Lesson 4 Flashcards
What is the carbohydrate-rich structure present on all cell surfaces and well-developed on the microvilli of epithelial cells, also containing various enzymes?
Glycocalyx
What are the structures on the lateral surfaces of epithelial cells that are responsible for cell attachment and communication?
Junctional complexes
What are some of the other terms used to describe structures responsible for holding epithelial cells together?
- Intercellular cement,
- intercellular bridges,
- desmosomes,
- terminal bars
What are the three main classifications of junctional complexes?
Adhering Junctions
Impermeable Junctions
Communicating Junctions
What are the three types of adhering junctions?
- Belt desmosome (Zonula adherens or intermediate junction)
- Spot desmosome
- Hemidesmosome
What is the ribbon-like adhering junction that does not encircle the cell and is found in cardiac muscle?
Fascia adherens
What type of adhering junction forms a continuous or encircling band around each interacting cell near the apical surface?
Belt desmosome (Zonula adherens or intermediate junction).
What filaments run along the cytoplasmic surface of the junctional plasma membrane in a belt desmosome?
Actin filaments
What are the actin filaments closely associated with in a belt desmosome?
The terminal web
How wide is the space separating adjacent cell membranes in a belt desmosome?
The space is 20 nm wide
What molecules anchor actin filaments to the cell membrane and adjacent membranes in a belt desmosome?
anchor means secure
Cadherins (calcium-dependent transmembrane proteins or adhesion molecules)
What is the function of belt desmosomes in cell adhesion?
They ensure that cells within tissues are bound together.
What is a ribbon-like adhering junction found in cardiac muscles at their longitudinal terminals?
Fascia adherens
What are the little structures distributed in a spotty way (macula-spot) around cells called?
Spot desmosomes (macula adherens)
What are the button-like points of contact or disk-like structures around 200 to 400 nm in diameter?
Spot desmosomes (macula adherens)
Shape of macula adherens?
button-like points of contact or disk-like structures
What is the width of the intercellular space in spot desmosomes, and what does it contain?
The intercellular space is about 20 nm wide; and contains fine filamentous material connecting adjacent plasma membranes.
What is found on the cytoplasmic surface of each interacting plasma membrane in spot desmosomes?
An attachment plaque
They are composed of a series of attachment proteins like desmoplakins and plakoglobins.
Attachment plaque
Found in spot desmosomes cytoplasmic surface
What network of filaments either terminates in or passes along the surface of the attachment plaques?
Keratin filaments
What is the function of spot desmosomes in epithelial sheaths?
- They serve as anchoring sites for keratin filaments.
- For forming a network of fibers across the epithelial sheath to resist mechanical stress and maintain structural integrity.
Where are spot desmosomes prominent, and how do they appear under the light microscope in processed tissues?
- They are prominent in the stratum spinosum of Epidermis
- They appear as dark-stained spiny processes (also called intercellular bridges).
Where are desmosomes abundant in, and what is their function in tissues?
Desmosomes are abundant in tissues subject to severe mechanical stress (Neck of Uterus, Cardiac Muscle, Skin)
What is the first and most superficial of the junctional complexes located near the apex of cells?
Zonula occludens (tight junction)
How are adjacent plasma membranes held together in tight junctions?
By continuous strands of junctional proteins. They meet across the intercellular space where they fuse or form ridges.
What transmembrane junctional proteins bind to each other at the fusion sites to seal the intercellular space?
Claudins and occludins
What structure is formed by the chain of junctional proteins in tight junctions, and what is its function?
A belt-like structure that completely encircles each cell in the sheet.
it acts as a seal between adjacent cells, preventing the passage of substances from the lumen to the cell interior or between cells.
Why are the tight junction and belt desmosome termed “zonula”?
zonula = a little encircling band
they encircle cells like a little band
What structures form gap junctions, and what are they made of?
formed by connecting channels made up of 6 integral membrane proteins (connexins), that assemble to form structures called connexons.
What is the pore size of the connecting channels in gap junctions, and what size molecules can pass through them?
The pore size is 1.5 nm, allowing the passage of molecules smaller than 1000 to 1500.
What is the common type of cell junction seen in many tissues, and what is its primary function?
Gap junctions;
they allow small water-soluble molecules to pass directly from the cytoplasm of one cell to another.
What are the two layers of the basement membrane under the electron microscope (EM)?
- The basal lamina
- lamina reticularis
What are the three essential functions of gap junctions?
- Conduction of electrical impulses (spread of action potentials in nerve cells).
- Functional synchronization (e.g., cardiac and smooth muscle synchronization).
- Metabolic cooperation of cells (passage of small water-soluble molecules).
is a dense, homogeneous structure described as a “structureless” membrane upon which all epithelia rest.
Basement Membrane
These are cytoplasmic folds on the lateral surfaces of adjacent cells that interdigitate with each other.
Cellular Interdigitations
What are the two layers of the basal lamina?
