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105 Cards in this Set
- Front
- Back
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role of connective tissue
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form continuum with other tissues to maintain a functionally integrated body
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All tissues consist of cells and extracellular matrix. Which one is more prevalent in connective tissue?
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extracellular matrix >>> cells
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functions of connective tissues (4)
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1. provide structural support for the body (most important)
2. storage of metabolites 3.defense and protection of the body (mediating immune, inflammatory and allergic responses) 4. repair other tissues and organs through formation of fibrous scar |
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The extracellular matrix consists of ________ and __________.
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fibers
and ground substance |
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3 main types of fibers in connective tissue
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1.collagen fibers
2. reticular fibers 3. elastic fibers |
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collagen and reticular fibers are composed of _______.
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different types of collagen
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elastic fibers are composed of _________.
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elastin and fibrillin
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collagen
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extracellular fibrillar protein
most abundant protien in the body |
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collagen fibers
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principal structural components of connective tissues
flexible with high tensile strength. 20 different types in body |
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where is collagen produced?
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principally in FIBROBLASTS
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collagen fibrils
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polymerized tropocollagen molecules which compose COLLAGEN and RETICULAR FIBERS
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tropocollagen
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formed by a trimer of collagen polypeptide chains that form a triple helix, measures ~300 nm
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Tropocollagen molecules are polymerized __________ and ______ to form ________.
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laterally and head-to-tail
COLLAGEN FIBRILS |
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microscopy of collagen fibrils
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NO light microscope
distinctive banding pattern on electron microscope |
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distinctive banding of collagen fibrils due to
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small gaps between tropocollagen molecules which absorb stain
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difference between collagen and reticular fibers
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collagen = UNbranched, thicker
reticular fibers = branched, thinner |
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collagen bundles
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larger structures of collagen fibers
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ONLY type of collagen that forms collagen bundles
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Type I
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Type I collagen
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principle type
found in dermis of skin, tendons, ligaments, fascia, bone, most connective tissues proper forms fibrils ---> fibers----> bundles |
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Type II collagen
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found in cartilage
forms fibrils --X-> fibers NO FIBERS, fibrils have glassy appearance in light microscope |
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Type III collagen
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found in loose connective tissue such as blood vessels, lymphoid tissues, bone marrow, smooth muscle, nerves, lung
fibrils---> reticular fibers |
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why are reticular fibers named so?
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they form a meshwork/network/reticulum
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Type IV collagen
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forms sheet-like beaded filaments found in the basal lamina
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Ehlers-Danlos syndrome
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congenital disorder caused by impaired extracellular modification of cartilage
(1 in 5000 births world wide) skin hyperelasticity, loose/unstable joints prone to dislocation, low muscle tone, deformities of spine, low bone density |
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function of elastic fibers
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allow skin to stretch and distention
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elactic fibers vs collagen fibers
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elastic= thinner, branching pattern forms a network
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two major types of fibrillar proteins that compose elastic fibers
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1. elastin
2. fibrillin |
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elastin
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protein that contains an hydrophobic domain, causes elastin molecues to coil in aqueous environment, crosslinked by covalent bonds
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2 forms of elastin
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1. fibers of varieble length
2. lamellar layers |
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fibrillin
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GLYCOprotein the forms thin microfibrils that surround the developing elastic fibers and provide substrate for their assembly.
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Marfan's syndrome
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congenital connective tissue disorder caused by mutations in the fibrillin gene
cardiovascular, skeletal, and ocular defects including mitral valve prolapse, rupture of elastic arteries, arachnodactylyly |
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ground substance
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fills spaces between fibers in the extracellular matrix
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3 main components of ground substance
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1.glucosaminoglycans (GAGs)
2. proteoglycans 3. multiadhesive glycoproteins |
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glucosoaminoglycans (GAGs)
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long-chain, unbranced, highly negatively (=HYDROPHILIC) charged polysaccharides
bind water forming highly hydrated gel (<--- main component of ground substance) |
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most abundant component of ground substance
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glucosoaminoglycans (GAGs)
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significance of gel-like composition of ground substance (2)
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helps resist compression and deformation
allows quick diffusion of water soluble particles |
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5 types of GAGs
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1.hyaluronic acid
2.chondroitin sulfate 3.dematan sulfate 4. keratan sulfate 5. haparan sulfate |
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hyaluronic acid + how it is different from oher types of GAGs
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always present in the extracellular matrix
3 differences: 1. much longer molecule 2. does not contain sulfate 3. DOES NOT FORM proteoglycans |
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proteoglycans
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composed of GAGs covalently attached to core proteins. GAGs repel each other and extend perpendicularly from protein forming a brush-like structure
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How do proteoglycans associate with hyaluronic acid?
