1/26/2018. Tissues - Learn and Understand. Tissue: The Living Fabric. Individual body cells specialized. Tissues. Histology. Tissues and Histology

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1 Tissues - Learn and Understand The composition of a tissue helps us understand what functions it is capable of. Concepts of cell surface area, attachment of tissues to others, mucus production, role of particular cell types within tissues, glandular secretion are discovered or reviewed. Various forms of proteins (mainly) and polysaccharides (secondarily) and inorganic materials form the critical, nonliving substances of the body. All organs are made up of two or more tissues (less than four tissues is uncommon) and the presence of particular tissues helps us understand what functions an organ is capable of. Inflammation is a natural, step-wise response to tissue damage that begins the healing process. Tissue: The Living Fabric Individual body cells specialized Each type performs specific functions that maintain homeostasis Tissues Groups of cells similar in structure that perform common or related function Histology Study of tissues Tissues and Histology Tissue classification based on structure of cells composition of extracellular matrix cell function 4 Types Epithelium cover Connective support Muscle movement Nervous control 1

2 Epithelial Tissue - Epithelium Functions Protection Covering and lining epithelia On external and internal surfaces Absorption primary way substances enter/exit body Filtration Excretion Secretion Glandular epithelia Sensory reception linked to nervous tissues Five Characteristics of Epithelial Tissues Polarity Apical surface (free) Basal surface (lower, attached via basal lamina) Both surfaces differ in structure and function Specialized lateral and basal contacts (Ch 3) tight junctions, desmosomes Cells form sheets Supported by connective tissues (CT) Non-living lamina attaches epithelium to CT Avascular, but innervated High regenerative capability If adequate nutrients, can replace lost cells by cell division Cell Surface Modifications ciliated surface May be ciliated or possess microvilli or smooth Consider increase in surface area for absorption, exchange, enzymatic function Brush border 2

3 Basement membrane Basement membrane = Basal lamina + reticular lamina Reinforces epithelial sheet and defines epithelial boundary Resists stretching and tearing Foundation for repair Underlying connective tissue Tubule lumen Epithelial layer Classification of Epithelial Tissue Number of layers of cells Simple Stratified Pseudostratified Shape of cells at surface Squamous Cuboidal Columnar Simple squamous epithelium Description: Single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of the epithelia. Function: Allows materials to pass by diffusion and filtration in sites where protection is not important; secretes lubricating substances in serosae. Air sacs of lung tissue Nuclei of squamous epithelial cells Location: Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; lining of ventral body cavity (serosae). Photomicrograph: Simple squamous epithelium forming part of the alveolar (air sac) walls (140 ). 3

4 Simple cuboidal epithelium Description: Single layer of cubelike cells with large, spherical central nuclei. Simple cuboidal epithelial cells Nucleus Function: Secretion and absorption. Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface. Basement membrane Connective tissue Photomicrograph: Simple cuboidal epithelium in kidney tubules (430 ). Simple columnar epithelium Description: Single layer of tall cells with round to oval nuclei; many cells bear microvilli, some bear cilia; layer may contain mucus-secreting unicellular glands (goblet cells). Microvilli Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action. Simple columnar epithelial cell Mucus of goblet cell Location: Nonciliated type lines most of the digestive tract (stomach to rectum), 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 mucosa (640 ). 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 cells and bear cilia. Goblet cell (contains mucus) Cilia Function: Secrete substances, particularly mucus; propulsion of mucus by ciliary action. Location: Nonciliated type in males sperm-carrying ducts and ducts of large glands; ciliated variety lines the trachea, most of the upper respiratory tract. Pseudostratified epithelial layer Basement membrane Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (780 ). Trachea 4

