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287 Cards in this Set
- Front
- Back
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ectoderm
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gives rise to the oral and nasal mucosae, cornea, epidermis of the skin, and glands of the skin and the mammary glands
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endoderm
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give rise to the liver, pancreas, lining of the respiratory and gastrointestinal tract
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mesoderm
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uriniferous tubules of the kidney, the lining of the male and female reproductive systems, the endothelial lining of the circulatory system, and the mesothelium of the body cavities
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functions of epithelial tissue
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protection
transcellular transport secretion absorption selective permeability detection of sensations |
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striated border vs. brush border
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striated border found in intestinal absorptive cells, brush border found in the kidney tubules
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terminal web
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composed of actin, spectrin, and intermediate filaments
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myosin I and calmodulin
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connect actin filaments in the terminal web to the microvillus to give support
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apical domain of epithelium
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rich in ion channels, carrier proteins, H+-ATPase, glycoproteins, hydrolytic enzymes, and aquaporins
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microvilli
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small finger like cytoplasmic projections emanating from the free surface of the cell into the lumen, represent the striated border of the intestinal absorptive cells and the brush border of the kidney proximal tubule cells, greatly INC SA, contains a core of 25 to 30 actin filaments, cross-linked by villin and attached to the terminal web
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glycocalyx
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represents carbohydrate residues attached to the transmembrane proteins of the plasmalemma, function in protection and cell recognition
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sterocilia
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long microvilli found only in the epididymis and on the sensory hair cells of the cochlea, function to INC SA (epididymis) and signal generation (hair cells)
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cilia
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long, motile, hair-like structures emanating from the apical cell surface, their core is composed of a complex arrangement of microtubules known as the axoneme, function to propel mucus and other substances, contains an axoneme (composed of microtubules in a 9+2 arrangement), attached basally to the basal body (which has 9 triplets and no singlets), doublets have a subunit A (13 protofilaments) and B (10)
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radial spokes
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project from subunit A inward toward the central sheath surrounding the two singlets
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nexin
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connect neighboring doublets, A -> B, elastic protein that restrains the movements of dynein somewhat
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dynein
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has ATPase activity, radiates from subunit A of one doublet toward subunit B of the neighboring doublet, provides energy for ciliary bending
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terminal bars
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where epithelial cells attach to each other, continuous around the entire circumference of the cell, are composed of junctional complexes
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junctional complexes
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three types:
1. occluding junctions-function in joining cells to form an impermeable barrier preventing material from taking an intercellular route 2. anchoring junctions-function in maintaining cell to cell or basal to cell lamina adherence 3. communicating junctions-function in permitting movement of ions or signaling molecules between cells |
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zonulae occludentes
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aka tight junctions, most apically located, belt-like, composed of claudins (reinforced by cadherins and Z01, Z02, and Z03 proteins) and occludins binding to each other, prevent the movement of membrane proteins from the apical domain to the basolateral domain, and they fuse plasma membranes of adjacent cells to prohibit water-soluble molecules from passing between cells (P-face has tight junction strands and E-face has corresponding grooves)
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zonulae adherentes
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assist joining cells to adhere to one another, located basal to the zonulae occludentes, cadherins (are Ca2+ dependent) bind to each other intercellularly and actin binds intracellularly (to anchor proteins catenin, vinculin and actinin), this junction joins the cell membrane to each other and links the cytoskeleton of the two cells, goes around entire circumference of cell
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desmosomes (maculae adherents)
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weld-like junctions along the lateral cell membranes that help to resist shearing forces, randomly distributed in the wall, have disk shaped attachment plaques that attach to each other on adjacent cell membranes, intermediate filaments insert into the plaques where they make a hairpin turn
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desmoplakins and pakoglobins
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attachment proteins of attachment plaques
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desmoglein and desmocollin
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members of the cadherin linker protein, found extracellulary in association w/ desmosomes, in the presence of Ca2+ they bind to linker proteins of the adjoining cell, in the presence of Ca2+ chelating agents the desmosomes halve
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gap junctions
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aka nexus or communicating junctions, regions of intercellular communication, couple adjacent cells metabolically and electrically, also widespread, found everywhere except the skeletal muscle cells, built by six closely packed transmembrane channel-forming proteins (connexins) that assemble to form channel structures called connexons, hydrophilic communication channel, regulated and may be opened and closed rapidly (close w/ low cytoscolic pH or INC in cytosolic Ca2+)
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basal surface specializations
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include the basal lamina, plasma membrane enfoldings and hemidesmosomes
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plasma membrane enfoldings
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INC SA available for transport at the basal end, mitochondria found within the enfoldings, use energy for transport
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hemidesmosomes
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attach the basal cell membrane to the underlying basal lamina, attachment plaques are present on the cytoplasmic side of the plasma membrane, keratin tonofilaments insert into these plaques, linker proteins (integrin not cadherin) bind to laminin and type IV collagen of the basal lamina
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parenchyma of a gland
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secretory units of a gland including the duct
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stroma of a gland
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represents the elements of the connective tissue that invade and support the parenchyma
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exocrine glands
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secrete their products via ducts onto the external or internal epithelial surface
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endocrine glands
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ductless, having lost their connections to the originating epithelium, secrete their products into the blood or lymphatic vessels for distribution
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cytokines
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responsible for cell-to-cell communications
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autocrine
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signaling cell is its own target, cell stimulates itself
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paracrine
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target cell is located in the vicinity of the signaling cell, cytokine does not have to enter the vascular system for distribution to its target
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endocrine
