connective tissues
TRANSCRIPT
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