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Transcript
Chapter 5 *Lecture PowerPoint Histology *See separate FlexArt PowerPoint slides for all figures and tables preinserted into PowerPoint without notes. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Introduction • There are 50 trillion cells of 200 different cell types • Four broad categories of tissues – Epithelial tissue – Connective tissue – Nervous tissue – Muscular tissue • Organ—structure with discrete boundaries that is composed of two or more tissue types • Histology (microscopic anatomy)—the study of tissues and how they are arranged into organs 5-2 The Study of Tissues • Expected Learning Outcomes – Name the four primary classes into which all adult tissues are classified. – Name the three embryonic germ layers and some adult tissues derived from each. – Visualize the three-dimensional shape of a structure from a two-dimensional tissue section. 5-3 The Primary Tissue Classes • Tissue—a group of similar cells and cell products that arise from the same region of the embryo and work together to perform a specific structural or physiological role in an organ • Four primary tissues differ from one another, as follows: – Types and functions of their cells – Characteristics of the matrix (extracellular material) – Relative amount of space occupied by cells versus matrix 5-4 The Primary Tissue Classes • Matrix (extracellular material) is composed of: – Fibrous proteins – Clear gel called ground substance, tissue fluid, extracellular fluid (ECF), interstitial fluid, or tissue gel 5-5 Embryonic Tissues • Human development begins as single cell, the fertilized egg – Divides to produce scores of identical, smaller cells – First tissues appear when these cells start to organize themselves into layers; First two, and then three strata 5-6 Embryonic Tissues • Three primary germ layers – Ectoderm (outer) • Gives rise to epidermis and nervous system – Endoderm (inner) • Gives rise to mucous membrane lining digestive and respiratory tracts, digestive glands, among other things – Mesoderm (middle) becomes gelatinous tissue called mesenchyme • Wispy collagen fibers and fibroblasts in gel matrix • Gives rise to muscle, bone, blood 5-7 Interpreting Tissue Sections • Preparation of histological specimens – Fixative prevents decay (formalin) – Histological sections: tissue is sliced into thin sections one or two cells thick – Stains: tissue is mounted on slides and artificially colored with histological stain • Stains bind to different cellular components • Sectioning reduces three-dimensional structure to two-dimensional slice 5-8 Interpreting Tissue Sections Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Sectioning a cell with a centrally located nucleus • Some slices miss the cell nucleus • In some, the nucleus is smaller (a) Figure 5.1a 5-9 Interpreting Tissue Sections Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Cross section of blood vessel, gut, or other tubular organ • Longitudinal section of a sweat gland—notice what a single slice could look like Figure 5.1b,c (b) (c) 5-10 Longitudinal, Cross, Oblique Sections Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Longitudinal sections • Longitudinal section (l.s.) – Tissue cut along long direction of organ Cross sections • Cross section (c.s. or x.s.) or transverse section (t.s.) – Tissue cut perpendicular to length of organ • Oblique section Oblique sections – Tissue cut at angle between cross and longitudinal sections Figure 5.2 5-11 Interpreting Tissue Sections • Smear—tissue is rubbed or spread across the slide – Spinal cord or blood • Spread—cobwebby tissue is laid out on a slide – Areolar tissue 5-12 Epithelial Tissue • Expected Learning Outcomes – Describe the properties that distinguish epithelium from other tissue classes. – List and classify eight types of epithelium, distinguish them from each other, and state where each type can be found in the body. – Explain how the structural differences between epithelia relate to their functional differences. – Visually recognize each epithelial type from specimens or photographs. 5-13 Epithelial Tissue • Consists of a flat sheet of closely adhering cells • One or more cells thick • Upper surface usually exposed to the environment or an internal space in the body • Covers body surface and lines body cavities • Forms the external and internal linings of many organs 5-14 Epithelial Tissue • Constitutes most glands • Extracellular material is so thin it is not visible with a light microscope • Epithelia allow no room for blood vessels • Lie on a layer of loose connective tissue and depend on its blood vessels for nourishment and waste removal 5-15 Epithelial Tissue • Basement membrane—layer between an epithelium and the underlying connective tissue – Collagen – Laminin and fibronectin adhesive glycoproteins – Heparin sulfate: large protein–carbohydrate complex • Anchors the epithelium to