© 2013 Pearson Education, Inc. Connective Tissue Most abundant and widely distributed of primary tissues Four main classes –Connective tissue proper –Cartilage

© 2013 Pearson Education, Inc.

Connective Tissue

• Most abundant and widely distributed of primary tissues

• Four main classes– Connective tissue proper– Cartilage– Bone – Blood


Table 4.1 Comparison of Classes of Connective Tissues (1 of 2)


Table 4.1 Comparison of Classes of Connective Tissues (2 of 2)


Major Functions of Connective Tissue

• Binding and support

• Protecting

• Insulating

• Storing reserve fuel

• Transporting substances (blood)


Characteristics of Connective Tissue

• Three characteristics make connective tissues different from other tissues– Have varying degrees of vascularity (blood

vessels)– Have extracellular matrix

• Connective tissue not composed mainly of cells• Largely nonliving extracellular matrix separates

cells– So can bear weight, withstand tension, endure abuse


Structural Elements of Connective Tissue

• Three elements– Ground substance– Fibers– Cells

• Composition and arrangement varies in different connective tissues


Ground Substance

• Unstructured material that fills space between cells– Medium through which solutes diffuse between blood

capillaries and cells

• Components– Interstitial fluid– Cell adhesion proteins ("glue" for attachment) – Proteoglycans

• Protein core + large polysaccharides (chrondroitin sulfate and hyaluronic acid)

• Trap water in varying amounts, affecting viscosity of ground substance


Connective Tissue Fibers

• Three types of fibers provide support– Collagen

• Strongest and most abundant type• Tough; provides high tensile strength

– Elastic fibers• Networks of long, thin, elastin fibers that allow for

stretch and recoil

– Reticular• Short, fine, highly branched collagenous fibers

(different chemistry and form than collagen fibers)• Branch, forming networks that offer more "give"


Cells

• "Blasts" cells– Immature forum; mitotically active; secrete ground

substance and fibers – Fibroblasts in connective tissue proper– Chondroblasts in cartilage– Osteoblasts in bone– Hematopoietic stem cells in bone marrow– "Cyte" cells– Mature form; maintain matrix– Chondrocytes in cartilage – Osteocytes in bone


Other Cell Types in Connective Tissues

• Fat cells– Store nutrients

• White blood cells– Neutrophils, eosinophils, lymphocytes– Tissue response to injury

• Mast cells– Initiate local inflammatory response against foreign

microorganisms they detect

• Macrophages– Phagocytic cells that "eat" dead cells,

microorganisms; function in immune system


Extracellular matrixGround substanceFibers• Collagen fiber• Elastic fiber• Reticular fiber

Capillary

Neutrophil

Mast cell

Fat cell

Lymphocyte

Fibroblast

Macrophage

Cell typesFigure 4.7 Areolar connective tissue: A prototype (model) connective tissue.


Types of Connective Tissues: Connective Tissue Proper

• All connective tissues except bone, cartilage and blood

• Two subclasses– Loose connective tissues

• Areolar• Adipose• Reticular

– Dense connective tissues (also called fibrous connective tissues)

• Dense regular• Dense irregular• Elastic


Areolar Connective Tissue

• Support and bind other tissues– Universal packing material between other tissues

• Most widely distributed• Provide reservoir of water and salts• Defend against infection• Store nutrients as fat• Fibroblasts• Loose arrangement of fibers• Ground substance• When inflamed soaks up fluid edema


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.

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.

Epithelium

Lamina propria

Photomicrograph: Areolar connectivetissue, a soft packaging tissue of the body (340x).

Elastic fibers

Ground substance

Fibroblast nuclei

Collagen fibers

Figure 4.8a Connective tissues.


Adipose Tissue

• White fat – Similar to areolar but greater nutrient storage– Cell is adipocyte

• Stores nutrients

– Scanty matrix– Richly vascularized– Shock absorption, insulation, energy storage

• Brown fat– Use lipid fuels to heat bloodstream not to

produce atp


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.

Photomicrograph: Adipose tissue fromthe subcutaneous layer under the skin (350x).

Nucleus of adipose(fat) cell

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. Fat droplet

Adipose tissue

Mammary glands

Figure 4.8b Connective tissues.


Reticular Connective Tissue

• Resembles areolar but fibers are reticular fibers

• Fibroblasts called reticular cells

• Supports free blood cells in lymph nodes, the spleen, and bone marrow


Connective tissue proper: loose connective tissue, reticular

Description: Network of reticular fibers in a typical loose ground substance; reticular cells lie on the network.

Photomicrograph: Dark-staining network of reticular connective tissue fibers forming the internal skeleton of the spleen (350x).

White blood cell(lymphocyte)Location: Lymphoid organs (lymph

nodes, bone marrow, and spleen).

Spleen

Reticular fibers

Function: Fibers form a soft internal skeleton (stroma) that supports other cell types including white blood cells, mast cells, and macrophages.

