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Questions and Answers
What are the two main components of the basement membrane?
What are the two main components of the basement membrane?
What distinguishes transitional epithelium from other epithelial types?
What distinguishes transitional epithelium from other epithelial types?
Which function does NOT pertain to the basement membrane?
Which function does NOT pertain to the basement membrane?
Which type of epithelial cells are classified as unicellular glands?
Which type of epithelial cells are classified as unicellular glands?
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What type of collagen fibers make up the lamina densa?
What type of collagen fibers make up the lamina densa?
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What happens to transitional epithelium as the urinary bladder fills with urine?
What happens to transitional epithelium as the urinary bladder fills with urine?
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Which specialized junction is responsible for preventing the passage of materials between cells?
Which specialized junction is responsible for preventing the passage of materials between cells?
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Which statement is true about exocrine glands?
Which statement is true about exocrine glands?
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What is the primary role of gap junctions?
What is the primary role of gap junctions?
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Which of the following glands is an example of a compound gland?
Which of the following glands is an example of a compound gland?
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Deep infoldings in the basal and lateral cell membranes serve what main purpose?
Deep infoldings in the basal and lateral cell membranes serve what main purpose?
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Which class of glands loses contact with the epithelial surface?
Which class of glands loses contact with the epithelial surface?
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What is one of the key characteristics of adherent junctions?
What is one of the key characteristics of adherent junctions?
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Which of the following describes the tight junctions in terms of distance between cell membranes?
Which of the following describes the tight junctions in terms of distance between cell membranes?
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Transitional epithelium is primarily located in which body system?
Transitional epithelium is primarily located in which body system?
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What feature characterizes multicellular exocrine glands?
What feature characterizes multicellular exocrine glands?
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Which type of epithelium is primarily involved in the secretion and absorption of molecules in the kidney tubules?
Which type of epithelium is primarily involved in the secretion and absorption of molecules in the kidney tubules?
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What is a characteristic feature of all epithelial tissues?
What is a characteristic feature of all epithelial tissues?
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In which location would you expect to find ciliated columnar epithelium primarily?
In which location would you expect to find ciliated columnar epithelium primarily?
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What is the primary function of simple squamous epithelium?
What is the primary function of simple squamous epithelium?
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Which epithelial type is characterized by being a single layer that appears stratified but is not?
Which epithelial type is characterized by being a single layer that appears stratified but is not?
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Which type of epithelium is responsible for providing a smooth and protective surface in body cavities?
Which type of epithelium is responsible for providing a smooth and protective surface in body cavities?
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Which of the following epithelia is typically keratinized?
Which of the following epithelia is typically keratinized?
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What distinguishes myo-epithelia from other types of epithelial tissue?
What distinguishes myo-epithelia from other types of epithelial tissue?
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What is the primary function of adherens junctions?
What is the primary function of adherens junctions?
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Which statement about desmosomes is true?
Which statement about desmosomes is true?
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What is the role of gap junctions in epithelial cells?
What is the role of gap junctions in epithelial cells?
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What unique structure do microvilli contain that aids in their function?
What unique structure do microvilli contain that aids in their function?
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Where are hemidesmosomes located?
Where are hemidesmosomes located?
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Which component is essential for forming gap junctions?
Which component is essential for forming gap junctions?
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What is the primary purpose of microvilli on epithelial cells?
What is the primary purpose of microvilli on epithelial cells?
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Which feature distinguishes desmosomes from adherens junctions?
Which feature distinguishes desmosomes from adherens junctions?
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What is the primary function of microvilli in the intestinal brush border?
What is the primary function of microvilli in the intestinal brush border?
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Which structure is responsible for the motility seen in cilia?
Which structure is responsible for the motility seen in cilia?
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What distinguishes stereocilia from microvilli?
What distinguishes stereocilia from microvilli?
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What is the primary function of cilia in the respiratory epithelium?
What is the primary function of cilia in the respiratory epithelium?
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What is the structural configuration of cilia at their core?
What is the structural configuration of cilia at their core?
