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Questions and Answers
What is the primary function of collagen fibers in connective tissue?
What is the primary function of collagen fibers in connective tissue?
Which component is considered the living part of a tissue?
Which component is considered the living part of a tissue?
What characterizes amorphous substance in connective tissue?
What characterizes amorphous substance in connective tissue?
What role does intercellular substance play in muscle and nervous tissue?
What role does intercellular substance play in muscle and nervous tissue?
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Which of the following is NOT a type of formed substance in connective tissue?
Which of the following is NOT a type of formed substance in connective tissue?
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What is the main chemical composition of amorphous substance?
What is the main chemical composition of amorphous substance?
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How do collagen fibers appear in a stretch preparation of areolar connective tissue?
How do collagen fibers appear in a stretch preparation of areolar connective tissue?
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Which of the following best describes the role of the intercellular substance in tissues?
Which of the following best describes the role of the intercellular substance in tissues?
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What characterizes simple squamous epithelium?
What characterizes simple squamous epithelium?
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Which type of epithelial tissue is classified as glandular epithelium?
Which type of epithelial tissue is classified as glandular epithelium?
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How are epithelial cells primarily classified?
How are epithelial cells primarily classified?
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What is the primary role of zonula occludens in epithelial tissues?
What is the primary role of zonula occludens in epithelial tissues?
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Which type of junction is characterized as forming a complete encircling belt around epithelial cells?
Which type of junction is characterized as forming a complete encircling belt around epithelial cells?
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What is NOT a component of lateral surface specialization in epithelial cells?
What is NOT a component of lateral surface specialization in epithelial cells?
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Which junctional complex is most commonly found within epithelial tissues?
Which junctional complex is most commonly found within epithelial tissues?
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What property does the impermeability provided by zonula occludens confer to the urinary tract?
What property does the impermeability provided by zonula occludens confer to the urinary tract?
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What is the primary function of tonofibrils in epithelial cells?
What is the primary function of tonofibrils in epithelial cells?
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What is the structure primarily responsible for separating adjacent epithelial cell membranes at the zonula adhaerens?
What is the structure primarily responsible for separating adjacent epithelial cell membranes at the zonula adhaerens?
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Which structure is specifically responsible for communication between adjacent epithelial cells?
Which structure is specifically responsible for communication between adjacent epithelial cells?
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Which components are found in the basement membrane produced by epithelial cells?
Which components are found in the basement membrane produced by epithelial cells?
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Which surface specialization is primarily found at the basal surface of epithelial cells?
Which surface specialization is primarily found at the basal surface of epithelial cells?
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What type of surface specialization helps in the adhesion of adjacent epithelial cells?
What type of surface specialization helps in the adhesion of adjacent epithelial cells?
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Which of the following best describes the appearance of the basement membrane in light microscopy?
Which of the following best describes the appearance of the basement membrane in light microscopy?
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What is the characteristic feature of microvilli compared to cilia?
What is the characteristic feature of microvilli compared to cilia?
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Basal folds (infoldings) are primarily associated with which cellular function?
Basal folds (infoldings) are primarily associated with which cellular function?
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What distinguishes hemidesmosomes from other junctions?
What distinguishes hemidesmosomes from other junctions?
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Which statement best describes the structure of the basement membrane as seen under transmission electron microscopy (TEM)?
Which statement best describes the structure of the basement membrane as seen under transmission electron microscopy (TEM)?
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What defines a multicellular gland?
What defines a multicellular gland?
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Which shape best describes an alveolar or acinar gland?
Which shape best describes an alveolar or acinar gland?
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Which type of gland is described as having secretory units that are both tubular and alveolar?
Which type of gland is described as having secretory units that are both tubular and alveolar?
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What characterizes a simple gland?
What characterizes a simple gland?
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Which example represents a simple coiled tubular gland?
Which example represents a simple coiled tubular gland?
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Which type of gland has two or more alveolar secretory units that converge into a single duct?
