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, non-

living 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’

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

May be ciliated or

possess microvilli or

smooth

ciliated surface

“Brush border”

Consider increase in surface area

for absorption, exchange, enzymatic

function

Epithelial

layer

Basement

membrane

Underlying

connective

tissueTubule lumen

Basement membrane = Basal lamina +

reticular laminaReinforces epithelial sheet and defines epithelial boundary

Resists stretching and tearing

Foundation for repair

Classification of Epithelial TissueNumber of layers of cells

• Simple

• Stratified

• Pseudostratified

Shape of cells at surface

• Squamous

• Cuboidal

• Columnar

Simple squamous epithelium

Description: Single layer offlattened cells with disc-shapedcentral nuclei and sparsecytoplasm; the simplest of theepithelia.

Air sacs oflung tissue

Nuclei ofsquamousepithelialcells

Function: Allows materials topass by diffusion and filtrationin sites where protection is notimportant; secretes lubricatingsubstances in serosae.

Location: Kidney glomeruli;air sacs of lungs; lining of heart,blood vessels, and lymphaticvessels; lining of ventral bodycavity (serosae).

Photomicrograph: Simple squamousepithelium forming part of the alveolar(air sac) walls (140×).

Simple cuboidal epithelium

Description: Single layerof cubelike cells with large,spherical central nuclei.

Simplecuboidalepithelialcells

Nucleus

Function: Secretion andabsorption. Basement

membrane

Location: Kidney tubules;ducts and secretory portionsof small glands; ovary surface.

Photomicrograph: Simple cuboidalepithelium in kidney tubules (430×).

Connectivetissue

Simple columnar epithelium

Description: Single layer of tall

cells with round to oval nuclei; manycells bear microvilli, some bear cilia;layer may contain mucus-secretingunicellular glands (goblet cells).

Microvilli

Simplecolumnarepithelialcell

Function: Absorption; secretion

of mucus, enzymes, and othersubstances; ciliated type propelsmucus (or reproductive cells) byciliary action.

Location: Nonciliated type lines

most of the digestive tract (stomachto rectum), gallbladder, and excretoryducts of some glands; ciliated varietylines small bronchi, uterine tubes,and some regions of the uterus.

Mucus ofgoblet cell

Photomicrograph: Simple columnarepithelium of the small intestine mucosa(640×).

Pseudostratified columnar epithelium

Description: Single layer of cells

of differing heights, some notreaching the free surface; nucleiseen at different levels; maycontain mucus-secreting cells andbear cilia.

Goblet cell(containsmucus)

Cilia

Pseudo-stratifiedepitheliallayer

Function: Secrete substances,

particularly mucus; propulsionof mucus by ciliary action.

Location: Nonciliated type in

males’ sperm-carrying ducts andducts of large glands; ciliatedvariety lines the trachea, most ofthe upper respiratory tract.

Basementmembrane

Photomicrograph: Pseudostratified ciliatedcolumnar epithelium lining the human trachea(780×).

Trachea

Stratified squamous epithelium

Description: Thick membrane

composed of several cell layers;basal cells are cuboidal or columnarand metabolically active; surfacecells are flattened (squamous); in thekeratinized type, the surface cells arefull of keratin and dead; basal cells

are active in mitosis and produce thecells of the more superficial layers.

Stratifiedsquamousepithelium

Function: Protects underlying

tissues in areas subjected toabrasion.

Location: Nonkeratinized type forms

the moist linings of the esophagus,mouth, and vagina; keratinized varietyforms the epidermis of the skin, a drymembrane.

Nuclei

Basementmembrane

Connectivetissue

Photomicrograph: Stratified squamousepithelium lining the esophagus (285×).

Transitional epithelium

Description: Resembles bothstratified squamous andstratified cuboidal; basal cellscuboidal or columnar; surfacecells dome shaped orsquamouslike, depending ondegree of organ stretch.

Transitionalepithelium

Function: Stretches readily,permits stored urine to distendurinary organ.

Location: Lines the ureters,bladder, and part of the urethra.

Basementmembrane

Photomicrograph: Transitional epithelium

lining the bladder, relaxed state (360×); notethe bulbous, or rounded, appearance of thecells at the surface; these cells flatten andelongate when the bladder fills with urine.

