BIO 210 LabInstructor Dr. Rebecca Clarke

Chapter 4 The Tissue Level of Organization

Tissue

Histology = study of tissuesTissue = group of cells that perform

specific, limited functions

Composition of TissuesBasic components

CellsMatrix

Surrounds cellsConsists of

Ground substanceProtein fibers or proteins

4 Major Groups of TissuesEpithelial tissueConnective tissueMuscle tissueNeural tissue

Epithelial Tissue Covers exposed surfacesLines internal passagewaysForms glands

Connective Tissue Fills internal spacesSupports other tissuesTransports materialsStores energy

Muscle Tissue Specialized for contraction movement

Neural Tissue Carries electrical signals (nerve impulses)

from one part of the body to another

Epithelial Tissue Includes

Epithelia = layers of cells that coverExternal/exposed surfaces (skin)Internal surfaces that line internal passageways and

cavitiesGlands = cellular structures that produce

secretions; are attached to or derived from epithelia

Classes of EpitheliaBased on cell shape and layers

Table 4–1

Figure 4–3a

Simple Squamous Epithelium

Figure 4–3b

Stratified Squamous Epithelium

Simple Cuboidal Epithelium

Figure 4–4a

Stratified Cuboidal Epithelium

Figure 4–4b

Transitional Epithelium

Figure 4–4c

Simple Columnar Epithelium

Figure 4–5a

Stratified Columnar Epithelium

Figure 4–5c

Pseudostratified Columnar Epithelium

Figure 4–5b

Glandular Epithelia

Endocrine and exocrine glands

Range from scattered cells to complex organs (glands)

Figure 4–6

Endocrine GlandsDuctless glandsRelease secretions (hormones) into

interstitial fluid or bloodRegulate/coordinate activities of many

tissues, organs, organ systems

Exocrine GlandsRelease secretions

onto epithelial surfaces, e.g., simplest = one-cell goblet cell (in respiratory and digestive tracts)

through ducts, e.g., sweat, digestive, lacrimal, mammary glands

What are the structures and functions of different types of connective tissues?

Characteristics of Connective Tissues

Fills internal spacesMany diverse functionsMany highly-specialized cellsMuch more matrix than cells

Components of ConnectiveTissueCells – highly varied, specialized

populationsMatrix

Consists ofGround substance Fills spaces between cells and surrounds connective

tissue fibers Clear, colorless, amorphous substance; changes

according to tissue Viscous (“syrupy”) due to proteoglycans and

glycoproteinsProtein fibers/proteins

Can be fluid, gel or solid, e.g., gelatin dessertDetermines specialized function

Classification of Connective TissuesConnective tissue proper

Connects and protectsLoose and dense connective tissues

Fluid connective tissuesTransport systemsBlood and lymph

Supporting connective tissuesStructural strengthCartilage and bone

Connective Tissue Proper

Figure 4–8

8 Cell Types of Connective Tissue ProperMesenchymal

cellsFibroblastsPhagocytes

MacrophagesMicrophages

Mast cellsAdipocytesMelanocytes Lymphocytes

Mesenchymal CellsMesenchyme = first connective tissue in

developing embryo (see text Fig 4-9)Are connective tissue stem cells; give

rise to all other connective tissue cellse.g., Respond to local injury/infection by

dividing daughter cells that differentiate into other connective tissue cells, e.g., fibroblasts, macrophages, etc.

Fibroblasts“Fiber builder”Most abundant cell typeFound in all connective tissue properSecrete

polysaccharide (+ protein proteoglycans viscous ground substance)

protein subunits large fibers

PhagocytesPhagocytes (“cell eaters”)

Macrophages (“big eaters”)Microphages (“little eaters”)

MacrophagesLarge, amoeba-like cells of the immune

systemEat pathogens and damaged cells;

“garbage disposal” cellsRelease chemicals that activate immune

system mobilizes body defenses2 classes

fixed macrophages stay in tissue; frontline defense

free macrophages migrate through tissues; reinforcements

Microphages(NOT in Fig 4-8)

Phagocytic white blood cells (WBCs), i.e., neutrophils and eosinophils

Attracted to site of infection/injury by chemicals released by macrophages

Mast CellsSmall mobile cellsStimulate inflammation after injury or

infectionCytoplasm filled with granules that

contain/release histamine and heparinBasophils are mast cells carried by blood

AdipocytesAdipose or fat cellsStore fatContain single, large lipid droplet; nucleus,

other organelles, cytoplasm squeezed to side class ring appearance

Number of cells varies with tissue, body region, individual

Melanocytes Synthesize, store melanin (brown pigment)

dark colorCommon in skin epitheliumDetermine skin, eye, hair color

LymphocytesSpecialized immune cells in lymphatic

systeme.g., plasma cells that produce antibodies;

one of body’s defense mechanismsWBCs that leave bloodstream and migrate

throughout bodyNumbers increase with tissue damage

Protein FibersProvide structural strength to connective

tissues3 types

CollagenReticularElastic

Collagen FibersMost common fibersLarge, long, straight, unbranchedStrong, flexible (like rope); very little

stretchPredominate in ligaments (connect bone to

bone) and tendons (connect muscle to bone)