the connective tissue below it • Basal surface—surface of an epithelial cell that faces the basement membrane • Apical surface—surface of an epithelial cell that faces away from the basement membrane 5-16 Epithelial Tissue • Stratified epithelium • Simple epithelium – Contains one layer of cells – Named by shape of cells – All cells touch the basement membrane – Contains more than one layer – Named by shape of apical cells – Some cells rest on top of others and do not touch basement membrane Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Classes of epithelium Simple (b) Pseudostratified columnar Stratified Cell shapes Squamous Cuboidal Figure 5.3 Columnar 5-17 Simple Epithelia • Four types of simple epithelia • Three named for their cell shapes – Simple squamous (thin, scaly cells) – Simple cuboidal (square or round cells) – Simple columnar (tall, narrow cells) 5-18 Simple Epithelia • Fourth type – Pseudostratified columnar • • • • Not all cells reach the free surface Shorter cells are covered over by taller ones Looks stratified Every cell reaches the basement membrane • Goblet cells—wineglass-shaped mucus-secreting cells in simple columnar and pseudostratified epithelia 5-19 Simple Epithelia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Squamous epithelial cells Nuclei of smooth muscle Basement membrane Figure 5.4a (a) (b) a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer • Simple squamous epithelium • • • • Figure 5.4b,i Single row of thin cells Permits rapid diffusion or transport of substances Secretes serous fluid Alveoli, glomeruli, endothelium, and serosa 5-20 Simple Epithelia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lumen of kidney tubule (a) Cuboidal epithelial cells Basement membrane (b) Figure 5.5a a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer • Simple cuboidal epithelium Figure 5.5b,i – Single layer of square or round cells – Absorption and secretion, mucus production and movement – Liver, thyroid, mammary and salivary glands, bronchioles, and kidney tubules 5-21 Simple Epithelia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brush border (microvilli) (a) Connective tissue Basement membrane Goblet Nuclei cell Columnar cells (b) Figure 5.6a • Simple columnar epithelium a: © Lester V. Bergman Figure 5.6b,i – Single row of tall, narrow cells – Oval nuclei in basal half of cell – Brush border of microvilli, ciliated in some organs, may possess goblet cells – Absorption and secretion; secretion of mucus – Lining of GI tract, uterus, kidney, and uterine tubes 5-22 Pseudostratified Epithelium Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cilia (a) Figure 5.7a Basement membrane Basal cells Goblet cell (b) a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer • Pseudostratified epithelium Figure 5.7b,i – Looks multilayered; some not reaching free surface; all touch basement membrane – Nuclei at several layers – With cilia and goblet cells – Secretes and propels mucus – Respiratory tract and portions of male urethra 5-23 Stratified Epithelia • Range from 2 to 20 or more layers of cells • Some cells resting directly on others – Only the deepest layer attaches to the basement membrane • Three stratified epithelia are named for the shapes of their surface cells – Stratified squamous – Stratified cuboidal – Stratified columnar (rare) • Fourth type – Transitional epithelium 5-24 Stratified Epithelia • Most widespread epithelium in the body • Deepest layers undergo continuous mitosis – Their daughter cells push toward the surface and become flatter as they migrate farther upward – Finally die and flake off—exfoliation or desquamation • Two kinds of stratified squamous epithelia – Keratinized—found on skin surface, abrasion resistant – Nonkeratinized—lacks surface layer of dead cells 5-25 Stratified Epithelia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dead squamous cells Living epithelial cells Dense irregular connective tissue Areolar tissue (a) Figure 5.8a (b) a: © The McGraw-Hill Companies, Inc./Joe DeGrandis, photographer • Keratinized stratified squamous Figure 5.8b,i – Multiple cell layers with cells becoming flat and scaly toward surface – Epidermis; palms and soles heavily keratinized – Resists abrasion; retards water loss through skin; resists penetration by pathogenic organisms 5-26 Stratified Epithelia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Living epithelial cells (a) Figure 5.9a Connective tissue (b) a: © Ed Reschke • Nonkeratinized stratified squamous Figure 5.9b,i – Same as keratinized epithelium without the surface layer of dead cells – Tongue, oral mucosa, esophagus, and vagina – Resists abrasion and penetration of pathogens 5-27 Stratified Epithelia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cuboidal cells Epithelium Connective tissue (b) (a) Figure 5.10a a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer • Stratified cuboidal epithelium Figure 5.10b,i – Two or more cell layers; surface cells square or round – Secretes sweat; sperm production and ovarian hormone production – Sweat gland ducts; ovarian follicles and seminiferous tubules 5-28 Stratified Epithelia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Basement membrane (a) Figure 5.11a Connective tissue Binucleate epithelial cell (b) a: Johnny R. Howze Figure 5.11b,i • Transitional epithelium – Multilayered epithelium surface cells that change from round to flat when stretched – Allows for filling of urinary tract – Ureter and bladder 5-29 Connective Tissue • Expected Learning Outcomes – Describe the properties that most connective tissues have in common. – Discuss the types of cells found in connective tissue. – Explain what the matrix of a connective tissue is and describe its components. – Name and classify 10 types of connective tissue, describe their cellular components and matrix, and explain what distinguishes them from each other. – Visually recognize each connective tissue type from specimens or photographs. 5-30 Connective Tissue: Overview • Connective tissue—a type of tissue in which cells usually occupy less space than the extracellular material • Binds organs to each other, supports and protects organs • Most cells of connective tissue are not in direct contact with each other – Separated by extracellular material • Highly vascular—richly supplied with blood vessels • Most abundant, widely distributed, and histologically variable of the primary tissues 5-31 Connective Tissue: Overview • • • • • • • • Binding of organs—tendons and ligaments Support—bones and cartilage Physical protection—cranium, ribs, sternum Immune protection—white blood cells attack foreign invaders Movement—bones provide lever system Storage—fat, calcium, phosphorus Heat production—metabolism of brown fat in infants Transport—blood 5-32 Fibrous Connective Tissue • Cells – Fibroblasts produce fibers and ground substance – Macrophages phagocytize foreign material and activate immune system when they sense foreign matter (antigen) • Arise from white blood cells called monocytes – Leukocytes, or white blood cells • Neutrophils wander about attacking bacteria • Lymphocytes react against bacteria, toxins, and other foreign material – Plasma cells synthesize disease-fighting antibodies • Arise from lymphocytes – Mast cells are found alongside blood vessels • Secrete heparin to inhibit clotting • Secrete histamine to dilate blood vessels – Adipocytes store triglycerides (fat molecules) 5-33 Fibrous Connective Tissue • Fibers – Collagenous fibers • • • • Most abundant of the body’s proteins—25% Tough, flexible, and resist stretching Tendons, ligaments, and deep layer of the skin are mostly collagen Less visible in matrix of cartilage and bone – Reticular fibers • Thin collagen fibers coated with glycoprotein • Form framework of such organs as spleen and lymph nodes – Elastic fibers • • • • • Thinner than collagenous fibers Branch and rejoin each other Made of protein called elastin Allows stretch and recoil Yellow fibers—fresh elastic fibers 5-34 Fibrous Connective Tissue • Ground substance – Usually a gelatinous to rubbery consistency resulting from three classes of large molecules – Glycosaminoglycans (GAG) • Long polysaccharide composed of unusual disaccharides called amino sugars and uronic acid • Play important role of regulating water and electrolyte balance in the tissues • Chondroitin sulfate—most abundant GAG – In blood vessels and bone – Responsible for stiffness of cartilage • Hyaluronic acid—viscous, slippery substance that forms an effective lubricant in joints and constitutes much of the vitreous body of the eyeball 5-35 Fibrous Connective Tissue Cont. – Proteoglycan • Gigantic molecule shaped like a test-tube brush • Forms thick colloids that create strong structural bond between cells and extracellular macromolecules; holds tissues together – Adhesive glycoproteins—bind components of tissues together 5-36 Types of Fibrous Connective Tissue Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Loose connective tissue – Much gel-like ground substance between cells – Types Tendons • Areolar • Reticular • Dense connective tissue – Fibers fill spaces between cells – Types vary in fiber orientation • Dense regular connective tissue • Dense irregular connective tissue © The McGraw-Hill Companies, Inc./Rebecca Gray, photographer/Don Kincaid, dissections Figure 5.13 5-37 Types of Fibrous Connective Tissue • Loosely organized fibers, abundant blood vessels, and a lot of seemingly empty space • Possess all six cell types • Fibers run in random directions – Mostly collagenous, but elastic and reticular also present • Found in tissue sections from almost every part of the body – Surrounds blood vessels and nerves • Nearly every epithelium rests on a layer of areolar tissue – Blood vessels provide nutrition to epithelium and waste removal – Ready supply of infection-fighting