5 Stratified squamous epithelium Description: Thick membrane 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 layers. Stratified squamous epithelium Function: Protects underlying tissues in areas subjected to abrasion. Location: Nonkeratinized type forms the moist linings of the esophagus, mouth, and vagina; keratinized variety forms the epidermis of the skin, a dry membrane. Photomicrograph: Stratified squamous epithelium lining the esophagus (285 ). Nuclei Basement membrane Connective tissue Transitional epithelium Description: Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamouslike, depending on degree of organ stretch. Transitional epithelium Function: Stretches readily, permits stored urine to distend urinary organ. Location: Lines the ureters, bladder, and part of the urethra. Photomicrograph: Transitional epithelium lining the bladder, relaxed state (360 ); note the bulbous, or rounded, appearance of the cells at the surface; these cells flatten and elongate when the bladder fills with urine. Basement membrane Connective tissue Epithelium classification Simple squamous Function Allows materials to pass by diffusion and filtration in sites where protection is not important; secretes lubricating substances in serosae Location Kidney glomeruli; air sacs of lungs; endothelium - lining of heart, blood vessels, and lymphatic vessels; lining of ventral body cavity Simple cuboidal Secretion and absorption Kidney tubules; ducts and secretory portions of small glands; ovary surface Simple columnar Stratified squamous Pseudostratified columnar Transitional Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action Protects underlying tissues in areas subjected to abrasion Secrete substances, particularly mucus; propulsion of mucus by ciliary action Stretches readily, permits stored urine to distend urinary organ Nonciliated type lines most of the digestive tract, gallbladder, and excretory ducts of some glands; ciliated variety lines small bronchi, uterine tubes Nonkeratinized type forms the moist linings of the esophagus, mouth, and vagina; keratinized variety forms the epidermis of the skin, a dry membrane Nonciliated type in male s sperm-carrying ducts and ducts of large glands; ciliated variety lines the trachea, most of the upper respiratory tract Lines the ureters, bladder, and part of the urethra 5

6 Glandular Epithelia Gland One or more cells that make and secrete an aqueous fluid or lipid-rich secretions Classified by Site of product release Endocrine or ductless glands Secrete (by exocytosis) hormones that travel through lymph or blood to their specific target organs Exocrine Secretions released onto body surfaces (skin) or into body cavities Secrete products into ducts Examples include mucous, sweat, oil, and salivary glands Relative number of cells forming the gland unicellular (e.g., goblet cells) or multicellular Unicellular Exocrine Found in epithelial linings of intestinal and respiratory tracts mucous cells and goblet cells All produce mucin (hydrophilic glycoprotein) Slimy protective, lubricating coating Multicellular Exocrine glands Composed of a duct and a secretory unit Usually surrounded by supportive connective tissue Supplies blood and nerve fibers Intestinal epithelium Goblet cell Connective Tissue General Characteristics Most abundant and widely distributed of primary tissues diverse in form and function Found in every organ but amount and type can vary greatly Performs variety of important functions Consists of cells separated by extracellular matrix Largely nonliving extracellular matrix dominates most CT So can bear weight, withstand tension, endure abuse Have varying degrees of vascularity and nerves 6

7 Functions of Connective Tissue Enclose organs as a capsule and separate organs into layers Connect tissues to one another Support and movement, but not contraction Storage Cushion and insulate Transport Protect Connective tissue proper - binding and support, insulating, storing reserve fuel Cartilage supporting, protecting, connecting Bone - supporting and protecting Blood - transporting substances, regulation 7

8 Structural Elements of Connective Tissue: Ground Substance Unstructured gels that fills space between cells Medium through which solutes diffuse between blood capillaries and cells Components Interstitial fluid Cell adhesion proteins sticky nectins Hydrophilic Proteoglycans Protein core and Glycosaminoglycans large polysaccharides» Example: chrondroitin sulfate and hyaluronic acid Trap water in varying amounts, affecting viscosity of ground substance Structural Elements of Connective Tissue: Fibers Collagen Cross-linked fibrils of tropocollagen protein Strongest and most abundant type, provides flexible, high-tensile strength Elastic fibers Networks of long, thin, elastin fibers that allow for stretch and recoil Stretch limited by collagen fibers present in tissue Reticular Short, fine, highly branched collagenous fibers (different chemistry and form than collagen fibers) Branch, forming spongy networks that offer more "give" Structural Elements of Connective Tissue: Cells "Blast" cells Immature form; mitotically active; secrete ground substance and fibers; reawaken when needed Fibroblasts in connective tissue proper Chondroblasts in cartilage Osteoblasts in bone Hemocytoblasts blood makers in bone marrow always active "Cyte" cells Mature form; maintain matrix; detect and respond to new stresses Chondrocytes in cartilage Osteocytes in bone Clast cells unique origin, destroy bone matrix in normal processes 8