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target cell and signaling cell are far, cytokine has to be transported either by the blood or lymph system
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mucous glands
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secrete mucinogens that swell to become thick lubricant called mucin (component of mucus), lighter colored
-ex: goblet cells and the minor salivary glands of the tongue and palate |
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serous glands
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secrete an enzyme rich watery fluid, darker colored
-ex: pancreas |
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mixed glands
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contain acini (secretory units) that produce mucous and serous secretions, some mucous acini possess serous demilunes (cells that secrete a serous fluid)
-ex: sublingual and submandibular glands |
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holocrine secretion
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entire secretory cell dies and becomes the secretory product
-ex: sebaceous glands |
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aporcrine secretion
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questioned existence, a small portion of the apical cytoplasm is released
-ex: mammary glands |
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merocrine glands
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occurs via exocytosis, cell membrane and cytoplasm are not part of the secretion
ex: parotid gland |
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diffuse neuroendocrine system (aka amine precursor uptake and decarboxylation cells APUD)
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make up endocrine cells widespread throughout the digestive tract and in the respiratory system, manufacture various paracrine and endocrine hormones
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Glycosaminoglycans (GAGs)
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negatively charged, long rod-like chains of repeating disaccharides that have the capability of binding large quantities of water, all but one GAG (hyaluronic acid) is sulfated
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the disaccharide of the GAG
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two subunits, one is always an amino sugar (N-acetylglucosamine or N-acetylgalactosamine) and the other is uronic acid
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amino sugar of GAG
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normally sulfated and (-) charged, attract Na+ which attracts extracellular fluid which assists in the resistance of compression
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sulfated GAGs
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keratin sulfate, heparin sulfate, heparin, chondroitin 4-sulfate, chondroitin 6-sulfate, and dermatan sulfate, these are usually linked to form proteoglycans, synthesized by the golgi
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hyaluronic acid
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nonsulfated GAG, doesn’t form covalent links to protein molecules, synthesized as a free linear polymer at the cytoplasmic face of the plasma membrane, proteoglycans (through protein cord) do attach here via link proteins
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proteoglycans
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composed of a protein core to which GAGs are covalently bonded, looks like a brush
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aggrecan
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type of proteoglycan, found in cartilage and CT proper
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hyaluronic acid with proteoglycans
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forms large macromolecule responsible for the gel state of the ECM, also accounts for slow diffusion
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function of proteoglycans
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resist compression, slow movement of microorganisms, molecular filters, binding sites for signaling molecules
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syndecan
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type of proteoglycan, act as transmembrane proteins, permit the cell to become attached to components of the matrix
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glycoproteins
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have binding sites for several components of the ECM that facilitate the attachment of cells to the ECM, usually bind to integrins, collagen fibers or proteoglycans
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types of glycoproteins
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fibronectin, laminin, entactin, tenascin, chodronectin and osteonectin
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fibronectin
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dimmer composed of two polypeptide subunits, has binding sites for extracellular components and integrins, has an RGD sequence for adhering, produced by fibroblasts, when they stretch expose binding sites for other fibronectins to bind forming the fibronectin matrix
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plasma fibronectin
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facilitates healing, phagocytosis and coagulation
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cell-surface fibronectin
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attached to the plasma membrane, regulates pathways for embryonic cells to reach their destination
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laminin
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three large polypeptide chains (A, B1, and B2), B’s wrap around A, found in the basal lamina and has binding sites for heparin sulfate, type IV collagen, entactin and the cell membrane
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entactin
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sulfated, binds to laminins three short arms to facilitate the collagen meshwork
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tenascin
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composed of six polypeptide chains, bug with six legs, has binding sites for the transmembrane proteoglycan syndecans and for firbronectin, usually found in embryonic tissue
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chondronectin
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similar to fibronectin, binds type II collagen, chondroitin sulfates, hyaluronic acid and integrins
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osteonectin
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binds type I collagen, proteoglycans, and integrins, may facilitate the binding of calcium hydroxapatite to type I collagen of bone
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collagen
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composed of tropocollagen subunits, resists tensile forces, constitutes about 20-25% of the body, three categories (fibril forming, fibril associated, and network forming), 67 nm cross bridge, made from collections of tropocollagens (each of which is composed of three alpha chains
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elastic fibers
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give the elastic property to CT, 50% of aorta, manufactured by fibroblasts, composed of elastin (rich in G, K, A, V, P), core of elastin surrounded by a sheath of microfibrils (composed of fibrillin)
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desmosine cross links
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hold elastin fibers together, 4 K molecules for covalent bonds with each other
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basal lamina
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composed of the lamina lucida and the lamina densa, functions in filtering and support
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lamina lucida
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consists mainly of laminn, entactin, and integrin
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lamina densa
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meshwork of type IV collagen, coated by perlacan,
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how is basal lamina bound to the reticular lamina
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dibronetin, anchoring fibrils, and microfibrils
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lamina reticularis
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derived from CT, responsible for affixing the lamina densa to the underlying CT, composed of type I and III collagen, made from fibroblast, thickness depends on the level of friction on the superficial epithelium
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integrins
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transmembrane proteins, linked to the cytoskeleton and binds to collagen, laminin and fibronectin, weak bonds, but numerous in the ECM, a heterodimer composed of alpha and beta glycoproteins, binding site on amino end, can also activate second messenger system cascades
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mesoderm
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origination of connective tissue, develops mesenchyme
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functions of connective tissue
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provide structural support, serve as an exchange medium, aid in defense and protection of the body, and form a site for storage of fat
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extracellular matrix