leukocytes that move about freely in areolar tissue 5-38 Types of Fibrous Connective Tissue Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ground substance (a) Figure 5.14a Elastic fibers Collagenous fibers Fibroblasts (b) a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer • Areolar tissue Figure 5.14b,i – Loosely organized fibers, abundant blood vessels, and a lot of seemingly empty space – Underlies all epithelia, in serous membranes, between muscles, passageways for nerves and blood vessels 5-39 Types of Fibrous Connective Tissue Leukocytes Reticular fibers Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Figure 5.15a (b) a: The McGraw-Hill Companies, Inc./Al Telser, photographer • Reticular tissue Figure 5.15b,i – Mesh of reticular fibers and fibroblasts – Forms supportive stroma (framework) for lymphatic organs – Found in lymph nodes, spleen, thymus, and bone marrow 5-40 Types of Fibrous Connective Tissue Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Collagen fibers (a) Figure 5.16a Ground substance Fibroblast nuclei (b) a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer • Dense regular connective tissue Figure 5.16b,i – Densely packed, parallel collagen fibers – Compressed fibroblast nuclei – Elastic tissue/fibers, wavy sheets • Tendons attach muscles to bones and ligaments hold bones together 5-41 Types of Fibrous Connective Tissue Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bundles of Gland collagen fibers ducts (a) Figure 5.17a Fibroblast Ground nuclei substance (b) a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer • Dense irregular connective tissue Figure 5.17b,i – Densely packed, randomly arranged, collagen fibers and few visible cells – Withstands unpredictable stresses – Deeper layer of skin; capsules around organs 5-42 Adipose Tissue • Adipose tissue (fat)—tissue in which adipocytes are the dominant cell type • Space between adipocytes is occupied by areolar tissue, reticular tissue, and blood capillaries • Fat is the body’s primary energy reservoir – The quantity of stored triglyceride and the number of adipocytes are quite stable in a person – Fat is recycled continuously to prevent stagnation – New triglycerides are constantly synthesized and stored – Old triglycerides are hydrolyzed and released into circulation 5-43 Adipose Tissue • Provides thermal insulation • Anchors and cushions organs such as eyeballs, kidneys • Contributes to body contours—female breast and hips – On average, women have more fat than men – Too little fat can reduce female fertility • Most adult fat is called white fat • Brown fat—in fetuses, infants, children—a heatgenerating tissue 5-44 Adipose Tissue Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Blood vessel (a) Figure 5.18a Adipocyte nucleus Lipid in adipocyte (b) a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer Figure 5.18b,i • Empty-looking cells with thin margins; nucleus pressed against cell membrane • Energy storage, insulation, cushioning – Subcutaneous fat and organ packing – Brown fat (hibernating animals) produces heat 5-45 Cartilage • Supportive connective tissue with flexible, rubbery matrix • Gives shape to ear, tip of nose, and larynx • Chondroblasts produce matrix and surround themselves until they become trapped in little cavities (lacunae) • Chondrocytes—cartilage cells in lacunae • Perichondrium—sheath of dense irregular connective tissue that surrounds elastic and most hyaline cartilage (not articular cartilage) – Contains a reserve population of chondroblasts that contribute to cartilage growth throughout life 5-46 Cartilage • No blood vessels – Diffusion brings nutrients and removes wastes – Heals slowly • Matrix rich in chondroitin sulfate and contains collagen fibers • Types of cartilage vary with fiber types – Hyaline cartilage, fibrocartilage, and elastic cartilage 5-47 Cartilage Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Matrix (a) Figure 5.19a Cell nest Perichondrium Lacunae Chondrocytes (b) a: © Ed Reschke • Hyaline cartilage Figure 5.19b,i – Clear, glassy microscopic appearance because of unusual fineness of the collagen fibers – Usually covered by perichondrium • Articular cartilage, costal cartilage, trachea, larynx, fetal skeleton • Eases joint movement, holds airway open, moves vocal cords 5-48 during speech Cartilage Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Perichondrium (a) Elastic fibers Lacunae Chondrocytes (b) Figure 5.20a a: © Ed Reschke • Elastic cartilage Figure 5.20b,i – Cartilage containing elastic fibers • Covered with perichondrium • Provides flexible, elastic support – External ear and epiglottis 5-49 Cartilage Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Collagen fibers (a) Figure 5.21a Chondrocytes (b) a: Dr. Alvin Telser • Fibrocartilage Figure 5.21b,i – Cartilage containing large, coarse bundles of collagen fibers • Never has perichondrium • Resists compression and absorbs shock – Pubic symphysis, menisci, and intervertebral discs 5-50 Bone • The term bone has two meanings: – An organ of the body: femur, mandible; composed of multiple tissue types – Bone tissue (osseous tissue) makes up most of the mass of bone • Two forms of osseous tissue – Spongy bone: spongy in appearance • Delicate struts of bone: trabeculae • Covered by compact bone • Found in heads of long bones and in middle of flat bones such as the sternum – Compact bone: denser, calcified tissue with no visible spaces • More complex arrangement • Cells and matrix surround vertically oriented blood vessels in long bones 5-51 Bone Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Concentric Central lamellae Lacunae Canaliculi of osteon canal Osteon (a) (b) Figure 5.22a a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer Figure 5.22b,i • Compact bone is arranged in cylinders that surround central (haversian or osteonic) canals that run longitudinally through shafts of long bones – Blood vessels and nerves travel through central canal • Bone matrix deposited in concentric lamella – Onionlike layers around each central canal 5-52 Bone • Osteon—central canal and its surrounding lamellae • Osteocytes—mature bone cells that occupy the lacunae • Canaliculi—delicate canals that radiate from each lacuna to its neighbors, and allow osteocytes to contact each other • Periosteum—tough fibrous connective tissue covering of the bone as a whole 5-53 Blood Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Fluid connective tissue Platelets Neutrophils Lymphocyte Erythrocytes Monocyte • Transports cells and dissolved matter from place to place • Plasma—blood’s liquid ground substance • Formed elements—cells and cell fragments – Erythrocytes—red blood cells: transport O2 and CO2 – Leukocytes—white blood cells: defense against infection and other diseases – Platelets—cell fragments involved in clotting and other mechanisms (b) Figure 5.23b,i 5-54 Nervous and Muscular Tissues— Excitable Tissues • Expected Learning Outcomes – Explain what distinguishes excitable tissues from other tissues. – Name the cell types that compose nervous tissue. – Identify the major parts of a nerve cell. – Visually recognize nervous tissue from specimens or photographs. – Name the three kinds of muscular tissue and describe the differences between them. – Visually identify any type of muscular tissue from specimens or photographs. 5-55 Nervous and Muscular Tissues— Excitable Tissues • Excitability—a characteristic of all living cells – Developed to highest degree in nervous and muscular tissues • Membrane potential—electrical charge difference (voltage) that occurs across the plasma membranes is the basis for their excitation – Respond quickly to outside stimulus by means of changes in membrane potential – Nerves: changes result in rapid transmission of signals to other cells – Muscles: changes result in contraction, shortening of the cell 5-56 Nervous Tissue Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nuclei of glial cells Axon Neurosoma Dendrites • Nervous tissue—specialized for communication by electrical and chemical signals • Consists of neurons (nerve cells) – Detect stimuli – Respond quickly – Transmit coded information rapidly to other cells (b) • Neuroglia (glial) – Protect and assist neurons – ―Housekeepers‖ of nervous system Figure 5.24b,i 5-57 Nervous Tissue Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Neuron parts Nuclei of glial cells Axon Neurosoma Dendrites – Neurosoma (cell body) • Houses nucleus and other organelles • Cell’s center of genetic control and protein synthesis – Dendrites • Multiple short, branched processes • Receive signals from other cells • Transmit messages to neurosoma – Axon (nerve fiber) • Sends outgoing signals to other cells • Can be more than a meter long (b) Figure 5.24b,i 5-58 Muscular Tissue • Muscular tissue—elongated cells that are specialized to contract in response to stimulation • Primary job is to exert physical force on other tissues and organs • Creates movements involved in body and limb movement, digestion, waste elimination, breathing, speech, and blood circulation • Important source of body heat • Three types of muscle: skeletal, cardiac, and smooth 5-59 Muscular Tissue • Skeletal muscle – Long, threadlike cells called muscle fibers • Most attach to bone • Exceptions: in tongue, upper esophagus, facial muscles, some sphincter muscles (ringlike or cufflike muscles that open and close body passages) • Contains multiple nuclei adjacent to plasma membrane • Striations—alternating dark and light bands • Voluntary—conscious control over skeletal muscles Nuclei Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Striations Muscle fiber (b) Figure 5.25a a: © Ed Reschke Figure 5.25b,i 5-60 Muscular Tissue • Cardiac muscle – Limited to the heart • Myocytes or cardiocytes are shorter, branched, and notched at ends • Contain one centrally located