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Questions and Answers
What is characteristic of the arrangement of cells in epithelial tissue?
What is characteristic of the arrangement of cells in epithelial tissue?
What is the function of the apical side of an epithelial cell?
What is the function of the apical side of an epithelial cell?
What is the function of the basal side of an epithelial cell?
What is the function of the basal side of an epithelial cell?
What is a characteristic of cells in most epithelia?
What is a characteristic of cells in most epithelia?
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What is the function of epithelial cells in specialized epithelia?
What is the function of epithelial cells in specialized epithelia?
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What is the function of the basement membrane in epithelia?
What is the function of the basement membrane in epithelia?
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Which of the following proteins is NOT produced by epithelial cells?
Which of the following proteins is NOT produced by epithelial cells?
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What is the main function of the reticular lamina in the basement membrane?
What is the main function of the reticular lamina in the basement membrane?
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What is the result of the basement membrane's role in regulating the passage of substances from connective tissue into epithelia?
What is the result of the basement membrane's role in regulating the passage of substances from connective tissue into epithelia?
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During tissue regeneration, what role does the basement membrane play?
During tissue regeneration, what role does the basement membrane play?
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What is the primary function of tight or occluding junctions in epithelial cells?
What is the primary function of tight or occluding junctions in epithelial cells?
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Which type of intercellular junction is characterized by hexameric complexes of transmembrane connexons?
Which type of intercellular junction is characterized by hexameric complexes of transmembrane connexons?
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What is the role of cadherin family proteins in epithelial cells?
What is the role of cadherin family proteins in epithelial cells?
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What is the function of desmosomes or maculae adherens in epithelial cells?
What is the function of desmosomes or maculae adherens in epithelial cells?
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What is the function of hemidesmosomes in epithelial cells?
What is the function of hemidesmosomes in epithelial cells?
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Which protein is involved in the formation of tight junctions in epithelial cells?
Which protein is involved in the formation of tight junctions in epithelial cells?
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What is the function of zonula adherens in epithelial cells?
What is the function of zonula adherens in epithelial cells?
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What is the primary function of microvilli in epithelial cells?
What is the primary function of microvilli in epithelial cells?
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Which type of apical structure has a specialized mechanosensory function in cells of the inner ear?
Which type of apical structure has a specialized mechanosensory function in cells of the inner ear?
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What is the composition of the core of cilia in epithelial cells?
What is the composition of the core of cilia in epithelial cells?
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What is the mechanism of ciliary movement in epithelial cells?
What is the mechanism of ciliary movement in epithelial cells?
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What is the function of cilia in epithelial cells?
What is the function of cilia in epithelial cells?
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What is the characteristic of simple epithelia?
What is the characteristic of simple epithelia?
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What happens to cells in stratified squamous epithelia as they move from the basal to the surface layers?
What happens to cells in stratified squamous epithelia as they move from the basal to the surface layers?
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What is the primary function of stratified squamous epithelia such as the epidermis?
What is the primary function of stratified squamous epithelia such as the epidermis?
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What is unique about pseudostratified epithelia?
What is unique about pseudostratified epithelia?
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What is the name of the type of epithelium found only in the lining of the urinary system?
What is the name of the type of epithelium found only in the lining of the urinary system?
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What is a characteristic of the surface cells of transitional epithelium or urothelium?
What is a characteristic of the surface cells of transitional epithelium or urothelium?
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What is the primary function of organs composed primarily of epithelial cells that synthesize and secrete specialized products?
What is the primary function of organs composed primarily of epithelial cells that synthesize and secrete specialized products?
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What is the characteristic of exocrine glands?
What is the characteristic of exocrine glands?
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What type of glands lack ducts and secrete hormones into the bloodstream?
What type of glands lack ducts and secrete hormones into the bloodstream?
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What is the mechanism by which merocrine glands secrete their products?
What is the mechanism by which merocrine glands secrete their products?
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What type of glands produce mucus or similar substances?
