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48 Cards in this Set
- Front
- Back
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Connective tissue (General Facts)
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-composed of connective tissue cells and structural fibers and specialized proteins known as ground substance
-fills the spaces between the other three cell types -includes bone, cartilage, blood, lymph -derived from mesoderm--> mesenchyme--> connective tissue except for in the head where progenitor cells from ectoderm give rise to ectomesenchyme -can be fixed or wandering |
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Mesenchymal Cells
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-stellate-shaped
-large, oval nuclei -prominent nucleolus -found in embryonic connective tissue -differentiate into many types of connective tissue and also into muscle cells, blood vessels, urogenital system and mesothelial cells |
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Fibrocytes
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-most common connective tissue cell
-spindle-shaped with elongated cytoplasmic processes -in tendons, where there is a lot of compact collagen, only the fibrocyte nucleus is visible |
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Fibroblast
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-larger than fibrocytes
-have an active, euchromatic nucleus and basophilic cytoplasm -derived from mesenchymal cells -can also arise from transformed fibrocytes during reparative processes -activated fibroblasts synthesize collagen and elastic fibers -important in inflammatory response |
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Reticular cells
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-similar appearance to fibrocytes
-synthesize reticular fibers making up the scaffolding of lymph nodes, spleen and bone marrow |
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Macrophages
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-phagocytic cells
-derived from bone marrow precursor cells that also produce monocytes and osteoclasts -some "wander" and some are "fixed" -large ovoid to spherical shaped cells -hard to see in H&E unless they are ingesting material -rich in lysosomal enzymes -play a key role in the immune response due to their major histocompatibililty complex molecules that allow the cells to integrate with helper CD4 T lymphocytes -macrophages can fuse together to make multinucleated giant cells or syncitial cells |
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Mast cells
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-derived from bone marrow stem cells
-seen in dermal layer of the skin and lamina propria of respiratory, GI and urogenital system (aggregate around small nerves and blood vessels) -have a round to oval cytoplasmic outline -have a central nucleus that can be obscured by numerous, dark blue bytoplasmic granules -store vasoactive substances that can release when activated by trauma, immunologic efffects, ctyokins or neurogenic stimuli (histamine, heparin, proteases) -allergic response |
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Histamine
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-smooth muscle constrictor
-causes vasoconstriction and increased permeability of small venules resulting in edema -can causes smooth muscle constriction in the lung causing signs of asthma |
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Heparin
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-glycosaminoglycan
-inhibits clotting of blood by combining with antithrombin III and platelet factor IV to block other coagulation factors |
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Proteases
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-tryptase: released with histamine (marker of mast cell activation)
-chymase: necessary for production of angiotensin II in response to vascular injury -mast cells are classified on basis of protease content |
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Mast cells and
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-mast cells have Fc receptors that can bind with IgE antibody found in patients with allergies
-when this antibody is exposed to the appropriate antigen an allergen rapid degranulation or activation of mast cells occurs=allergic reaction |
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Adipocytes
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-specialized cells derived from mesenchymal cells
-in the adventitia of small blood vessels -differentiate into lipoblasts -as lipoblasts differentiate the lipid inclusions appear at one pole -mature adipocytes have a single, large, lipid inclusion which pushes the nucleus off to the side -appears as a clear, empty meshwork because histo preps extract lipid |
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White fat
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-common in adult mammals
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Brown fat
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-prealent during fetal life
-smaller than white adipocytes -filled with many tiny fat droplets instead of one large one -its metabolism generates heat regulated by norepinephrine -hibernating animals have a lot of brown fat |
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Lipomas
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-adipose tumors
-common -found in middle-aged and older dogs and people -composed of white fat |
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Hibernomas
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-benign tumors of brown fat
-uncommon |
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Lymphoctyes
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-appear as small, round cells with some basophilic cytoplasm and a dense , heterochromatic nucleus
-prominent in the lamina propria of respiratory and GI tracts -3 classes based on cluster differentiation proteins on the outer cell membrane: T cells, B cells, Natural Killer cells |
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T cells
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-important types include CD2, 3 and 7
-cell-mediated immunity |
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B cells
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-include CD9, 19, 20, 24
-antibody-mediated immunity |
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Natural Killer (NK) cells
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-CD 16, 56, 94
-do not participate in cell or antibody-mediated immunity -destroy virus infected cells and some tumor cells by cytotoxic mechanisms |
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Plasma Cells
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-antibody producing cells derived from B lymphocytes
-found in connective tissues of GI and respiratory tracts -round to oval -basophilic cytoplasm due to high rER content -golgi can been seen as a clear region in the cytoplasm |
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Myofibroblasts
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-elongated, spindle cells