9 Other Cell Types in Connective Tissues Fat cells - adipocytes Store nutrients, insulate, pad White blood cells Several types whose names will be learned later Tissue response to injury Mast cells Initiate local inflammatory response upon detection of foreigners Secrete substances to control inflammation Macrophages Phagocytic cells that "eat" dead cells, microorganisms, abnormal cells; function in immune system Cell types Macrophage Fibroblast Extracellular matrix Ground substance Fibers Collagen fiber Elastic fiber Reticular fiber Lymphocyte Fat cell Mast cell Figure 4.7 Areolar connective tissue: A prototype (model) connective tissue. Neutrophil Capillary Connective tissue proper: loose connective tissue, areolar Description: Gel-like matrix with all three fiber types; cells: fibroblasts, macrophages, mast cells, and some white blood cells. Elastic fibers Function: Wraps and cushions organs; its macrophages phagocytize bacteria; plays important role in inflammation; holds and conveys tissue fluid. Location: Widely distributed under epithelia of body, e.g., forms lamina propria of mucous membranes; packages organs; surrounds capillaries. Ground substance Fibroblast nuclei Collagen fibers Epithelium Photomicrograph: Areolar connective tissue, a soft packaging tissue of the body (340 ). Lamina propria 9

10 Connective tissue proper: loose connective tissue, adipose Description: Matrix as in areolar, but very sparse; closely packed adipocytes, or fat cells, have nucleus pushed to the side by large fat droplet. Function: Provides reserve food fuel; insulates against heat loss; supports and protects organs. Location: Under skin in subcutaneous tissue; around kidneys and eyeballs; within abdomen; in breasts. Adipose tissue Photomicrograph: Adipose tissue from the subcutaneous layer under the skin (350 ). Nucleus of adipose (fat) cell Fat droplet Mammary glands Connective tissue proper: loose connective tissue, reticular Description: Loose network of reticular fibers in a gel-like ground substance; reticular cells lie on the network. Function: Fibers form a soft internal skeleton (stroma) that supports other cell types including white blood cells, mast cells, and macrophages. Location: Lymphoid organs (lymph nodes, bone marrow, and spleen). White blood cell (lymphocyte) Reticular fibers Photomicrograph: Dark-staining network of reticular connective tissue fibers forming the internal skeleton of the spleen (350 ). Spleen CT Proper Function Location Loose and loose fibrous CT Areolar Adipose Reticular Wraps and cushions organs; its macrophages phagocytize bacteria; plays important role in inflammation; holds and conveys tissue fluid Provides reserve food fuel; insulates against heat loss; supports and protects organs Fibers form a soft internal skeleton (stroma) that supports other cell types including white blood cells, mast cells, and macrophages Widely distributed under epithelia of body, e.g., forms lamina propria of mucous membranes; packages organs; surrounds capillaries Under skin in subcutaneous tissue; around kidneys and eyeballs; within abdomen; in breasts Lymphoid organs (lymph nodes, bone marrow, and spleen) Connective Tissue Proper: All connective tissues except bone, cartilage and blood Note: Most CT have been studied in the laboratory so micrographs are not provided here. There are many micrographs located in lab and lecture texts and via internet image searches 10