What type of glands produce mucus or similar substances?
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What is special about the staining properties of the oligosaccharide components of mucus?
What is special about the staining properties of the oligosaccharide components of mucus?
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What is the name of the secretory mechanism in which terminally differentiated cells filled with lipid product are released?
What is the name of the secretory mechanism in which terminally differentiated cells filled with lipid product are released?
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What type of glands are characterized by producing largely enzymes and staining darkly with H&E?
What type of glands are characterized by producing largely enzymes and staining darkly with H&E?
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Why do serous glands stain darkly with H&E?
Why do serous glands stain darkly with H&E?
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What is the main product of serous glands?
What is the main product of serous glands?
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What is the function of the enzymes produced by serous glands?
What is the function of the enzymes produced by serous glands?
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What type of cellular structure is abundant in serous glands and stains darkly with H&E?
What type of cellular structure is abundant in serous glands and stains darkly with H&E?
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Study Notes
Epithelial Tissue
- Epithelium is a tissue type characterized by tightly bound cells forming a sheetlike or tubular structure with minimal extracellular material.
- Cells in epithelia have two distinct sides: apical (facing the free surface) and basal (facing the basement membrane and underlying connective tissue).
- Epithelia are specialized for various functions, including:
- Absorption
- Transcytosis
- Pinocytosis (at the apical side)
- Exocytosis (at the basolateral side)
- Most epithelial cells exhibit continuous renewal, with:
- Stem cells located in specific areas
- Variable rates of cell turnover depending on the specialized epithelium
Basement Membrane
- Consists of two parts: basal lamina and reticular lamina
- Basal lamina is a thin meshwork composed of type IV collagen and laminin
- Basal lamina is produced by epithelial cells
- Reticular lamina contains type III collagen and anchoring fibrils of VII collagen
- Reticular lamina components are secreted by cells of the adjacent connective tissue
- Functions of basement membrane:
- Attaches epithelia to connective tissue
- Regulates (filtrates) substances passing from connective tissue into epithelia
- Provides a guide or scaffold during tissue regeneration after injury
- Compartmentalizes epithelial cells from other tissues
Intercellular Junctions in Epithelia
- Intercellular junctions are well-developed in epithelia and consist of three major types with different functions.
Tight or Occluding Junctions
- Formed by interacting transmembrane proteins such as claudin and occludin.
- Linear arrangements of these linked proteins surround the apical ends of cells.
- Prevent paracellular passage of substances between cells.
Adherent or Anchoring Junctions
- Formed by interacting proteins of the cadherin family.
- Points of strong attachment holding together cells of the epithelium.
- May form zonula adherens that encircle epithelial cells just below their tight junctions.
- May also form scattered, spot-like attachment sites called desmosomes or maculae adherens.
- Attached to cytoplasmic keratins.
Hemidesmosomes
- Composed of transmembrane integrins.
- Attach cells to proteins of the basal lamina.
Gap or Communicating Junctions
- Points of cell contact where both plasma membranes have numerous hexameric complexes of transmembrane connexons.
- Each forming a channel allowing passage of small molecules from one cell to the other.
Apical Structures of Epithelial Cells
- Microvilli are small membrane projections with cores of actin filaments that increase the apical surface area of epithelial cells for absorption.
- Stereocilia are a type of microvilli with specialized mechanosensory functions, found in cells of the inner ear, and for absorption in tissues of the male reproductive tract.
- Stereocilia are longer than microvilli.
Cilia
- Cilia are larger projecting structures with a well-organized core of microtubules in a 9 + 2 arrangement called the axoneme.
- The axoneme is responsible for ciliary movement, which propels material along an epithelial surface.
- Ciliary movement is caused by restricted, dynein-based sliding of microtubules.
Morphological Types of Epithelia
- Epithelia with one cell layer are classified as simple, with cells varying in height from thin/squamous to cuboidal to tall/columnar.