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composed of ground substance and fibers, resist compression and stretching
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aggrecan aggregates
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the name for the complex of hyaluronic acid and proteoglycans
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ground substance
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hydrated, amorphous material composed of glycosaminoglycans, proteoglycans (which link glycosaminoglycans) and adhesive glycoproteins
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collagen fibers
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inelastic, have great tensile strength, composed of three alpha-chains wrapped around one another in a helical configuration, most common forms are glycine, proline, hydroxyproline, and hydroxylysine
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Type 1 collagen fibers
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found in tissue proper, bone, dentin, and cementum
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Type 2 collagen fibers
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found in hyaline and elastic cartilages
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Type 3 collagen fibers
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found in reticular fibers
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Type 4 collagen fibers
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found in lamina dansa of the basal lamina, not assembled into fibers
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Type 5 collagen fibers
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found in the placenta, associated with type 1 collagen
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Type 7 collagen fibers
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found attached to the basal lamina to the lamina reticularis
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elastic fibers
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composed of elastin (made mainly of glycine and proline) and microfibrils (fibrillin), highly elastic
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fixed cells of connective tissue
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resident cells that remain in the CT, fibroblasts, adipose cells, pericytes, mast cells, macrophages
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transient cells of CT
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originate mainly in bone marrow and circulate in the blood stream to the CT, include plasma cells, lymphocytes, neutrophils, eosinophils, basophils, monocytes, and macrophages
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fibroblasts
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most abundant cell type in the CT, responsible for the synthesis of almost all of the extracellular matrix, has dark staining nucleus w/ nucleolus, immature fibroblasts may differentiate into different cells of the CT, has prominent golgi and numerous RER
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myofibroblasts
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modified fibroblasts, abundant in areas of wound healing where they function in wound contractrion, similar to smooth muscle cells, also found in the periodontal ligament where they assist in tooth eruption
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pericytes
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surround endothelial cells of capillaries and small venules, have their own basal lamina, also similar to smooth muscle cells (contain actin, myosin) may function in contraction
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adipose cells
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fully differentiated (no cell division), function in the synthesis, storage and release of fat (triglycerides), may be given rise by fibroblasts, 2 types (white, unilocular and brown multilocular), have cytoplasm and nucleus displaced peripherally, presence of small Golgi, a few mito, sparse RER, but lots of free ribosomes
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white fat vs. brown fat
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white fat more abundant, brown are smaller and more polygonal, brown also carry more mito but fewer ribosomes, do have SER
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chylomicrons
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complex of triglycerides and protein, carried to bloodstream by lymph and may enter a adipocyte
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transport and storage of fat
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lipids transported to bloodstream as chylomicrons and VLDLs, lipoprotein lipase hydrolyzes the lipids to fatty acids and glycerol, fatty acids enter the adipocyte and are resterified into triglycerides for storage, when needed, they are hydrolyzed by hormone sensitive lipase, these fatty acids enter the capillary and attach to albumin and are transported in the blood
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insulin and fat formation
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can stimulate adipose cells to convert glucose and amino acids into fatty acids
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norepinephrine and epinephrine in fat
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binds to receptors which activates cAMP cascade which activates hormone-sensitive lipase, this cleaves triglycerides in adipocytes into fatty acids and glycerol and release them into bloodstream
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mast cells
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arise from bone marrow stem cell and function in mediating the inflammatory process and immediate hypersensitivity reactions, have numerous granules in the cytoplasm containing heparin, contain histamine (primary mediator, present in granules, also has ECF and NCF) and other secondary mediators (formed at the time of release), contains several mito, sparse RER, and small golgi
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mucosal mast cells
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found in the alimentary tract (respiratory and digestive tracts) and contain chondoritin sulfate as opposed to heparin
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immediate hypersensitivity reaction
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induced by antigens and subsequent formation of IgE antibodies (which bind to the FceRI receptors, steps include
1. binding of the antigen causing cross-linking of IgE and clustering of receptors 2. activation of adenylate cyclase 3. activation of protein kinase 4. phosphorylation of protein 5. INC in intracellular [Ca2+] leading to degranulation of primary mediators (heparin, histamine, ECF, NCF) 6. for secondary release, activation of phospholipases which acts on membrane phospholipids to form arachidonic acid 7. arachidonic acid is converted into secondary mediators and secretion of leukotrienes, thromboxanes and prostaglandins occurs this causes an initiation of the inflammatory response, attracting leukocytes to sites of inflammation and modulates the degree of inflammation |
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histamine
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causes vasodilation and INC vascular permability, causes bronchiospasm and INC mucus production
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neutral proteases
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cleavage of proteins to activate other agents of inflammation
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eosinophil chemotactic factor (ECF)
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attracts eosinophils to site of inflammation, phagocytose antigen-antibody complexes, destroys parasites
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neutrophil chemotactic factor (NCF)
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attracts neutrophils to site of inflammation, phagocytose and kill microorganisms
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leukotrienes C4, D4, and E4
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INC vascular permeability and cause bronchiospasm, more potent than histamine
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prostaglandin D2
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causes bronchiospasm and INC secretion of mucus
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Platelet activating factor (PAF)
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causes greater vascular permeability
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Thromboxane A2
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vasoconstrictor, platelet aggregate mediator
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bradykinin
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vascular dilator, responsible for pain
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macrophages
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belong to the mononuclear phagocytic system (which arise from bone marrow stem cells) and are subdivided into two groups of cells (phagocytes and antigen presenting cells), can be fixed or transient, fxn in removing cellular debris and in protecting the body against foreign invaders, as well as initiating the immune response, use their lysosomes to degrade ingested material, has well developed golgi, prominent ER, lott of lysosomes
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macrophage colony stimulating factor (M-CSF)
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activate the transformation of monocytes into macrophages