Connectivetissue

Epithelium

classification

Function Location

Simple

squamous

Allows materials to pass by

diffusion and filtration in sites

where protection is not important;

secretes lubricating substances in

serosae

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

Absorption; secretion of mucus,

enzymes, and other substances;

ciliated type propels mucus (or

reproductive cells) by ciliary action

Nonciliated type lines most of the

digestive tract, gallbladder, and excretory

ducts of some glands; ciliated variety

lines small bronchi, uterine tubes

Stratified

squamous

Protects underlying tissues in

areas subjected to abrasion

Nonkeratinized type forms the moist

linings of the esophagus, mouth, and

vagina; keratinized variety forms the

epidermis of the skin, a dry membrane

Pseudostratified

columnar

Secrete substances, particularly

mucus; propulsion of mucus by

ciliary action

Nonciliated type in male’s sperm-carrying

ducts and ducts of large glands; ciliated

variety lines the trachea, most of the

upper respiratory tract

Transitional Stretches readily, permits stored

urine to distend urinary organ

Lines the ureters, bladder, and part of the

urethra

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

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

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

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

Extracellular matrix

Ground substanceFibers

• Collagen fiber

• Elastic fiber

• Reticular fiber

Capillary

Neutrophil

Mast cell

Fat cell

Lymphocyte

Fibroblast

Macrophage

Cell types

Figure 4.7 Areolar

connective tissue:

A prototype (model)

connective tissue.

Connective tissue proper: loose connective tissue, areolar

Description: Gel-like matrix with

all three fiber types; cells:fibroblasts, macrophages, mastcells, and some white blood cells. Elastic

fibers

Function: Wraps and cushions

organs; its macrophagesphagocytize bacteria; playsimportant role in inflammation;holds and conveys tissue fluid.

Groundsubstance

Fibroblastnuclei

Collagen

fibers

Location: Widely distributed

under epithelia of body, e.g.,forms lamina propria of mucousmembranes; packages organs;surrounds capillaries.

Epithelium Photomicrograph: Areolar connective tissue,a soft packaging tissue of the body (340×).

Lamina

propria

Connective tissue proper: loose connective tissue, adipose

Description: Matrix as inareolar, but very sparse; closelypacked adipocytes, or fat cells,have nucleus pushed to theside by large fat droplet.

Function: Provides reservefood fuel; insulates againstheat loss; supports andprotects organs.

Location: Under skin insubcutaneous tissue; aroundkidneys and eyeballs; withinabdomen; in breasts.

Adiposetissue

Photomicrograph: Adipose tissue from thesubcutaneous layer under the skin (350×).

Nucleus ofadipose(fat) cell

Fat droplet

Mammary

glands

Connective tissue proper: loose connective tissue, reticular

Description: Loose networkof reticular fibers in a gel-likeground substance; reticularcells lie on the network.

Function: Fibers form a softinternal skeleton (stroma) thatsupports other cell typesincluding white blood cells,mast cells, and macrophages.

Whiteblood cell(lymphocyte)

Reticularfibers

Location: Lymphoid organs(lymph nodes, bone marrow,and spleen).

Photomicrograph: Dark-staining networkof reticular connective tissue fibers formingthe internal skeleton of the spleen (350×).

Spleen

CT Proper Function Location

Loose and loose fibrous CT

Areolar Wraps and cushions organs; its

macrophages phagocytize bacteria;

plays important role in inflammation;

holds and conveys tissue fluid

Widely distributed under

epithelia of body, e.g., forms

lamina propria of mucous

membranes; packages

organs; surrounds capillaries

Adipose Provides reserve food fuel; insulates

against heat loss; supports and

protects organs

Under skin in subcutaneous

tissue; around kidneys and

eyeballs; within abdomen; in

breasts

Reticular Fibers form a soft internal skeleton

(stroma) that supports other cell types

including white blood cells, mast cells,

and macrophages

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

Connective tissue proper: dense connective tissue, dense regular

Description: Primarily parallelcollagen fibers; a few elasticfibers; major cell type is thefibroblast.

Function: Attaches muscles tobones or to muscles; attachesbones to bones; withstandsgreat tensile stress whenpulling force is applied in onedirection.

Location: Tendons, mostligaments, aponeuroses.

Collagenfibers

Nuclei offibroblasts

Shoulderjoint

Photomicrograph: Dense regular connectivetissue from a tendon (430×).

Ligament

Tendon

Connective tissue proper: dense connective tissue, dense irregular

Description: Primarilyirregularly arranged collagenfibers; some elastic fibers;fibroblast is the major cell type.

Nuclei of

fibroblasts

Function: Withstands tensionexerted in many directions;provides structural strength.

Location: Fibrous capsules oforgans and of joints; dermis ofthe skin; submucosa ofdigestive tract.

Shoulder

joint

Photomicrograph: Dense irregular connectivetissue from the fibrous capsule of a joint (430×).

Fibrousjointcapsule

Collagen

fibers

Connective tissue proper: dense connective tissue, elastic

Description: Dense regularconnective tissue containing ahigh proportion of elastic fibers.

Function: Allows tissue torecoil after stretching; maintainspulsatile flow of blood througharteries; aids passive recoil oflungs following inspiration.

Elastic

fibers

Location: Walls of largearteries; within certain ligamentsassociated with the vertebralcolumn; within the walls of thebronchial tubes.

