BIO 201: Histology
BIO 201: Histology BIO 201
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This 19 page Class Notes was uploaded by ASUNursing19 on Thursday February 18, 2016. The Class Notes belongs to BIO 201 at Arizona State University taught by Dr. Penkrot in Winter 2016. Since its upload, it has received 43 views. For similar materials see Human Anatomy/Physiology I in Biology at Arizona State University.
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Date Created: 02/18/16
The Study of Tissues 50 trillion cells of 200 different cell types Four broad categories of tissues: o Epithelial tissue o Connective tissue o Nervous tissue o Muscular tissue Organ : structure with discrete boundaries that is composed of two or more tissue type Histology (microscopic anatomy): the study of tissues and how they are arranged into organs 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 For primary tissues differ from one another in the: o Types and functions of their cells o The characteristics of the matrix ( = extracellular material) o The relative amount of space occupied by cells versus matrix Matrix: extracellular material composed of: o Fibrous proteins o A clear gel known as ground substance , tissue fluid, extracellular fluid (ECF), interstitial fluid, or tissue gel Embryonic Tissues 3 primary germ layers o Ectoderm (outer) Gives rise to epidermis, nervous system, tooth enamel, etc. o Endoderm (inner) Gives rise to mucous membrane lining digestive and respiratory tracts (except part of mouth), digestive glands, urinary system, etc. o Mesoderm (middle) becomes gelatinous tissue: mesenchyme (embryonic CT) Wispy collagen fibers and fibroblasts in gel matrix Gives rise to muscle, bone, blood Interpreting Tissue Sections Preparation of histological specimens o Fixative prevents decay (e.g., formalin) o Histological sections: tissue is sliced into thin sections one or two cells thick o Stains: tissue is mounted on slides and artificially colored with histological stain Stains bind to different cellular components Sectioning reduces 3D structure to 2D slice Sectioning Solid Objects Sectioning a cell with a centrally located nucleus Some slices miss the cell nucleus In some the nucleus is smaller Sectioning Hollow Structures Cross section of blood vessel, gut, or other tubular organ Longitudinal section of a sweat gland: notice what a single slice could look like Types of Tissue Sections Longitudinal section (l.s.) o Tissue cut along long direction of organ Cross section (c.s. or x.s.) or transverse section (t.s.) o Tissue cut perpendicular to length of organ Oblique section o Tissue cut at angle between cross and longitudinal section NonSectioned Preparation Smear : tissue is rubbed or spread across the slide o CSF or blood Spread : cobwebby tissue is laid out on a slide o Areolar tissue 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 Constitutes most glands Extracellular material is so thin it is not visible with a light microscope Lie on a layer of loose connective tissue and depend on its blood vessels for nourishment and waste removal NO BLOOD VESSELS VISIBLE Special Characteristics of Epithelial Tissues Epithelial tissue has five distinguishing characteristics: 1. Polarity 2. Specialized contacts 3. Connective Tissue Support 4. Avascular, but innervated 5. Regeneration 1 Polarity o Cells have polarity (top and bottom) o Apical surface, upper free side, is exposed to surface or cavity Most apical surfaces are smooth, but some have specialized fingerlike projections called microvilli o Open surface = "apical surface" o Basal surface, lower attached side, faces inwards toward body Attaches to basal lamina, an adhesive sheet that holds basal surface or epithelial cells to underlying cells o Both surfaces differ in structure and function 2 Specialized contacts o Epithelial tissues need to fit closely together Many form continuous sheets o Specialized contact points bind adjacent epithelial cells together Lateral contacts include: Tight junctions Desmosomes 3 Connective Tissue Support o All epithelial sheets are supported by connective tissue o Reticular lamina Deep to basal lamina Consists of network of collagen fibers o Basement membrane Made up of basal and reticular lamina Reinforces epithelial sheet Resists stretching and tearing Defines epithelial boundary 4 Avascular, but innervated o No blood vessels are found in epithelial tissue Must be nourished by diffusion from underlying connective tissues o Epithelia are supplied by nerve fibers, however 5 Regeneration o Epithelial cells have high regenerative capacities o Stimulated by loss of apicalbasal polarity and broken lateral contacts o Some cells are exposed to friction, some to hostile substances, resulting in damage Must be replaced Requires adequate nutrients and cell division Classification of Epithelia All