Chapter 4: Tissues A Tissue is a group of closely associated cells that perform related functions and are similar in structure. Four Basic Tissue Types and Basic Functions: Epithelial covering (Chapters 4 and 5) Connective support (Chapters 4, 5, 6, and 9) Muscle movement (Chapters 10 and 11) Nervous control (Chapters 12 16 and 25) Epithelial Tissue Covers a body surface or lines a body cavity Forms parts of most glands Functions of epithelia Protection Diffusion Absorption, secretion, and ion transport Filtration Forms slippery surfaces Special Characteristics of Epithelia Special Characteristics of Epithelia Cellularity Cells separated by minimal extracellular material Specialized contacts Cells joined by special junctions Polarity Cell regions of the apical surface differ from the basal surface Supported by connective underneath Avascular but innervated Epithelia receive nutrients from underlying connective Regeneration Lost cells are quickly replaced by cell division Epithelium Connective Cilia Narrow extracellular space Nerve ending Capillary Microvilli Apical region of an cell Cell junctions Tight junction Adhesive belt Desmosome Gap junction Basal region Basal lamina Reticular fibers Figure 4.1 How Epithelia is classified 2 criteria: Classifications of Epithelia Apical surface First name of indicates number of cell layers: Simple one layer of cells on a basement Stratified more than one layer of cells with basla layer attached to basement Basal surface Simple Apical surface Squamous Last name of describes shape of cells on the apical surface: Squamous cells are wider than tall (plate-like) Cuboidal cells are as wide as tall, like cubes Columnar cells are taller than they are wide, like columns Basal surface Stratified (a) Classification based on number of cell layers Cuboidal Columnar (b) Classification based on cell shape Figure 4.2 1
Simple Squamous Epithelium Simple Cuboidal Epithelium (a) Simple squamous epithelium (b) Simple cuboidal epithelium Description: Single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of the epithelia. Description: Single layer of cubelike cells with large, spherical central nuclei. Function: Allows passage of materials by diffusion and filtration in sites where protection is not important; secretes lubricating substances in serosae. Location: Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; lining of ventral body cavity (serosae). Air sacs of lung Nuclei of squamous cells Function: Secretion and absorption. Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface. Simple cuboidal cells Connective Photomicrograph: Simple squamous epithelium forming part of the alveolar (air sac) walls (200 ). Photomicrograph: Simple cuboidal epithelium in kidney tubules (430 ). Figure 4.3a Figure 4.3b Simple Columnar Epithelium (c) Simple columnar epithelium Description: Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucussecreting unicellular glands (goblet cells). Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action. Location: Nonciliated type lines most of the digestive tract (stomach to anal canal), gallbladder, and excretory ducts of some glands; ciliated variety lines small bronchi, uterine tubes, and some regions of the uterus. Photomicrograph: Simple columnar epithelium of the stomach mucosa (1150 ). Simple columnar cell Figure 4.3c Epithelial s. Simple columnar epithelium Description: Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucus-secreting unicellular glands (goblet cells). Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action. Location: Nonciliated type lines most of the digestive tract (stomach to anal canal), gallbladder, and excretory ducts of some glands; ciliated variety lines small bronchi, uterine tubes, and some regions of the uterus. Photomicrograph: Simple columnar epithelium of the small intestine (650 ). Microvilli Goblet cell Simple columnar cell Figure 4.3c Pseudostratified Columnar Epithelium Pseudostratified Columnar Epithelium Description All cells originate at basement Only tall cells reach the apical surface May contain goblet cells and bear cilia Nuclei lie at varying heights within cells Gives false impression of stratification Function secretion of mucus; propulsion of mucus by cilia Locations Nonciliated type Ducts of male reproductive tubes Ducts of large glands Ciliated variety Lines trachea and most of upper respiratory tract 2