Figure 4.8c Connective tissues.


Dense Regular Connective Tissue

• Closely packed bundles of collagen fibers running parallel to direction of pull– White structures with great resistance to

pulling– Fibers slightly wavy so stretch a little

• Fibroblasts manufacture fibers and ground substance

• Few cells

• Poorly vascularized


Connective tissue proper: dense connective tissue, dense regular

Description: Primarily parallelcollagen fibers; a few elastic fibers;major cell type is the fibroblast.

Function: Attaches muscles tobones or to muscles; attachesbones to bones; withstands greattensile stress when pulling force isapplied in one direction.

Location: Tendons, mostligaments, aponeuroses.

Shoulderjoint

Ligament

Tendon

Collagenfibers

Nuclei offibroblasts

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

Figure 4.8d Connective tissues.


Dense Irregular Connective Tissue

• Same elements but bundles of collagen thicker and irregularly arranged

• Resists tension from many directions– Dermis– Fibrous joint capsules– Fibrous coverings of some organs


Connective tissue proper: dense connective tissue, dense irregular

Description: Primarily irregularlyarranged collagen fibers; someelastic fibers; fibroblast is themajor cell type.

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

Location: Fibrous capsules oforgans and of joints; dermis of theskin; submucosa of digestive tract.

Shoulderjoint

Fibrousjointcapsule

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

Collagenfibers

Nuclei offibroblasts

Figure 4.8e Connective tissues.


Elastic Connective Tissue

• Some ligaments very elastic– Those connecting adjacent vertebrae

• Many of larger arteries have in walls


Connective tissue proper: dense connective tissue, elastic

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

Function: Allows tissue to recoilafter stretching; maintains pulsatileflow of blood through arteries; aidspassive recoil of lungs followinginspiration.

Location: Walls of large arteries;within certain ligaments associatedwith the vertebral column; withinthe walls of the bronchial tubes.

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

Aorta

Heart

Elasticfibers

Figure 4.8f Connective tissues.


Cartilage

• Chondroblasts and chondrocytes• Tough yet flexible• Lacks nerve fibers• Up to 80% water - can rebound after

compression• Avascular

– Receives nutrients from membrane surrounding it• Perichondrium

• Three types of cartilage:– Hyaline cartilage– Elastic cartilage– Fibrocartilage


Cartilage: hyaline

Description: Amorphous but firmmatrix; collagen fibers form animperceptible network;chondroblasts produce the matrixand when mature (chondrocytes)lie in lacunae.

Function: Supports and reinforces;serves as resilient cushion; resistscompressive stress.

Location: Forms most of theembryonic skeleton; covers theends of long bones in joint cavities;forms costal cartilages of the ribs;cartilages of the nose, trachea, andlarynx.

Costalcartilages Photomicrograph: Hyaline cartilage from

a costal cartilage of a rib (470x).

Matrix

Chondrocytein lacuna

Figure 4.8g Connective tissues.


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

Figure 4.8h Connective tissues.


Cartilage: fibrocartilage

Description: Matrix similar to butless firm than that in hyalinecartilage; thick collagen fiberspredominate.

Function: Tensile strength allowsit to absorb compressive shock.

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

Photomicrograph: Fibrocartilage of anintervertebral disc (125x). Special stainingproduced the blue color seen.

Collagenfiber

Chondrocytesin lacunae

Intervertebraldiscs

Figure 4.8i Connective tissues.


Bone

• Also called osseous tissue• Supports and protects body structures• Stores fat and synthesizes blood cells in cavities• More collagen than cartilage• Has inorganic calcium salts• Osteoblasts produce matrix• Osteocytes maintain the matrix• Osteons – structural units• Richly vascularized


Others: bone (osseous tissue)

Description: Hard, calcifiedmatrix containing many collagenfibers; osteocytes lie in lacunae.Very well vascularized.

Function: Supports and protects(by enclosing); provides levers forthe muscles to act on; storescalcium and other minerals andfat; marrow inside bones is thesite for blood cell formation(hematopoiesis).

Location: Bones

Photomicrograph: Cross-sectional viewof bone (125x).

Lamella

Centralcanal

Lacunae

Figure 4.8j Connective tissues.


Blood

• Most atypical connective tissue – is a fluid

• Red blood cells most common cell type

• Also contains white blood cells and platelets

• Fibers are soluble proteins that precipitate during blood clotting

• Functions in transport


Connective tissue: blood

Description: Red and white bloodcells in a fluid matrix (plasma).

Function: Transport respiratorygases, nutrients, wastes, and othersubstances.

Location: Contained within bloodvessels.

Photomicrograph: Smear of human blood(1670x); shows two white blood cellssurrounded by red blood cells.

Plasma

White bloodcells:• Lymphocyte• Neutrophil

Red bloodcells(erythrocytes)

Figure 4.8k Connective tissues.


