Connective Tissue
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I. Classification of Connective Tissue (CT)
A. Embryonic CT
§ Mesenchyme
§ Mucous
B. Adult CT
§ Connective Tissue Proper
Loose/areolar
Dense irregular
Dense regular
§ Specialized Connective Tissue
Adipose tissue
Cartilage
Bone
Blood
II. Composition of CT
A. Cells embedded in extracellular matrix
§ Extracellular maxtrix includes fibers, ground substance, and tissue fluid
§ Variations in components responsible for different types of connective tissue
B. Supportive and protective functions
C. Originates from mesoderm
§ Some from neural crest (ectoderm)
§ Mesenchymal cells form tissue called mesencyme (large nucleus, prominent nucleoli, barely visible cyto, large amount of ground substance, few fibers)
III. Ground Substance
§ Colorless, transparent mixture of proteins between cells and fibers of CT
§ High viscosity= lubricant and physical barrier (bacteria)
§ Composed of glycosaminoglycans (GAGs), proteoglycans, glycoproteins
A. Glycosaminoglycans
§ Long unbranched polysaccharide chains consisting of repeating disaccharide units (all sulfated and have net negative charge, except hyaluronic acid)
§ Major GAGs: hyaluronic acid, chondroitin sulfate, dermatan sulfate, keratan sulfate, heparan sulfate
B. Proteoglycans
§ All GAGs covalently bind to protein core =large proteoglcans (80-90% carbohydrate and attract water to form gel that gives support to connective tissue matrix)
§ Particular GAG bound to protein core det where proteoglycans are found
Dermatan sulfate-skin, tendons, ligaments
Chondroitin sulfate-hyalin and elastic cartilage
Keratan sulfate-cornea
Heparan sulfate-reticular fibers in aorta, lung liver basal laminae
C. Glycoproteins
§ Also contain protein core and carbohydrates
§ Protein component predominate, carbohydrate moiety is branched not linear
§ Function in adhesion of cells to each other and to extracellular fibers
|
Made by |
Mediates |
|
|
Fibrillin |
Fibroblast |
Adhesion b/t fibers |
|
Fibronectin |
Fibroblasts |
Normal cell adhesion |
|
Laminin |
Epithelial cells |
Adhesion of cells to basement membrane |
|
Chondronectin |
Chondrocytes |
Adhesion to surrounding collagen |
§ Integrins- transmembrane proteins that serve as receptor sites for glycoproteins
IV. Fibers of CT
A. Collagen Fibers
§ Composed of protein collagen
§ Important components of tissues requiring rigidity, elasticity, and strength
§ Synthesized by fibroblasts, chondroblasts, osteoblasts, smooth muscles, endothelial and epithelia cells. Most abundant protein in body.
§ Synthesis
In RER, plypep chain call procollagen formed
Chains transported outside cell, acted on by proteases, rsulting chain join to form triple helix tropocollagen
Tropocollagen spont assemble into collagen fibrils (long, thin striations overlapping tropoco subunits)
Fibrils crosslink to form collagen fibers
Fibers form larger collagen bundles (eosinophilic)
§ 20 types/ Know the following:
|
Collagen |
Appearance |
Micros. |
Distribution |
Main function |
|
Type I |
Fibrils, fibers, bundles |
LM |
Connective tissue proper, dermis, bone tendon, fibrocartilage |
Resist. To tension and stretch |
|
Type II |
Fibrils |
TEM |
Hyaline cartilage, intervertebral disc |
Resistance to pressure |
|
Type III |
Fibrils, very thin fibers |
Special stains |
Loose CT, reticular tissue, lamina reticularis |
Maint. Of structure in expansible organs |
|
Type IV |
No fibrils |
Special stains |
Basal lamina (lamina densa) |
Support of delaicate struc. |
B. Reticular Fibers
§ Thin fibers, mainly type III collagen with high glycoprotein content
§ Affinity for silver salts that cause fibers to stain black- argyrophilia
§ Provide supporting frame work for organs
§ Found in: sm.. muscle, nerves, bl. Vess, lymphatics, parenchyma of lymph nodes, spleen, liver, endocrine glands
C. Elastic Fibers
§ Mainly protein elastin (allows fibers to stretch in response to tension b/c a.a. desmosine and isodesmosine