Figure 4.3d Epithelial s. Pseudostratified columnar epithelium Description: Single layer of cells of different heights, some not reaching the free surface; nuclei seen at different levels; may contain mucus-secreting goblet cells and bear cilia. Cilia Goblet cell Pseudostratified Ciliated Columnar Epithelium(a type of simple epithelia) (d) Pseudostratified columnar epithelium Description: Single layer of cells of differing heights, some not reaching the free surface; nuclei seen at different levels; may contain mucus-secreting goblet cells and bear cilia. Cilia Mucus of goblet cell Function: Secretion, particularly of mucus; propulsion of mucus by ciliary action. Location: Nonciliated type in male s sperm-carrying ducts and ducts of large glands; ciliated variety lines the trachea, most of the upper respiratory tract. Trachea Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (780 ). Pseudostratified layer Function: Secretion, particularly of mucus; propulsion of mucus by ciliary action. Location: Nonciliated type in male s sperm-carrying ducts and ducts of large glands; ciliated variety lines the trachea, most of the upper respiratory tract. Trachea Pseudostratified layer Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (780 ). Figure 4.3d Stratified Epithelia Properties Contain two or more layers of cells Regenerate from below (basal layer) Major role is protection Named according to shape of cells at apical layer Stratified Squamous Epithelium Description Many layers of cells are squamous in shape Deeper layers of cells appear cuboidal or columnar Thickest Adapted for protection from abrasion Stratified Squamous Epithelium Two types keratinized and non-keratinized Keratinized Location epidermis (superficial layer of skin) Contains the protective protein keratin Waterproof Surface cells are dead and full of keratin Non-keratinized Forms moist lining of body openings Function Protects underlying s in areas subject to abrasion Location Keratinized forms epidermis Nonkeratinized forms lining of mucous s Esophagus Mouth Anus Vagina Urethra Stratified Squamous Epithelium (e) Stratified squamous epithelium Description: Thick composed of several cell layers; basal cells are cuboidal or columnar and metabolically active; surface cells are flattened (squamous); in the keratinized type, the surface cells are full of keratin and dead; basal cells are active in mitosis and produce the cells of the more superficial Stratified squamous layers. epithelium Nuclei Function: Protects underlying s in areas subjected to abrasion. Location: Nonkeratinized type forms the Connective moist linings of the esophagus, mouth, and vagina; keratinized variety forms the epidermis of the skin, a dry. Photomicrograph: Stratified squamous epithelium lining the esophagus (430 ). Figure 4.3e 3
Stratified Cuboidal Epithelium Stratified Columnar Epithelium (f) Stratified cuboidal epithelium (g) Stratified columnar epithelium Description: Generally two layers of cubelike cells. Description: Several cell layers; basal cells usually cuboidal; superficial cells elongated and columnar. Function: Protection Cuboidal cells Location: Largest ducts of sweat glands, mammary glands, and salivary glands. Duct lumen Function: Protection; secretion. Location: Rare in the body; small amounts in male urethra and in large ducts of some glands. Stratified columnar epithelium Photomicrograph: Stratified cuboidal epithelium forming a salivary gland duct (285 ). Urethra Photomicrograph: Stratified columnar epithelium lining of the male urethra (315 ). Underlying connective Figure 4.3f Figure 4.3g Transitional Epithelium (a type of stratified [layed] epithelium) (h) Transitional epithelium Description: Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamous-like, depending on degree of organ stretch. PowerPoint Lecture Slides prepared by Leslie Hendon University of Alabama, Birmingham C H A P T E R Transitional epithelium Part 1 Function: Stretches readily and permits distension of urinary organ by contained urine. Location: Lines the ureters, bladder, and part of the urethra. Connective Photomicrograph: Transitional epithelium lining the bladder, relaxed state (390 ); note the bulbous, or rounded, appearance of the cells at the surface; these cells flatten and become elongated when the bladder is filled with urine. Figure 4.3h Glands (a special type of epithelium) 2 general types: endocrine and exocrine. Endocrine glands Ductless glands that secrete directly into surrounding fluid Produce messenger molecules called hormones Covered in detail in chapter 17 Exocrine glands Ducts carry products of exocrine glands to surface Include the following diverse glands Mucus-secreting glands Sweat and oil glands Salivary glands Liver and pancreas Unicellular Exocrine Glands (The Goblet Cell) Goblet cells produce mucin Mucin + water! mucus Protects and lubricates many internal body surfaces Goblet cells are a unicellular exocrine gland Multicellular Exocrine Glands Have two basic parts: Epithelium-walled duct Secretory unit Classified by structure of duct Simple Compound Categorized by secretory unit Tubular Alveolar Tubuloalveolar 4
