Block Connective Tissue

8/12/2019 Block Connective Tissue

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Connective TissueDr. Jan Tambayong, PHK

Histologi FK-UPH


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Connective Tissue

Connective tissue is formed by 3 classes

of components:

1. cells

2. fibers

3. ground substance

The major constituent of connective tissue

is the extracellular matrix.


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Cells of the connective tissue

Fibroblasts

Synthesize fibers and ground substance

The most common cell in connective tissue

Two stages of activity: active & quiescent Active fibroblast: abundant and irregularly branched

cytoplasm. Its nucleus is ovoid, large, and pale-

staining, with fine chromatin and a prominent

nucleolus. Quiescent fibroblast (Fibrocyte) is smaller, tends to be

spindle-shaped, a smaller, darker, elongated nucleus.


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Fibroblast dan fibrocyte

Fibroblast

Branched cytoplasm

Large, oval nucleus,

with fine chromatin

Fibrocyte

Spindle-shaped

Smaller, darker,

elongated nucleus


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Connective cell lineage

Simplified representation of theconnective tissue cell lineagederived from the multipotentialembryonic mesenchyme cell.

Dotted arrows indicate thatintermediate cell types existbetween the examplesillustrated. Note that the cellsare not drawn in proportion toactual sizes, eg, adipocyte,

megakaryocyte, and osteoclastcells are significantly largerthan the other cells illustrated


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Macrophages and Mononuclear Phagocyte

System

Phagocytic ability

Morphologic feature: correspond to their

state of functional activity and to the tissue

they inhabit.

Oval, kidney-shaped, or indented nucleus,

with coarser chromatin granules than that

of fibroblasts

Cytoplasm: vacuolated or granulated


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Macrophages and Mononuclear Phagocyte

System

Macrophages derive from bone marrowprecursor cells that divide, producing monocytesthat circulate in the blood. Monocytes can crossthe walls of venules and capillaries to penetratethe connective tissue, where they mature andbecome macrophages.

Macrophages, which are distributed throughoutthe body, are present in most organs andconstitute the mononuclear phagocyte system(Kupffer cells, microglial cells, Langerhans cells,osteoclasts).


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Mast cells

Oval to round connective tissue cells

Cytoplasm is filled with basophilic secretorygranules.

Small, spherical nucleus is centrally situated,frequently obscured by the cytoplasmicgranules.These granules contain pre-formedmediators such as histamine and proteoglycans.

Function: storage of chemical mediators of theinflammatory response.

Mats cell granules are metachromatic


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Mast Cell

Section of rat tongue.

Several mast cells in

the connective tissuesurround muscle cells

and blood vessels. PT

stain. Medium

magnification.


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Plasma Cells

Plasma cell

Large ovoid cell, with

basophilic cytoplasm

The nucleus is spherical,

eccentrically placed

Coarse heterochromatin,

alternating with lighter

areas (resembles the face

of a clock)

Average life: 10-20 days


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Adipose Cells

Photomicrograph of unilocularadipose tissue of a youngmammal. Arrows show nucleiof adipocytes (fat cells)compressed against the cell

membrane. Note that, althoughmost cells are unilocular, thereare several cells (asterisks)with small lipid droplets in theircytoplasm, an indication thattheir differentiation is not yet

complete. Pararosanilinetoluidine blue (PT) stain.Medium magnification.


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Connective Tissue Fibers

The 3 main types of fibers are:

Collagen

Reticular

Elastic

The predominant fiber type is responsible

for conferring specific properties on the

tissue.


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Collagen

Representing 30% of the bodys dry weight Fibrillar

Birefringent

640 (64 nm) periodicity

Specific stain: Mallory : purple blue

Masson : green

van Gieson : red


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Collagen

Consist of tropocollagen molecules Length : 280 nm

Width : 1.5 nm

Triple helixconsists of 3 polypeptide chain (= chain) makeup of 3 amino acids

1. other than (2) and (3)

2. proline

3. always glycineDifferences in the chemical structure of thesepolypeptide chains are responsible for the varioustypes of collagen