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Which type of cilia are non-motile and have a sensory function?
Which type of cilia are non-motile and have a sensory function?
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What is the key feature of flagella in human anatomy?
What is the key feature of flagella in human anatomy?
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What connects cilia to the cell structure at their base?
What connects cilia to the cell structure at their base?
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Study Notes
Epithelial Tissue Characteristics
- Very cellular with little intercellular space.
- Cells rest on a basement membrane (BM).
- Numerous nerve endings.
- Lack lymph vessels.
- Avascular (no blood vessels)
- Cells exhibit polarity with specialized apical and basal regions.
- Display surface modifications, such as microvilli, cilia, and stereocilia.
- Perform various functions, including absorption (intestine), protection (skin), secretion (thyroid), and exchange (lung).
Classifications of Epithelia
- Covering or Lining Epithelia: Cells form continuous sheets that cover surfaces, line cavities, and form glands.
- Secretory Epithelia and Glands: Specialized cells for the production of specific substances.
- Myo-Epithelia: Modified epithelial cells with contractile properties, found in glands and other structures.
- Neuroepithelia: Epithelial cells with sensory functions, found in special sense organs, such as the retina of the eye.
Covering or Lining Epithelia
Simple Squamous Epithelium
- Cells appear as thin scales.
- Flat nuclei.
- Locations:
- Endothelium lining of capillaries.
- Lung alveoli for gas diffusion and parts of kidney tubules.
- Mesothelium, the lining of body cavities and internal organs.
- Function: Provides a smooth, protective surface.
Simple Cuboidal Epithelium
- Round, centrally located nuclei.
- Locations:
- Kidney tubules.
- Ducts of glands.
- Thyroid follicles.
- Function: Active in secretion and absorption of molecules.
Simple Columnar Epithelium (Non-Ciliated)
- Elongated nuclei positioned basally.
- Locations:
- Sections of the digestive system.
- Sections of the female reproductive tract.
- Function: Active in secretion and absorption of molecules.
Ciliated Columnar Epithelium
- Elongated nuclei positioned basally.
- Cells possess cilia on their apical surfaces.
- Locations:
- Fallopian tubes.
- Parts of the respiratory system.
- Function: Ciliary beating helps remove particulate matter.
Pseudostratified Columnar Epithelium
- Appears stratified, but consists of a single layer of irregularly shaped cells.
- All cells contact the basal lamina.
- Locations:
- Respiratory tract with some cells possessing cilia.
Stratified Epithelia
Stratified Squamous Epithelium
- Deeper layers are columnar, becoming flattened (squamous) towards the surface.
- Can be keratinized (skin) or non-keratinized (mouth cavity).
- Locations:
- Mammalian skin (keratinized).
- Mouth cavity (non-keratinized).
Stratified Cuboidal Epithelium
- Found in certain glands and ducts.
- Uncommon in the human body.
Stratified Columnar Epithelium
- Similar to stratified cuboidal epithelium.
Transitional Epithelium
- Appears to change in shape and layering depending on the state of the organ it lines.
- Location: Urinary system, specifically ureters and urinary bladder.
- Features:
- Facet cells or Umbrella cells: The superficial cell layer lining the lumen, dome-shaped with many binucleated cells.
- Acts as an osmotic barrier against the contents of the urinary tract, relatively impermeable to water and salts.
Secretory Epithelia and Glands
- Specialized epithelial cells involved in secretion.
- Can be unicellular (e.g., goblet cells in the intestine) or multicellular.
Multicellular Glands
- Develop as diverticula from epithelial surfaces.
- Secretory elements are the distal parts, ducts are the proximal parts.
Gland Classification by Mode of Secretion
- Endocrine Glands: Lose contact with the epithelial surface they originated from and secrete directly into the bloodstream.
- Exocrine Glands: Secrete onto an epithelial surface, directly or through ducts.
Exocrine Gland Classification:
-
Branching of Ducts:
- Simple: All secretory cells discharge into a single duct.
- Compound: Several groups of secretory cells each discharging into their own duct.