epithelial tissues have two names o First name indicates number of cell layers Simple epithelia are a single layer thick Stratified epitheli are two or more layers thick and involved in protection (example: skin) o Second name indicates shape of cells Squamous: flattened and scalelike Cuboidal : boxlike, cube Columnar: tall, columnlike o In stratified epithelia, shape can vary in each layer, so cell is named according to the shape in apical layer Basement Membrane Basement membrane : layer between an epithelium and the underlying connective tissue Basement membrane consists: o Collagen o Laminin and fibronectin adhesive glycoproteins o Heparin sulfate: large proteincarbohydrate complex Anchors the epithelium to the connective tissue below it: clinically relevant > spread of cancers 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 Simple Epithelia Four types of simple epithelia Three named for their cell shapes o Simple squamous (thin scaly cells) o Simple cuboidal (square or round cells) o Simple columnar (tall narrow cells) Fourth type: o Pseudostratified columnar Not all cells reach the free surface Shorter cells are covered over by taller ones Looks stratified, but really isn't Every cell reaches the basement membrane Goblet cells : wineglassshaped mucus secreting cells in simple columnar and pseudostratified epithelia Simple Squamous Epithelia Single row of thin cells Permits rapid diffusion or transport of substances Secretes serous fluid Alveoli (in lungs), glomeruli (in kidneys), endothelium, and serosa Simple Cuboidal Epithelium Single layer of square or round cells Absorption and secretion , mucus production and movement Liver, thyroid, mammary and salivary glands, bronchioles, and kidney tubules Simple Columnar Epithelia Single row tall, narrow cells o Oval nuclei in basal half of cell o Brush border of microvilli, ciliated in some organs, may possess goblet cells Absorption and secretion; mucus secretion Lining of GI tract, uterus, kidney and uterine tubes Pseudostratified Epithelium ( pseudo = false) Looks multilayered; some not reaching free surface; all touch basement membrane o Nuclei at several layers with cilia and goblet cells Secretes and propels mucus Respiratory tract and portions of male urethra 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 o Stratified squamous o Stratified cuboidal o Stratified columnar (rare) Fourth type o Transitional epithelium Most widespread epithelium in the body Deepest layers undergo continuous mitosis o Their daughter cells push toward the surface and become flatter as they migrate farther upward o Finally die and flake off: xfoliation or esquamation Two kinds of stratified squamous epithelia o Keratinized: found on skin surface, abrasion resistant o Nonkeratinized : lacks surface layer of dead cells Keratinized Stratified Squamous 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 Nonkeratinized Stratified Squamous Same as keratinized epithelium without the surface layer of dead cells Tongue, oral mucosa, esophagus and vagina Resists abrasion and penetration of pathogens Stratified Cuboidal Epithelium Two or more cell layers; surface cells square or round Secretes sweat; sperm production and produces ovarian hormones Sweat gland ducts; ovarian follicles and seminiferous tubules Transitional Epithelium Multilayered epithelium surface cells that change from round to flat when stretched Allows for filling of urinary tract Extremely waterproof Primarily uterus and bladder Types of Glands Endocrine o Products (hormones) are released directly into the bloodstream o No system of ducts o Distant target organ(s) o Thyroid, pituitary, hypothalamus, adrenal, etc. Exocrine o Product is released onto an epithelial surface via a system of ducts o Acinus (pl. = acini) and ducts o Salivary, sweat, mammary Dualfunction glands o Have features of both endocrine and exocrine types o Gonads, pancreas, liver Glandular Epithelia Gland o One or more cells that makes and secretes an aqueous fluid called a tion Classified by: o Site of product release: Endocrine: internally secreting (example: hormones) Exocrine : externally secreting (example: sweat) o Relative number of cells forming the gland Unicellular (example: goblet cells) or multicellular (example: salivary) Endocrine glands o Ductless glands Secretions are not released into a duct; are released into surrounding interstitial fluid, which is picked up by circulatory system o Secrete (by exocytosis) rmones , messenger chemicals that travel through lymph or blood to their specific target organs o Target organs respond in some characteristic way Exocrine glands o Secretions are released onto body surfaces, such as skin, or into body cavities o More numerous than endocrine glands o Secrete products into ducts o Examples: mucous, sweat, oil, and salivary glands o Can be: Unicellular