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plasma cells
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derived from B lymphocytes and manufacture antibodies, responsible for humorally mediated immunity, have clock face nucleus, present in greatest amounts in areas of chronic inflammation, lots of RER, few mito, large golgi, pair of centrioles
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leukocytes
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exit the bloodstream during inflammation, invasion by foreign elements, immune responses in order to perform various functions, white blood cells, types include monocytes, neutrophils, eosinophils, basophils, and lymphocytes
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neutrophils
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phagocytose and digest bacteria, result in formation of pus
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eosinophils
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combat parasites by releasing cytotoxins, moderate the allergic reaction and phaocytose antibody-antigen complexes
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basophils
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release preformed and newly synthesized pharmacological agents, control inflammatory response, like mast cells
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messenchymal CT
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contain mesenchyma cells and ground substance containing reticular fibers, only found in embryos and maybe the pulp of teeth
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Wharton’s jelly
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found only in the umbilical cord and subdermal CT of the embryo, composed of hyaluronic acid and Type 1 and 3 collagen fibers and fibroblasts
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loose (areolar) CT
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fills in the spaecs of the body just deep to the skin, lies below the mesothelial lining of the internal body cavity, adventitia of blood vessels and surrounds the parenchyma of glands, has nerve fibers and blood vessels coursing throughout, first site where the body fights antigens, bacteria, and foreign invaders
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dense irregular CT
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coarse collagen fibers that resists stress from all directions, also has some elastic fibers, constitutes the dermis of the skin, the sheaths of nerves and the capsules of the spleen, testes, ovary, kidney and lymph nodes
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dense regular collagenous CT
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composed of coarse collagen bundles oriented in parallel sheets that resist tensile forces, make up tendonds, ligaments, and aponeuroses
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dense regular elastic CT
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coarse elastic fibers with only a few collagenous ones, arranged parallel direction, found in large blood vessels, ligamenta flava, and suspensory ligament of peni
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reticular tissue
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composed of type 3 collagen, forms framework of liver sinusoids, adipose tissue, spleen and islets of Langerhans
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white (unilocular) adipose tissue
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single lipid droplet, heavily vascular, septa partition fat into lobules, in men found in the neck, shoulders, hips, and in women found in breasts, buttocks, hips and thighs
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brown (multilocular) adipose tissue
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store fat in multiple droplets, heavily vascular, abundant mito, innervated directly, found in newborns, can oxidize fatty acids 20 times the rate of white, INC body heat
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cartilage vasculature
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is avascular, lacks nerves and lymphatic vessels as well
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functions of Cartilage
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resists mechanical stresses
shock absorber friction free movement of joints |
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hyaline cartilage
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contains type II collagen (40% of dry weight, basophillic), most abundant cartilage in the body, forms template for endochondral bone formation, can resist both tension (interaction of proteoglycans w/ collagen) and compression (aggrecans)
found in nose and larynx, ends of ribs, trachea and bronchi |
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elastic cartilage
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contains type II collagen and elastic fibers, more chondrocytes than in hyaline, elastic fibers in perichondrium as well
found in pinna of ear, epiglottis |
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fibrocartilage
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contains type I collagen (acidophilic), no perichondrium
found in IV disks, pubic symphysis, and articular disks |
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perichondrium
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vascular CT, an outer fibrous layer (type I collagen and fibroblasts) and an inner cellular layer (chondrogenic cells), responsible for growth and maintanence of the cartilage
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chondrification centers
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dense masses of mesenchymal cells that differentiate into chondroblasts
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interstitial growth of hyaline cartilage
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when isogenous groups manufacture matrix and push away from each other forming two separate chondrocytes, occurs only in the early stages, serves to lengthen bone
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appositional growth of hyaline cartilage
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when chondrogenic cells of the cellular layer of the perichondrium differentiate into fibroblasts and secrete matrix on the periphery of the cartilage
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territorial matrix
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surrounds lacunae, poor in collagen but rich in chondroitin sulfate, stain darker
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interterritorial matrix
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righer in type II collagen and poorer in proteoglycans
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pericellular capsule
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surrounds the lacunae, may protect chondrocytes from mechanical stress
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thyroxine, testosterone, and somatotropin effect on hyaline cartilage
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stimulate cartilage growth and matrix formation
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cortisone, hydrocortisone, and estradiol effect on hyaline cartilage
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inhibit cartilage growth and matrix formation
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hypovitaminosis A effect on hyaline cartilage
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reduces width of epiphyseal plates
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hypervitaminosis A effect on hyaline cartilage
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accelerates ossification of epiphyseal plates
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hypovitaminosis C effect on hyaline cartilage
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inhibits matrix synthesis and deforms architecture of epiphyseal plate, scurvy
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absence of vita D
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results in deficiency in absorption of calcium, matrix is not calcified resulting in rickets
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pressure vs. tension on bone
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pressure leads to resorption of bone while tension on bone results on development of new bone
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endosteum
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lines the central cavity of bone, a thin CT layer composed of osteoprogenitor cells and osteoblasts
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osteoclasts
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multinucleated giant cells derived from fused bone marrow precursors responsible for bone resorption and remodeling
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advantage and disadvantage for decalcified vs. ground sections of bone
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decalcified-distorted osteocytes
ground-cells are destroyed and the lacunae and canaliculi are filled in with bone debris |
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inorganic component of bone
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calcium hydroxyappatite, mostly calcium and phosphorous, 65% of dry weight, gives bone its hardness and strength, has a hydration shell that permits ion exchange with the EC fluid (crystals attract H2O)
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organic component of bone
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type I collagen, 35% of dry weight, stained with PAS bec. of sulfated GAGs
