Lesson 5: Apical and basolateral specializations of epithelial cells Flashcards
What are the two main types of epithelial tissues?
Lining epithelia and glandular/secreting epithelia.
What key feature distinguishes epithelial cells?
Polarity, with apical, lateral, and basal domains.
How do epithelial cells adhere to each other?
Through specialized junctions.
What role does epithelial tissue play in the body?
Acts as a barrier and mediates absorption, secretion, and transport.
What is morphological-functional polarity in epithelial cells?
The structural and biochemical differences between the apical and basal sides.
What is the role of the cytoskeleton in cell polarity?
Provides structural support and contributes to the function of the apical and basal specializations.
Name three types of apical specializations in epithelial cells.
Microvilli, cilia, and stereocilia.
What is the primary function of microvilli?
To increase the cell’s absorptive surface area.
What forms the structural basis of microvilli?
Actin microfilaments.
How do cilia differ structurally from microvilli?
Cilia are larger and contain microtubules in a 9+2 arrangement.
What is the function of motile cilia?
To move fluid or particles across the epithelial surface.
What are primary (monocilia) cilia, and what is their function?
Non-motile cilia functioning as sensory structures.
Where are stereocilia commonly found?
In the epididymis and inner ear.
What is the structural difference between stereocilia and cilia?
Stereocilia are made of actin filaments, not microtubules.
What are the three main types of lateral cell junctions?
Occluding, anchoring, and communicating junctions.
What is the function of tight junctions?
To prevent diffusion of water and substances between cells.
Which proteins are involved in tight junctions?
Claudins, occludins, and junctional adhesion molecules (JAMs).
What is the primary function of adherens junctions?
To connect the actin cytoskeletons of adjacent cells.
What transmembrane proteins are key in adherens junctions?
Cadherins and nectins.
What is the function of desmosomes?
To anchor intermediate filaments between cells, providing mechanical stability.
Which proteins are critical for desmosome function?
Desmocollin and desmoglein.
What is the role of gap junctions?
To allow direct communication between adjacent cells.
What structures form the channels in gap junctions?
Connexons.
What is the basement membrane?
A specialized structure linking epithelial cells to underlying connective tissue.
What are the two layers of the basement membrane?
Basal lamina and reticular lamina.
What composes the basal lamina?
Laminin, entactin, glycoproteins, and type IV collagen.
What is the function of hemidesmosomes?
To anchor epithelial cells to the basement membrane.
Which proteins mediate hemidesmosome adhesion?
Integrins and laminin.
How do basal infoldings aid in cell function?
They increase surface area for transport and are associated with mitochondria.
What is EMT?
Epithelial-to-Mesenchymal Transition: A process where epithelial cells acquire mesenchymal traits, enhancing mobility.
How does E-cadherin downregulation affect EMT?
It reduces cell adhesion, facilitating EMT.
What role does EMT play in cancer?
It contributes to carcinoma progression and metastasis.
What is the significance of tight junctions in disease?
Their dysfunction can lead to increased permeability and conditions like leaky gut.
What is pemphigus foliaceus, and how is it related to desmosomes?
An autoimmune disease caused by the loss of desmoglein 1, weakening cell adhesion.
How do gap junctions contribute to cardiac function?
They facilitate electrical coupling between cardiomyocytes.
Why is the basement membrane important in cancer metastasis?
It acts as a barrier; its disruption can enable cancer cell invasion.
What is the glycocalyx, and where is it found?
A layer of glycoproteins and glycosaminoglycans covering microvilli, found on the apical surface of intestinal epithelial cells.
How does the movement of cilia help in the respiratory system?
Cilia move mucus and trapped particles out of the airways, aiding in continuous cleaning.
What structure is the basal body of a cilium derived from?
The centriole, which organizes microtubules.
What is the primary structural component of stereocilia?
Actin microfilaments.
What cytoplasmic proteins do occludins and claudins bind to in tight junctions?
ZO-1, ZO-2, and ZO-3 proteins.
Which type of junction allows ions and small molecules to pass directly between cells?
Gap junctions.
What are adherens junctions connected to within the cell?
The actin cytoskeleton.
Why are desmosomes particularly abundant in the epidermis?
To provide mechanical strength in areas exposed to friction and abrasion.
