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What are the three main surface domains of epithelial cells?
What are the three main surface domains of epithelial cells?
What is the primary component of the basal lamina in the basement membrane?
What is the primary component of the basal lamina in the basement membrane?
Which of the following is NOT a characteristic of epithelial tissue?
Which of the following is NOT a characteristic of epithelial tissue?
Which type of junction allows for communication between adjacent epithelial cells?
Which type of junction allows for communication between adjacent epithelial cells?
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What do exocrine glands primarily do?
What do exocrine glands primarily do?
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Which of the following describes a characteristic feature of epithelial tissue?
Which of the following describes a characteristic feature of epithelial tissue?
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What type of gland is characterized by the secretion of both serous and mucous substances?
What type of gland is characterized by the secretion of both serous and mucous substances?
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Which junction type is critical for anchoring epithelial cells to the basement membrane?
Which junction type is critical for anchoring epithelial cells to the basement membrane?
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What type of collagen is primarily found in the reticular lamina?
What type of collagen is primarily found in the reticular lamina?
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Which cell shape is characterized by a height much less than width and functions mainly for diffusion?
Which cell shape is characterized by a height much less than width and functions mainly for diffusion?
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Where is simple cuboidal epithelium primarily located?
Where is simple cuboidal epithelium primarily located?
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What is the primary function of non-ciliated simple columnar epithelium?
What is the primary function of non-ciliated simple columnar epithelium?
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Which type of epithelium is typically found in the loop of Henle in the kidney?
Which type of epithelium is typically found in the loop of Henle in the kidney?
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What distinguishes ciliated simple columnar epithelium from its non-ciliated counterpart?
What distinguishes ciliated simple columnar epithelium from its non-ciliated counterpart?
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What is a primary role of the reticular lamina?
What is a primary role of the reticular lamina?
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Which of the following best describes the function of cuboidal cells?
Which of the following best describes the function of cuboidal cells?
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What is the primary function of stratified cuboidal epithelium?
What is the primary function of stratified cuboidal epithelium?
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Where is transitional epithelium primarily found?
Where is transitional epithelium primarily found?
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Which type of epithelium is characterized by a surface layer of flattened, keratinized cells?
Which type of epithelium is characterized by a surface layer of flattened, keratinized cells?
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What is a common characteristic of stratified columnar epithelium?
What is a common characteristic of stratified columnar epithelium?
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What type of epithelial tissue comprises multiple layers of cube-shaped cells?
What type of epithelial tissue comprises multiple layers of cube-shaped cells?
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Which feature distinguishes transitional epithelium from other types of epithelial tissue?
Which feature distinguishes transitional epithelium from other types of epithelial tissue?
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What is the primary location of stratified squamous keratinized epithelium?
What is the primary location of stratified squamous keratinized epithelium?
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Which type of epithelium is primarily involved in the duct systems of glands?
Which type of epithelium is primarily involved in the duct systems of glands?
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What is the role of cell adhesion molecules (CAMs)?
What is the role of cell adhesion molecules (CAMs)?
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Which type of junction functions as a tight seal to prevent leakage of larger solute molecules?
Which type of junction functions as a tight seal to prevent leakage of larger solute molecules?
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What type of junction helps anchor muscle cells to the extracellular matrix through interaction with the actin cytoskeleton?
What type of junction helps anchor muscle cells to the extracellular matrix through interaction with the actin cytoskeleton?
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What is one clinical correlation associated with desmosomes?
What is one clinical correlation associated with desmosomes?
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Which of the following is NOT a function of gap junctions?
Which of the following is NOT a function of gap junctions?
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Hemidesmosomes primarily function to attach cells to which structure?
Hemidesmosomes primarily function to attach cells to which structure?
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Which type of cell junction is characterized by its ability to coordinate electrical activity between muscle cells?
Which type of cell junction is characterized by its ability to coordinate electrical activity between muscle cells?
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What is a common function of occluding junctions?
What is a common function of occluding junctions?
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What characterizes bullous pemphigoid?
What characterizes bullous pemphigoid?
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Which type of gland has a secretory end piece that is tubular?
Which type of gland has a secretory end piece that is tubular?
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Which type of gland involves the complete loss of cytoplasm in its mode of secretion?
Which type of gland involves the complete loss of cytoplasm in its mode of secretion?
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What type of secretion is characteristic of serous glands?
What type of secretion is characteristic of serous glands?