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osteocalcin
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a glycoprotein, binds to hydroxyapatite
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osteopontin
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a glycoprotein, binds to hydroxyapatite but has additional binding sites for integrins
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bone siaolprotein
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binding sites for matrix components and integrins
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osteoprogenitor cells location
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can be found in the cellular layer of periosteum, on the inner lining of the haversian canal, and in the endosteum
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bone morphogenic protein (BMP) and transforming growth factor-beta
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turn osteoprogenitor cells into osteoblasts
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osteoid
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substance secreted by osteoblasts, it is an uncalcified bone matrix
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bone-lining cells
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inactive osteoblasts, more flattened, can be reactivated by the proper stimulus
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osteoblast cell membrane
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has integrins and parathyroid hormone receptors, when PTH binds it stimulates osteoblasts to secrete osteoprotegerin ligand (OPGL) (induces differentiation of preosteoclasts into osteoclasts, INC RANKL (receptor for NF-kappa B) expression
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osteocytes
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bone maintanence, also implicated in mechanotrsnduction (respond to stimuli that place tension on bone by releasing cAMP and osteocalcin that recruit osteoblasts to assist in bone remodeling)
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periosteocytic space
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interval between the osteocyte plasmalemma and the walls of the lacunae, filled with EC fluid (~1.3 L of space) and exposed to as much as 20 g of calcium for exchange
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osteoclasts
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acidophilic cytoplasm, has receptors for osteoclast stimulating factor, colongy-stimulating factor, osteoprotegerin (OPG) and calcitonin, precursors arise from bone marrow, part of the mononuclear phagocyte system
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regulation of osteoclast differentiation
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three signals released by osteoblasts (but osteoclast may be activated by different cells of other tissues, such as cardiovascular or lung):
1. macrophage colony stimulating factor (M-CSF)-binds to a receptor on a macrophage and stimulates it to become a osteoclast precursor, also induces expression of RANK (receptor for NF-kappa B) 2. RANKL-binds to RANKL receptor on the osteoclastic precursor and activating it 3. osteoprotegerin (OPG)-member of TNF receptor family, serves as a decoy by interacting with RANKL, inhibiting osteoclast formation |
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inhibition of osteoclast resorption
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can be inhibited by cytokines, peptides, hormones or even tensional forces
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regions of ostecolast resorption
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1. basal zone-farthest from the Howship lacunae, houses most of the organelles
2. ruffled border-portion of the cell responsible for bone resorption, have finger-like processes that project into the subosteoclastic compartment (resorption compartment) 3. clear zone-immediately surrounds the periphery of the ruffled border, organelle free, contains actin that forms an actin ring (which is regulated by the presence of OPGL), helps integrins stay in contact with the Howship lacunae (forms sealing zone) 4. vesicular zone-consists of numerous endocytotic and exocytotic vesicles that ferry lysosomal enzymes into the subosteoclastic compartment and the products of bone degradation into the cell, between the basal zone and the ruffled border |
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mechanism of bone resorption
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presence of carbonic anhydrase, have Na+ bind to bicarbonate ion and leave through capillary, H+ pumps in the ruffled border pump H+ into the subosteoclastic compartment to DEC pH dissolving the inorganic compartment
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lysosomal hydrolases and metalloproteinases (function in bone resoprtion)
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ex: collagenase and gelatinase
responsible for degrading the organic component, byproducts broken down by osteoclasts into aa’s and monosaccharides which are then released into capillaries |
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hormonal control of bone resorption
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PTH and calcitonin
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periosteum
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covers diaphysis of bone (except where muscle or tendons attach), not epiphysis, also absent from sesamoid bones, a dense irregular CT, outer fibrous layer responsible for the blood and nerve supply to the bone, inner cellular layer house osteoprogenitor cells and osteoblasts
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calvaria
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skull cap
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primary (immature) bone
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first bone to form during fetal development and repair, abundant osteocytes and irregular collagen bundles, DEC mineral content
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secondary (mature) bone
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composed of parallel or concentric bony lamellae, osteocytes dispersed at regular intervals, canaliculi present, more calcified matrix, stronger bone, parallel collagen bundles
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lamellar system of compact bone
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4 layers
1. outer circumferential-just deep to the periosteum, containing Sharpey’s fibers 2. inner circumferential-completely encircles the marrow cavity, trabeculae extend from here into the marrow cavity 3. osteons-haversian canal system, bounded by cementing line (calcified ground substance w/ some collagen fibers) 4. interstitial lamellae-remnants of osteons, irregular arcs of lamellar fragments |
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intramembranous bone formation
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makes most flat bone, formation occurs within mesenchymal tissue, mesenchyme differentiates into osteoblasts, osteoblasts secrete bone matrix that becomes spicules and trabeculae (which are randomly oriented initially), calcification occurs and osteocytes form, vascular CT is transformed into bone marrow while uncalcified mesenchymal tissue becomes the periosteum and endosteum, spongy bone just deep to the pericranium and dura matter becomes compact bone
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endochondral bone formation
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occurs from a hyaline cartilage template, most of the long and short bones
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at the primary center of ossification:
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1. perichondrium at the midriff of diaphysis becomes vascularized
2. osteoblasts secrete matrix, forming subperiosteal bone collar 3. chondrocytes within the diaphysis core hypertrophy, die and degenerate 4. osteoclasts etch holes in subperiosteal bone collar, permitting entrance of osteogenic bud 5. calcified cartilage/calcified bone complex is formed 6. osteoclasts begin resorbing the calcified cartilage/bone complex 7. subperiosteal bone collar thickens, beings growing toward the epiphyses |
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at the secondary center of ossification
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1. ossification begins at the epiphysis (no bone collar, osteoblasts lay down bone matrix on calcified cartilage scaffold)
2. growth of bone occurs at epiphyseal plate (growth added to epiphyseal end of plate, bone is added at the diaphyseal end) 3. epiphysis and diaphysis become continuous |
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bone growth in length
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depends on the epiphyseal plate, 5 zones:
1. zone of reserve cartilage-mitotically active chondrocytes 2. zone of proliferation-rapidly proliferating chondrocytes in rows of isogenous groups 3. zone of maturation and hypertrophy-accumulate glycogen here 4. zone of calcification-lacunae become confluent, hypertrophied chondrocytes die, and cartilage matrix becomes calcified 5. zone of ossification-osteoprogenitor cells invade the area and differentiate into osteoblasts, place matrix on the calcified cartilage |
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bone growth in width
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appositional, osteoprogenitor cells proliferate and differentiate into osteoblasts that place bone matrix on the subperiosteal bone surface
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stimulation of calcification