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


Skeletal muscle

Description: Long, cylindrical,multinucleate cells; obviousstriations.

Function: Voluntary movement;locomotion; manipulation of theenvironment; facial expression;voluntary control.

Location: In skeletal musclesattached to bones or occasionallyto skin.

Photomicrograph: Skeletal muscle(approx. 440x). Notice the obvious bandingpattern and the fact that these large cells aremultinucleate.

Striations

Nuclei

Part of musclefiber (cell)

Figure 4.9a Muscle tissues.


Cardiac muscle

Description: Branching, striated,generally uninucleate cells thatinterdigitate at specializedjunctions (intercalated discs).

Function: As it contracts, itpropels blood into the circulation;involuntary control.

Location: The walls of the heart.

Photomicrograph: Cardiac muscle (900x);notice the striations, branching of cells, andthe intercalated discs.

Striations

Nucleus

Intercalateddiscs

Figure 4.9b Muscle tissues.


Smooth muscle

Description: Spindle-shapedcells with central nuclei; nostriations; cells arranged closelyto form sheets.

Function: Propels substances orobjects (foodstuffs, urine, a baby)along internal passageways;involuntary control.

Location: Mostly in the walls ofhollow organs.

Photomicrograph: Sheet of smoothmuscle (720x).

Smoothmusclecell

Nuclei

Figure 4.9c Muscle tissues.


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, spinalcord, and nerves.

Photomicrograph: Neurons (350x).

Neuronprocesses

Nuclei ofsupportingcells

Cell bodyof a neuron

Neuron processes Cell body

Axon Dendrites

Figure 4.10 Nervous tissues.


Covering and Lining Membranes

• Composed of at least two primary tissue types– An epithelium bound to underlying connective

tissue proper– Are simple organs

• Three types– Cutaneous membranes– Mucous membranes– Serous membranes


Cutaneous Membranes

• Skin

• Keratinized stratified squamous epithelium (epidermis) attached to a thick layer of connective tissue (dermis)

• Dry membrane


Cutaneous membraneThe cutaneous membrane(the skin) covers the body surface.

Cutaneousmembrane (skin)

Figure 4.11a Classes of membranes.


Mucous Membranes

• Mucosa indicates location not cell composition• All called mucosae

– Line body cavities open to the exterior (e.g., Digestive, respiratory, urogenital tracts)

• Moist membranes bathed by secretions (or urine)

• Epithelial sheet lies over layer of connective tissue called lamina propria

• May secrete mucus


Mucous membranes

Mucous membranes line bodycavities that are open to theexterior.

Mucosa ofnasal cavity

Mucosa ofmouthEsophagusliningMucosa oflung bronchi

Figure 4.11b Classes of membranes.


Serous Membranes

• Serosae—found in closed ventral body cavity• Simple squamous epithelium (mesothelium)

resting on thin areolar connective tissue • Parietal serosae line internal body cavity walls• Visceral serosae cover internal organs• Serous fluid between layers• Moist membranes• Pleurae, pericardium, peritoneum


Visceralperitoneum

Parietalperitoneum

Parietalpericardium

Visceralpericardium

Visceralpleura

Parietalpleura

Serous membranes line body cavities that are closed to the exterior.

Serous membranes

Figure 4.11c Classes of membranes.


Tissue Repair

• Necessary when barriers are penetrated• Cells must divide and migrate• Occurs in two major ways

– Regeneration• Same kind of tissue replaces destroyed tissue• Original function restored

– Fibrosis• Connective tissue replaces destroyed tissue• Original function lost


Steps in Tissue Repair: Step 1

• Inflammation sets stage– Release of inflammatory chemicals– Dilation of blood vessels– Increase in vessel permeability– Clotting occurs


Figure 4.12. Tissue repair of a nonextensive skin wound: regeneration and fibrosis. 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



• Organization restores blood supply– The blood clot is replaced with granulation

tissue– Epithelium begins to regenerate– Fibroblasts produce collagen fibers to bridge

the gap– Debris is phagocytized


Slide 2Figure 4.12. Tissue repair of a nonextensive skin wound: regeneration and fibrosis.

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



• Regeneration and fibrosis– The scab detaches– Fibrous tissue matures; epithelium thickens

and begins to resemble adjacent tissue– Results in a fully regenerated epithelium with

underlying scar tissue


Slide 3Figure 4.12. Tissue repair of a nonextensive skin wound: regeneration and fibrosis.

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

• 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


Aging Tissues

• Normally function well through youth and middle age if adequate diet, circulation, and infrequent wounds and infections

• Epithelia thin with increasing age so more easily breached

• Tissue repair less efficient• Bone, muscle and nervous tissues begin to

atrophy• DNA mutations possible increased cancer

risk

Documents

© 2013 Pearson Education, Inc. Connective Tissue Most abundant and widely distributed of primary tissues Four main classes –Connective tissue proper –Cartilage