Multicellular Unicellular exocrine glands o The only important unicellular glands arecous cells and goblet cells o Found in epithelial linings of intestinal and respiratory tracts o All produce ucin , a sugarprotein that can dissolve in water to form mucus, a slimy protective, lubricating coating Multicellular exocrine glands o Multicellular exocrine glands are composed of a duct and a secretory unit o Usually surrounded by supportive connective tissue that supplies blood and nerve fibers to gland Connective tissue can form capsule around gland, and also extend into gland, dividing it into lobes o Classified by: Structure Mode of secretion o Structure Simple exocrine glands have unbranched ducts, but compound glands have branched ducts In a tubular gland, secretory cells form a duct, whereas in veolar glands, secretory cells form sacs Tubuloalveolar glands have both types o Mode of secretion Merocrine: most secrete products by exocytosis as secretions are produced (sweat, pancreas) Holocrine: accumulate products within, then rupture (sebaceous oil glands) Apocrine: accumulate products within, but only apex ruptures, whether this type exists in humans is controversial (maybe mammary cells?) Connective Tissue Connective tissue : a type of tissue in which cells usually occupy less space than the extracellular material Binds organs to each other Support and protects organs Most cells of connective tissue are not in direct contact with each other o Separated by extracellular material Highly vascular richly supplied with blood vessels Most abundant, widely distributed and histologically variable of the primary tissues Functions of Connective Tissue 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 fats in infants Transport: blood 4.3 Connective Tissue Connective tissue is the most abundant and widely distributed of primary tissues Major functions: binding and support, protective, insulating, storing reserve fuel, and transporting substances (blood) Four main classes 1. Connective tissue proper 2. Cartilage 3. Bone 4. Blood Common Characteristics of Connective Tissue Three characteristics make connective tissues different form other primary tissues: 1. All have common embryonic origin: all arise from mesenchyme tissue as their tissue of origin 2. Have varying degrees of vascularity (cartilage is avascular, bone is highly vascularized) 3. Cells are suspended/embedded in extracellular matrix (ECM) (proteinsugar mesh) o Matrix supports cells so they can bear weight, withstand tension, endure abuse Structural Elements of Connective Tissue All connective tissues have three main elements o Ground substance o Fibers o Cells o The first two elements (ground substance and fibers) together make up the extracellular matric o Composition and arrangement of these three elements vary considerably in different types of connective tissues Ground substance o Unstructured gellike material that fills space between cells o Medium through which solutes diffuse between blood capillaries and cells o Components o Interstitial fluid o Cell adhesion proteins ("glue" for attachment) o Proteoglycans (sugar proteins), made up of protein core + large polysaccharides Example: chondroitin sulfate and hyaluronic acid o Water also is trapped in varying amounts, affecting viscosity of ground substance Connective Tissue Fibers Three types of fibers provide support o Collagen o Strongest and most abundant type o Tough; provides high tensile strength o Elastic fibers o Networks of long, thin, asti fibers that allow for stretch and recoil o Reticular o Short, fine, highly branched collagenous fibers (different chemistry and form from collagen fibers) o Branching forms networks that offer more "give" Cells o "Blast" cells o Immature form of cell that actively secretes ground substance and ECM fibers o Fibroblasts found in connective tissue proper o Chondroblasts found in cartilage o Osteoblasts found in bone o Hematopoietic stem cells in bone marrow o "Cyte" cells o Mature, less active form of "blast" cell that now becomes part of and helps maintain health of matrix Other cell types in connective tissues o Fat cells o Store nutrients o White blood cells o Neutrophils, eosinophils, lymphocytes o Tissue response to injury o Mast cells o Initiate local inflammatory response against foreign microorganisms they detect o Macrophages o Phagocytic cells that "eat" dead cells, microorganisms; function in immune system Types of Connective Tissues There are four main classes of connective tissue: o Connective tissue proper o Cartilage o Bone o Blood Connective Tissue Proper (= fibrous CT) o Consists of all connective tissues except bone, cartilage, and blood o Two subclasses o CT proper: loose connective tissues Areolar connective tissue Most widely distributed CT Supports and binds other tissues Universal packing material between other tissues