Connective Tissues

Connective TissuesResponsible for providing and maintaining form in the body

HistogenesisMesodermal in origin

General CharacteristicsAre made up of fewer cells that are

set far apartThey are supported by abundant

intercellular substanceThey also contain connective tissue

fibersThe different contents of

intercellular substance, CT cells and fibers account for the difference in appearance of the various connective tissues

General FunctionsProvide a matrix that serves to connect

and bind the cells and organsGive mechanical support to the bodyStorage of fat and certain minerals like

calcium in the bonesExchange of metabolites between blood

and tissuesSignificant role in the repair and healing

of woundsFor protection against infection

ClassificationI. Connective Tissue Proper Loose connective Tissue Dense connective tissue – regular & irregularII. Connective Tissue with special properties

Adipose CTElastic CTHematopoietic CT(lymphatic and myeloid)Mucous CT

III. Suporting Connective Tissue Cartilage Bone

Composition of Connective TissuesConnective tissue

cellsConnective tissue

fibersIntercellular or

Ground substanceBlood vessels –

except in Mucous CT and in cartilage

Connective Tissue cellsFixed or permanent Wandering cellsAre native to the

tissue in which they are found:1. undifferentiated mesenchymal cells2. fibroblasts3. macrophages4. fat cells

Are immigrant cells usually from blood or bone marrow. Some retain their original characteristics and may take up permanent residence there:1. mast cells2. plasma cells3. pigment cells4. blood leukocytes

Fixed Connective Tissue Cells

Undifferentiated Mesenchymal cellsPrecursor of most cells indigenous to CT

including fibroblasts and adipose cellsAdventitial cells remain undiifferentiated in adult

CT and constitute a reserve population of stem cells

Perivascular cells, often located along the walls of blood vessels

Are difficult to distinguish from active fibroblasts – recognition come not with the microscope but from numerous observations of their responses to certain stimuli

Pluripotential cells, capable of differentiation either into the usual cell types or into other cell types such as smooth muscle cells

FibroblastsPredominant CT cellsConsidered to be responsible for the

formation of the fibers and are also thought to elaborate most, if not all, of the amourpous ground substance

Are large, flat branching cells which appear fusiform or spindle shaped in profile

Classified as: lamellar or pyriform-shaped (youngest)Spindle or fusiform (intermediate in age)Stellate or star-shaped (mature)

Fibroblasts

MacrophagesAs numerous as fibroblasts in loose CTOften termed histiocytes, are most abundant

in richly vascularized areasMay either be:

Fixed or resting (attached to the fibers of the matrix)

Free, wandering (derived from the immigration of monocytes from the blood)

Capable of ameboid movement – very irregular in outline with pseudopodia extending in numerous directions

MacrophagesAct as scavengers,

(motility and phagocytic activity) engulfing extravasated blood cells, dead cells, bacteria and foreign bodies

Fat cellsFully differentiated cells and are incapable of

mitotic divisionSignet-ring appearance – cytoplasm is so

thinned that it appears as a narrow rim around the edge of a single large lipid droplet with the nucleus fused to one side of the cell membrane

Types:Yellow or white – found in most of the bulk

of the human bodyBrown fat cells – concerned with heat

production, particularly important in newborn and young animals

Fat cells

Wandering Connective Tissue Cells

Mast cellsRound to oval CT cells whose cytoplasm is

filled with basophilic granulesThe rather small and spherical nucleus is

centrally situated and is frequently obscured by the cytoplasmic granules

Produce an anticoagulant similar if not identical to heparin

Produce histamine in allergic response to some foreign proteins

Mast cellsAlso elaborate

serotonin, a vasoconstrictor

Are only seen along the course of small blood vessels

Plasma cellsSpherical cells with rounded or

irregular nuclei generally eccentrically located , whose chromatin materials exhibit a characteristic “checker-board”, “clock-faced”, “cart-wheel” appearance

Has an important function in resistance to disease and known as the: principal producer of antibodies

Plasma Cells

Pigment cellsResemble the fibroblast but whose

cytoplasm contains pigment granules that never invade the nucleus

Types:Dermal chromatophore – found in the

dermis of the skin, retina, choroid and iris of eyeball

Epidermal melanocytes, found in common mole and are responsible for the manufacture of melanin granules

Blood Leukocytes

LymphocytesSmallest, with

rounded nucleus which occupies most of the cytoplasm

Concerned with antibody production

EosinophilsHave bilobed

nucleus with spherical, darkly staining acidophilic granules

Found abundant in lactating breasts, respiratory and alimentary tracts, and in certain allergic reactions

NeutrophilsFirst line of

defense, seen in regions of acute inflammation

Have a segmented nucleus (3-5 lobes) having fine granules which are purple or violet in color

MonocytesLargest, they

have a kidney-shaped nucleus and are considered as the phagocytes of the blood

Connective tissue cells

Ground Substance

Ground substanceColorless, transparent and homogenousFills the space between cells and fibers of

the CTIt is viscous and acts as lubricant and also

as a barrier to the penetration of the tissues by foreign particles

Formed mainly by two classes of components:GlycosaminoglycansStructural glycoproteins

Connective Tissue Fibers1. Collagen formed by the protein

collagen, 2. Reticular most abundant protein of

the body3. Elastic – composed mainly of the protein

elastin

Collagen fibersMost numerous fiber in CTFibers are colorless stands, but when

present in great numbers, they cause the tissue in which it lie to be white

Are inelastic and have a tensile strength greater than steel

Imparts a unique combination of flexibility and strength to the tissues in which it lies

Collagen fibersConsists of closely packed thick fibrils

with an average diameter of 75 nmIn many parts of the body, are organized

in parallel array forming collagen bundlesIn H & E sections, large or small bundles

of fibrils or individual fibrils exhibit acidophilic staining properties

Types of Collages fibersCollagen type I

Most abundant and has a widespread distribution (90% of the collagen in the body)

Found in the dermis of the skin, tendons, bone, teeth and virtually all CT

Collagen type IIPresent mainly in hyaline and elastic

cartilageOnly very thin fibrils are formed

Types of collagen fibersCollagen type III

Often found in association with type I and is probably the major collagenous components of reticular fibers

Can copolymerize with other types of collagenCollagen type IV

Is the major collagen type in basal laminaDoes not form fibrils or fibers

Collagen type VPresent in fetal membranes and blood vessels

and in small amounts in other tissues

Reticular fibersAre extremely thin, with a diameter

between 0.5 and 2 μmNot visible in hematoxylin and eosin stains

but can be easily stained black by impregnation with silver salts

Argyrophilic fibers – affinity to silver saltsDuring embryogenesis, inflammatory

processes, and wound healing, most connective tissues have an abundance of reticular fibers, but these are subsequently replaced by regular collagen fibers

Reticular fibersParticularly abundant in

smooth muscles, endoneurium, and the framework of hematopoietic organs (e.g. spleen, lymph nodes, red bone marrow) and constitute a network around the cells of parenchymal organs (e.g. liver, kidney, endocrine glands)

Elastic fibersConsists of an albuminoid protein called

elastinRange in diameter from 0.1 to 10 µmHistologically contains few charged amino

acids so it stains poorly with standard ionic dyes

Special stains such as Verhoeff’s stain and Weigert’s Resorcin-fushsin stain are used in light microscope

Are extremely pliable and elastic Can be stretched to 150% of their length

without breaking and then return to their original length

Elastic fibersFound where their

mechanical properties are necessary to allow tissues to stretch or expand and then return to their original shape, e.g. in arterial walls, interalveolar septa, bronchi and brionchioles of the lungs, vocal ligaments and ligamenta flava of the vertebral column