4 Connective Tissue

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  1. Connective Tissue Functions
    • Provides the structural integrity of tissues & organs ("glue" for stability)
    • Provides mechanical properties – offering both tensile & compressive properties as needed
    • Provides environment for differentiation & residence for immune cells (eg. plasma cells, macrophages)
    • Facilitates exchange of metabolites, electrolytes & water
    • Energy storage (eg. white adipose tissue)
    • Heat production (eg. brown adipose tissue)1
    • Repair & restoration of tissue architecture following damage (eg. nerve regeneration)
  2. Connective Tissue (CT)
    • one of the four basic tissue types that functions to support other tissues; made up of cells & the matrix
    • it consists of several cell types & extracellular products which, together, provide essential functions of mechanical reinforcement, immune surveillance, transport/diffusion of nutrients and wastes, & energy storage (fat)
    • Embryonically, connective tissue is derived from mesoderm/mesenchyme
  3. What are the 2 different types of cellular components of the connective tissue?
    Indigenous cells & Immigrant cells
  4. Indigenous Cells
    • connective tissue cells that originate in the connective tissue itself
    • Mesenchymal Cells
    • Fibroblasts
    • Adipocytes
    • Osteogenic Cells (+ derivatives)
    • Chondrogenic Cells (+ derivatives)
  5. Mesenchymal Cells
    • multipotent stem cells that can differentiate into: myocytes (muscle cells), adipocytes (fat cells), chondrocytes (cartilage cells), osteoblasts (bone building cells), & neurons
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    • mostly looking at cells’ nuclei & cytoplasm extends off into long processes
    • typically reside in a very hydrated extracellular matrix
  6. Fibroblasts
    • most common cell in most CTs, both regular & irregular dense CT
    • synthesize most ECM components (collagen, elastin, proteoglycans, glycoproteins)
    • cytoplasm & ECM stain similarly - you usually just see nuclei
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    • they have an elongated appearance with flattened, surf-board-like nuclei and cytoplasm with lots of RER & golgi
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    • they have the capacity to differentiate into myofibroblasts (under both normal & wound-healing conditions)
  7. Adipose Tissue
    • indigenous cell of CT that comes in two major varieties:
    • white adipose tissue - lipid storage, unilocar
    • brown adipose tissue - heat production, multilocar
    • both derived from mesenchymal cells
  8. White Adipose Tissue
    • unilocular, meaning there’s one large lipid droplet per cell that’s so large it pushes the nucleus out to the periphery
    • all you can really see for cytoplasm is a faint thin pink rim - most of the cell consists of a large lipid droplet
    • between cells is a small amount of loose connective tissue with blood vessels (gives a “chicken-wire’ appearance)
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  9. Brown Adipose Tissue
    • multilocular because there are lots of lipid droplets in each cell
    • used for heat production so there’s a rich blood supply that can help to convey the heat that’s produced to the rest of the body
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    • called brown because cells have numerous mitochondria (containing colored cytochromes) + LOTS of blood vessels between cells
  10. Immigrant Cells
    connective tissue cells that originate from hematopoietic stem cells in bone marrow, circulate in the blood, then move into connective tissue where they differentiate & subsequently function

    • 1. Macrophages (derived from monocytes)
    • 2. Mast cells
    • 3. Lymphocytes
    • 4. Plasma Cells (derived from B- Lymphocytes)
  11. Macrophage (Immigrant Cell)
    • large cells derived from blood monocytes that have migrated into CTs that phagocytose cellular debris, foreign bodies, & air-born particles
    • have many roles in addition to scavenging debris, including important functions in both the innate & adaptive immune systems + infammation
    • distinguishing characteristics: large size & their nuclei, which are large & irregularly shaped
    • their cytoplasm is full of vacuoles (phagosomes) that contain phagocytosed material
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  12. Mast Cells
    • type of immigrant cell of the CT that are critical for allergic reactions
    • are derived from bone marrow
    • have a spherical central nucleus surrounded by a cytoplasm PACKED with basophilic granules (polyanions, negatively charged molecules)
    • exhibit metachromasia
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    • degranulation of mast cell granules & release of histamine/heparin can lead to anaphylaxis (+ drop in BP, bronchoconstriction, rash)
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  13. Lymphocytes
    • are present in CTs but are called recirculating cells because they can move between blood & CTs
    • typically they’re ubiquitous - aren’t many places where they can’t be found
    • hallmark: small, dark nucleus surrounded only by a little cytoplasm
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    • “if you see a cell nucleus that really doesn’t fit with the nuclei around it, consider it to be a wandering lymphocyte”
  14. Plasma Cells
    • residents of CTs, will never see them in the blood (B cells can be found in blood, but terminally differentiated they’re only in CT)
    • are specialized for antibody (Ig) production
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    • characteristic appearance: oval-shaped, with the nucleus on one side & an "apron” of eiosinophilic cytoplasm on the other
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    • heterochromatin in nucleus have distinctive “wagon wheel”/“clock-face” appearance
    • contain lots of RER (synthesizing Igs) in cytoplasm, so they stain basophilically
    • clear area between eiosinophilic cytoplasm & nucleus is the Golgi (where glycosylation + further processing of the IgGs occurs)
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  16. Where do plasma cells come from?