Reticular FibersSame protein subunits as collagen but

Thinner, shorterArranged differently branched network of

interwoven fibers (stroma)Strong, flexibleStabilizes functional cells of organs

(parenchyma), e.g., hepatic cells of liverStabilizes position of blood vessels,

nerves, etc.Connects epithelium to body

Elastic FibersContain protein elastinBranched and wavyReturn to original length after stretchinge.g., elastic ligaments of vertebrae

Categories of Connective Tissue ProperLoose connective tissue

more ground substance, less fibers e.g., fat (adipose tissue)

Dense connective tissuemore fibers, less ground substancee.g., tendons

Loose Connective TissueFew soft fibers loose, open framework;

“packing materials” of bodyFills spaces between organsCushions, stabilizes cellsSupports epithelia, blood vessels, nerves

Loose Connective Tissue (cont.)3 types

Areolar tissueAdipose tissueReticular tissue

Areolar TissueLeast specializedOpen framework of cells/fibersCan distort, return to original shape

because of elastic fibers Most of volume is viscous ground

substanceHighly vascular, e.g., subcutaneous

layer under skin, common injection siteFig 4-8

Adipose Tissue

Primarily adipocytes (adipose cells)

Figure 4–10a

Adipose CellsAdipocytes in adults do not divide

expand to store fatshrink as fats are released

Mesenchymal cells divide and differentiateto produce more fat cellswhen more storage is needed

Reticular TissuePrimarily reticular fibers

Figure 4–10b

Reticular TissueComplex, 3-dimensional networkSupportive fibers (stroma)

support functional cells (parenchyma)Reticular organs

spleen, liver, lymph nodes, and bone marrow

Dense Connective TissuesTightly packed with high numbers of

collagen or elastic fibersMany fibroblastsVery strong tissuesTypes of dense connective tissues

dense regular connective tissuedense irregular connective tissueelastic tissue

Dense Regular Connective TissueTightly packed, parallel collagen fibersMake up tendons, ligaments, aponeuroses

Figure 4–11a

Dense Regular Connective TissuesTendons - attach skeletal muscles to bonesLigaments - connect bone to bone and

stabilize organsAponeuroses - attach in sheets on large,

flat muscles

Dense Irregular Connective TissueStrength in many directions

Figure 4–11b

Dense Irregular Connective Tissues

Interwoven meshwork of collagen fibers layered in skinaround cartilages (perichondrium)around bones (periosteum)form capsules around some organs (e.g.,

liver, kidneys, spleen)

Elastic TissueMade of elastic fibers

e.g., elastic ligaments of spinal vertebrae

Figure 4–11c

Fluid Connective TissuesBlood and lymphCells suspended in fluid matrix = watery

ground substance with dissolved proteins

Blood Formed Elements

RBCs (erythrocytes)WBCs (leukocytes)Platelets

Figure 4–12

LymphCells – 99% lymphocytes, rest are

macrophages or microphages Matrix = fluid from CVS exits at capillaries

interstitial fluid enters lymphatic vessels (= lymph) that return it to CVS (recirculatory system)

Along way, cells of immune system monitor composition of lymph and respond to signs of injury or infection

Essential to homeostasis – eliminates local differences in nutrients, wastes, toxins, maintains blood volume, alerts immune system

Fluid Tissue Transport SystemsCardiovascular system (blood)

arteriescapillariesveins

Lymphatic system (lymph)lymphatic vessels

Supporting Connective TissuesSupport soft tissues and body weight

Cartilage for shock absorption and protection

Bone for weight support

Supporting Connective TissuesCharacteristics

Provide strong framework that supports bodyCells – less diverse than CTMatrix

Dense ground substanceCartilage – rubbery, gel-likeBone - calcified, crystalline, solid matrix

Many fibers

Cartilage ComponentsCells

Chondrocytes = only cells presentOccupy lacunae (small chambers)

Matrix Ground substance = firm gel with…Chondroitin sulfates (polysaccharide

derivatives); form complexes with proteins proteoglycans

Protein fibersType and number + proteoglycans determine

physical properties

Cartilage StructureAvascular = no blood vessels

chondrocytes produce antiangiogenesis factor

Perichondriumsurrounds cartilage and separates it from

tissue

Types of CartilageHyaline cartilage

translucent matrixno prominent fibers

Elastic cartilagetightly packed elastic fibers

Fibrocartilagevery dense collagen fibers

Hyaline Cartilage

Figure 4–14a

Hyaline CartilageMost commonMatrix - contains closely packed

collagen fibers tough, flexible supportReduces friction between bonesExamples

Connects ribs and sternumNasal cartilagesCartilages that support respiratory

passageways, e.g., tracheaArticular cartilages – cover bone surfaces

within synovial joints, e.g., elbow, knee; reduce friction

Elastic Cartilage

Figure 4–14b

Elastic CartilageMany elastic fibers resilient, flexible

structures; supports but bends easilyExamples

auricle/pinna of outer earepiglottis (in larynx) auditory tube (airway to middle ear)small cartilages in larynx