§ In walls of some blood vessels, elastin forms sheets called elastic laminae
V. Cells of CT [pg. 44]
A. Fibroblast
§ Weaver of CT
§ Formation and maintenance of all three types of fibers and ground substance
§ Active fibroblast have large oval nucleus and prominent nucleolus, a lot of cytoplasm
§ Resting fibroblast is smaller, spindle shaped and has slender elongated dark nucleus. In dense CT nuclei tend to be orented in direction of collagen fibers
B. Adipocyte
§ Synthesis and storage of lipid as energy source, also provides padding
§ Cytoplasm is filled with large globule of fat that compresses the nucleus up against the side of the cell
§ H&E nucleus prominent, cytoplasm clear
C. Macrophage
§ Large eater
§ Make up mononuclear phagocyte system
§ Present in most organs of body
§ From stem cells in bone marrow that enter blood stream ass monocytes
§ Monocytes into connective tissue and mature into macrophages
§ Nurse cell
§ Functions: ingestion and digestion of foreign substances, relase inflammatory mediators, and antigen recognition and processing
|
Name |
Location |
|
Macrophage |
Ct proper, lung, spleen, lymph |
|
Kupffer cell |
Liver |
|
Microglia cell |
CNS |
|
Osteoclast |
Bone |
|
Langerhans cell |
Skin |
D. Mast Cell
§ Participates in inflammatory and allergic responses by releasing histamine, leukotrienes, and eosinophil chemotactic factor of anaphylaxis
§ Originate from stem cells in bone marrow
§ Most abundant in skin, GI tract, around blood vessels
§ Cytoplasm full of large basophilic granules filled with above, only visible with toluidine blue
E. Plasma Cell
§ From B-lympocyes and function in syn of antibodies
§ Most numerous in areas prone to bacterial invasion GI tract
§ Large oval cells with eccentrically placed nucleus, cypoplasm stains basophilic due to RER, prominent golgi are near nucleus (light staining “hof”)
§ Nucleus has a lot of euchromatin. Alternating euchromatin and heterochromation give clock face appearance.
F. Eosinophil
§ Involved n parasitic infection and allergic reactions
§ Presence indicates inflammatory response is occurring in tissue
§ Only in intestinal tract
§ Cytoplasm filled with large dense granules that contain major basic protein, toxic to parasites
§ Granules account for eosinophilia of cytoplasm
§ Granules appear bright orange red,
§ Bilobed nucleus
VI. Embryonic CT
A. Mesenchyme
§ Stellate shaped mesenchymal cells embedded in fluid gtound substance, few fibers
§ CT of embryo, give rise to adult CT and support tissue
§ Nucleus large, pale
B. Mucous
§ Abundance of grond substance and few fibers or cells (mostly fibroblasts)
§ Principal component of umbilical cord where it is known as Wharton’s jelly
VII. Connective Tissue Proper
A. Loose (or areolar) CT
§ Delicate, lossely arranged collagen with abundant ground substance and cells of all types.
§ Most numerous are fibroblsts and macrophages
§ All fiber types are present and well vascularized
§ Flexibility and not resistant to stress
B. Dense irregular CT
§ Has all components of CT
§ Collagen fibers predominate, few cells
§ Fibers are arranged in bundles oriented in two or more direction without definite structure
§ Less flexible, more resistant to stress
§ Dermis of skin, walls of vagina, periosteum, pericondrium, epineurium, organ capsules
C. Dense regular CT
§ Collagen fibers arranged in one direction. Provides protection against prolonged stress exerted in one direction
§ Tendons, ligaments, aponneuroses
VIII. Remember Basement Membrane
§ Basal lamina- Type IV collagen (lamina lucida and lamina densa)
§ Lamina reticularis-Type III collagen
Tags: Adipocyte, Chondroblasts, Chondroitin sulfate, connective tissue, cytoplasm, disaccharide units, Embryonic, endothelial, Eosinophil, epithelia cells, Extracellular maxtrix, fibroblasts, glycoproteins, glycosaminoglycans, Keratan sulfate, mast cell, mesenchymal cells, Mesenchyme, Mucous, osteoblasts, plasma cell, polysaccharide chains, protein elastin, proteoglycans, smooth muscles, Tropocollagen spont