nucleus surrounded by lightstaining glycogen • Intercalated discs join cardiocytes end to end – Provide electrical and mechanical connection • Striated and involuntary (not under conscious control) Intercalated discs Striations Glycogen Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) (b) Figure 5.26a © Ed Reschke Figure 5.26b,i 5-61 Muscular Tissue Nuclei Muscle cells Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) (b) Figure 5.27a a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer • Smooth muscle Figure 5.27b,i – Lacks striations and is involuntary • Relatively short, fusiform cells (thick in middle, tapered at ends) • One centrally located nucleus • Visceral muscle—forms layers of digestive, respiratory, and urinary tract: propels contents through an organ, regulates diameter of blood vessels 5-62 Cell Junctions, Glands, and Membranes • Expected Learning Outcomes – Describe the junctions that hold cells and tissues together. – Describe or define different types of glands. – Describe the typical anatomy of a gland. – Name and compare different modes of glandular secretion. – Describe the way tissues are organized to form the body’s membranes. – Name and describe the major types of membranes in the body. 5-63 Cell Junctions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intercellular space Plasma membrane Cell-adhesion proteins (a) Tight junction Intercellular space Cell-adhesion proteins Plaque Intermediate filaments of cytoskeleton (b) Desmosome Proteins Connexon Pore (c) Gap junction Basement membrane (d) Hemidesmosome Figure 5.28, • Cell junctions—connections between one cell and another • All cells (except blood and metastatic cancer cells) are anchored to each other or their matrix by intercellular junctions • Resist stress and communicate with each other 5-64 Tight Junctions • Tight junction—a region in which adjacent cells are bound together by fusion of the outer phospholipid layer of their plasma membranes – In epithelia, forms a zone that completely encircles each cell near its apical pole – Seals off intercellular space – Makes it impossible for substance to pass between cells Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intercellular space Plasma membrane Cell-adhesion proteins (a) Tight junction Intercellular space Cell-adhesion proteins Plaque Intermediate filaments of cytoskeleton (b) Desmosome Proteins Connexon Figure 5.28 Pore (c) Gap junction Basement membrane (d) Hemidesmosome 5-65 Desmosomes • Desmosomes—patch that holds cells together (like a clothing snap) • Serves to keep cells from pulling apart—resists mechanical stress • Hooklike J-shaped proteins arise from cytoskeleton – Approach cell surface – Penetrate into thick protein plaques linked to transmembrane proteins • Hemidesmosomes—anchor the basal cells of epithelium to the underlying basement membrane – Epithelium cannot easily peel away from underlying tissues Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intercellular space Plasma membrane Cell-adhesion proteins (a) Tight junction Intercellular space Cell-adhesion proteins Plaque Intermediate filaments of cytoskeleton (b) Desmosome Proteins Figure 5.28 Connexon Pore (c) Gap junction Basement membrane (d) Hemidesmosome 5-66 Gap Junctions • Gap (communicating) junction—formed by a ringlike connexon – Consists of six transmembrane proteins arranged like segments of an orange – Surrounding water-filled pores – Ions, glucose, amino acids, and other solutes pass from one cell to the next Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intercellular space Plasma membrane Cell-adhesion proteins (a) Tight junction Intercellular space Cell-adhesion proteins Plaque Intermediate filaments of cytoskeleton (b) Desmosome Proteins Figure 5.28 Connexon Pore (c) Gap junction Basement membrane (d) Hemidesmosome 5-67 Glands • Gland—cell or organ that secretes substances for use elsewhere in the body or releases them for elimination from the body – Composed of epithelial tissue in a connective tissue framework and capsule – May produce product synthesized by the gland (digestive enzymes) or products removed from tissues and modified by the gland (urine) • Secretion—product useful to the body • Excretion—waste product 5-68 Endocrine and Exocrine Glands • Exocrine glands—maintain their contact with the body surface by way of a duct (epithelial tube that conveys secretion to surface) – Sweat, mammary, and tear glands • Endocrine glands—lose their contact with the surface and have no ducts – Hormones: secretion of endocrine glands – Secrete (hormones) directly into blood – Thyroid, adrenal, and pituitary glands 5-69 Endocrine and Exocrine Glands • Some organs have both endocrine and exocrine functions – Liver, gonads, pancreas • Unicellular glands—found in epithelium that is predominantly nonsecretory – Can be endocrine or exocrine – Mucus-secreting goblet or endocrine cells of stomach and small intestine 5-70 