11 Connective tissue proper: dense connective tissue, dense regular Description: Primarily parallel collagen fibers; a few elastic fibers; major cell type is the fibroblast. Function: Attaches muscles to bones or to muscles; attaches bones to bones; withstands great tensile stress when pulling force is applied in one direction. Collagen fibers Nuclei of fibroblasts Location: Tendons, most ligaments, aponeuroses. Shoulder joint Photomicrograph: Dense regular connective tissue from a tendon (430 ). Ligament Tendon Connective tissue proper: dense connective tissue, dense irregular Description: Primarily irregularly arranged collagen fibers; some elastic fibers; fibroblast is the major cell type. Nuclei of fibroblasts Function: Withstands tension exerted in many directions; provides structural strength. Location: Fibrous capsules of organs and of joints; dermis of the skin; submucosa of digestive tract. Collagen fibers Shoulder joint Fibrous joint capsule Photomicrograph: Dense irregular connective tissue from the fibrous capsule of a joint (430 ). Connective tissue proper: dense connective tissue, elastic Description: Dense regular connective tissue containing a high proportion of elastic fibers. Function: Allows tissue to recoil after stretching; maintains pulsatile flow of blood through arteries; aids passive recoil of lungs following inspiration. Elastic fibers Location: Walls of large arteries; within certain ligaments associated with the vertebral column; within the walls of the bronchial tubes. Photomicrograph: Elastic connective tissue in the wall of the aorta (250 ). Aorta Heart 11

12 CT Proper Function Location Dense fibrous CT Dense regular Dense irregular Elastic Attaches muscles to bones or to muscles; attaches bones to bones; withstands great tensile stress when pulling force is applied in one direction Withstands tension exerted in many directions; provides structural strength Allows tissue to recoil after stretching; maintains pulsatile flow of blood through arteries; aids passive recoil of lungs following inspiration Tendons, most ligaments, aponeuroses Fibrous capsules of organs and of joints; dermis of the skin; submucosa of digestive tract Walls of large arteries; within certain ligaments associated with the vertebral column; within the walls of the bronchial tubes Cartilage: hyaline Description: Amorphous but firm matrix; collagen fibers form an imperceptible network; chondroblasts produce the matrix and when mature (chondrocytes) lie in lacunae. Function: Supports and reinforces; serves as resilient cushion; resists compressive stress. Location: Forms most of the embryonic skeleton; covers the ends of long bones in joint cavities; forms costal cartilages of the ribs; cartilages of the nose, trachea, and larynx. Chondrocyte in lacuna Matrix Photomicrograph: Hyaline cartilage from a costal cartilage of a rib (470 ). Costal cartilages Cartilage: fibrocartilage Description: Matrix similar to but less firm than that in hyaline cartilage; thick collagen fibers predominate. Function: Tensile strength allows it to absorb compressive shock. Location: Intervertebral discs; pubic symphysis; discs of knee joint. Intervertebral discs Chondrocytes in lacunae Collagen fiber Photomicrograph: Fibrocartilage of an intervertebral disc (125 ). Special staining produced the blue color seen. 12

13 Cartilage: elastic Description: Similar to hyaline cartilage, but more elastic fibers in matrix. Function: Maintains the shape of a structure while allowing great flexibility. Chondrocyte in lacuna Location: Supports the external ear (pinna); epiglottis. Matrix Photomicrograph: Elastic cartilage from the human ear pinna; forms the flexible skeleton of the ear (800x). Others: bone (osseous tissue) Description: Hard, calcified matrix containing many collagen fibers; osteocytes lie in lacunae. Very well vascularized. Function: Supports and protects (by enclosing); provides levers for the muscles to act on; stores calcium and other minerals and fat; marrow inside bones is the site for blood cell formation (hematopoiesis). Central canal Lacunae Lamella Location: Bones Photomicrograph: Cross-sectional view of bone (125 ). Connective tissue: blood Description: Red and white blood cells in a fluid matrix (plasma). Function: Transport respiratory gases, nutrients, wastes, and other substances. Red blood cells (erythrocytes) White blood cells: Lymphocyte Neutrophil Location: Contained within blood vessels. Plasma Photomicrograph: Smear of human blood (1670 ); shows two white blood cells surrounded by red blood cells. 13