Lamina lucida
Lamina densa
Situated just beneath the epithelium and composed mainly of extracellular glycoproteins (laminin, entactin) and transmembrane glycoproteins (integrins and dystroglycans)
Lamina lucida
A meshwork of type IV collagen, proteoglycan (perlacan), heparin sulfate, and fibronectin.
Lamina densa
1.
They are transmembrane proteins similar to cell membrane receptors that form bonds with ligands.
Integrins
They are important for adhesion and can activate signaling pathways leading to cell cycle activation, differentiation, cytoskeletal reorganization, apoptosis, and gene expression.
Integrins
They are glycoproteins composed of β-dystroglycan and extracellular δ-dystroglycan that bind laminin of the basal lamina.
Dystroglycans
Dystroglycans are glycoproteins composed of what materials?
β-dystroglycan and extracellular δ-dystroglycan
δ is delta, β is beta
It consists of type I and type III collagen, manufactured by fibroblasts.
Lamina Reticularis
What is the function of the lamina reticularis?
It functions to attach the lamina densa to the underlying connective tissue.
What are the four functions of the basement membrane?
- Separates cells from the underlying or surrounding connective tissue (e.g., epithelial cells, Schwann cells, and fat cells).
- Functions as a highly selective membrane (e.g., kidney glomerulus and lung alveolus).
- Induces cell differentiation and influences cell metabolism.
- Provides scaffolding support for tissue regeneration after injury (e.g., for muscles and epithelia).
They are vesicular structures associated with the transport of fluids and solutes across the cell membrane, particularly in endothelial and epithelial cells.
Caveolae or Pinocytotic Vesicles
They resemble spot desmosomes but consist of only one-half of the spot desmosome.
Hemidesmosomes or Half-desmosomes
They attach the basal surface of epithelial cells to the underlying basal lamina.
Hemidesmosomes
They are seen in the stratum basale of the epidermis, where they anchor epithelial cells to the underlying basement membrane.
Hemidesmosomes
Where are hemidesmosomes seen?
Hemidesmosomes are seen in the stratum basale of the epidermis
What specific examples show how membrane proteins in the luminal surface of epithelial cells differ from those in the lateral or basal membrane?
- Kidney tubular epithelial membranes contain alkaline phosphatase.
- Intestinal epithelial cell membranes contain enzymes to hydrolyze sugars.
1.
They are responsible for increasing the surface area for absorption.
Microvilli
How will you describe the appearance of Microvilli?
They are slender, cylindrical (finger-like) cellular processes projecting from the apical or luminal surfaces of the cells, giving the surface a striated or brush border appearance.
What is the structure of each microvillus? (Individual microvilli)
- Each microvillus is covered by the cell membrane.
- The core is composed of 40 actin filaments that run in parallel bundles across its length.
- The actin filaments are embedded in amorphous material at the tip.
- At the base, the microvillus extends into the terminal web, a perpendicular network of filaments consisting of myosin and actin.
What is the role of actin filaments in microvilli?
Actin filaments are responsible for the extension, retraction, and mechanical stiffening of microvilli.
Where are microvilli highly developed?
Microvilli are highly developed in the cells of the small intestine and the proximal tubules of the kidney.
They are found in the epithelium of the epididymis, where they serve an absorptive function.
Stereocilia
These are extremely long, branched microvilli that are non-motile and have an absorptive function.
Stereocilia
What is the structure of stereocilia?
Stereocilia contain a core of actin filaments responsible for their rigidity and ability to detect minute movements of their fluid medium.
Why is the name “stereocilia” considered a misnomer?
misnomer means a wrong or inaccurate name or designation.
Because stereocilia do not have the same structure as cilia
These are motile processes found in the epithelial lining of the respiratory system and male and female reproductive tracts.
Kinocilia
Where are kinocilia found?
- In the respiratory tract, they entrap and transport foreign particles.
- In the reproductive tract, they aid in the movement of ova or spermatozoa.
1.
Long, cylindrical, tapered (hair-like) processes containing an axoneme and covered by a cell membrane.
Tubules extend from the apex to the basal body at the base of the cilium.
Kinocilia
How are kinocilia’s microtubules structurally described?
Microtubules are arranged with a central pair surrounded by nine doublets connected by fine filaments.
What is the primary function of kinocilia?
To propel fluid or mucus films over the surface epithelium through vibratory movement.
What is a flagellum, and where is it found?
A flagellum is a single long cilium found in mammalian spermatozoa, where it may measure several hundred micrometers long.
It propels the cell through undulatory movements.
Flagellum
They are invaginations of the cell membrane during pinocytosis.
Caveolae or Pinocytic Vesicles
How do simple epithelia that are not differentiated for absorption and secretion regenerate?
They regenerate by mitosis of the epithelial cells themselves.
How do highly differentiated simple epithelia regenerate?
They regenerate by mitosis of undifferentiated stem cells, such as those at the bases of intestinal glands.
How do stratified epithelia regenerate?
By mitosis of stem cells located at the basal layer of the epithelium, such as in the stratum basale of the epidermis.