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Collagen Types

Collagen type I

Location

skin (loose connective tissue)

tendon

bone, dentin

Function

Resistance to tension


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Collagen Types

Collagen type II

Location

Cartilage

Vitreous body

Function

Resistance to pressure


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Collagen Types

Collagen type III

Location

Skin

Muscle

Blood vessels

Function

Structural maintenance in expansible

organs


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Collagen Types

Collagen type IV

Location

All basement membranes

Function

Support of delicate structures

Filtration


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Collagen Types

Collagen type V Location and function

Fetal tissues

Skin Bone

Placenta

Most interstitial tissues

Function: Participates in type I collagenfunction


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Elastic Fiber

Elastic

Homogenous

Can branch Resistant to boiling, acid and alkali

extractions

Specific stains: Orcein brown

Resorcin fuchsinpurple blue


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Reticular Fibers

Are extremely thin, collagen III fibers Not birefringent

64 nm periodicity

Form extensive network in certain organs,

particular abundant in smooth muscle,endoneurium, and the framework ofhematopoietic organs, and constitute a networkaround the cells of parenchymal organs.

Specific stain Silver Impregnation (eg Bielschowsky method) PAS (periodic acid Schiff)


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Ground Substance

The intercellular ground substance is a highlyhydrated, complex mixture ofglycosaminoglycans, proteoglycans, andmultiadhesive glycoproteins.

Glycosaminoglicans (originally called acidmucopolysaccharides) are linearpolysaccharides formed by repeatingdisaccharide units, usually a uronic acid and ahexosamine.

The proteoglycans are composed of a coreprotein with 4 main glycosaminoglycans,


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Types of Connective Tissue

Connective tissue proper Loose connective tissue (areolar)

Dense connective tissue

Regular Irregular

Collagen

Elastic


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Connective Tissue with special

properties

Adipose tissue

common (univacuolar/unilocular/yellow)

brown (multilocular)

Elastic tissue

Hematopoietic tissue (lymphatic and

myeloid) Mucous tissue


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Supporting Connective Tissue

Supporting connective tissue:

Cartilage

Hyaline

Elastic

Fibrocartilago

Bone

Compact bone Cancellous bone


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Connective Tissue Proper

Loose connective tissue

Fills spaces between muscle cells, supportsepithelial tissue, and forms a layer that

sheathes the lymphatic and blood vessels. The most numerous cells are fibroblasts and

macrophages

Dense connective tissue

Is adapted to offer resistance and protection.

Fewer cells and predominance of collagenfibers. Dense regular and dense irregular.


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Common Adipose Tissue

Color: white to yellow

One large lipid droplet(unilocular/univacuolar)

Lipid removed, eachcell appears as a thinring of cytoplasmsurrounding the

vacuole, called signetring cell

Eccentric and flattenednuclei


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Common Adipose Tissue

Storage of energy (triglycerides)

Thermal insulation

Shock absorbers (soles and palms)

Shape the body (subcutaneous fat)

Found throughout the human body, except

the eyelids, the penis, the scrotum, auricle Developed from lipoblast (mesenchym)


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Multilocular Adipose Tissue

Smaller cell

Multiple lipid droplets

and numerous

mitochondria (coloredcytochromes)

Limited distribution

Nucleus at the center Function: heat

production


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Supporting Tissue

Cartilage

Avascular, no lymphatics or nerves

Nourished by diffusion of nutrients from

capillaries in perichondrium or by synovialfluid from joint cavities.

Perichondrium: dense connective tissue. Joint

cartilage is devoid of perichondrium (nutrientsfrom synovial fluid).

Growth: interstitial + appositional


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Hyalin Cartilage

Chondroblasts at theperiphery

Chondrocytes in lacunae

Homogenous matrix

Territorium: matrixsurrounding chondrocytes

is metachromatic due to

glycosaminoglycans

Nest/isogenous cells A perichondrium present

Location


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Elastic Cartilage

Location: auricle,

eustachian tube,

epiglottis, walls of

external auditory canal,the cuneiform cartilage of

the larynx

Matrix appear dirty

(elastic fibers)

A perichondrium present


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Fibrocartilago

Always between dense connective tissueand hyaline cartilage.

The border areas is not clear-cut.

Chondrocytes usually in rows or singlyseparated by coarse collagen type I fibers

Location: intervertebral disks and

symphysis pubis

No perichondrium


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Photomicrograph of Fibrocartilago

Note the rows of

chondrocytes

separated by collagen

fibers. Fibrocartilago is

frequently found in

the insertion of

tendons on theepiphyseal hyaline

cartilage.


