Cartilage and bone

Question 1

Chondrocyte

Answer 1

• synthesize and release matrix ⇒ ground substance + fibers
• arranged singly or in clusters (mostly 8 in cluster)
• located in lacunae
• fully mature chondrocytes ⇒ larger + contain lipid vacuoles and glycogen granules
• matrix around= capsule
• territorial matrix= region around cluster, sulphated proteoglycan rich area
• chondron= chondrocyte + capsule + territorial matrix
• interterritorial matrix= around chondrons

Question 2

27. Compact bone (unstained)

Answer 2

• calcified intercellular bone matrix + cells located in lacunae
• cells communicate via canaliculi
• Haversian canal ⇒ neurovascular longitudinal channel, composed of concentric bony lamellae
• Haversian osteon ⇒ haversian canal + lacuna of osteocytes
• Volkmann’s canal ⇒ transverse connection between haversian canals
• Interstitial bone ⇒ remnant of osteon, fragmentary lamellae
• Outer circumferential lamellae
• Inner circumferential lamellae⇒ laid down by osteoprogenitor cells

Question 3

28. Intramembranous ossification (HE)

Answer 3

• at center of ossification in highly vascular membranes of embryonic mesenchyme ⇒ mesenchymal stem cells differentiate into osteoprogenitor cells ⇒ proliferate around capillaries + secrete collagen and osteoid ground substance
• Osteoblast ⇒ polygonal, cuboidal/columnar cells with basophilic cytoplasm
  
  • secrete osteoid⇒⇒ osteocyte
• spicules⇒ islands of developing bone
• CT among bone spicules is penetrated by hemopoietic tissue from which bone marrow develops
• on surface of spicules ⇒ osteoprogenitor mesenchymal cells ⇒ new osteoblast
• Osteoclast ⇒ multinucleate cells, light basophilic cytoplasm ⇒ in lacunae of Howship

Question 4

31. Endochondral ossification (HE)

Answer 4

• intramembranous formation of perichondral bony collar around diaphysis of cartilage model
• osteoblasts differentiate from mesenchymal cells in deep layer of perichondrium
• cartilagineous epiphysis separated from diaphysis by epiphyseal growth plate
• transitional zone ⇒ metaphysis

Question 5

Layers of bone development

Answer 5

1. Zone of reserve cartilage
   - typical hyaline cartilage
2. Zone of proliferation
   - dividing cells form columns of chondrocytes
3. Zone of maturation, hypertrophy and calcification
   - no further division
   - chondrocytes increase in size
   - calcified matrix is strongly basophilic
4. Zone of cartilage degeneration and osteogenic zone
   - chondrocytes degenerate
   - lacuna of calcified matrix invaded by osteogenic cells and capillaries
   - calcified cartilage remnants resorbed by osteoclasts

Question 6

Layers of Perichondrium

Answer 6

1. Outer fibrous layer
   - dense fibrous CT
2. Inner chondrogenic/cellular layer
   - chondroblasts

Question 7

24. Hyaline cartilage (toluidine blue)

Answer 7

• extracellular matrix: metachromatic ground substance + collagen III
• cartilage is avascular (penetrating blood vessels ⇒ degeneration)
• no lymph vessels or nerves

Question 8

2. Fibrocartilage (HE)

Answer 8

• avascular
• thin hyaline cartilage
• ant and post longitudinal ligaments
• anulus fibrosus + nucleus pulposus
• fibrocartilage: hyaline + dense CT; collagen, chondrocytes
• no perichondrium

Question 9

Compact bone staining

Answer 9

Schmorl