Photomicrograph: Elastic connective tissuein the wall of the aorta (250×).

Aorta

Heart

CT Proper Function Location

Dense fibrous CT

Dense regular Attaches muscles to bones or to

muscles; attaches bones to bones;

withstands great tensile stress

when pulling force is applied in one

direction

Tendons, most ligaments,

aponeuroses

Dense

irregular

Withstands tension exerted in many

directions; provides structural

strength

Fibrous capsules of organs

and of joints; dermis of the

skin; submucosa of digestive

tract

Elastic Allows tissue to recoil after

stretching; maintains pulsatile flow

of blood through arteries; aids

passive recoil of lungs following

inspiration

Walls of large arteries; within

certain ligaments associated

with the vertebral column;

within the walls of the

bronchial tubes

Cartilage: hyaline

Description: Amorphous butfirm matrix; collagen fibers forman imperceptible network;chondroblasts produce thematrix and when mature(chondrocytes) lie in lacunae.

Function: Supports andreinforces; serves as resilientcushion; resists compressivestress.

MatrixLocation: Forms most of theembryonic skeleton; covers theends of long bones in jointcavities; forms costal cartilagesof the ribs; cartilages of thenose, trachea, and larynx.

Photomicrograph: Hyaline cartilage froma costal cartilage of a rib (470×).

Chondrocyte

in lacuna

Costal

cartilages

Cartilage: fibrocartilage

Description: Matrix similar tobut less firm than that in hyalinecartilage; thick collagen fiberspredominate.

Function: Tensile strengthallows it to absorb compressiveshock.

Chondrocytes

in lacunae

Collagen

fiber

Location: Intervertebral discs;pubic symphysis; discs of kneejoint.

Intervertebral

discs

Photomicrograph: Fibrocartilage of an

intervertebral disc (125×). Special stainingproduced the blue color seen.

Cartilage: elastic

Description: Similar to hyalinecartilage, but more elastic fibersin matrix.

Function: Maintains the shape ofa structure while allowing greatflexibility.

Location: Supports the externalear (pinna); epiglottis.

Photomicrograph: Elastic cartilage fromthe human ear pinna; forms the flexibleskeleton of the ear (800x).

Chondrocytein lacuna

Matrix

Others: bone (osseous tissue)

Description: Hard, calcifiedmatrix containing manycollagen fibers; osteocyteslie in lacunae. Very wellvascularized.

Function: Supports andprotects (by enclosing);provides levers for the musclesto act on; stores calcium andother minerals and fat; marrowinside bones is the site forblood cell formation(hematopoiesis).

Location: Bones

Central

canal

Lacunae

Lamella

Photomicrograph: Cross-sectional view ofbone (125×).

Connective tissue: blood

Description: Red and whiteblood cells in a fluid matrix(plasma). Red blood

cells(erythrocytes)

White blood

cells:• Lymphocyte• Neutrophil

Function: Transportrespiratory gases, nutrients,wastes, and other substances.

Location: Contained withinblood vessels.

Plasma

Photomicrograph: Smear of human blood (1670×);shows two white blood cells surrounded by redblood cells.

CT Type Function Location

Hyaline

cartilage

Supports and reinforces; serves as

resilient cushion; resists

compressive stress

Lacks nerves, blood vessels

Most abundant type

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

Elastic

cartilage

Maintains the shape of a structure

while allowing great flexibility

Supports the external ear (pinna);

epiglottis

Fibro-

cartilage

Matrix similar to but less firm than

that in hyaline cartilage; thick

collagen fibers predominate

Intervertebral discs; pubic

symphysis; discs of knee joint

Bone 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

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

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 arebranching cells; cell processesthat may be quite long extend fromthe nucleus-containing cell body;also contributing to nervous tissueare nonexcitable supporting cells.

Function: Neurons transmitelectrical signals from sensoryreceptors and to effectors (musclesand glands) which control theiractivity; supporting cells supportand protect neurons.

Location: Brain, spinal

cord, and nerves.

Photomicrograph: Neurons (350x).

Neuronprocesses

Nuclei ofsupportingcells

Cell bodyof a neuron

Neuron processes Cell body

Axon Dendrites

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

Slide 1

Scab

Blood clot inincised wound

Epidermis

Vein

Inflammatorychemicals

Migrating whiteblood cell

ArteryInflammation 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.

1

Regenerating epithelium

Area of granulationtissue ingrowth

Macrophage

Budding capillary

Fibroblast

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.

2

Regeneratedepithelium

Fibrosed area

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.

3

Regenerative Capacity in Different Tissues

A. Regenerate extremely well

– Epithelial tissues, bone, areolar connective tissue,

dense irregular connective tissue, blood-forming

tissue

B. Moderate regenerating capacity

– Smooth muscle and dense regular connective tissue

C. 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