-characteristics of both fibroblasts and smooth muscle cells -prominent ER and golgi -bundles of longitudinally arranged actin filaments and dense bodies similar to those in smooth muscle cells -play a role in wound contraction |
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Pericytes (adventitial cells)
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-found around capillaries and small venules
-similar to endothelial cells -endothelial cells, pericytes and fibroblasts work together during wound healing where new CT and blood vessels are required |
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Collagen fibers
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-most abundant type of connective tissue fiber
-appear as find, thread-like, eosinophilic structures -CT stains like Masson's trichrom or mallory's CT stain work to make the fibers dark blue to distinguish them from muscle fibers |
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Collagenous fiber construction
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-collagenous fibers contain many fibrils
-fibrils contain many microfibrils -microfibrils contain collagen molecules -collagen molecules have 3 polypeptide chains |
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Collagen formation
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-collagen molecule is composed of 3 polypeptide chains synthesized in the rER
-the chains intertwine to form a right-handed triple helix which can be homo or heterotrimeric -sugar groups join the helix so collagen is classified as a glycoprotein |
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Cells types capable of producing collagen
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-fibroblasts
-chondrocytes -osteoblasts -perictyes -epithelial cells synthesize the collagen in basement membranes |
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Control of collagen formation
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-regulated by transforming growth factor Beta (TGF-beta) and platelet-derived growth factor (PDGF)
-steroid hormones (glucocoricoids) inhibit collagen synthesis |
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Types of collagen
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-27 types are recognized
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Collagen Type I
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-accounts for 09% of all collagen found in vertebrates
-provides tensile strength to tendons and cornea |
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Collagen Type III
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-composed of thinner fibrils
-supports distensible organs like blood vessels |
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Collagen Type II
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-fibrillar but buried in cartilage
-hyaline cartilage of joints |
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Collagen Type IV
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-basement membrane collagen
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Collagen Type VIII
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-Descemet's membrane of the cornea
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Ehelr-Danlos Syndrome
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-congenital collagen disease
-skin tear easily or is hyperextensible |
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Scurvy
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-vitamin C deficiency
-defective hydroxylation resulting in reduced cross linking and loss of fiber strength |
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Granulation tissue
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-occurs in leg wounds in which the skin cannot be closed
-there is excess collagen production |
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Hepatic cirrhosis
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-disease in which excessive production of collagen in the liver impairs liver function
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Elastic fibers
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-produced by fibroblasts
-thinner than collagen fibers -arranged in a branching pattern to form a 3D network that interweaves with collagen fibers -composed of elastin which is a glycoprotein similar to collagen -rich in proline and glycine (but not hydroxyproline like collagen) -need to use silver stain to distinguish them from collagen fibers -major extracellular substance in vertebral ligaments, larynx and large elastic arteries -synthesis is similar to collagen production |
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Reticular Fibers
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-principle supporting CT fiber in lymph nodes and spleen
-stain well in periodic acid-Schiff stain and silver stains where they appear black -composed of type III collagen arranged in a loose, mesh-like pattern -predominate in initial stages of wound healing -produced by fibroblasts |
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Ground Substance
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-surrounds cells and fibers of CT
-composed of Glycosaminoglycans and proteoglycans -forms a clear, hydrated gel with a slippery feel -in H&E appears as a gland, pale pink or bluish |
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Glycosaminoglycans (GAGs)
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-most abundant component of ground substance
-composed of long chain non-branching polysaccharides made up of reapeating, disaccharide units -disaccharides have either 2 sugar molecules (N-acetylgalactosamine) or 1 sugar and 1 uronic acid moecule -highly negatively charged due to sulfate or carboxyl groups |
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Important GAGs
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-hyaluronic acid
-chondroitin sulfate -keratin sulfate -heparin sulfate -heparin |
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Proteoglycans
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-composed of GAGs linked at right angles to a protein core
-found in ground substance as membrane-bound molecules on the surfaces of cells |
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Mucopolysaccharidosis
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-innability to break down proteoglycans
-results from inactivity of lysosomal enzymes |
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Multiadhesive Glycoporteins
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-small group of ECM proteins
-linke ECM to cell surfaces -possess binding sites for collagen, GAGs and proteoglycans -includes fibronectin and laminin |
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Fibronectin
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-multiadhesive glycoprotein
-binds to cell membranes and attaches cells to the ECM -binds with collagen ,elastin and other proteoglycans |
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Laminin
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-multiadhesive glycoprotein
-found in basement membranes -binds to type IV collagen -signaling molecule that stabilizes many cell surface receptors |
