Download Block 1: Pathology Dr. Rosezweig Test 1: Connective Tissue

Block 1: Pathology
Dr. Rosezweig
Test 1: Connective Tissue
Introduction
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maintain form of organs throughout body
major constituent: ECM
o diff protein fibers and ground substance
o ground substance: anionic, hydrophilic GAGs and multiadhesive glycoproteins
extracellular volume exceeds that of cells
derived from embryonic mesoderm which differentiates into mesenchyme (and/or mucoid
tissue)
o mesenchyme: diff into wide variety of adult forms of CT
o small amts mesenchyme in adults (eg: wound healing)
Mesenchyme:
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viscous ground substance with few collagen fibers
undiff., spindle-shaped cells
large, euchromatic nuclei
prominent nucleoli high levels of synthetic activity.
ground substance rich in hyaluronan, little collagem
Cells of Connective Tissue
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Fibroblasts
o most common
o produce/maintain most of extracellular components
o “spindle” shaped
o large, active nuclei
o eosinophilic cytoplasm
o can distinguish between active/quiescent fibros:
 active: large, euchromatic nuclei, basophilic cytoplasm
 quiescent: smaller, more heterochromatic nuclei
Cells of immune system (loose CT)
o macros
 derived: monocytes
 bone marrow
 aka “histiocytes”
o mast cells
 derived: basophils
 bone marrow
 abundant basophilic granules
 located near small blood vessels
 oval shaped
o plasma cells
 derived: B lymphocytes
 Ab producing cells
 basophilic cytoplasm
 abundant RER
 spherical, eccentrically placed nucleus
 peripheral clumps heterochromatin “clock face” appearance
 more abundant in infected tissue (duh!)
o other immune cells will enter CT in inflammatory situations
 lymphocytes, neutros, eosinophils
ECM
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Fibers
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Block 1: Pathology
Dr. Rosezweig
Test 1: Connective Tissue
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o elongated structures from proteins that polymerize after secretion from fibros
Collagen Fibers
o triple helical structure; 2 identical chains (1) and an additional chain, differing slightly
in chemical composition (2)
o extremely strong and resistant to shearing and tearing forces
o secreted by fibroblasts
o key element of all connective tissues
o 28 diff types
o fibrillar collagens (eg: types I, II, III)- bundle together to form large fibers
o sheet forming collagens (eg: type IV)- produced by epithelial cells, form basal lamina
of epithelia
o linking/anchoring collagens (eg: type VII)- link other collagens to one another, and
to other components of ECM
o Type 1 collagen bundled together to provide increased tensile strength, forming large,
easily visible structures with H&E staining
o Diseases of mutated Collagen:
 Ehler-Danlos:
 diff forms due to mutations in diff genes
 most affect skin, joints, blood vessels
 osteogenesis imperfecta:
 point mutation in collagen gene
 brittle bone disease, and other symptoms
 scurvy:
 vitamin C used as cofactor for an enzyme involved in extracellular
assembly of collagen
 bleeding gums, hemorrhages
Reticular Fibers
o type III collagen
o extensive network of extremely thin fibers
o secreted by fibroblasts
o “scaffolding” of other cells structure to certain organs
o component of reticular lamina of basement membrane
o stained with silver salts (RFs are argyrophilic)
o supportive stroma in most lymphoid and hematopoietic organs and many endocrine
glands
o heavily glycosylated type III collagen produces black argyrophilia
Elastic Fibers
o physical properties similar to rubber
o stretch and return to original shape
o cross-linked elastin
o special stains:
 eg: aldehyde fuschin
o bundled together and woven into sheets
o secreted by fibroblasts and smooth muscle cells
o multiple random-coild domains that can be stretched
o desmosine: cross-links the elastin subunits
 4 converted lysine’s in two elastin molecules make the cyclice desmosine
molecule
o Marfan syndrome
 mutation in gene for fibrillin (scaffolding protein in elastic fibers)
 long limbs, dislocated lenses, aortic root dilation
Ground Substance
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highly hydrated, transparent complex mixture of macromolecules from…
o GAGs
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Block 1: Pathology
Dr. Rosezweig
Test 1: Connective Tissue
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o proteoglycans
o multiadhesive glycoproteins
fills space between fibers in CT and varies in consistency from fluid to semi-solid
Glycoproteins: globular proteins with branched oligosaccharide side-chains; polypeptide
content> polysaccharide content
proteoglyclans: core of protein, with one/many side chains of sulfated GAGs as well as
branched oligosaccharides; more carbs than glycoproteins
o aggrecan: major proteoglycan in cartilage
 hyaluronan= core protein
 hydrated chondroitin sulfate and keratan sulfate side chains attached by link
proteins
Types of Connective Tissues
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Embryonic CT
o Mesenchyme:
 progenitor of all other connective tissues
 cells have long processes and matrix almost totally lacking in fibers
o Mucoid:
 similar to mesenchyme except for presence of small collagen fibers
Connective Tissue Proper
o Loose (areolar) CT
 packing, anchoring, and/or embedding material in virtually every organ
 fluid-like ground substance with random collagen and elastic fibers
 fibrosis: when this CT replaces other tissues after injury
o Dense IRRegular CT
 large collagen fibers arranged in random fashion
 few elastic and reticular fibers; very little matrix
 tough fibrous sheets (eg: capsules that surround various organs)
 dermis of skin
o Dense Regular CT
 densely packed fibers coursing parallel to each other
 ligaments and tendons
Specialized CT
o Reticular CT
 branching network of reticular fibers that form the framework of certain organs
o Adipose Tissue
 lipid storing cells embedded in reticular framework
 usually found in association with loose CT
 energy storage, thermal insulation, shock absorption
 Types:
 unilocular (white fat): lipids stored in one large vacuole that occupies
majority of cell
 multilocular (brown fat): lipids in many vacuoles
o heat production- energy produced in krebs cycle lost as heat bc of
uncoupling protein in mitochondria
o animals that hibernate have increased amts of brown fat
o cartilage
o bone
o blood
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