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An Introduction to Tissues
Structures with discrete structural and functional properties Tissues in combination form organs, such as the heart or liver Organs can be grouped into 11 organ systems
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4-1 Four Types of Tissue Tissue
Are collections of cells and cell products that perform specific, limited functions Four types of tissue Epithelial tissue Connective tissue Muscle tissue Neural tissue
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4-1 Four Types of Tissue Epithelial Tissue Connective Tissue
Covers exposed surfaces Lines internal passageways Forms glands Connective Tissue Fills internal spaces Supports other tissues Transports materials Stores energy
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4-1 Four Types of Tissue Muscle Tissue Neural Tissue
Specialized for contraction Skeletal muscle, heart muscle, and walls of hollow organs Neural Tissue Carries electrical signals from one part of the body to another
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4-2 Epithelial Tissue Epithelia Glands
Layers of cells covering internal or external surfaces Glands Structures that produce secretions
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4-2 Epithelial Tissue Characteristics of Epithelia Form cell junctions
Polarity (apical and basal surfaces) Attachment (basement membrane or basal lamina) Avascularity Regeneration
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Figure 4-1 The Polarity of Epithelial Cells
Cilia Microvilli Apical surface Golgi apparatus Nucleus Mitochondria Basement membrane Basolateral surfaces 7
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4-2 Epithelial Tissue Functions of Epithelial Tissue
Provide Physical Protection Control Permeability Provide Sensation Produce Specialized Secretions (glandular epithelium)
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4-2 Epithelial Tissue Specializations of Epithelial Cells Polarity
Move fluids over the epithelium Move fluids through the epithelium (permeability) Produce secretions (protection and messengers) Polarity Apical surfaces Microvilli increase absorption or secretion Cilia (ciliated epithelium) move fluid Basolateral surfaces
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4-2 Epithelial Tissue Maintaining the Integrity of Epithelia
Intercellular connections Attachment to the basement membrane Epithelial maintenance and repair
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4-2 Epithelial Tissue Intercellular Connections
Support and communication CAMs (cell adhesion molecules) Intercellular cement
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4-2 Epithelial Tissue Intercellular Connections Cell junctions
Form bonds with other cells or extracellular material Tight junctions Gap junctions Desmosomes
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4-2 Epithelial Tissue Tight Junctions Between two plasma membranes
Prevents passage of water and solutes Isolates wastes in the lumen
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4-2 Epithelial Tissue Gap Junctions Allow rapid communication
Are held together by special channel proteins Allow ions to pass Coordinate contractions in heart muscle
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4-2 Epithelial Tissue Desmosomes
CAMs, dense areas, and intercellular cement Spot desmosomes Tie cells together Allow bending and twisting
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Figure 4-2 Cell Junctions
Interlocking junctional proteins Tight junction Tight junction Adhesion belt Terminal web Spot desmosome Adhesion belt Gap junctions Hemidesmosome Embedded proteins (connexons) Intermediate filaments Clear layer Basement membrane Dense layer Dense area Cell adhesion molecules (CAMs) Proteoglycans 16
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Figure 4-2a Cell Junctions
Tight junction Adhesion belt Terminal web Spot desmosome Gap junctions Hemidesmosome This is a diagrammatic view of an epithelial cell, showing the major types of intercellular connections. 17
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Figure 4-2b Cell Junctions
Interlocking junctional proteins Tight junction Terminal web Adhesion belt A tight junction is formed by the fusion of the outer layers of two plasma membranes. Tight junctions prevent the diffusion of fluids and solutes between the cells. A continuous adhesion belt lies deep to the tight junction. This belt is tied to the microfilaments of the terminal web. 18