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Proteoglycans attach non-covalently through a link protein to the long chains of hyalyronic acid and form giant HYDROPHILIC aggregates
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2 functions of proteoglycan hyaluronic acid aggregates
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1. responsible for the gel state of extracellular matrix (hydrophilic)
2.account for ability of the connective tissue (esp. cartilage) to resist compression without losing flexibility |
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2 functions of multi-adhesive glycoproteins
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1. serve as cross-links between collagen, extracellular matrix, and cells
2. stabilize the extracellular matrix by binding to integrin transmembrane proteins in hemidesmosomes and focal adhesions |
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2 types of multi-adhesive glycoproteins
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1. fibronectin
2. laminin |
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fibronectin
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can assemble into thin fibrils
contains domains that interact with different ECM molecules including collage I, II, III collagen, GAGs, fibrin, integrins |
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most abundant glycoprotein in the connective tissue
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fibronectin
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laminin
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present in the basement membrane
has bining sited cor collagen type IV, integrin, etc |
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2 categories of connective tissue cells
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1. resident
2. transient |
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resident (fixed cells)
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undergo mitosis within the connective tissue and spend most of their lifespan in the connective tissue
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4 types of resident cells
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1. fibroblasts
2. adipocytes 3. macrophages 4. mast cells |
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fibroblasts
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principle resident cell
responsible for producing components of the ECM such as collagen and elastic fibers, GAGs, proteglycans, multiadhesive glycoproteins |
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how to recognize a fibroblast on a slide
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usually reside in close proximity of collagen fibers
euchromatic nucleus (very active, lays down lots of fibers) |
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4 kinds of fibroblasts
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1. active fibroblasts
2. inactive fibroblasts (fibrocytes) 3.myofibroblasts 4. mesenchymal cells |
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active fibroblasts
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present in actively growing connective tissue/wound repair, loose connective tissue
abundant cytoplasm with many thin processes, abundatnt RERE and Golgi. oval shaped, palue euchromatic nucleus, onre or more well-expressed nucleoli |
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inactive fibroblasts
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(fibrocytes)
found in dense connective tissues that are not growing limited cytoplasm, less developed RER and Golgi apparatus dark, elongated, more heterochromatic nucleus |
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myofibroblasts
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found in wound sites, assist in wound closure
display properties of both fibroblasts and smooth muscle cells contain RER and Golgi, bundles of actin filaments and dense bodies similar to those of smooth muscle cells |
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Myofibroblasts ARE/ARE NOT a type of smooth muscle. What is similar, what is different?
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ARE NOT
similar- ability to contract different- no external lamina |
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mesenchymal cells
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present in embryonc connective tissues, uperficially resemble active fibroblasts:
pale, euchromatic nuclei and well developed RER and Golgi pluripotent, give rise to fibroblasts, chondroblasts, osteoblasts, adipocytes |
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adipocytes
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connective tissue cells that are specialized to store fat and produce a variety of hormones
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2 types of adipocytes
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1. unilocular
2 multilocular |
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unilocular adipocytes
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(most common)
large, spherical cells, single large lipid droplet with cytoplasm and flattened nucleus forming a rim found either singularly within loose connective tissue or forming aggregates called white adipose tissue |
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white adipose tissue
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aggregates of unilocular adipocytes
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multilocular adipocytes
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brown adipose tissue
characterized by multple fat droplets and presence of large number of mitochondria centrally placed nuclus, not flattened. |
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macrophages
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phagocytic cells derived from monocytes
in connective tisse, can divide mitotically to increase number presence of ingested material in the cytoplasm, indented (kidney shaped) nucleus |
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monocytes
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originiate from precursor in the bone marrow, circulate through blood and migrate to connective tissue, where they become macrophages
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3 defense mechanism functions of macrophages
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1. phagocytosis of bacteria and cell debris
2. present antigens to toher cells of immune system (helper Ts) 3. produce cytokines that activate immune system |
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mononuclear phagocytic system
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macrophage cells derived from the same precursor in the bone marrow, of the cell monocyte lineage
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6 cells of the mononuclear phagocytic system
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1. histiocytes/macrophages --> connective tissue
2. alveolar macrophages ---> lungs 3. kupferr cells ---> liver 4. osteoclasts ---> bone 5. langherhans cells ---> skin 6. dendritic cells lymphoid organs 6.microglial cells ---> CNS |
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mast cells
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originate in the bone marrow, proliferate + differentiate in connective tissue
absent from CNS, found in skin and mucous membranes |
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4 structural characteristics of mast cells
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1. very large (one of largest) 20-30µm
2. oval in shape 3. centrally placed spherical nucleus 4. ***presence of a large number of large, basophilic granules in cytoplasm |
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4 substances found in mast cell granules
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1. histamine
2. heparin sulfate (acidic GAG) 3. chondroitin sulfate 4.chemotactic mediators |
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What is found on the surface of mast cells?
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Specifc receptors for IgE (immunoglobulin E)
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What cell are mast cells similar to, even though they differ in nuclear morphology?