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by osteonectin and bone sialoprotein
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heterogeneous nucleation
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collagen fibers are nucleation sites for calcium and phosphate solution which begins to crystallize in the gap region, once nucleated, calcification proceeds
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nidi of crystallization
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calcium hydroxyapatite released from matrix vesicles fosters the calcification of matrix
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bone remodeling
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cortical and cancellous bone remodeling is under the influence of bone marrow paracrine hormones (IL-1, TNF-alpha), compact bone remodeling is under the influence of systemic factors (PTH and calcitonin)
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absorption cavities
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site of bone remodeling and resorption for osteoclasts, once resorbed to the right amount, it become vascularized and osteoblasts lay down new bone matrix
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coupling in terms of bone remodeling
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bone resorption followed by bone replacement
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bone repair
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involves both intramembanous and endochondral bone formation as well as cartilage formation, involves three zones
1. a layer of new bone cemented to the bone of the fragment 2. an intermediate layer of cartilage 3. a proliferating osteogenic surface layer |
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granulation tissue in bone repair
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invasion of a blood clot by small capillaries and fibroblasts
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internal callus
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bony trabeculae from the clot being invaded by osteoprogenitor cells of the endosteum
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somatotropin
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growth hormone, influence bone development, stimulating growth of the epiphyseal plates
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IL-1 in bone-related function
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released by osteoblasts, activates osteoclasts proliferation and stimulation
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TNF in bone-related function
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released by activated macrophages, acts similar to IL-1
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Colony-stimulating factor-1 in bone-related function
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released by bone marrow stromal cells, induces osteoclast formation
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OPG in bone-related function
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inhibits osteoclast differentiation
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IL-6 in bone-related function
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released by various bone cells, stimulates the formation of other osteoclasts
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interferon-gamma in bone-related function
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released by T lymphocytes, inhibits differentiation of osteoclast precursors into osteoclasts
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transforming growth factor beta
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induces osteoblasts to manufacture bone matrix
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synarthroses joints
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bones closely bound together with only a minimum of movements, 3 types
1. synostosis-skull bones in adult, joint-uniting tissue is bone 2. synchondrosis-joint of first rib and sternum, joint uniting tissue is hyaline cartilage 3. syndesmosis-pubic symphisis, joint uniting tissue is dense connective tissue |
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diarthrosis (synovial joint)
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joints in which the bones are free to articulate with a wide range of motion, covered by hyaline cartilage, 2 kinds of cells:
1. type A cells-macrophages, remove debris from the joint space 2. type B cells-resemble fibroblasts, secrete synovial fluid (high conc. of hyaluronic acid and lubricin |
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mesoderm
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gives rise to muscle tissue
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myoblasts
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precursors of muscle fibers
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myotubes
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long multinucleated cells formed by the fusion of myoblasts
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strength of a muscle fiber as opposed to the strength of the entire muscle
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muscle fiber strength dependent on the length of the muscle fiber while the entire muscle’s strength is dependent on number and thickness of its component fibers
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red slow muscle fibers
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rich vascular supply
smaller nerve fibers small fiber diameter slow, repetitive, weaker contraction, not easily fatigued not extensive sarcoplasmic reticulum numerous mitochondria rich myoglobin rich in oxidative enzymes, poor in ATP |
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white fast muscle fibers
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poor vascular supply
larger nerve fibers large fiber diameter fast, stronger contraction, easily fatigued extensive sarcoplasmic reticulum few mitochondria poor myoglobin poor in oxidative enzymes, rich in ATP |
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type of muscle fiber depends on:
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innervation, if switched then can switch fiber type
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epimysium
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outer layer surrounding entire muscle, dense irregular CT
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endomysium
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has reticular fibers and an external lamina
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satellite cells
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act as regenerative cells
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T-tubules
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lie specifically at the junction of the A and I band
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terminal cisternae
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a meshwork of sarcoplasmic reticulum around each myofibril at each A-I junction
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triad
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a t-tubule flanked by two terminal cisternae
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what holds myofibrils together
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intermediate filaments desmin and vimentin, secure the periphery of Z disk to each other
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dystrophin
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protein that binds to actin
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myomesin (C protein)
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compose the M line that bisects the H band, responsible for cross-linking thick filaments
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Huxley’s sliding filament theory
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theory of contraction, actin slides over myosin towards the center
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muscle fiber arrangement
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each thick filament is surrounded by 6 thin filaments
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titin
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help in the positioning of thick filaments within the sarcomere, an elastic protein, 2 for each half that projects to the Z disk, so 4 total that anchor a thick filament to the z disk
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alpha actinin
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rod shaped protein that holds thin filaments in their position
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Cap Z
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holds plus end (z-disk side) of the thin filament in place, also prevents the addition or subtraction of G-actin molecules to or from the thin filament
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nebulin
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two wrap around the entire length of each thin filament, further anchoring it to the Z disk, acts as a ruler ensuring the precise length of the actin
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tropomodulin
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cap on the minus end (near the center) of the actin that helps nebulin ensure proper size of thin filament
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thick filament composition
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composed of 200 to 300 myosin II molecules, each myosin II has two identical heavy chains and two pairs of light chains (so 2 heavy chains and 4 light chains), each myosin II also has two flexible regions (at the junction of the heavy and light meromyosin and the junction of the S1 and S2 subfragments)