14 CT Type Function Location Hyaline cartilage Elastic cartilage Supports and reinforces; serves as resilient cushion; resists compressive stress Lacks nerves, blood vessels Most abundant type Maintains the shape of a structure while allowing great flexibility Forms most of the embryonic skeleton; covers the ends of long bones in joint cavities; forms costal cartilages of the ribs; cartilages of the nose, trachea, and larynx Supports the external ear (pinna); epiglottis Fibrocartilage Bone Matrix similar to but less firm than that in hyaline cartilage; thick collagen fibers predominate Supports and protects; provides levers for the muscles to act on; stores calcium and other minerals and fat; marrow inside bones is the site for blood cell formation Intervertebral discs; pubic symphysis; discs of knee joint doh Blood Transport respiratory gases, nutrients, wastes, and other substances Contained within blood vessels Muscle Tissue Highly vascularized Responsible for most types of movement Three types Skeletal muscle tissue Found in skeletal muscle Voluntary Cardiac muscle tissue Found in walls of heart Involuntary Smooth muscle tissue Mainly in walls of hollow organs other than heart Involuntary Microscopic Comparison of Muscle Types Skeletal Smooth Cardiac 14

15 Nervous Tissue Main component of nervous system Brain, spinal cord, nerves Regulates and controls body functions Neurons Specialized nerve cells that generate and conduct nerve impulses Neuroglia Supporting cells that support, insulate, and protect neurons Nervous tissue Description: Neurons are branching cells; cell processes that may be quite long extend from the nucleus-containing cell body; also contributing to nervous tissue are nonexcitable supporting cells. Neuron processes Cell body Axon Dendrites Function: Neurons transmit electrical signals from sensory receptors and to effectors (muscles and glands) which control their activity; supporting cells support and protect neurons. Location: Brain, spinal cord, and nerves. Nuclei of supporting cells Cell body of a neuron Neuron processes Photomicrograph: Neurons (350x). Tissue Repair Necessary when barriers are penetrated and tissues are damaged Temporary tissues form to close the breach Cells divide and migrate to replace temporary tissue Dead cells, debris, foreign invaders must be removed Occurs in two major ways Regeneration Same kind of tissue replaces destroyed tissue Original function restored Fibrosis or Replacement Connective tissue scar replaces destroyed tissue Original function lost More likely in severe injury 15

16 Scab Slide 1 Epidermis Blood clot in incised wound Inflammatory chemicals Vein Migrating white blood cell Artery 1 Inflammation sets the stage: Severed blood vessels bleed. Inflammatory chemicals are released. Local blood vessels become more permeable, allowing white blood cells, fluid, clotting proteins, and other plasma proteins to seep into the injured area. Clotting occurs; surface dries and forms a scab. Regenerating epithelium Area of granulation tissue ingrowth Fibroblast Macrophage Budding capillary 2 Organization restores the blood supply: The clot is replaced by granulation tissue, which restores the vascular supply. Fibroblasts produce collagen fibers that bridge the gap. Macrophages phagocytize dead and dying cells and other debris. Surface epithelial cells multiply and migrate over the granulation tissue. Regenerated epithelium Fibrosed area 3 Regeneration and fibrosis effect permanent repair: The fibrosed area matures and contracts; the epithelium thickens. A fully regenerated epithelium with an underlying area of scar tissue results. 16

17 Regenerative Capacity in Different Tissues Regenerate extremely well Epithelial tissues, bone, areolar connective tissue, dense irregular connective tissue, blood-forming tissue Moderate regenerating capacity Smooth muscle and dense regular connective tissue Virtually no functional regenerative capacity Cardiac muscle and nervous tissue of brain and spinal cord New research shows cell division does occur Efforts underway to coax them to regenerate better 17