Contains fibroblasts that secrete loose arrangement of mostly collagen fibers Loose fibers allow for increased ground substance, which can act as water reservoir by holding more interstitial fluid Macrophages and fat cells are contained in spaces Adipose tissue White fat Similar to areolar tissue but greater nutrient storage Cells are called ipocytes Scanty matrix Richly vascularized Functions in shock absorption, insulation, and energy storage Brown fat Use lipid fuels to heat bloodstream rather than to produce ATP, as does white fat Reticular connective tissue Resembles areolar tissue, but fibers are thinner reticular fibers Fibroblast cells are called ticular cells Secrete reticular fibers made up of thin collagen Reticular fibers form a meshlike stroma that acts as a support for blood cells in lymph nodes, spleen, and bone marrow o CT proper: dense connective tissues Dense regular connective tissue Very high tensile strength; can withstand high tension and stretching Closely packed bundles of thick collagen fibers run parallel to direction of pull Fibers appear as white structures Great resistance to pulling Fibers slightly wavy, so stretch a little Fibroblasts manufacture collagen fibers and ground substance Very few cells and ground substance, mostly fibers Poorly vascularized Example: tendons and ligaments Dense irregular connective tissue Same elements as dense regular, but bundles of collagen are thicker and irregularly arranged Forms sheets rather than bundles Resists tension from many directions Found in: Dermis Fibrous joint capsules Fibrous coverings of some organs Elastic connective tissue Some ligaments are very elastic Example: ligaments connective adjacent vertebrae must be very elastic Also found in walls of many large arteries Arteries need to stretch when blood enters and recoil to push blood out Cartilage o Matrix secreted from chondroblasts (during growth) and hondrocytes (adults) o Chondrocytes found in cavities called lacunae o 80% water, with packed collagen fibers and sugar proteins (chondroitin and hyaluronic acid) o Tough yet flexible material that lacks nerve fibers o Avascular : receives nutrients form membrane surrounding it (richondrium ) o Perichondrium gives rise to chondroblasts and chondrocytes o Three types of cartilage: o Hyaline cartilage Most abundant; "gristle" Appears as shiny bluish glass Found as tips of long bones, nose, trachea, larynx, and cartilage of the ribs o Elastic cartilage Similar to hyaline but with more elastic fibers Found in ears and epiglottis o Fibrocartilage Properties between hyaline and dense regular tissue Strong, so found in areas such as intervertebral discs and knee Bone o Also called osseous tissue o Supports and protects body structures o Stores fat and synthesized blood cells in cavities o Has more collagen compared to cartilage o Has inorganic calcium salts o Osteoblasts produce matrix o Osteocytes maintain the matrix o Reside in cavities in matrix called lacunae o Osteons: individual structural units o Richly vascularized Blood o Most atypical connective tissue because it is fluid o Consists of cells surrounded by matrix (plasma) o Red blood cells are most common cell type o Also contains white blood cells and platelets o Fibers are soluble proteins that precipitate during blood clotting o Functions in transport and in carrying nutrients, wastes, gases, and other substances Excitable Tissues Muscular & Nervous Excitability: a characteristic of all living cells o Developed to highest degree in nervous and muscular tissues Membrane potential : electrical charge difference (voltage) that occurs the plasma membranes is the basis for their excitation o Respond quickly to outside stimulus by means of changes in membrane potential o Nerves : changes result in rapid transmission of signals to other cells o Muscles : changes results in contraction, shortening of the cell Muscular Tissue Muscular tissue: elongated cells (especially in skeletal muscle) 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 4.4 Muscle Tissue Highly vascularized Responsible for most types of movement o Muscle cells possess myofilaments made up of actin and myosin proteins that bring about contraction Three types of muscle tissues: o Skeletal muscle o Cardiac muscle o Smooth muscle Skeletal Muscle Skeletal muscle tissue: attached to and causes movement of bones Also called voluntary muscle o Skeletal muscles can by consciously controlled (usually) Cells are called uscle fibers o Contain multiple nuclei Appear striated or banded Cardiac Muscle Found only in walls of heart Involuntary muscle Like skeletal muscle, contains striations; but cells have only one nucleus Cells can have many branches that join branches of other cardiac cells o Intercalated discs are special joints where cardiac cells are joined Smooth Muscle Tissue Found mainly in