Exocrine Gland Structure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Capsule—connective covering of most glands – Septa or trabeculae: extensions of capsule that divide the interior of the gland into compartments (lobes) – Further divided into smaller lobules Lobules Secretory acini Lobes Duct Parenchyma Secretory vesicles Stroma: Capsule Septum (a) Duct Acinus (b) Figure 5.30 5-71 Exocrine Gland Structure • Stroma—connective tissue framework of the gland – Supports and organizes glandular tissue • Parenchyma—cells that perform the tasks of synthesis and secretion – Typically cuboidal or simple columnar epithelium 5-72 Exocrine Gland Structure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Simple coiled tubular Compound acinar Compound tubuloacinar Example: Sweat gland Example: Pancreas Key Duct Secretory portion Example: Mammary gland Figure 5.31 • Simple—unbranched duct • Compound—branched duct • Shape of gland – Tubular: duct and secretory portion have uniform diameter – Acinar: secretory cells form dilated sac (acinus or alveolus) – Tubuloacinar: both tubular and acinar portions 5-73 Types of Secretions • Serous glands – Produce thin, watery secretions • Perspiration, milk, tears, digestive juices • Mucous glands – Produce glycoprotein, mucin, which absorbs water to form a sticky secretion called mucus – Goblet cells: unicellular mucous glands • Mixed glands – Contain both cell types and produce a mixture of the two types of secretions • Cytogenic glands – Release whole cells, sperm and egg cells 5-74 Modes of Secretion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Merocrine glands (eccrine glands) have vesicles that release their secretion by exocytosis – Tear glands, pancreas, gastric glands, and others Exocytosis Nucleus Secretory vesicle • Apocrine glands—primarily merocrine mode of secretion – Axillary sweat glands, mammary glands (a) Merocrine gland Figure 5.32a 5-75 Modes of Secretion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 5.32b (b) Holocrine gland • Holocrine glands—cells accumulate a product and then the entire cell disintegrates – Secretion of a mixture of cell fragments and synthesized substance – Oil glands of scalp, glands of eyelids 5-76 Membranes • Membranes line body cavities and cover their viscera • Cutaneous membrane (the skin)—largest membrane in the body – Stratified squamous epithelium (epidermis) resting on a layer of connective tissue (dermis) – Relatively dry layer serves protective function 5-77 Membranes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mucous coat Cilia Epithelium Mucin in goblet cell Ciliated cells of pseudostratified epithelium Basement membrane Mucous membrane (mucosa) Blood vessel Lamina propria Collagen fibers Fibroblast Elastic fibers (a) Figure 5.33a Muscularis mucosae • Mucous membrane (mucosa) lines passages that open to the external environment 5-78 Membranes Cont. – Digestive, respiratory, urinary, and reproductive tracts – Epithelium, absorptive, ciliated, and other types of cells – Lamina propria—areolar connective tissue – Muscularis mucosae—smooth muscle layer • Absorptive, secretory, and protective functions • Goblet cells produce mucus 5-79 Membranes • Serous membrane (serosa)—internal membrane – Simple squamous epithelium resting on a layer of areolar tissue – Produces serous fluid that arises from blood – Covers organs and lines walls of body cavities • Endothelium lines blood vessels and heart • Mesothelium lines body cavities (pericardium, peritoneum, and pleura) • Synovial membrane—lines joint cavities – Connective tissue layer only, secretes synovial fluid 5-80 Tissue Growth, Development, Repair, and Degeneration • Expected Learning Outcomes – Name and describe the modes of tissue growth. – Define adult and embryonic stem cells and their varied degrees of developmental plasticity. – Name and describe the ways that a tissue can change from one type to another. – Name and describe the modes and causes of tissue shrinkage and death. – Name and describe the ways the body repairs damaged tissues. 5-81 Tissue Growth • Tissue growth—increasing the number of cells or the existing cells grow larger • Hyperplasia—tissue growth through cell multiplication • Hypertrophy—enlargement of preexisting cells – Muscle growth through exercise – Accumulation of body fat • Neoplasia—development of a tumor (neoplasm) – Benign or malignant – Composed of abnormal, nonfunctional tissue 5-82 Tissue Development • Tissues can change types within certain limits • Differentiation – Unspecialized tissues of embryo become specialized mature types • Mesenchyme to muscle • Metaplasia – Changing from one type of mature tissue to another • Simple cuboidal tissue of vagina before puberty changes to stratified squamous after puberty • Pseudostratified columnar epithelium of bronchi of smokers to stratified squamous epithelium 5-83 Stem Cells • Stem cells—undifferentiated cells that are not yet