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heavy chain of myosin
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can be cleaved by trypsin into a light meromyosin and heavy meromyosin
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light meromyosin
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rod-like tail composed of most of the two rod-like polypeptide chains wrapped around each other, functions in proper assembly
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heavy meromyosin
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two globular heads with the attendant short proximal proation of the two rod-like chains, cleaved further into 2 S1 globular moieties and a short, helical S2 rod
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S1 subfragment of heavy meromyosin
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binds ATP and functionsin the formation of cross-bridges between the thick and thin myofilaments
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light chain of myosin
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two types, one of each type is associated with each S1 subfragment
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thin filament composition
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2 F-actin components (+ end bound to Z-disk and minus end extending toward the center of the sarcomere) wound around each other
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tropomyosin
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occupy the shallow grooves of the double stranded actin helix masking the active site of the F-actin
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troponin
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binds to tropomyosin, composed of three globular polypeptides (TnT (tropomyosin), TnC (Ca2+), and TnI (actin))
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calsequestrin
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binds Ca2+ ions that are driven back into the sarcoplasmic reticulum when the stimulus for muscle contraction ceases
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phosphogen energy system
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composed of both ATP and creatine phosphate in the skeletal muscle cells, enough energy for about 9 seconds of maximal muscle activity (3 for ATP and 6 for creatine phosphate)
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glycolysis
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anaerobic system of energy that brings about a build up of lactic acid, about 90 to 100 sec. worth of energy
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aerobic energy system
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manufactures ATP through the normal diet and aerobically, can sustain indefinite contraction as long as nutrition levels are kept where they need to be
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phosphocreatine kinase
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switches phosphate group from creatine phosphate to ADP to make ATP
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myotendinous junction
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allows for the transfer of the muscle contraction to reach the tendon that the muscle is attached to
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motor unit
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group of muscle fibers that are innervated by one motor neuron, muscles contract in unison
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junctional folds (secondary synaptic clefts)
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modifications of the sarcolemma that allow for INC SA for synaptic transmission
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sarcoplasm in the vicinity of the synaptic cleft
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rich in glycogen, nuclei, ribosomes, and mito
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dense bars
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linearly arranged structures that house the voltage gated Ca2+ channels
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sodium-choline symport
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transports choline back into the axon terminal after degradation by acetylcholinseterase
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choline acetyl transferase
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within the axon terminal, catalyzes the production of acetylcholine from the transported choline and activated acetate (produced in mito) and puts it back into synaptic vesicles
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clathrin coated endocytotic vesicles
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allow for the recycling of synaptic vesicle membranes, becomes the newly formed synaptic vesicles
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muscle spindles
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provide feedback about the changes in muscle length as well as the rate of alteration in muscle length, an encapsulated sensory receptor located among the muscle cells, composed of 8-10 intrafusal fibers surrounded by the fluid-containing periaxial space, which in turn is covered by the capsule
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intrafusal fibers
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two types (nuclear bag fibers (static and dynamic) and nuclear chain fibers)
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golgi tendon organs
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monitor the tension as well as the rate at which the tension is being produced during movement (the intensity of contraction), composed of wavy collagen fibers, when the muscle contracts it places tensile forces on the collagen fibers, straightening them, the rate of firing of the entwined nerve ending is related to the amount of tension placed on the tendon, provide an inhibitory feedback resulting in relaxation of the contracting muscle
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mito in cardiac muscle
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mito occupy about half the volume of cardiac muscle cells attesting to the great energy consumption, energy supply of the heart provided by glycogen (some) and triglycerides (most)
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atrial natriuretic peptide
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substance that functions to lower blood pressure, acts by DEC the capabilites of renal tubules to resorb (conserve) sodium and water
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intercalated disks
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has a transverse portion (where fasciae adherents (analogous to Z disks) and desmosomes abound) and lateral portions (rich in gap junctions)
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thin myofilaments
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attach to fasciae adherents
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dyad in cardiac muscle
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T-tubule is only approximated by one small terminal of sarcoplasmic reticulum, located at the vicinity of the Z-line, Ca2+ still comes through the T-tubule, but the supply comes from the extracellular fluid (and also from the (-) charge T-tubule which also has some stores)
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fast sodium channels
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open and close rapidly leading to the generation of a very rapid action potential
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slow sodium channels (Ca2+-Na+ channels)
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slow to open initially, remain open for a considerable time, Na+ and Ca2+ enter the cardiac muscle cell cytoplasm and INC [Ca2+], also K+ leaves quickly, restoring the membrane potential quickly
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multiunit smooth muscle
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contract independently of one antoher, each muscle has its own nerve supply
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unitary smooth muscle
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form gap juntions with those of contiguous smooth muscle cells, nerve fibers form synapses with only a few of the muscle fibers, these cannot contract independently of each other
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dense bodies
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adhere to the cytoplasmic aspect of the cell membrane of smooth muscle cells, insertion point for intermediate filaments and thin filaments (like Z disk),
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thin filaments of smooth muscle
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composed of actin (with its associated caldesmon (which blocks the active site) and tropomyosin)
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thick filaments of smooth muscle
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also composed of myosin II, the S1 heads project throughout the length of the fiber, with the ends lacking the heavy meromyosin, also light meromyosin covers the actin binding site on myosin II, this arrangement allows for contractions of long duration
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all or none and smooth muscle
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doesn’t exist, only a portion of the cell may contract, or all
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caveolae