Fibrocartilage

Figure 4–14c

FibrocartilageVery little ground substanceMatrix dominated by densely

interwoven collagen fibers extremely durable, toughResists compressionActs as shock absorberPrevents bone-to-bone contact

Examples:Intervertebral discs = pads between

vertebraeBetween pubic bonesPads knee joints

BoneAlso called osseous tissueOsteocyte = bone cell

Arranged around central canalSmall channels through matrix (canaliculi)

access blood supplyPeriosteum

covers bone surfaceHelps attach bone to surrounding tissues,

tendons, ligaments

Bone

Figure 4–15

Bone Ground Substance Very small amount of ground substance 2/3 of matrix is calcium salts (minerals) =

hydroxyapatiteCalcium phosphateCalcium carbonate

1/3 of matrix dominated by collagen fibers Minerals organized around collagen fibers Remarkable properties of bone

Strong (calcified salts) + somewhat flexible structure (collagen fibers)

Highly resistant to shattering (like steel-reinforced concrete mineralized matrix like concrete collagen fibers equiv to steel reinforcing rods

Comparing Cartilage and Bone

Table 4–2

What are the structures and functions of the three types of muscle tissue?

Muscle TissueSpecialized for contraction; produces all

body movementDistinct organelles and processesMultinuclearHas many fibers; orderly appearanceunder voluntary or involuntary controlOne of two kinds of cells/tissues in body

that stop replicating past stage of growth and development; (other is neural tissues/neurons)

3 Types of Muscle TissueSkeletal muscle - large body muscles

responsible for movementCardiac muscle - found only in the heartSmooth muscle - found in walls of hollow,

contracting organs (blood vessels; urinary bladder; respiratory, digestive and reproductive tracts)

Classification of Muscle CellsStriated (muscle cells with a banded

appearance) or nonstriated (not banded)

Single nucleus or multinucleate

Controlled voluntarily (consciously)or involuntarily (automatically)

Skeletal Muscle Striated, voluntary, multinucleated

Figure 4–18a

Skeletal Muscle CellsVery long (some > 1 ft) and thin; called muscle

fibersMultinucleate; 100s of nuclei/cellCytoskeleton contains actin and myosin filaments

Filaments organized into repeating groups striated/banded appearance

Contract when stimulated by nerves; provide voluntary control over muscle activities

Adjacent muscle fibers connected by collagen and elastic fibers that blend into attached tendon or aponeurosis; when contract, pull on attached bone, producing movement

Can’t divide; new muscle fibers produced through divisions of satellite (stem) cells; can partially repair after injury

Cardiac Muscle TissueStriated, involuntary, single nucleus

Figure 4–18b

Cardiac Muscle Cells Cardiac muscle cell = cardiocyte

Smaller than skeletal muscle cellUsually one centrally positioned nucleusActin and myosin filaments arranged in same way as in

skeletal muscle; striations Cells form branching networks; connected at specialized

regions = intercalated discs (like dovetail joints) Ion movement through gap junctions helps coordinate

contractions throughout heart Rely on pacemaker cells to establish regular rate of

contraction; neural stimulation not required Involuntary muscle contractions Very limited ability to repair

Smooth Muscle TissueNonstriated, involuntary, single nucleus

Figure 4–18c

Smooth Muscle Cells Smooth muscle cell

small, spindle-shaped cell, tapered endssingle oval nucleusactin and myosin filaments organized differently from those

of skeletal and cardiac muscles, no striations “smooth” appearance

Nervous system does not provide voluntary control over contractions; hence, smooth muscle = involuntary muscle

Cells can divide and regenerate after injury Location:

Walls of blood vesselsAround hollow organs, e.g., urinary bladder In layers around respiratory, circulatory, digestive,

reproductive tracts

What is the basic structure and role of neural tissue?

Neural (Nervous) TissueSpecialized for conducting electrical

impulsesRapidly senses internal or external

environmentProcesses information and controls

responses

Neural Tissue98% concentrated in central nervous

system (CNS)brainspinal cord

Remaining 2% in peripheral nervous system (PNS)

2 Types of Neural Cells1. Neurons

nerve cells perform electrical communication

2. Neuroglia support cells repair and supply nutrients to neurons

Neuron

Figure 4–19

Cell Parts of a NeuronCell body

contains the nucleus and nucleolusDendrites

short branches extending from the cell bodyreceive incoming signals

Cell Parts of a NeuronAxon (nerve fiber)

long, thin extension of the cell bodycarries outgoing electrical signals to their

destination

Characteristics of NeuronsLongest cells in body – some > 1 meterCannot divide under normal circumstances

so very limited ability to repair selvesOne of only two kinds of cells/tissues in

body that stop replicating after stage of growth and development (other is muscle tissue)

Neuroglia

Figure 4–19