5 Cartilage & Bone

  1. Types of Cartilage
    • 1. Hyaline
    • 2. Elastic
    • 3. Fibrocartilage
    • Image Upload 1
    • hyaline cartilage (left), elastic cartilage (upper right), and fibrocartilage (lower right)
  2. Cartilage
    • contains collagen II
    • contains sulfated proteoglygans (eg. aggrecan) + other ECM proteins depending on the cartilage type
    • has a NET NEGATIVE charge (stains basophilic)
    • is avascular & aneural
    • the cells of cartilage, Chondrocytes, exist in isogenous groups - “back to back” Ds shape
    • Image Upload 2
  3. Hyaline (‘Translucent’) Cartilage
    • most prevalent kind of cartilage
    • exists at all synovial joints
    • articular surfaces are MADE of hyaline cartilage
    • Image Upload 3
    • is extremely hydrated - resists compression
  4. Chondrocytes
    • synthesize hydrated proteoglycans that are released into cartilage matrix
    • proteoglycans can be seen as a dark, basiphilic layer just surrounding the cells - this is called a Territorial Matrix
  5. Territorial & Interterritorial Matrices
    • Territorial: proteoglycan-rich region outside the chondrocytes
    • Interterritorial matrix: area between the territorial matrices
  6. Lacunae (‘Lake’) Artifact
    cells shrink & pull away from the place they ‘existed in during life’ - white spaces are artifacts, living cells should occupy entire space
  7. Perichondrium
    • fibrous (DENSE) connective tissue over the surface of most cartilages (EXCEPT articular cartilages) that attaches the cartilage to adjacent tissue
    • perichondrial chondrogenic cells are fibroblast-like cells
    • hyaline cartilage has a perichondrium at its edges but NOT at its articular surfaces
  8. Why don't articular cartilages have a perichondrium?
    because they need a smooth surface for frictionless contact
  9. What are the 2 types of hyaline cartilage growth?
    1. Interstitial Growth: chondrocytes WITHIN the matrix divide, deposit more matrix between themselves, & gradually move apart

    2. Appositional Deposition: perichondrial cells transform into chondroblasts & synthesize cartilage matrix at the SURFACE of the cartilage - once cells move into the cartilage, they’re called chondrocytes

    Image Upload 4
  10. Arthritis
    • an irreversible destruction of cartilage matrix (& sometimes adjacent bone)
    • matrix metalloproteinases (MMPs) & enzymes stimulated by inflammatory cytokines degrade cartilage proteoglycans
  11. What are the two general forms of arthritis?
    Osteoarthritis (OA): comes from general wear & tear

    Rheumatoid Arthritis (RA): is an autoimmune disorder
  12. Osteoarthritis (OA)
    • disease caused by progressive wear & tear where you end up degrading the hyaline cartilage at the articular surfaces
    • because cartilage is aneural, sometimes you won’t know there’s an issue until a lot of damage has been done
    • & because cartilage is avascular, would healing can be very slow & even nonexistent
    • Image Upload 5
    • can’t recover from readily, can just do your best to minimize further damage
  13. Rheumatoid Arthritis (RA)
    • systemic autoimmune, inflammatory disease characterized by chronic joint inflammation & destruction of bone/articular cartilage
    • synovium is thought to play a major role in the destructive processes (only a minor role in OA)
    • it becomes enlarged & thickened due to the influx of monocytes/lymphocytes from circulation
    • Image Upload 6
    • see lots of inflammatory cells + a very irregular surface
  14. Elastic Cartilage
    • very similar to hyaline, but 1 difference is that it also contains ELASTIC fibers
    • still see isogenous groups (Ds), Territorial & Interterritorial Matrix, the perichondrium, interstitial/appositional groups
    • found in the external ear, Eustachian tube, & epiglottis
    • Image Upload 7
  15. Fibrocartilage
    • contains fibroblasts, the cells that synthesize type I collagen - can see their nuclei as well as chondrocyte cells/nuclei
    • still has Isogenous groups (back-to-back Ds)
    • does NOT have an obvious Territorial Matrix (even though in lecture he points it out…)
    • the Interterritorial Matrix is less obvious? because there’s collagen in the “backdrop” of the slide
    • does not have a distinct perichondrium because there are already fibroblasts
    • found in the intervertebral discs (annulus fibrosus), temporomandibular joints, & pubic symphysis
    • Image Upload 8 
    • characterized by visible collagen fibers and chondrocytes; merges with surrounding CT
  16. More Fibrocartilage
    • contains both type I collagen & type II collagen, however is more abundant in type I
    • this accounts for it being high in tensile strength
    • is hydrated, so it also resists compression
    • has features of both hyaline cartilage + dense CT
    • does exhibit interstitial/appositional growth (so all cartilage does this)
    • Image Upload 9
  17. Two Types of Bone
    1. Woven (young)

