CT Flashcards
Constituents of CT
In ECM: fibers (elastic, reticular, and collagen) and ground substance (GAGs, proteoglycans, and glycoproteins)
Resident cells: fibroblasts, mesenchymal, adipocytes, chondrocytes, osteocytes, and mature mast cells
Migrating cells: macrophages, monocytes, lymphocytes/plasma cells, immature mast cells, and granulocytes
CT Cytoskeletal Elements
In contrast, intracellular cytoskeletal elements consists of microtubules, intermediate filaments, and microfilaments (actin).
Fibroblasts: flat and skinny; heterochromatic and flat nucleus; make different fibers, but do not confuse with cellular elements that are already there like microtubules
Gel like matrix to allow for hydration and flexibility
5 Major Types of Collagen
Each collagen is a triple helix made of amino acids arranged in alpha chains; ground substance of proteoglycans
Type I: skin, bone, cornea, and tendons
Type II: very fine and found in all types of cartilage
Type III: reticular fibers and very thin; found in loose CT, support for glands, lymph, and spleen
Type IV: found in sheets in basement membrane (seen in light microscope) or lamina (see basement membrane in eletron microscope and see different layers)
Type VII: anchoring fibrils in basement membrane
Reticular Fibers
Thinner (0.5-2 um diam)
type III collagen - form a fine, supportive meshwork; in liver, spleen, lymph node
higher carbohydrate content than other collagen fibers
supportive framework for some organs and glands: lymph nodes, spleen
Usually need special stains (silver or PAS) to see reticular fibers in the light microscope.
Ground substance made of glycoproteins
Elastic Fibers
Extremely thin (0.2-1 um), coiled, branching fibers
non-collagenous
Microfibrils of fibrillin embedded in an amorphous core of elastin (glycoprotien)
Relatively rigid regions alternate with random-coil structure resilience or elasticity
May be stretched up to 150% of resting length without tearing
Require special staining to be seen in LM
Provide elastic support of arteries, trachea & mesenteries
Ground substance made of GAGs
Marfan Syndrome
Marfan Syndrome – mutations in the fibrillin gene FBN1; autosomal dominant
Because large arteries contains lots of elastic fibers, Marfan patients often experience aortic rupture (life-threatening).
Ground Substance
a gel-like matrix rich in tissue fluid composed of:
A. Proteoglycans – ex: aggrecan, syndecan
B. Glycoproteins – globular proteins with attached branched chains of monosaccharides; ex: collagen, elastin, fibrillin, fibronectin, laminin
Proteoglycans
proteins covalently linked with glycosaminoglycans (GAGs)
GAGs – long, unbranched polysaccharides made of repeating disaccharide units
frequently sulfated which, with carboxyl groups high negative charge.
Thus, stain how in H&E stain?
Common GAGs: keratan sulfate, chondroitin sulfate, hyaluronan
Proteoglycan Properties
Neg charge
Occupy large volumes
Mobilize water
Make solutions viscous (e.g., mucus) or even rigid
Remain porous
Supportive & lubricating in cartilage and joints
Matrix Metalloproteases (MMPs)
Collagenases & gelatinases secreted by invading organisms or tumor cells; digest the ECM
ECM will provide a barrier to infectious organism and tumors
Tumors have developed ways to infiltrate ECM by secreting matrix metalloproteases (MMPs) and are enzymes that chew up the ECM so tumor can invade into epithelium
Neutrophils and other WBCs also can also secrete MMPs to get to sites of infection
Glycoproteins
ex: fibronectin, laminin, others; entactin/nidogen in basal lamina
attachment and migration of cells along ECM
protein component is more important for biological activities than the sugar
are short, have branching, smaller, and medium sugar content
Fibronectin
ECM glycoprotein synthesized by fibroblasts and some epithelial cells.
helps mediate cell adhesion and migration
two large polypeptides disulfide-bonded together at the carboxyl end.
contains specific binding regions for fibrin, heparin, fibrinogen, collagen, and eukaryotic cells
Laminin
ECM glycoprotein with cross like structure
Promotes adhesion of cells to basal laminae
Cell - ECM Interactions
Cell-surface molecules (integrins) bind to fibronectin, laminin, and collagens in the ECM
Integrins are poking out of the membrane and into the ECM and binds to proteins (laminins and fibronectins)
As the integrin binds to different things in ECM, signals cell actin molecules to get longer and extend to help move the integrins around the cell; be able to regulate cell movement and shape by integrins getting an idea of what is going on in the ECM
Integrins
transmembrane glycoprotein;
Links ECM proteins (collagens, laminin, fibronectin) with the intracellular cytoskeleton (actin, intermediate filaments)
Regulate cell adhesion, control cell movement and shape