Which type of gland has two or more alveolar secretory units that converge into a single duct?
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What distinguishes a simple straight tubular gland?
What distinguishes a simple straight tubular gland?
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Which of the following is NOT a type of simple gland?
Which of the following is NOT a type of simple gland?
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What distinguishes stratified epithelium from simple epithelium?
What distinguishes stratified epithelium from simple epithelium?
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Which shape of epithelial cells is characterized as being tall and prismatic?
Which shape of epithelial cells is characterized as being tall and prismatic?
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Which type of simple epithelium is best suited to facilitate the flow of fluids?
Which type of simple epithelium is best suited to facilitate the flow of fluids?
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What feature is common to all epithelial cells when viewed from the top?
What feature is common to all epithelial cells when viewed from the top?
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Where is simple squamous epithelium commonly found?
Where is simple squamous epithelium commonly found?
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What is a characteristic of cuboidal epithelial cells?
What is a characteristic of cuboidal epithelial cells?
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Which type of epithelium consists of extremely thin flat cells?
Which type of epithelium consists of extremely thin flat cells?
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What is a key limitation of surface epithelium?
What is a key limitation of surface epithelium?
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Study Notes
Tissues
- Tissues are groups of cells that work together to perform a specific function.
- The basic components of a tissue include cells, intercellular substance, and fluid.
Cells
- Cells are the living components of a tissue and vary in number, shape, and arrangements depending on the type of tissue.
Intercellular Substance
- The major component of connective tissue and is minimal in muscle and nervous tissues.
- It is non-living material produced by cells and can fill the spaces between cells.
- There are two types of intercellular substance:
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Amorphous substance
- Has a viscous, gel-like consistency.
- Binds to large quantities of water.
- Forms the ground substance of tissues.
- Composed of glycoproteins (mucopolysaccharides) and proteoglycans.
- Functions as a barrier to bacteria and acts as a shock absorber.
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Formed substances
- Are fibrous in nature and composed of neutral mucosubstances (glycoproteins).
- Classified into three types: collagen fibers, elastic fibers, and reticular fibers.
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Collagen fibers
- Predominant fiber in most proper connective tissues.
- Provides high tensile strength and prevents over-distension.
- Appear as wavy thick bands in areolar connective tissue.
- Composed of collagen fibrils, which in turn are composed of overlapping tropocollagen molecules.
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Elastic fibers
- Found in tissues that require flexibility and resilience.
- Thinner than collagen fibers and are more branched.
- Composed of the protein elastin.
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Reticular fibers
- Found in tissues that support delicate structures, like the liver and spleen.
- Made of a special type of collagen and are thin and branched.
- Form a fine network.
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Amorphous substance
Epithelium
- Covers the outer surfaces of the body and lines the lumen of tubular organs.
- Classified according to:
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Number of cell layers
- Simple epithelium has one layer of cells resting on the basal membrane.
- Stratified epithelium has two or more layers of cells.
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Shape of superficial cells
- Columnar cells are tall and prismatic.
- Cuboidal cells have equal sides.
- Squamous cells are thin and flat.
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Number of cell layers
Types of Simple Epithelium
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Simple squamous epithelium
- One layer of thin, flat cells.
- Suited to lining structures where fluid flow is needed.
- Found in the glomerular capsule, blood vessels, and body cavities.
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Simple cuboidal epithelium
- One layer of cube-shaped cells.
- Found in glands and ducts.
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Simple columnar epithelium
- One layer of tall, columnar cells.
- Often contains goblet cells which secrete mucus.
- Found in the lining of the digestive tract.
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Pseudostratified columnar epithelium
- One layer of cells, but appears to have multiple layers.
- Contains cilia, which move mucus.
- Found in the lining of the respiratory tract.
Surface Specialization of Surface Epithelium
-
Lateral surface specializations
- Glycocalyx - a carbohydrate coat that surrounds the cell membrane and helps with cell-to-cell recognition.