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Bones

Main constituent of adult skeleton

Supports fleshy structures, protects vital organs

(thorax, cranium), harbors the bone marrow.

Reservoir of calcium, phosphate, and other ions Bone matrix with 3 cell types: osteoblasts

(synthesize organic components), osteocytes (in

lacunae), and osteoclasts (resorption and

remodeling of bone tissues).

A periosteum present


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Bone

Long bone diaphysis

Showing haversiansystems, outer and innercircumferential lamellae.

The protruding haversiansystem on the left showsthe orientation of collagenfibers in each lamella. Atthe right is a haversian

system showing lamellae,a central blood capillaryand many osteocytes withtheir processes.


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Osteoblasts

Synthesize organic components of bone matrix.

Newly formed bone matrix: osteoid (not yetcalcified)

Located at the surfaces of bone tissue Once surrounded by newly formed matrix, these

cells are now called osteocytes, located inlacunae and connected to one another via

canaliculi, each housing cytoplasmic processesof osteocytes.

Growth: appositional


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Part of a haversian system

Note the numerouscanaliculi that permitcommunicationbetween lacunae and

the haversian canal.In adjacent lamellae,the collagen fibers areoriented in different

directions, whichprovide the bone withgreat strength.


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Osteocytes

Osteocytes derived from osteoblasts, lie in

lacunae situated between lamellae.

One osteocyte is found in each lacuna.

The thin, cylindrical matrix canaliculi house

cytoplasmic processes of osteocytes.

Actively involved in the maintenance of the

bony matrix.


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Osteoclasts

Multinuclear cells (5-50 nuclei in 1 cell)

Lie within enzymatically etched depressionin the matrix known as Howships lacuna

Secretes collagenase and other enzymesand pumps protons into a subcellularpocket, promoting digestion of collagen

and dissolving calcium salt crystals. Its activity is controlled by cytokines andhormones.


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Bone Matrix

Inorganic matter represents 50% of the dryweight of bone matrix.

Storage of calcium and phosphor

Organic matter: type I collagen and ground

substance. After bone decalcification, its shape is preserved

but become as flexible as tendon

Removal of the organic part of the matrix, mainly

collagen, also leaves the bone with its originalshape; however, it becomes fragile, breakingand crumbling easily when handled.


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Types of Bone

Compact and cancellous (spongy) bone

Epiphysis consists of spongy bone

covered by a thin layer of compact bone

Diaphysis is almost totally compact bone

Flat bones have two layers of compact

bone called plates, separated by a layer of

spongy bone called diplo.


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Histogenesis

Bone can be formed in 2 ways:

Intramembranous ossification

Endochondral ossification

Newly formed bone (osteoid) is primary boneand soon replaced by the definitive lamellar,

secondary bone.

The combination of bone synthesis and removal

(remodeling) occurs not only in growing bones

but also throughout adult life.


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Remodeling


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Intramembranous Ossification

Also called desmal ossification

Is so called, because it takes place withincondensations of mesenchymal tissue.

Forming of flat bones The starting point for ossification is called a

primary ossification center.

It begins with the differentiation of osteoblasts,

forming bone matrix which calcifies, formingislands of developing bone. Several islands fuseto form spongy bone.


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Endochondral Ossification

Takes place within a piece of hyaline

cartilage whose shape resembles a small

version (model) of the bone to be formed.

Principally responsible for the formation of

short and long bones.

Endochondral ossification of a long bone

consists of the following sequence ofevents.


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Growing at the epiphyseal plate


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Epiphyseal Plate

Resting zone : no morphologic changes

Proliferative zone: chondrocytes divide rapidly

and form columns of stacked cells parallel to the

long axis of bone Hypertrophic zone: large chondrocytes whose

cytoplasm has accumulated glycogen.

Calcification zone: calcification, death of

chondrocytes,

Ossification zone: bone tissue appears


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Fracture Repair

Bone fracturehemorrhage + clotting

Fibroblasts + blood capillaries enters blood

clotgranulation tissuefibrous dense

connective tissuecartilage formation

endochondral ossificationcallus

formation (bone trabeculae reunite both

ends of fractured bone). Spongy bone replaced by lamellar bone

B R i


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Bone Repair

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