walls of hollow organs (other than heart) Involuntary muscle Has no visible striations Spindleshaped cells with one nucleus 4.5 Nervous Tissue Main component of nervous system (brain, spinal cord, nerves) o Regulates and controls body functions Made up of two specialized cells: o Neurons: specialized nerve cells that generate and conduct nerve impulses o Supporting cells that support, insulate, and protect neurons 4.6 Covering and Lining Membranes Composed of at least two primary tissue types: and epithelium bound to underlying connective tissue proper layer Three types o Cutaneous membranes o Mucous membranes o Serous membranes Cutaneous Membranes o Another name for skin o Keratinized stratified squamous epithelium (idermis) attached to a thick layer of connective tissue (mis ) o Unlike other membranes, skin is a dry membrane Mucous Membranes o Mucosa indicates location, not cell composition o Also called ucosae o Line body cavities that are open to the exterior (example: digestive, respiratory, urogenital tracts) o Moist membranes bathed by secretions (or urine) o Epithelial sheet lies over layer of loose connective tissue called propria o May secrete mucus Serous Membranes o Also called erosae o Found in closed ventral body cavities o Constructed from simple squamous epithelium (called mesothelium) resting on thin areolar connective tissue o Parietal serosae line internal body cavity walls o Visceral serosae cover internal organs o Cavity between layers is filled with slippery serous fluid, so these are moist membranes o Special names given to show location: eurae (lungs), ricardium (heart), peritoneum (abdomen) 4.7 Tissue Repair When the body's barriers are compromised, the inflammatory* and immune responses are activated Repair starts very quickly Repair is the function of the inflammatory process Steps in Tissue Repair Repair can occur in two major ways: o Regeneration : same kind of tissue replaces destroyed tissue, so original function is restored o Fibrosis: connective tissue replaces destroyed tissue, and original function lost (scarring) Step 1: Inflammation sets stage o Release of inflammatory chemicals causes: o Dilation of blood vessels o Increase in blood vessel permeability o Clotting of blood occurs o Bleeding from a cut means you've reached the dermis Step 2: Organization restores blood supply o Organization begins as the blood clot is replaced withnulation tissue (new capillaryenriched tissue) o Epithelium begins to regenerate o Fibroblasts produce collagen fibers to bridge the gap until regeneration is complete o Any debris in area is phagocytized Step 3: Regeneration and fibrosis effect permanent repair o The scab detaches o Fibrous tissue matures into a scar o Epithelium thickens and begins to resemble adjacent tissue o Results in a fully regenerated epithelium with underlying scar tissue, which may or may not be visible Regenerative Capacity of Different Tissues Tissues that regenerate extremely well include: o Epithelial tissues, bone, areolar, connective tissue, dense irregular connective tissue, bloodforming tissue Tissue with moderate regenerating capacity: o Smooth muscle and dense regular connective tissue Tissues with virtually no functional regeneration capacity: o Cardiac muscle and nervous tissue of brain and spinal cord, skeletal muscle o New research shows cell division does occur, and efforts are underway to coax them to regenerate better Tissue Growth Tissue growth: increasing the number of cells or the existing cells grow larger Hyperplasia : tissue growth through cell multiplication o Much of growth through childhood & adolescence Hypertrophy : enlargement of preexisting cells o Muscle growth through exercise o Accumulation of body fat Neoplasia: development of a tumor (neoplasm; neo = new, plasia = growth) o Benign or malignant o Composed of abnormal, nonfunctional tissue Changes in Tissue Types Tissues can change types by: Differentiation o Unspecialized tissues of embryo become specialized mature types o E.g., mesenchyme to cartilage o Metaplasia o 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 Atrophy Atrophy: shrinkage of tissue through a loss in cell size or number o Senile atrophy through normal aging o Disuse atrophy from lack of use (astronauts) Apoptosis Apoptosis : programmed cell death o Normal death of cells that have completed their function and best serve the body by dying and getting out of the way Necrosis Necrosis : premature, pathological death of tissue die to trauma, toxins, or infections o Infarction: sudden death of tissue when blood supply is cut off o Gangrene : tissue necrosis due to insufficient blood supply o Decubitus ulcer: bed sore or pressure sore Pressure reduced blood flow to an area A form of dry gangrene o Gas gangrene: anaerobic bacterial infection
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