- Shape of the Secretory Unit: Varies based on the specific gland.
- Nature of Secretions: Can be serous (watery), mucous (viscous), or mixed.
-
Manner of Secretion:
- Merocrine: Release secretions without cell damage.
- Apocrine: Part of the cell is released along with the secretion.
- Holocrine: The entire cell becomes part of the secretion.
Basement Membrane
- Located between epithelial cells and underlying connective tissue.
- Composed of a basal lamina (near epithelial cells) and a reticular lamina (near connective tissue).
- Basal Lamina:
- Lamina densa: Type IV collagen fibers.
- Lamina lucida: Glycoproteins.
- Functions:
- Strong adhesion between epithelium and connective tissue.
- Barrier to diffusion of molecules.
- Influences the regeneration of peripheral nerves.
- Scaffold for rapid epithelial repair and regeneration.
Lateral Surface Specializations (Cell Junctions)
- Located between adjacent epithelial cells.
- Functions:
- Strong cell attachment.
- Prevent passage of materials between cells.
Classification by Distance Between Membranes
- Tight Junctions (Occluding Junctions): Zero distance; forms a seal between cells.
- Adhering Junctions (Anchoring Junctions): 20 nm distance; site of strong cell adhesion.
- Gap Junctions (Communicating Junctions): 2 nm distance; channels for communication between cells.
Classification by Junction Shape
- Zonula Junctions: Forms a band or girdle around the cell.
- Fascia Junctions: Forms a band of attachment between cells.
- Macula Junctions: Form a spot or patch of attachment between cells.
Specific Types of Cell Junctions
-
Tight Junctions (Zonulae Occludens):
- Found at the most apical end of the cells.
- Prevents movement of molecules between the apical, lateral, and basal surfaces.
-
Adherens Junctions (Zonula Adherens):
- Encircles the epithelial cell, below the tight junction.
- Firmly anchors a cell to its neighbors.
-
Desmosomes:
- Resemble spots, not forming a belt around the cell.
- Thickened areas (plaques) on the cell membranes with a 25 nm gap.
- Rich in glycoproteins.
- Intermediate filaments insert into the plaques for strong cell adhesion.
-
Gap Junctions:
- Mediate intercellular communication.
- Form circular patches in the plasma membrane.
- Transmembrane proteins (connexins) form hexameric complexes called connexons.
- Allows passage of small molecules for coordinated cell activity.
-
Hemidesmosomes:
- Half of a desmosome.
- Found between the base of epithelial cells and the basal lamina.
- Helps attach epithelial cells to the basement membrane.
Apical Cell Surface Specializations
- Apical ends of epithelial cells may have specialized structures.
- Functions: Increase surface area for absorption and move substances along the epithelial surface.
Microvilli
- Uniform length.
- Found in cells lining the small intestine.
- Densely packed, visible as a brush border.
- Contain bundles of actin filaments.
- Functions:
- Increases surface area by 20-30 times.
- Provides membrane-bound proteins and enzymes for digestion.
Stereocilia
- Less common apical processes, found in the male reproductive system.
- Resemble microvilli with similar diameters and attachments.
- Much longer and less motile than microvilli.
- Function: Increase surface area, aiding in absorption.
Cilia
- Long, motile apical structures, larger than microvilli.
- Contain internal arrays of microtubules (not microfilaments).
- Visible as hair-like projections.
- Composed of microtubules coated by the plasma membrane.
- Attached to the cell at the basal body (similar to centrioles).
- Have dynamic tubulin protofilaments forming rootlets for cytoskeletal anchoring.
- Functions:
- Move in a coordinated wave.
- Transport fluids, mucous, and small solids.
- May have sensory roles (olfactory cilia).
Flagella
- Larger processes with the same basic structure as cilia.
- The best example is the sperm tail.
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Description
This quiz explores the characteristics and classifications of epithelial tissue, including its structure, functions, and the various types such as covering, secretory, myo-epithelia, and neuroepithelia. Test your understanding of epithelial tissue and its roles in the human body.