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Figure 4-2c Cell Junctions
Embedded proteins (connexons) Gap junctions permit the free diffusion of ions and small molecules between two cells. 19
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Figure 4-2d Cell Junctions
Intermediate filaments Cell adhesion molecules (CAMs) Dense area Proteoglycans A spot desmosome ties adjacent cells together. 20
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Figure 4-2e Cell Junctions
Clear layer Basement membrane Dense layer Hemidesmosomes attach a cell to extracellular structures, such as the protein fibers in the basement membrane. 21
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4-2 Epithelial Tissue Epithelial Maintenance and Repair
Epithelia are replaced by division of germinative cells (stem cells) Near basement membrane
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4-3 Classification of Epithelia
Singular = Epithelium; Plural = Epithelia Classes of Epithelia Based on shape Squamous epithelia — thin and flat Cuboidal epithelia — square shaped Columnar epithelia — tall, slender rectangles Based on layers Simple epithelium — single layer of cells Stratified epithelium — several layers of cells
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Table 4-1 Classifying Epithelia
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Table 4-1 Classifying Epithelia
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Figure 4-3a Squamous Epithelia
Simple Squamous Epithelium LOCATIONS: Mesothelia lining ventral body cavities; endothelia lining heart and blood vessels; portions of kidney tubules (thin sections of nephron loops); inner lining of cornea; alveoli of lungs FUNCTIONS: Reduces friction; controls vessel permeability; performs absorption and secretion Cytoplasm Nucleus Connective tissue LM 238 Lining of peritoneal cavity 26
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Figure 4-3b Squamous Epithelia
Stratified Squamous Epithelium LOCATIONS: Surface of skin; lining of mouth, throat, esophagus, rectum, anus, and vagina FUNCTIONS: Provides physical protection against abrasion, pathogens, and chemical attack Squamous superficial cells Stem cells Basement membrane Connective tissue Surface of tongue LM 310 27
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Figure 4-4a Cuboidal and Transitional Epithelia
Simple Cuboidal Epithelium LOCATIONS: Glands; ducts; portions of kidney tubules; thyroid gland Connective tissue FUNCTIONS: Limited protection, secretion, absorption Nucleus Cuboidal cells Basement membrane Kidney tubule LM 650 28
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Figure 4-4b Cuboidal and Transitional Epithelia
Stratified Cuboidal Epithelium LOCATIONS: Lining of some ducts (rare) FUNCTIONS: Protection, secretion, absorption Lumen of duct Stratified cuboidal cells Basement membrane Nuclei Connective tissue Sweat gland duct LM 500 29
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Figure 4-4c Cuboidal and Transitional Epithelia
Transitional Epithelium LOCATIONS: Urinary bladder; renal pelvis; ureters FUNCTIONS: Permits expansion and recoil after stretching Epithelium (relaxed) Basement membrane Connective tissue and smooth muscle layers Empty bladder LM 400 Epithelium (stretched) Basement membrane LM 400 Connective tissue and smooth muscle layers Full bladder LM 400 Urinary bladder 30
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4-3 Classification of Epithelia
Columnar Epithelia Simple columnar epithelium Absorption and secretion Pseudostratified columnar epithelium Cilia movement Stratified columnar epithelium Protection
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Figure 4-5a Columnar Epithelia
Simple Columnar Epithelium LOCATIONS: Lining of stomach, intestine, gallbladder, uterine tubes, and collecting ducts of kidneys Microvilli Cytoplasm FUNCTIONS: Protection, secretion, absorption Nucleus Basement membrane Loose connective tissue Intestinal lining LM 350 32
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Figure 4-5b Columnar Epithelia
Pseudostratified Ciliated Columnar Epithelium LOCATIONS: Lining of nasal cavity, trachea, and bronchi; portions of male reproductive tract Cilia Cytoplasm FUNCTIONS: Protection, secretion, move mucus with cilia Nuclei Basement membrane Loose connective tissue Trachea LM 350 33
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Figure 4-5c Columnar Epithelia
