5 Cartilage & Bone

• 1. Hyaline
• 2. Elastic
• 3. Fibrocartilage
• 
• hyaline cartilage (left), elastic cartilage (upper right), and fibrocartilage (lower right)

• 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
• 

• most prevalent kind of cartilage
• exists at all synovial joints
• articular surfaces are MADE of hyaline cartilage
• 
• is extremely hydrated - resists compression

• 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

• Territorial: proteoglycan-rich region outside the chondrocytes
• Interterritorial matrix: area between the territorial matrices

cells shrink & pull away from the place they ‘existed in during life’ - white spaces are artifacts, living cells should occupy entire space

• 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

because they need a smooth surface for frictionless contact

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

• an irreversible destruction of cartilage matrix (& sometimes adjacent bone)
• matrix metalloproteinases (MMPs) & enzymes stimulated by inflammatory cytokines degrade cartilage proteoglycans

Osteoarthritis (OA): comes from general wear & tear

Rheumatoid Arthritis (RA): is an autoimmune disorder

• 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
• 
• can’t recover from readily, can just do your best to minimize further damage
• OSTEO PICTURE

• 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
• 
• see lots of inflammatory cells + a very irregular surface

• 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
• 

• 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
•  
• characterized by visible collagen fibers and chondrocytes; merges with surrounding CT

• 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)
• 

1. Woven (young)

2. Lamellar (mature, either compact or spongy)

all contain calcium hydroxyapatite

• 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

• highly organized with collagen fibers in parallel sheets (lamellae)
• sheet fibers differ in orientation which gives it strength

• 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)

• 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

• 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
• 

• 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
• 

• 
• 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

• 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

within lamella collagen fibers change orientation which imparts structural strength to the osteon (& to the bone tissue overall)

• 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

• little canals in the bone through which osteocyte processes travel to allow each cell to form gap junctional connections with their neighbors
• 

• interconnect adjacent Haversian (blood vessel) cannals
• histologically won’t be surrounded by concentric lamellae
• 

• Interstitial Lamellae: older Haversian system that are now only partially intact due to remodeling - histologically look like PARTIALLY complete circles
• 

Circumferential Lamellae: outer runs around the perimeter of each long bone (for eg.); an inner one runs right next to the Endosteum



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

• 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

• 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
• 

spongy does NOT have Haversian canals because nutrients can just diffuse through the marrow cavity

• cells that lay down new bone
• takes ~1 day for the bone to get mineralized

• 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
• 

cells within the bone

• 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
• 

• isolated pockets/cavity formed by Osteoclasts so the degree of damage during bone removal is controlled
• 

• 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)
• 

• 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

• 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
•