    2. Lamellar (mature, either compact or spongy)

    all contain calcium hydroxyapatite
  18. Woven Bone
    • immature bone that contains disorderly arrangement of collagen
    • less strong than Lamellar bone
    • produced early in development & the early stage in fractures healing
    • characterized by coarse interlaced collagen fiber bundles
    • has more osteocytes than matrix (compared to lamellar bone)
    • nourished by blood vessels in the adjacent connective tissue
  19. Lamellar Bone
    • highly organized with collagen fibers in parallel sheets (lamellae)
    • sheet fibers differ in orientation which gives it strength
  20. Compact Lamellar Bone
    • outer edge that’s the thickest part of any bone
    • extremely dense & found in areas that require maximum support (eg. the wall of the shaft of a long bone)
    • contains Haversian systems, concentric lamellae, osteocytes interconnected by processes within canaliculi, a central Haversian canal, interstitial lamellae, a periosteum (P), & endosteum (En)
  21. Spongy (Cancellous, Trabecular) Lamellar Bone
    • found in the middle/marrow cavity
    • contains lamellae, osteocytes interconnected by processes within canaliculi, & endosteum
    • forms a porous meshwork consisting of branching & anastomosing delicate pieces of bone tissue called spicules or trabeculae
    • it doesn't have transverse canals because blood vessels can just move through open matrix
  22. Ground Section
    • black spots correspond to organic tissue - Lacunae, where you had osteocytes in life
    • the fine strands correspond to Canaliculi, connecting canals between Lacunae
    • fine detail is visible in this section
    • Image Upload 10
  23. Decalcified Section
    • treat the bone so the mineral content is removed - once that’s done, you can cut a section & stain with H&E
    • red eiosinophilic staining = jam packed with Collagen
    • nuclei correspond to Osteocytes throughout tissue
    • fine detail is less visible in this section
    • Image Upload 11
  24. Long Bone Epiphyseal Plate
    • Image Upload 12
    • diaphysis/shaft is the bottom of the picture - where new (woven) bone is forming
    • middle = the disc itself, known as the growth plate
    • top = epiphysis
  25. Haversian Systems (Osteons)
    • the units that make up Compact Lamellar Bone
    • consists of layer upon layer of bone surrounding a central Haversian canal
    • the Haversian canal itself is a vascular channel that contains blood vessels, nerves, & lymphatics
    • osteons are the strongest & most organized kind of bone
  26. What imparts strength onto Osteons?
    within lamella collagen fibers change orientation which imparts structural strength to the osteon (& to the bone tissue overall)
  27. Osteocytes
    • the cells that makeup bone
    • they live in the lacunae of the bone matrix
    • because they make fewer proteins than Osteoblases they stain WEAKLY basophilic & have a small Golgi + sparse RER
  28. Canaliculi
    • little canals in the bone through which osteocyte processes travel to allow each cell to form gap junctional connections with their neighbors
    • Image Upload 13
  29. Volkman (Transverse) Canal
    • interconnect adjacent Haversian (blood vessel) cannals
    • histologically won’t be surrounded by concentric lamellae
    • Image Upload 14
  30. Complete v. Partially Digested Haversian Systems
    • Interstitial Lamellae: older Haversian system that are now only partially intact due to remodeling - histologically look like PARTIALLY complete circles
    • Image Upload 15
  31. Non-Haversian Regions of Compact Bone
    Circumferential Lamellae: outer runs around the perimeter of each long bone (for eg.); an inner one runs right next to the Endosteum

    Image Upload 16

    can see tendon (type I collagen) extending into the outer part of the bone → known as Sharpey’s fibers

    Image Upload 17
  32. Spongy (Cancellous, Trabecular) Lamellar Bone
    • mature form of bone found in the middle/marrow cavity
    • histologically see spicules (pieces) of bone running in & out of section + the marrow cavity which contains hematopoietic cells
    • in a really high power section you’d see osteocytes
  33. Spicules
    • spongy bone is still lamellar, so the spicules still contain concentric layering of bone being deposited by osteoblasts
    • when they get embedded into the bone → osteocytes
    • Image Upload 18
  34. How does spongy bone differ from compact bone?
    spongy does NOT have Haversian canals because nutrients can just diffuse through the marrow cavity
  35. Osteoblasts
    • cells that lay down new bone
    • takes ~1 day for the bone to get mineralized
  36. Osteoid
    • newly laid down bone that hasn’t yet been calcified (shows up as a light pink line histologically)
    • ANYTIME you see a layer of Osteoblasts, you should also see an intervening line between them & the bone → Osteoid
    • Image Upload 19
  37. Osteocytes
    cells within the bone
  38. Osteoclasts
    • large multi-nucleated cells that break down bone
    • are derived from the bone marrow
    • (in any given section aren’t going to see ALL the nuclei - might see fewer than all of them)
    • can tell osteoclasts from other cells because they have a bight red eosinophilic cytoplasm due to the fact that they have lots of mitochondria + enzymes to break down bone
    • Image Upload 20
  39. Howship’s Lacunae
    • isolated pockets/cavity formed by Osteoclasts so the degree of damage during bone removal is controlled
    • Image Upload 21
  40. Constant Bone Remodeling
    • occurs because of STRESS & because bone is the main storage place for CALCIUM in the body
    • ↓Ca levels → bone breakdown (↑osteoclast)
    • ↑Ca levels → bone formation (↑osteoblast)
    • Image Upload 22
  41. Osteoporosis
    • bone remodeling balance is offset - end up with more degradation of bone than formation
    • physiologic estrogen levels inhibit bone resorption, so when estrogen levels drop after menopause you’re no long able to inhibit bone resorption
    • therefore osteoporosis is more prevalent in WOMEN
    • Kyphosis (outward curvature of the spine due to vertebral compression) is a hallmark of osteoporosis
  42. Osteogenesis Imperfecta (OI)
    • brittle bone disease, most result from mutations in type I collagen that affect glycine residues (exist every 3rd amino acid to allow for triple helix formation)
    • if you have mutations that affect glycine, you can’t form efficient collagen molecules, or fibrils
    • OI spicules are much less sparse than healthy spicules - are a lot less strong & more prone to breaking
    • Image Upload 23
Card Set
5 Cartilage & Bone
Histology Exam 2