Connective Tissue
Connective Tissue Elements Individual cells Extracellular matrix»fibers» Collagen» Elastic» Reticular»Ground Substance» PG (proteoglycans)» GAG (glycosaminoglycan)» GP (glycoprotein)
Connective tissue cells classification Resident cell populations (permanent cells) fibroblasts - fibrocytes (condro-, osteo-) myofibroblasts adipocytes (uni-, multilocular) macrophages mast cells reticular cells Wandering cell populations (transient cells) plasma cell granulocytes B and T lymphocytes monocytes
Fibroblasts The most frequent cell type Morphology: elongated cell branched cell processes cytoplasm - basophilic nucleus oval-shaped, euchromatic Function: Produces elements of the extracellular matrix: procollagen proelastin fibrillin GAG, PG and GP
Fibrocytes Less active than fibroblasts Morphology: smaller, elongated/spindle shaped, a few short unbranched processes cytoplasm scarce, acidophilic nucleus - elongated and heterochromatic
Fibroblasts vs Fibrocytes
Unilocular (white) adipocytes Morphology round (when isolated) or polygonal in groups cytoplasm a thin rim at the periphery one large lipid droplet (inclusion) nucleus - flattened, heterochromatic ( signet ring ) Location: hypodermis, around kidney, in bone cavities (adults)
White adipocytes, HE, 400x BV A A A A Ross HM, Histology: A Text and Atlas, 6 th ed. Adipose tissue: A white adipocyte, BV blood vessel
White adipocytes, Sudan III Ob. 40x Ob. 20x
Multilocular (brown) adipocytes Morphology: Smaller cells Cytoplasm: Many smaller lipid droplets in the foamy appearance Nucleus: round, central Mostly found before birth and in neonates Role in thermogenesis
Brown adipocytes Methylene blue stain, ob. 20x Azan stain, ob. 40x
Reticular cells Morphology star-shaped cells long and thin processes, forming networks nucleus - round, central, pale. Role: produce reticular fibers!!!!! Should not be confused with the reticulocyte, the immature erythrocyte.
Lymph node Reticular tissue, Giemsa, ob. 20x Reticular cells
Macrophages Origin: peripheral blood monocytes, a family of cells with various shapes, locations and names: Histiocytes: connective tissue Kupffer cells: liver Langerhans cells: intraepidermal Alveolar macrophages/dust Cells : lung Osteoclasts: bone Microglia: central nervous system Role: phagocytosis and inflammatory response
Macrophages Macrophages part of the mononuclear phagocyte system (MPS/ RES*). Morphology: irregular shapes cytoplasm: can have various heterogeneous inclusions ingested material nucleus: round, oval or kidney-shaped, eccentric *RES - reticuloendothelial system
Macrophages, HE Ob. 40x Ob. 100x
Mast cells, toluidine blue stain, ob. 60x Mast cells Distribution: in most of the loose connective tissue areas, along blood vessels Morphology: oval shaped cytoplasm has numerous basophilic, metachromatic granules nucleus: round, small and centrally located Function: immediate hypersensitivity reaction (allergies)
Mast cells, toluidine blue stain, ob. 100x
Plasma cells Plasma cells Distribution: lymphoid organs and connective tissues associated with the mucosa of the respiratory and digestive tract Origin: terminal differentiation of B lymphocytes Morphology: ovoid/ pear shaped cells cytoplasm: basophilic, with a perinuclear pale area; +/- acidophilic Russel bodies (secretory granules) nucleus: eccentric, with hetero- and euchromatin in a characteristic pattern: cart wheel or clockface
Plasma cells TB stain, ob. 100x HE, ob. 40x
Mesenchymal cells undifferentiated cell capable of differentiation in all connective cell types found in mature connective tissue Morphology: star shaped cytoplasm: irregular branched extensions acidophilic nucleus: oval with dispersed chromatin and nucleolus
Mesenchymal cells
Fibers of the Connective Tissue Collagen Elastin Reticular Fibers
Fibers of the Connective Tissue
Collagen fibers the most abundant type of connective tissue fiber many types that differ in their origin, chemical composition, functions, distribution thicker and unbranched, wavy appearance acidophilic
Elastic fibers Isolated, thin fibers or arranged in networks Distribution: lung, urinary bladder, skin, aorta and elastic cartilage Special staining : orcein
Reticular fibers Provide a supporting framework for the cellular constituents of various tissues and organs. Thin fibers, forming networks Distribution : liver, spleen, lymph nodes, haematopoietic organs Special staining: silver impregnation
Spleen Reticular fibers, silver staining & HE, ob. 40x
Reticular fibers, silver staining
Ground Substance Highly hydrated semi-solid gel Participates to binding cells to fibers Colorless and transparent in usual stains Composed primarily of GAGs and PG