Stratified Columnar Epithelium LOCATIONS: Small areas of the pharynx, epiglottis, anus, mammary glands, salivary gland ducts, and urethra Loose connective tissue Deeper basal cells FUNCTION: Protection Superficial columnar cells Lumen Lumen Cytoplasm Nuclei Basement membrane Salivary gland duct LM 175 34
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4-3 Classification of Epithelia
Glandular Epithelia Endocrine glands Release hormones Into interstitial fluid No ducts Exocrine glands Produce secretions Onto epithelial surfaces Through ducts
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4-3 Classification of Epithelia
Glandular Epithelia Modes of Secretion Merocrine secretion Apocrine secretion Holocrine secretion
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4-3 Classification of Epithelia
Merocrine Secretion Produced in Golgi apparatus Released by vesicles (exocytosis) For example, sweat glands Apocrine Secretion Released by shedding cytoplasm For example, mammary glands
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4-3 Classification of Epithelia
Holocrine Secretion Released by cells bursting, killing gland cells Gland cells replaced by stem cells For example, sebaceous glands
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Figure 4-6 Modes of Glandular Secretion
Secretory vesicle Golgi apparatus Nucleus TEM 3039 Salivary gland Breaks down Mammary gland Golgi apparatus Secretion Regrowth Hair Sebaceous gland Cells burst, releasing cytoplasmic contents Hair follicle Cells produce secretion, increasing in size Cell division replaces lost cells Stem cell 39
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Figure 4-6a Modes of Glandular Secretion
Secretory vesicle Salivary gland Golgi apparatus Nucleus Mammary gland TEM 3039 Merocrine. In merocrine secretion, secretory vesicles are discharged at the apical surface of the gland cell by exocytosis. Hair Sebaceous gland Hair follicle 40
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Figure 4-6b Modes of Glandular Secretion
Salivary gland Breaks down Mammary gland Golgi apparatus Secretion Regrowth Apocrine. Apocrine secretion involves the loss of apical cytoplasm. Inclusions, secretory vesicles, and other cytoplasmic components are shed in the process. The gland cell then undergoes growth and repair before it releases additional secretions. Hair Sebaceous gland Hair follicle 41
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Figure 4-6c Modes of Glandular Secretion
Salivary gland Cells burst, releasing cytoplasmic contents Mammary gland Cells produce secretion, increasing in size Cell division replaces lost cells Stem cell Hair Holocrine. Holocrine secretion occurs as superficial gland cells burst. Continued secretion involves the replacement of these cells through the mitotic division of underlying stem cells. Sebaceous gland Hair follicle 42
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4-3 Classification of Epithelia
Glandular Epithelia Types of Secretions Serous glands Watery secretions Mucous glands Secrete mucins Mixed exocrine glands Both serous and mucous
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4-3 Classification of Epithelia
Glandular Epithelia Gland Structure Unicellular glands Multicellular glands
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4-3 Classification of Epithelia
Gland Structure Multicellular glands Structure of the duct Simple (undivided) Compound (divided) Shape of secretory portion of the gland Tubular (tube shaped) Alveolar or acinar (blind pockets) Relationship between ducts and glandular areas Branched (several secretory areas sharing one duct)
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Figure 4-7 A Structural Classification of Exocrine Glands
SIMPLE GLANDS Duct Gland cells SIMPLE TUBULAR SIMPLE COILED TUBULAR SIMPLE BRANCHED TUBULAR Examples: Examples: Examples: • Intestinal glands • Merocrine sweat • Gastric glands glands • Mucous glands of esophagus, tongue, duodenum SIMPLE ALVEOLAR (ACINAR) SIMPLE BRANCHED ALVEOLAR Examples: Examples: • Not found in adult; a • Sebaceous (oil) stage in development of simple branched glands glands 46
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Figure 4-7 A Structural Classification of Exocrine Glands
COMPOUND GLANDS COMPOUND TUBULAR COMPOUND ALVEOLAR (ACINAR) COMPOUND TUBULOALVEOLAR Examples: Examples: Examples: • Mucous glands (in mouth) • Mammary glands • Salivary glands • Bulbo-urethral glands (in • Glands of respiratory male reproductive system) passages • Testes (seminiferous tubules) • Pancreas 47
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