Simple Epithelia
- Characterized by a single cell layer
- Cell heights range from very thin (squamous) to very tall (columnar)
Stratified Epithelia
- Comprise two or more layers of cells
- Almost all stratified epithelia are stratified squamous
- Outer cell layers are thin and flattened
- Cells migrate from basal to surface layers, changing shape and becoming filled with keratin intermediate filaments
Functions of Stratified Squamous Epithelia
- Protect underlying tissues from excess water loss (dehydration) and microbial invasion
- Found in the epidermis, covering the body surface
Pseudostratified Epithelia
- Appear to have several cell layers
- All cells attach to the basal lamina, but not all extend to the free epithelial surface
- Thick epithelial layers
Transitional Epithelium (Urothelium)
- Found only in the lining of the urinary system
- Stratified epithelium with large rounded surface cells
- Protective against urine
Epithelial Secretion and Glands
- Epithelial cells have a major function in synthesizing and secreting specialized products, forming organs called glands.
Types of Glands
- Exocrine glands have epithelial ducts that carry secretions to specific sites, with two types:
- Simple glands: unbranched ducts
- Compound glands: branched ducts
- Endocrine glands lack ducts, and secreted substances (hormones) are carried throughout the body by interstitial fluid and blood, with specificity produced by hormone receptors of target cells.
Secretory Mechanisms
- Three basic secretory mechanisms:
- Merocrine: uses exocytosis
- Holocrine: terminally differentiated cells filled with lipid product are released
- Apocrine: apical, product-filled areas of cells are extruded
Mucous Glands
- Exocrine glands producing mucus, or individual cells called goblet cells, are called mucous glands
- Oligosaccharide components of mucus stain poorly with routine dyes but stain well with PAS stain
Epithelial Tissue
- Epithelial tissue is a type of tissue where cells are tightly bound together to form a sheet-like or tubular structure with minimal extracellular material between cells.
- Each cell has an apical side facing the free surface and a basal side facing the basement membrane and underlying connective tissue.
- Epithelial cells are often specialized for absorption, transcytosis, pinocytosis, or exocytosis.
Basement Membrane
- The basement membrane is a thin extracellular layer of specialized proteins, consisting of two parts: a basal lamina and a reticular lamina.
- The basal lamina is a thin meshwork of type IV collagen and laminin produced by epithelial cells.
- The reticular lamina contains type III collagen and anchoring fibrils of VII collagen, secreted by adjacent connective tissue cells.
Intercellular Junctions
- Intercellular junctions are well-developed in epithelial tissue and consist of three major types: tight junctions, adherent junctions, and gap junctions.
- Tight junctions prevent paracellular passage of substances between cells.
- Adherent junctions hold cells together, forming strong attachment points.
- Gap junctions allow passage of small molecules between cells.
Apical Structures of Epithelial Cells
- Microvilli are small membrane projections that increase epithelial cells' apical surface area for absorption.
- Stereocilia are long microvilli with specialized mechanosensory function in cells of the inner ear and for absorption in male reproductive tract tissues.
- Cilia are larger projecting structures that propel material along an epithelial surface.
Morphological Types of Epithelia
- Epithelia can be classified as simple, stratified, pseudostratified, or transitional.
- Simple epithelia have one cell layer, with varying cell heights.
- Stratified epithelia have two or more cell layers, often with outer layers being thin and flattened.
- Pseudostratified epithelia appear to have multiple layers, but all cells attach to the basal lamina.
- Transitional epithelia are found in the urinary system and have large rounded surface cells.
Epithelial Secretion and Glands
- Epithelial cells synthesize and secrete specialized products, with organs composed primarily of these cells called glands.
- Exocrine glands have epithelial ducts carrying secretions to specific sites, with secretory portions forming round or elongated structures.
- Endocrine glands lack ducts, and secreted substances are hormones carried by the interstitial fluid and blood.
- Glands have three basic secretory mechanisms: merocrine, holocrine, and apocrine.
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Description
Learn about the structure and function of epithelial tissue, including cell organization and specialization for absorption and transport.
