
Keratinized stratified squamous epithelium
What is the function of the basement membrane?
It acts as a semipermeable filter for substances reaching epithelial cells from below
What components in the basement membrane can often be stained and visualized with a light microscope?
Glycoproteins and other components
What is the basal lamina?
A thin
What is the reticular lamina?
A more diffuse and fibrous layer beneath the basal lamina
How are “basement membrane” and “basal lamina” sometimes used interchangeably?
Basal lamina usually denotes the fine extracellular layer seen ultrastructurally
What type of collagen is found in the basal lamina?
Type IV collagen
What is laminin?
A large glycoprotein that attaches to transmembrane integrin proteins in the basal cell membrane
What is nidogen?
A short
What is perlecan?
A proteoglycan that also cross-links laminins to the type IV collagen network
How is the reticular lamina bound to the basal lamina?
By anchoring fibrils of type VII collagen
Who produces type III collagen and type VII collagen?
Cells of the connective tissue
How is polarity generally exhibited in epithelial cells?
Organelles and membrane proteins are distributed unevenly within the cell
Why is polarity crucial for epithelial cells?
It is crucial for performing specialized functions such as absorption
What does the lateral domain of an epithelial cell face?
Neighboring epithelial cells linked by cell adhesion molecules and junctional complexes
What is the basal domain associated with?
A basement membrane that separates the epithelium from underlying connective tissue
What is present in the basal domain besides the basement membrane?
Cell-to-extracellular matrix (ECM) junctions
From which germ layers do epithelial cells derive?
Ectoderm mesoderm and endoderm
How do most epithelial cells renew?
Continuously by mitosis
How do epithelial cells receive nutrients?
By diffusion
What is the amount of free intercellular substances in epithelial cells?
Almost none
How is the cohesive nature of epithelium maintained?
By cell adhesion molecules and junctional complexes
What anchors epithelial cells?
A basal lamina
What features do epithelial cells have in terms of polarity?
Structural and functional polarity
What provides adhesion and communication between epithelial cells?
Several membrane-associated structures
Are the structures providing adhesion and communication in epithelial cells present in other tissues?
Yes
What are anchoring junctions?
Sites of strong cell adhesion
What are the three major types of anchoring junctions?
Desmosomes adherens junctions focal adhesions and hemidesmosomes
What are the two types of anchoring junctions that connect cells to each other?
Desmosomes (spot-like) and adherens junctions (belt-like)
What are the two types of anchoring junctions that connect cells to the extracellular environment?
Focal adhesions and hemidesmosomes (spot-like)
What is the function of gap junctions?
They are channels for communication between adjacent cells
What type of seal do tight junctions form between epithelial cells?
Not a continuous seal but a series of focal fusions
What do tight junctions separate?
The luminal space from the intercellular space and connective tissue compartment
What are the three main transmembrane proteins found in tight junctions?
Occludin claudins and junctional adhesion molecule (JAM)
How many transmembrane domains does JAM have?
One transmembrane domain
What do the associated proteins of the occluding junction (ZO-1 ZO-2 ZO-3) do?
They interact with each other
What does ZO-1 interact with in the cell cytoskeleton?
It binds actin filaments
What is the function of the plasma (cell) membrane?
The plasma (cell) membrane acts as a barrier but allows nutrients to enter and wastes to exit.
What determines what moves in and out of a cell?
Permeability determines what moves in and out of a cell.
What does selectively permeable mean for the plasma membrane?
A selectively permeable plasma membrane allows some materials to move freely while restricting others.
What are the factors that selective permeability is based on?
Selective permeability restricts materials based on size electrical charge molecular shape and lipid solubility.