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Which gland is an example of a compound tubular gland?
Which gland is an example of a compound tubular gland?
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Which gland primarily provides lubrication and protection through viscous secretion?
Which gland primarily provides lubrication and protection through viscous secretion?
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What distinguishes mixed glands?
What distinguishes mixed glands?
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Which of the following glands secretes by apocrine mode?
Which of the following glands secretes by apocrine mode?
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What type of secretion is typically produced by the parotid gland?
What type of secretion is typically produced by the parotid gland?
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Which type of gland is usually characterized by a flask-shaped secretory end piece?
Which type of gland is usually characterized by a flask-shaped secretory end piece?
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What is the primary function of serous acini?
What is the primary function of serous acini?
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Which of the following describes a sebaceous gland?
Which of the following describes a sebaceous gland?
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What characteristic best defines the structure of a mixed gland?
What characteristic best defines the structure of a mixed gland?
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What type of gland is involved in secreting primary lipid content?
What type of gland is involved in secreting primary lipid content?
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Study Notes
Epithelial Tissues and Glands
- Epithelial tissues are derived from all three embryonic germ layers and have a minimal amount of intracellular matrix.
- Epithelial cells are closely apposed and adhere to each other through specialized cell-to-cell junctions.
- Epithelial tissues exhibit functional and morphological polarity with three surface domains: free surface/apical domain, lateral domain, and basal domain.
- The basal surface of epithelial tissues is attached to the underlying basement membrane through cell-to-matrix junctions.
- Epithelia line hollow organs, such as the stomach, and cover outside surfaces, such as skin.
- Most epithelia rest on connective tissue.
- Epithelial cells are modified to form glands.
Basement Membrane
- The basal surface of all epithelial tissues rests on a thin sheet of extracellular macromolecules called the basement membrane.
- It is semi-permeable and provides structural support to the overlying epithelium.
- The basement membrane functions as an impermeable barrier that allows only water and small molecules to pass through.
- It has two layers: basal lamina and reticular lamina.
Cell Shapes
- Squamous cells: Flattened cells with height much less than width. They show a central thickening at the site of the nucleus and function for diffusion.
- Cuboidal cells: Cube-like cells with about the same height and width and a spherical nucleus. They function for secretion or absorption.
- Columnar cells: Taller than they are wide cells with an elongated/ovoid nucleus. They protect underlying tissue, may have cilia, and function for secretion or absorption.
Classification of Epithelial Tissues
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Simple Epithelium: Composed of a single layer of cells.
- Simple Squamous Epithelium: Formed by flattened cells. It is present in the loop of Henle in the kidney, lining all blood vessels, and forming Bowman’s capsule in the renal cortex. Functions include gas exchange, lubrication, reducing friction, and lining membrane.
- Simple Cuboidal Epithelium: Cells appear as squares with round central nuclei. Present in the duct of exocrine glands, surface of the ovary, thyroid follicles, kidney tubules, and thyroid follicles. Functions include secretion, absorption, and surface barrier.
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Simple Columnar Epithelium: Consists of a single layer of rectangular cells. It can be ciliated or non-ciliated.
- Non-ciliated Simple Columnar Epithelium: Found in the stomach, small and large intestine, and the gallbladder where they perform secretion and absorption. Specialized cells containing microvilli perform absorption, and goblet cells secrete mucus.
- Ciliated Simple Columnar Epithelium: Consists of a single layer of ciliated rectangular cells. Aids in movement.
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Stratified Epithelium: Composed of multiple layers of cells.
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Stratified Squamous Epithelium: Has many layers of cells with cells closer to the underlying connective tissue usually cuboidal or low columnar. Cells become irregular in shape and flatten as they accumulate keratin in the process of keratinization.
- Keratinized Stratified Squamous Epithelium: Found mainly in the epidermis of skin. The surface layer of cells helps protect against water loss, is resistant to friction, and helps repel bacteria.
- Non-keratinized Stratified Squamous Epithelium: Found lining moist surfaces like the mouth, esophagus, vagina, and anus.
- Stratified Cuboidal Epithelium: Consists of several layers of cells in which the top layer is cube-shaped. Function is mainly absorption and secretion. Located in testis tubules, ducts of sweat glands, sebaceous glands, some ducts of salivary gland, and part of the lactiferous sinus of mammary gland.
- Stratified Columnar Epithelium: Consists of several layers of cells in which the top layer is rectangular. Protects and secretes mucus. Found in the conjunctiva lining the eyelids, portion of the male urethra, some parts of the salivary gland, and mammary gland.