    B-lymphocytes that have left the circulation and move to the connective tissue; in the CT they differentiate and initiate the synthesis of immunoglobulins
  17. Collagen Fibers
    • comprised of fibrils
    • collagen alpha chains have glycines @ every 3rd residue
    • 3 chains form a triple helix
    • cross-linking between triple helices is what maintains collagen’s structural integrity - occurs between hydroxylysine & hydroxyproline
    • this cross-linking is catalyzed by lysyl- & prolyl-hydroxylase, which REQUIRE co-factor ascorbic acid (vitamin C)
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  18. Fibrillar Collagens
    • I – nearly everywhere; most abundant protein in the body
    • II – cartilage mostly, especially articular
    • III – many organs, forms reticular fibers
  19. What is scar tissue mostly comprised of?
    • Type I Collagen
    • keloids can result from localized collagen accumulation (excess scar production)
  20. Type II Collagen
    • abundant in hyaline cartilage (found in all synovial joints)
    • found in many organs during development
    • in an adult, it can be found in the vitreous humor of the eye & the inner ear
  21. Type III Collagen (Reticular Fibers)
    • highly branched (unlike the other 2 kinds of collagen)
    • visualization requires special silver stain
    • located in many lymphoid organs, the liver, & reticular dermis (skin)
    • reticular in latin means “little net” - type III collagen can have filtration functions
  22. Reticular Tissue
    • filled with reticular fibers, aka branched type III collagen
    • it supports channels in liver, lymph nodes, & spleen
    • is also present in other organs for support (eg. dermis)
    • again, requires a special silver stain to visualize
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    • LOTS of branching (twigs on a tree)
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  23. Non-fibrillar Collagens
    • includes Type IV, which is one of the main components of the basement membrane
    • many non-fibrillar collagens are associated with fibrils
    • these represent most known collagens (28 & counting)
    • generally aren’t too abundant; need special stains to visualize (eg. immunohistochemistry where you have an Ig specific to a component of the collagen)
  24. Elastic Fibers
    • made up of elastin + microfibrils
    • to synthesize, you start with a core of fibrilin, a glycoprotein that forms the “scaffold”
    • can deposit tropoelastin on the fibrilin
    • once tropoelastin is cross-linked, it becomes elastin
    • the same enzyme that cross-links collagen (lysyl oxidase) also cross-links elastin (don’t forget vit C cofactor)
  25. Marfan Syndrome
    • caused by a mutation in fibrillin-1, meaning there is no effective “scaffold” to deposit tropoelastin on
    • elastin molecules don’t work very well, which can lead to aneurisms, scoliosis, & hyperextensible joints
    • in addition to acting as a scaffolf, fibrilin-1 also sequesters TGF-β & regulates its bioavailability
    • excess TGF-β in Marfans may predispose to many of the phenotypes
  26. Cutis Laxa
    • caused by mutations in elastin protein that leads to loose, wrinkled skin that lacks elasticity
    • in severe cases, internal organs may be affected
  27. What can be found in the ground substance of the extracellular matrix?
    • Water
    • Proteoglycans
    • Glycosaminoglycans (GAGs)
    • Glycoproteins
    • it's the background material within which all other connective tissue elements are embedded
    • consists mainly of water that provides a route for communication + transport (by diffusion) between tissues
    • a complex of GAGs, proteoglycans, & glycoproteins stabilizes the water
  28. Ground Substance
    • is highly charged – has to do with an abundance of sulfate groups -thus hygroscopic (hydrated)
    • this charge confers compressive resistance (eg. articular cartilage - lots of negative charges repel each other & therefore resist compression)
    • there is very little protein in the ground substance which is why it stains poorly - often looks like an empty space
    • permits nutrient/gas exchange (especially in
    • avascular tissues like hyaline cartilage)
  29. Proteoglycans
    • linear polymers of repeating disaccharides [GAGs] covalently linked to a protein core
    • are hydrophilic, negatively charged due to SULFATE groups on the sugar residues
    • they account for the porous nature of CT that allows diffusion of metabolites & waste products to traverse to & from blood vessels
  30. Types of Connective Tissue
    • Dense Regular
    • Dense Irregular
    • Loose (Areolar)
    • Elastic
    • Adipose
    • Reticular
    • Cartilage
    • Bone
  31. Dense Regular CT
    • see this in tendons (connecting muscle to bone) & ligaments (connecting bone to bone) where it provides tensile strength
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    • red staining = densely packed type I collagen fibers arranged in parallel; fibroblasts are present wherever they can fit & are arranged in the same direction as the collagen
  32. Dense Irregular CT
    • composed of densely packed collagen fibers arranged irregularly through the tissue
    • they still impart strength to the tissues in which they are found (eg. skin dermis)
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  33. Loose (Areolar) CT
    • a loose arrangement of fibers & cells surrounded by an abundance of ground substance
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    • hallmark: lots & lots of “space” which is ground substance
    • holds organs in place & attaches epithelial tissues to itself + other underlying tissues
    • surrounds blood vessels & nerves
  34. Dense v. Loose CT
    • Loose connective tissues contain FEWER extracellular fibrils, but are RICHER in cells (including fibroblasts)
    • if CT is Loose, it’s automatically going to be irregular
  35. Elastic Tissues
    • connective tissue that has a lot of elastic fibers
    • can exist in 2 different forms:
    • in blood vessels (elastic artery wall), you have sheets (lamellae) of elastic fibers
    • can find branches elastic fibers in many other regions of the body (eg. dermis, skin is very elastic)
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    • typically elastin stain is needed to visualize
Card Set:
4 Connective Tissue
2016-09-20 02:07:18
MedFoundationsI Histology Exam2
Histology Exam 2
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