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act as T-tubules in regulating the cytosolic free Ca2+ ion concentration
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calmodulin and smooth muscle contraction
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Ca2+ binds here (through the help of caveolae), then binds to caldesmon, causing its release from the active site on actin and activates myosin light chain kinase
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myosin light chain kinase and smooth muscle contraction
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phosphorylates the regulatory chain on the myosin light chain permitting the unfolding of the light meromyosin moiety to form the typical gold club shape myosin II permitting the interaction between actin and the S1 subfragment of myosin II resulting in contraction
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smooth muscle contraction
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takes longer, prolonged and requires less energy
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hypolemmal cisternae
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formed from SER that enters the dendrites and axon, function in sequestering Ca2+ and containing protein
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mitochondria of cell body
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numerous, but most abundant in the axon terminals
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melanin granules in nervous tissue
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thought to be a by-product of the synthesis of dopamine and noreadrenaline
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lipofuscin
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remnant of lysosomal enzymatic activity, not found in Purkinje cells of the cerebellum
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types of neurofibrils in neuron
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microtubules
neurofilaments microfilaments |
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lack of ER and mito in the nervous tissue
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at the axon hillock and at the nodes of Ranvier
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horseradish peroxidase
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when injected into the axon terminal, can follow to the cell body, helped in the study of axonal retrograde transport
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kinesin
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a microtubule associated protein used in anterograde transport, one end attaches to a vesicle and the other end interacts in a cyclical fashion with a microtubule
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dynein
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responsible for moving vesicles along the microtubules in retrograde transport
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unipolar neurons
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impulse transmission does not involve the cell body, found in the DRG and some cranial nerve ganglia
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types of neuroglia
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astrocytes
oligodendrocytes microglial cells ependymal cells Schwann cells |
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astrocytes
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provide structural and metabolic support to neurons and act as scavengers of ions and neurotransmitters released into the extracellular space, largest of the neuroglial cells, consist of two types (protoplasmic and fibrous), may assist in maintaining the blood-brain barrier, may also form cellular scar tissue
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protoplasmic astrocytes
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found in the gray matter of the CNS, tips of some processes (which are short) end as pedicels that come into contact with blood vessels, can form pia-glial membrane, may also act as satellite cellsfibrous astrocytes
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fibrous astrocytes
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present mainly in the white matter of the CNS, store glycogen, may be released to the cerebral cortex by insulin stimulation, may assist in maintaining the blood-brain barrier, may also form cellular scar tissue
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oligodendrocytes
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myelination in the CNS, darkest staining neuroglial cells
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microglial cells
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members of the mononuclear phagocyte system, function as phagocytes
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ependymal cells
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form limiting membranes and function in the transport of CSF, line ventricles of the brain and central canal of the spinal cord, may be ciliated, participate in the formation of the choroid plexus
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choroid plexus
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responsible for secreting and maintaining the chemical composition of the CSF, simple cuboidal epithelium, composed of folds of pia matter
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Meissner’s plexus and Auerbach’s plexus
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axons of the parasympathetic system project to these terminal ganglia, are in the walls of the lower GI tract, synaps on cell bodies of postganglionic parasympathetic neurons
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cerebral cortex
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responsible for learning, memory, sensory integration and motor responses
1. molecular layer-composed mostly of nerve terminals originating in other areas of the brain, horizontal cells, and neuroglia, deep to the pia matter 2. external granular layer-contains mostly granule (stellate) cells and neuroglial cells 3. external pyramidal layer-neuroglial cells and pyramidal cells 4. internal granular layer-closely arragned granule cells, pyramidal cells and neuroglia, greatest cell density 5. internal pyramidal layer-contains the largest pyramidal cells and neuroglia, lowest cell density 6. multiform layer-consists of Martinotti cells and neuroglia |
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cerebrellar cortex
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responsible for balance, equilibrium, muscle tone, and muscle coordination, the layer of gray matter
1. molecular layer-below the pia matter, superficial stellate cells, dendrites of Purkinje cells and unmyelinated axons from the granular layer 2. purkinje cell layer-purkinje cells (dendrites in molecular layer, axons in white matter), purkinje cells always have an inhibitory output using GABA 3. granular layer-consists of small granule cells and glomeruli (place of synapse) |
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neuron regeneration
|
damage to CNS is permanent
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peripheral nerve fiber regeneration
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attempts are made to repair the damage, regenerate the process and restore function by activating the axon reaction, cuts must be near each other or regeneration is unsuccessful
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axon reaction
|
reaction to the trauma is localized to three regions
1. at the site of damage (local changes) 2. distal to the site of damage (anterograde changes) 3. proximal to the site of damage (retrograde changes) |
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local reaction in axon reaction
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involves repair and removal of debris by neuroglial cells, ends fuse to prevent loss of axoplasm, macrophages and fibroblasts secrete cytokines and growth factors and upregulate the expression of their receptors
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anterograde reaction in axon reaction
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1. the axon terminal becomes hypertrophied and degenerates within a week, Schwann cells proliferate and phagocytose remnants of the axon terminal and a new Schwann cell occupies the synaptic space
2. undergo wallerian degeneration (orthograde degeneration), the axon and myelin disintegrate, Schwann cells dedifferentiate and myelin synthesis is discontinued, phagocytosis of disintegrated remnants 3. schwann cells proliferate, forming a column of Schwann cells |
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retrograde reaction and regeneration in axon reaction
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1. perikaryon of damaged neuron becomes hypertrophied, nissl bodies disperse and nucleus is displaced (all three called chromatolysis), soma produces free ribosomes and proteins, proximal axon stump and myelin degenerate to the nearest collateral axon
2. from the proximal axon stump, several sprouts of axons emerge and are guided by the Schwann cells to their target cell 3. Schwann cells redifferentiate and begin to manufacture myelin |
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transneuronal degeneration
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where target cells of the dead neuron atrophy and degenerate
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glial scar
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mass of glial cells that occupy a space made by microglia that phagocytose injured cells in the CNS, these hinder repair
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