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Junctional complexes
- Zonula occludens (ZO) or tight junction - most superficial junction; forms a belt that encircles cells near their apical borders; controls intercellular passage of molecules.
- Zonula adherens (ZA) or intermediate junction - located just below the zonula occludens; also encircles individual cells completely; provides adhesion between adjacent cells.
- Macula adhaerens (MA) or Desmosome - most common junctional complex; spot-like structures that are distributed around individual cells; anchors cells together; provides strength and coherence.
- Lateral interdigitations - cytoplasmic folds on lateral surfaces of adjacent cells that intertwine to increase surface area.
- Gap junctions - not for adhesion; facilitate communication between adjacent cells by allowing for the passage of ions and small molecules.
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Basal surface specializations
- Basement membrane (BM) - non-living amorphous substance produced by epithelial cells; composed of proteoglycans, laminin, fibronectin, and Type IV collagen; provides structural support.
- Basal folds (infoldings) or caveolae - invaginations of the basal cell membrane associated with active transport.
- Hemidesmosome - half desmosome facing the basement membrane; helps to anchor epithelial cells to the basement membrane.
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Apical surface specializations
- Microvilli - long, finger-like cytoplasmic projections on the apical surface of epithelial cells, giving the epithelium a striated or brush border; increase surface area for absorption.
- Cilia - hair-like projections that beat rhythmically to move fluids or particles.
- Stereocilia - long, non-motile microvilli-like projections found in the epididymis and inner ear; functions in sensory reception.
Glands
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Glandular epithelium
- Specialized epithelium designed for secretion.
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Types of glands
- Exocrine glands - secrete products into ducts.
- Endocrine glands - secrete products directly into the bloodstream.
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Multicellular glands
- Intraepithelial glands - clusters of secretory cells in the surface epithelium.
- Secretory units - organized groups of cells that produce and secrete substances.
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Classification of glands
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According to their location
- Surface glands - located on the surface of the body or lining a body cavity.
- Invaginated glands - located deeper in the underlying connective tissue.
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According to the shape of their secretory units (exocrine glands only)
- Tubular glands - have a hollow cylinder-shaped secretory unit.
- Alveolar or acinar glands - have a pear-shaped secretory unit.
- Tubuloalveolar or tubuloacinar glands - have both tubular and alveolar secretory units.
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According to the degree of division of ducts (exocrine glands only)
- Simple glands - consist of branched or unbranched secretory units that empty into a single, undivided duct.
- Compound glands - have branched ducts.
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According to their location
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Types of simple glands
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Simple straight tubular gland
- Has a tubular secretory unit at the end of a main secretory duct.
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Simple coiled tubular gland
- Has a tubular and coiled secretory unit that empties into a straight duct.
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Simple branched tubular gland
- Has two or more tubular secretory units that converge into a single duct.
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Simple branched tubuloalveolar or tubuloacinar gland
- Has two or more tubular and alveolar secretory units that converge into a single duct.
-
Simple alveolar or acinar gland
- Has a pear-shaped secretory unit that connects with a single duct.
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Simple branched alveolar or acinar gland
- Has two or more alveolar secretory units that converge into a single duct.
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Simple straight tubular gland
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Types of compound glands
-
Compound tubular glands
- Secretory units are shaped like tubules.
- Example: intestinal gland.
- **Compound alveolar or acinar glands **
- Secretory units are shaped like alveoli or acini.
- Examples: sebaceous glands.
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Compound tubuloalveolar or tubuloacinar glands
- Secretory units are a combination of both tubular and alveolar shapes.
- Examples: salivary glands.
- Compound branched tubular glands
- Compound branched alveolar or acinar glands
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Compound tubular glands
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Modes of secretion (exocrine glands only)
- Merocrine secretion - The cells release their secretions without any loss of cytoplasm; most common method.
- Apocrine secretion - The cells release their secretions, along with a portion of their cytoplasm.
- Holocrine secretion - - The entire cell is destroyed and released along with its product.
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