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basophil (WBC)
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function of mast cells
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inflammatory and hypersensitivity reactions, allergy, anaphylaxis
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Describe the immuno-reaction of mast cells
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1. First exposure: large amounts of IgE from plasma cells bind surface of mast cell and activate it
2. Subsequent exposure: antigen bings to IgE causing cross-linking. 3. Crosslinking of IgE results in clustering of receptors on the cytoplasmic cide of the plasma membrane, causes degranulation 4. Degranulation: histamine causes vasodilation and increases vascular permeability , white blood cells enter the connective tissue 5. Histamine and several other agents cause bronchoconstriction and increased mucus production in bronchial mucosa 6.Chemotactic mediators attract WBCs, eosinophils and nuetrophils |
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transient cells
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derived from precursors in the bone marrow, involved in immune cells
conective tissue is final destination, do NOT DIVIDE within the |
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2 main types of transient cells
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1. plasma cells
2. white blood cells (luekocytes)` |
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plasma cells
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antibody producing cells derived from B-lumphocytes
most numerous in areas of inflammation/infection specialized for protein (immunoglobulin) secretion |
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2 ways to recognize a plasma cell
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1. clock-face/cartwheel patter of dark heterochromatin alternating with pale euchromatin
2. prominent RER and Golgi |
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leukocytes
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white blood cells
found in connective tissues, especially inflammed areas |
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lymphocytes
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main function is production of antibodies and regulation of immune response
round, dark heterochromatic nucleus |
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monocytes
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phagocytic cells that are precursors for tissue macrophages
kidney shaped nucleus |
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neutrophils
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phagocytic cells aimed at bacteria, very aggresive, form bulk of pus
elongated, segmented, multi-lobed nucleus |
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5 types of leukocytes
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1. lymphocytes
2. monocytes 3. nuetrophils 4. eosinophils 5. basophils |
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eosinophils
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involved in reaction to parasitic infections, like grenades, slow down allergic response
characterized by presence of intensely staining eosinophilic granules and BILOBED nucleus connected by isthmus |
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basophils
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produce histamine in allergic response
rare in blood and connective tissue BILOBED nucleus, large number of basophilic granules in cytoplasm |
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On which characteristics is classification of connective tissue based? (2)
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1. composition of of extracellular and intracellular components
2. organization of extracellular and intracellular components |
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3 main groups of connective tissues
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1. embryonic connective tisssue
2. connective tissue proper 3. specialized connective tissue |
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embryonic connective tissue
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almost all connective tissue arises from this tissue (through differentiation)
found in embryo and umbilical cord |
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2 types of embryonic connective tissues
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1. mesenchyme
2. mucous connective tissue |
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mesenchyme
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found in embryo
3-D network of mesenchymal cells abundant ground substane, very few collagen/reticular fibers |
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mucous connective tissue
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only found in umbilical cord
gelatin like appearance: Wharton's jelly contains large amounts of hyaluronic acid very few collagen/reticular fibers |
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2 types of connective tissues proper
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1. loose
2. dense (based on relative amount of collagen type 1 fibers) |
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loose connective tissue
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(areolar)
highly cellular with thin relatively sparse collagen type I fibers. usually doe not contain bundles abundant viscous gel-like ground substance |
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Most fibroblasts present in loose connective tissue are _______________.
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active fibroblasts
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filter tissue
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loose connective tissue located beneath epithelia that cover internal surfaces of body, surrounds blood and lymphatic vessels and nerves
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dense connective tissue
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large number of collagen type I fibers and BUNDLES with fewer cells
little ground substance, fewer cells, than loose can be regular or irregular |
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dense vs loose connective tissue
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loose: NO collagen BUNDLES, lots of cells
dense: collagen bundles, lots of fibers, less ground substance |
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dense irregular connective tissue
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oriented in various directions and interwoven into a meshwork that resists stress from all directions
large number of collagen fibers, therefore provides significant strength fine network of elastic fibers often scattered around collagen bundles found in dermis of skin, capsules of spleen and testes |
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main type of cell present in dense irregular connective tissue
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inactive fibroblasts
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dense regular connective tissue
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composed of densely packed collagen bundles, oriented in the same direction to resist tensile forces ---> found in tendons, ligaments aponeuroses
very little space left for cells and ground substance thin, sheet like inactive fibroblasts with extremely elongated heterochromatic nuclei found here |
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4 types of specialized connective tissue
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1.adipose tissue
2. reticular connective tissue 3. cartilage 4. bone |
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adipose tissue
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largest repository of energy (triglycerides) in body
separated into lobules by connective tissue septa receives rich blood supply, innervated by autonomic nervous system contains receptors for several hormones |
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white adipose tissue
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-accumulates energy
-growth hormone, insulin, noradrenalin receptors -poor heat conductor, used for insulation -fills spaces between internal organs, keeps them in place -shock absorption |
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brown adipose tissue
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contains cells (multilocular adipocytes) with a large # of mitochondra to oxidize fatty acids at up to 20X rate in white adipose tissue, increasing heat production 3X
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reticular connective tissue
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found in stroma of organs of the lymphoid system (lymph nodes, spleen, bone marrow)
supported by network of reticular fibers that form thin, branching, interconnected threads |
