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Connective tissue
Connective tissue consists of cells and extracellular matrix
• Connective tissue proper• Cartilage• Bone• Adipose tissue
Connective tissue
Mechanical (structural) role – supportive and connecting
Defence – immune response and physical barrier
Nutrition – vessels (blood supply) Storage of metabolites – Ca, fat Tissue repair after injury
Connective tissue proper Cells:
Fixed: fibroblasts, reticular cells, adipocytes
Blood derived: macrophages, plasma cells, mast cells, leucocytes
Fibres: collagen, reticular and elastic
Ground substance: glycoproteins and proteoglycans
Fibroblast
Spindle -shaped cell with elliptic nucleus
Proteosynthesis (GER and GA): collagen, elastin, proteoglycans and glycoproteins
Synthesis of collagen Preprocollagen with signal peptide – into RER Procollagen – hydroxylation of lysine and proline
(RER) GA – packing nad secretion of procollagen,
glycosylation, formation of disulphidic bounds Removal of nonhelical endings Tropocollagen Polymeration outside of cell Periodicity 64 nm
Types of collagens
I. Bone, tendon, dentin, skin II. Hyalinne and elastic cartilage III. Reticular lamina (BM) and
reticular fibres IV. Basale lamina V. Chorion and amnion
Elastin
Proelastin – secretion of tropoelastin Interaction with fibrillin to organize
immature elastic fibers Aggregation – mature elastic fibers Content of desmosin and
isodesmosin (AA)- cross-linking of elastic fibers
EM: microfibrils+MAGPs+fibrillin
Clinical significance:
Vitamine C – necessary for hydroxylation of collagen (hydroxyproline and hydroxylysine)
Ehlers-Danlos syndrome – hyperelasticity of skin and hypermobility of joints – defect of procollagen peptidase or lysyl hydroxylase – impairment of cross-linking formation in collagen fibres
Clinical significance
Marfan syndrome – autosomal dominant – defect of fibrillin
– Myopy, lens ectopy, skeletal defects
arachnodactyly, prolapse of the mitral
valve, dilatation of aorta ascendens.
Ground substance
Glycoproteins – fibronectin, chondronectin, laminin etc.
Proteoglycans – Glycosaminoglycans – polysaccharides
formed from hexosamine and uronic acide: chondroitin sulphate, heparan sulphate, dermatan suphate keratan sulphate
Core protein, linker protein, hyaluronan molecule
Interaction between cells and matrix
Integrins – receptors for molecules of extracellular matrix (hemidesmosomes and focal adhesions)
Intracellular attachment to the cytoskeleton (paxilin, vinculin, talin, β-catenin)
Ground substance
Hydratation of glycosaminoglycan molecules, presence of growth factors
Degradation – metalloproteinases – collagenase, kathepsin, stromelysin, gelatinase,
Significance : tumor invasion – degradation of basement membrane
Cells decrease expression of integrines – attachment to BL
Regeneration
After injury or impairment of tissue Cell division – scar formation Myofibroblasts – wound healing -
wound contraction characteristics of both, fibroblast and smooth muscle cell
Synthesis of growth factors (during development, too)
Macrophages
Phagocytic cells, derived from monocytes Contain of lysosomes, phagosomes
(vacuoles) Stainable by vital dyes – trypan blue Function: turn over the senescent fibers and
ECM Antigen presenting cells (MHC) Production of cytokines – interleukin 1, TNFα
Macrophages Monocytes Histiocytes Osteoclasts Dendritic cells Mikroglia Kupffer cells Langerhans cells Epiteliod cells, multinuclear giant cells –
segregation of foreign bodies
Mast cells Derives from bone
marrow Vasoactive
mediators: histamine, heparin, chemotactic mediators – leukotrienes
Metachromasia
Mast cells Mucosal mast cells (lungs and gut) Connective tissue mast cells Activation – antigen - bounds to two IgE
receptors Release – histamine, proteases,
proteoglycans Synthesis of mediators derived from
arachidonic acid- prostaglandins and leukotrienes
Plasma cells Activated B-
lymphocytes – immunoblasts – plasma cells
Proteosynthesis -GER and GA
Cartwheel nucleus
Connective tissue
Embryonic – mesenchyme, mucoid connective tissue – Wharton´s jelly
Adult – loose and dense collagen connective tissue, reticular connective tissue, elastic connective tissue
Special – white and brown adipose tissue
Connective tissue
Collagen connective tissue Loose Dense
Elastic Reticular White adipose tissue Brown adipose tissue
Embryonic connectives
Mesenchyme – embryonic tissue starlike cells with little amount of ECM – allow cells to migrate
Mucoid connective tissue – fetal – fibroblasts, collagen V, hyaluronic acid – umbilical cord (Warthon´s jelly), chorion
Collagen connective tissue
Loose – many cells (blood deriveds, too) less fibers. Occurence in lamina propria, muscles ect.
Dense – more fibres and less cells Regular (tendon, fascia, aponeurosis) Irregular (dermis)
Elastic connective tissue
Bundles of elastic fibers, thin collagen fibers and fibroblasts
Yellow ligament Suspensory
ligament of the penis
Reticular connective tissue Three-dimensional
network - reticular cells and fibers – microenvironment for haemopoesis and lymphatic organs: bone marrow, spleen, lymph nodes
Unilocular adipose tissue 50-150um, signet ring cell Excentric nuclei Only one big lipid droplet, it is not
surrounded by membrane - triglycerids (Glut-4)
Surrounded by basal lamina Hormone: insulin,GH, thyroxin,
katecholamins, glucocorticods, prostaglandins,
Function:
Insulator agains heat loss Reserve of energy Fills spaces and cushions Shock absorber in soles and
mechanic support (kidney, eye). Synthesis: leptin, adiponectin,
estrogens
Multilocular adipose tissue Multilocular Nucleus in the
centra of cell, many mitochondria
Present in fetuses and newborns