performing any specialized function – Have potential to differentiate into one or more types of mature functional cells • Developmental plasticity—diversity of mature cell types to which stem cells can give rise 5-84 Stem Cells • Embryonic stem cells – Totipotent: have potential to develop into any type of fully differentiated human cell • Source—cells of very early embryo – Pluripotent: can develop into any type of cell in the embryo • Source—cells of inner cell mass of embryo • Adult stem cells—undifferentiated cells in tissues of adults – Multipotent: bone marrow producing several blood cell types – Unipotent: most limited plasticity; only epidermal cells produced 5-85 Tissue Repair • Damaged tissues can be repaired in two ways: – Regeneration: replacement of dead or damaged cells by the same type of cell as before • Restores normal function • Skin injuries and liver regenerate – Fibrosis: replacement of damaged cells with scar tissue • Holds organs together • Does not restore normal function – Severe cuts and burns, healing of muscle injuries, scarring of lungs in tuberculosis 5-86 Tissue Repair Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Healing of a cut in the skin: – Severed blood vessels bleed into cut – Mast cells and damaged cells release histamine – Dilates blood vessels – Increases blood flow to area – Makes capillaries more permeable 1 Bleeding into the wound Figure 5.34 (1) • Blood plasma seeps into the wound carrying: – Antibodies – Clotting proteins – Blood cells 5-87 Tissue Repair Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Blood clot forms in the tissue – Loosely knitting edges of cut together – Inhibits spread of pathogens from injury site to healthy tissue Scab Blood clot Macrophages • Forms scab that temporarily seals wound and blocks infection • Macrophages phagocytize and digest tissue debris Fibroblasts Leukocytes 2 Scab formation and macrophage activity Figure 5.34 (2) 5-88 Tissue Repair • New capillaries sprout from nearby vessels and grow into wound • Deeper portions become infiltrated by capillaries and fibroblasts – Transform into soft mass called granulation tissue – Macrophages remove the blood clot – Fibroblasts deposit new collagen – Begins 3–4 days after injury and lasts up to 2 weeks Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Scab Macrophages Fibroblasts Blood capillary Granulation tissue 3 Formation of granulation tissue (fibroblastic phase of repair) Figure 5.34 (3) 5-89 Tissue Repair • Surface epithelial cells around wound multiply and migrate into wound area beneath scab • Epithelium regenerates • Connective tissue undergoes fibrosis • Scar tissue may or may not Epidermal show through epithelium regrowth Scar tissue • Remodeling (maturation) (fibrosis) phase begins several weeks after injury and may last up to 2 years Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4 Epithelial regeneration and connective tissue fibrosis (remodeling phase of repair) Figure 5.34 (4) 5-90 Tissue Degeneration and Death • Atrophy—shrinkage of a tissue through a loss in cell size or number – Senile atrophy through normal aging – Disuse atrophy from lack of use (astronauts) • Necrosis—premature, pathological death of tissue due to trauma, toxins, or infections – Infarction—sudden death of tissue when blood supply is cut off – Gangrene—tissue necrosis due to insufficient blood supply – Decubitus ulcer—bed sore or pressure sore • Pressure reduces blood flow to an area • Form of dry gangrene – Gas gangrene—anaerobic bacterial infection 5-91 Tissue Degeneration and Death • Apoptosis—programmed cell death – Normal death of cells that have completed their function and best serve the body by dying and getting out of the way • Phagocytized by macrophages and other cells • Billions of cells die by apoptosis • Every cell has a built-in ―suicide program‖ – Extracellular suicide signal binds receptor protein in the plasma membrane called Fas – Fas activates enzymes: endonuclease chops up DNA and protease destroys proteins 5-92 Tissue Engineering • Tissue engineering—artificial production of tissues and organs in the lab for implantation in the human body – Framework of collagen or biodegradable polyester fibers – Seeded with human cells – Grown in ―bioreactor‖ (inside of mouse) • Supplies nutrients and oxygen to growing tissue 5-93 Tissue Engineering • Skin grafts already available – Research in progress on heart valves, coronary arteries, bone, liver, tendons – Human outer ear grown on back of mouse and recent replacement of urinary bladder wall sections Figure 5.35 5-94 The Stem-Cell Controversy • Possible treatment for diseases caused by loss of functional cell types by embryonic stem cells – Cardiac muscle cells, injured spinal cord, insulinsecreting cells • Skin and bone marrow stem cells have been used in therapy for years • Adult stem cells have limited developmental potential – Difficult to harvest and culture 5-95