Goblet Cells unicellular exocrine gland Types of Multicellular Exocrine Glands Microvilli Secretory vesicles containing mucin Rough ER Golgi apparatus Nucleus (a) (b) Figure 4.4 Figure 4.5 Lateral Surface Features Cell Junctions Factors binding cells together Adhesion proteins link plasma s of adjacent cells Contours of adjacent cell s Special cell junctions Lateral Surface Features Cell Junctions Tight junctions (zona occludens) close off intercellular space Found at apical region of most s types Some proteins in plasma of adjacent cells are fused Prevent certain molecules from passing between cells of Tight Junction Lateral Surface Features Cell Junctions Interlocking junctional proteins Intercellular space Adhesive belt junctions (zonula adherens) anchoring junction Trans linker proteins attach to actin microfilaments of the cytoskeleton and bind adjacent cells With tight junctions, these linker proteins form the tight junctional complex around apical lateral borders of s (a) Tight junctions: Impermeable junctions prevent molecules from passing through the intercellular space. Figure 4.6a 5
Lateral Surface Features Lateral Surface Features Desmosomes main junctions for binding cells together Scattered along abutting sides of adjacent cells Cytoplasmic side of each plasma has a plaque Plaques are joined by linker proteins Desmosomes (continued) Intermediate filaments extend across the cytoplasm and anchor at desmosomes on opposite side of the cell Are common in cardiac muscle and Desmosome Intermediate filament (keratin) Intercellular space Plaque Linker glycoproteins (cadherins) (b) Desmosomes: Anchoring junctions bind adjacent cells together and help form an internal tension-reducing network of fibers. Figure 4.6b Lateral Surface Features Cell Junctions Gap junctions passageway between two adjacent cells These let small molecules move directly between neighboring cells Cells are connected by hollow cylinders of protein Function in intercellular communication Gap Junction Intercellular space Channel between cells (connexon) (c) Gap junctions: Communicating junctions allow ions and small molecules to pass from one cell to the next for intercellular communication. Figure 4.6c Basal Feature: The Basal Lamina Noncellular supporting sheet between the ET and the CT deep to it Consists of proteins secreted by ET cells Functions Acts as a selective filter, determining which molecules from capillaries enter the epithelium Acts as scaffolding along which regenerating ET cells can migrate Basal lamina and reticular layers of the underlying CT deep to it form the basement 6
Epithelial Surface Features Apical surface features Microvilli fingerlike extensions of plasma Abundant in ET of small intestine and kidney Maximize surface area across which small molecules enter or leave Act as stiff knobs that resist abrasion Microvillus Actin filaments Epithelial Surface Features Apical surface features Cilia whiplike, highly motile extensions of apical surface s Contain a core of microtubules held together by cross-linking and radial proteins Microtubules arranged in pairs called doublets Movement is generated when adjacent doublets grip each other with the motor protein dynein Cilia originate as microtubules assemble around centrioles Figure 4.7 A Cilium Connective Tissue Outer microtubule doublet Central microtubule Dynein arms Cross-linking proteins inside outer doublets Radial spoke Plasma The doublets also have attached motor proteins, the dynein arms. The outer microtubule doublets and the two central microtubules are held together by cross-linking proteins and radial spokes. Cilium Power, or Recovery stroke, when propulsive, cilium is returning to stroke its initial position 1 2 3 4 5 6 7 (b) Phases of ciliary motion Layer of mucus Cell surface Most diverse and abundant Main classes Connective proper Cartilage Bone Blood Cells separated by a large amount of extracellular matrix Extracellular matrix is composed of ground substance and fibers Common embryonic origin mesenchyme Basal body (centriole) (a) Structure of a cilium (c) Traveling wave created by the activity of many cilia acting together propels mucus across cell surfaces. Figure 4.8 Classes of Connective Tissue Structural Elements of Connective Tissue (a) Embryonic connective : mesenchyme Description: Embryonic connective Mesenchymal ; gel-like ground substance cell containing fibers; star-shaped mesenchymal cells. Ground substance Function: Gives rise to all other connective types. Location: Primarily in embryo. Fibers Photomicrograph: Mesenchymal, an embryonic connective (600 ); the clear-appearing background is the fluid ground substance of the matrix; notice the fine, sparse fibers. Connective s differ in structural properties Differences in types of cells Differences in composition of extracellular matrix (fibers and ground substance [dissolved or suspended molecules]). However, connective s all share structural elements Loose areolar connective This C.T. will illustrate connective features: Cells, Fibers, and Ground substance Figure 4.10a 7
Structural Elements of Connective Tissue Cells primary cell type of connective produces matrix Fibroblasts Make protein subunits Secrete molecules that form the ground substance Chondroblasts secrete matrix in cartilage Osteoblasts secrete matrix in bone Blood cells are an exception Do not produce matrix Areolar connective contains Fat cells White blood cells Mast cells Structural Elements of Connective Tissue Extracellular matrix is composed of fibers and ground substance Fibers function in support and have unique properties Types: Collagen fibers strongest; resist tension Reticular fibers bundles of special type of collagen Cover and support structures Elastic fibers contain elastin Recoil after stretching Structural Elements of Connective Tissue Ground substance Is produced by primary cell type of the Is usually gel-like Cushions and protects body structures (can be spongy ) Holds fluid Blood is an exception Plasma is not produced by blood cells Structural Elements of Connective Tissue Cell types Extracellular matrix Macrophage Ground substance Fibers Collagen fiber Elastic fiber Fibroblast Reticular fiber Lymphocyte Fat cell Capillary Mast cell Neutrophil Figure 4.9 Connective Tissue Proper Table 4.2 Comparison of Classes of Connective Tissues (1 of 2) Has two subclasses Loose connective Areolar, adipose, and reticular Dense connective Dense irregular, dense regular, and elastic 8
Table 4.2 Comparison of Classes of Connective Tissues (2 of 2) Areolar Connective Tissue A Model Connective Tissue Areolar connective Underlies Surrounds small nerves and blood vessels Has structures and functions shared by other CT Borders all other s in the body Major Functions of Connective Tissue Areolar Connective Tissue Structure of areolar connective reflects its functions Support and binding of other s Holding body fluids (interstitial fluid! lymph) Defending body against infection Storing nutrients as fat Fibers provide support Three types of protein fibers in extracellular matrix Collagen fibers Reticular fibers Elastic fibers Fibroblasts produce these fibers Areolar Connective Tissue Description Gel-like matrix with all three fiber types Cells of areolar CT Fibroblasts, macrophages, mast cells, and white blood cells Function Wraps and cushions organs Holds and conveys fluid (interstitial fluid) Important role in inflammation Locations Widely distributed under epithelia Packages organs Surrounds capillaries Areolar Connective Tissue (b) Connective proper: loose connective, areolar Description: Gel-like matrix with all three fiber types; cells: fibroblasts, macrophages, mast cells, and some Elastic white blood cells. fibers Function: Wraps and cushions organs; its macrophages phagocytize bacteria; Collagen plays important role in inflammation; fibers holds and conveys fluid. Location: Widely distributed under Fibroblast epithelia of body, e.g., forms lamina nuclei propria of mucous s; packages organs; surrounds capillaries. Epithelium Photomicrograph: Areolar connective, a soft packaging of the body (360 ). Lamina propria Figure 4.10b 9
Areolar Connective Tissue Areolar Connective Tissue Tissue fluid (interstitial fluid) Watery fluid occupying extracellular matrix Tissue fluid derives from blood Ground substance Viscous, spongy part of extracellular matrix Consists of sugar and protein molecules Made and secreted by fibroblasts Main battlefield in fight against infection Defenders gather at infection sites Macrophages Plasma cells Mast cells White blood cells Neutrophils, lymphocytes, and eosinophils 10