What protein family mediates the attachment of hemidesmosomes to the basement membrane?
Integrins.
What layer of the basement membrane directly contacts the plasma membrane?
The lamina lucida.
What type of collagen is predominantly found in the lamina densa?
Type IV collagen.
How does the basement membrane regulate epithelial repair?
It acts as a scaffold for cell migration and proliferation during tissue regeneration.
What staining technique highlights the basement membrane?
Periodic Acid-Schiff (PAS) staining.
What biochemical changes occur in EMT?
Downregulation of E-cadherin and upregulation of mesenchymal markers like vimentin.
How does EMT enhance the metastatic potential of cancer cells?
By increasing their migratory and invasive capabilities.
What role does β-catenin play in EMT?
It translocates to the nucleus to activate gene transcription supporting mesenchymal traits.
Which cell junction type is most affected during EMT?
Adherens junctions, due to E-cadherin downregulation.
What environmental or genetic factors can trigger EMT?
Hypoxia, mutations, and transcriptional repression of epithelial markers.
How are gap junctions visualized in research?
Using atomic force microscopy or fluorescent tagging.
What condition arises from the loss of desmoglein in desmosomes?
Pemphigus foliaceus, an autoimmune blistering disease.
How do hemidesmosomes contribute to tissue stability?
By anchoring epithelial cells firmly to connective tissue, crucial in the skin and oral cavity.
Why is the basement membrane considered a selective barrier?
It controls the passage of cells and molecules, critical in preventing metastasis.
How does EMT play a role in tissue development?
It is essential for processes like gastrulation and wound healing.
What are the main protein components of the terminal web in microvilli?
Actin and filamin.
How do tight junctions influence membrane protein distribution?
By preventing apical membrane proteins from diffusing into the lateral membrane.
What happens to cilia in conditions like primary ciliary dyskinesia?
Their motility is impaired, leading to issues like chronic respiratory infections.
What feature allows desmosomes to endure mechanical stress?
Their anchoring to intermediate filaments like keratin.
In what tissues are stereocilia critical for function?
The epididymis (sperm maturation) and the inner ear (sensory function).
What are the three domains of epithelial cell polarity?
Apical, lateral, and basal domains.
How do cadherins mediate cell-cell adhesion?
By forming homophilic bonds and linking to actin filaments via catenins.
What is the ultrastructure of cilia called?
The axoneme, featuring a 9+2 microtubule arrangement.
How does the lamina lucida differ from the lamina densa?
The lamina lucida is clear and close to the plasma membrane, while the lamina densa is dense and contains type IV collagen.
Why is cell polarity important in epithelial function?
It ensures directional processes like absorption, secretion, and barrier function.
What cytoskeletal components contribute to epithelial cell polarity?
Microtubules, microfilaments (actin), and intermediate filaments (keratin).
What type of intermediate filaments are present in epithelial cells?
Keratin filaments.
How do microvilli contribute to epithelial function?
They increase the surface area for absorption, especially in intestinal cells.
What is the terminal web, and how is it related to microvilli?
The terminal web is a dense network of actin filaments at the base of microvilli, providing structural support.
What forms the striated or brush border of intestinal epithelial cells?
Microvilli together with the glycocalyx.
What is the basal body, and what is its function in cilia?
The basal body is derived from the centriole and organizes the microtubules of cilia.
What structural difference exists between motile cilia and primary cilia?
Primary cilia lack the central microtubules (9+0 arrangement) and do not have motor proteins.
How do stereocilia differ from motile cilia?
Stereocilia are made of actin filaments and are non-motile, while motile cilia are made of microtubules.
How long can stereocilia grow?
Up to 100 µm in length.
What is the role of ZO proteins in tight junctions?
They link transmembrane proteins to the actin cytoskeleton.
How do gap junctions contribute to the function of osteocytes in bone tissue?
They enable nutrient and signal exchange through long cytoplasmic projections.
What components are found in the lamina lucida?
Laminin and integrins
What is the function of the reticular lamina in the basement membrane?
It connects the basement membrane to underlying connective tissue.
What are the main cellular changes during EMT?
Loss of cell polarity, reduced adhesion, and increased motility.
How do tight junctions help maintain the blood-brain barrier?
By preventing the diffusion of harmful substances into the brain.