- Transitional Epithelium (Urothelium): It is capable of stretching. Consists of several layers of cells whose appearance is variable, whether stretched or relaxed. Represents the transition stage between stratified squamous and stratified cuboidal epithelium. It is found lining the urinary tract.
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Stratified Squamous Epithelium: Has many layers of cells with cells closer to the underlying connective tissue usually cuboidal or low columnar. Cells become irregular in shape and flatten as they accumulate keratin in the process of keratinization.
Cell Adhesion & Cell Adhesion Molecules
- Cell adhesion is the process by which cells are anchored to each other and to the extracellular matrix (ECM).
- Cell adhesion molecules (CAMs) are transmembrane proteins that mediate cell adhesion.
- Collections of CAMs are called cell junctions.
Lateral Specializations of Cells
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Occluding Junctions:
- Tight junction (zonula occludens): Functions as a tight seal on the apical surface to prevent leakage of larger solute molecules from cell to cell.
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Anchoring Junctions:
- Adhering junctions (zonula adherens): Maintain physical integrity of cells by assisting with cell attachment to adjacent cells.
- Desmosomes (macula adherens): Help anchor cells to the extracellular matrix (ECM) through interaction with the actin cytoskeleton.
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Communicating Junctions:
- Gap junctions: Present in various tissues like epithelium, muscle (smooth and cardiac), and nerves. They help coordinate activity between adjacent cells.
Basal Specializations of Cells
- Hemidesmosome: Anchoring junctional complex that connects cells to the extracellular Matrix. Helps to anchor epithelial cells to the basement membrane. Transmembrane proteins are integrins.
Glandular Epithelium
- A gland is a structure that secretes substances into ducts, onto the surface of the body, or directly into the blood.
- Exocrine glands: Secrete products into ducts that open onto a surface.
- Endocrine glands: Secrete products directly into the bloodstream.
- Unicellular glands: Single-celled exocrine glands like goblet cells that secrete mucus.
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Multicellular glands: Composed of many cells.
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Classification of Multicellular Exocrine Glands based on duct structure:
- Simple glands: Un-branched duct. Example: Sebaceous gland, Urethral gland.
- Compound glands: Branched duct. Example: Mammary gland.
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Classification of Multicellular Exocrine Glands based on shape of secretory end piece:
- Tubular: Secretory end piece is like a tubule (straight, branched, or coiled). Example: Compound tubular glands like large intestinal glands.
- Alveolar: Secretory end piece is flask-shaped with a large lumen. Example: Sebaceous gland.
- Acinar: Secretory end piece is round-shaped with a small lumen. Example: Parotid gland.
- Tubulo-alveolar/acinar: Combination of tubular and alveolar/acinar. Example: Sublingual gland, submandibular gland.
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Classification of Multicellular Exocrine Glands based on mode of secretion:
- Merocrine: Secretion discharged through intact cell membrane by exocytosis. No loss of cytoplasm. Example: Parotid gland, pancreas, typical sweat gland.
- Apocrine: Apical portion of the cell disintegrates to discharge its secretion. Partial loss of cytoplasm. Nucleus and basal portion remain intact. Example: Lipid content of mammary gland, atypical sweat gland (Axilla and groin).
- Holocrine: Entire cell disintegrates to discharge its secretion. Complete loss of cytoplasm. Example: Sebaceous gland.
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Classification of Multicellular Exocrine Glands based on duct structure:
Serous, Mucous, and Mixed Glands
- Serous Acinus/Gland: Thin, watery secretion rich in enzymes and protein. Cells are pyramidal and small with indistinct boundaries. Cytoplasm is granular and stains darkly with H/E stain. Nuclei are rounded and basal/central. Example: Parotid and lacrimal glands.
- Mucous Acinus/Gland: Thick, viscous secretion. Cells are low columnar and large with distinct boundaries. Cytoplasm contains mucinogen droplets that stain very lightly with H/E stain. Nuclei are flattened and basal. Example: Sublingual glands.
- Mixed Acinus/Gland: Contain both serous and mucous secretory units. Example: Submandibular gland.
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Description
Test your knowledge on epithelial tissues and glands with this quiz. Explore the structure, functions, and characteristics of various epithelial tissues, including their relationships with the basement membrane and surrounding connective tissues. Enhance your understanding of histology and cell biology.
