• 012-001
• 012-002
• 013-001
• 013-002
• 013-003
• 013-004
• 014-001

Most bones have a dense outer cortex consisting of compact bone and an inner trabecular region consisting of spongy bone. The cut surface of compact bone appears solid, while the cut surface of spongy or cancellous bone has the appearance of a sponge.

• Coetzee et al p91-97
• Stevens and Lowe p234-248
• Wheater p172-183

• Osteoprogenitor cells are derived from mesenchyme. They are the stem cells of bone and form osteoblasts.

• Osteoblasts synthesize and secrete the organic component of bone matrix. The abundant rough ER, typical of active protein secreting cells, makes the cytoplasm distinctly basophilic.

• Osteocytes are osteoblasts surrounded by mineralized bone and are situated in lacunae. The cells are flattened and spindle shaped and communicate with each other via long cytoplasmic processes. These are found in the canaliculi that connect the lacunae to each other. It is thought that the osteocytes maintain the osteoid.

• Osteoclasts are large multinucleated cells derived from monocytes. They play a major role in bone remodeling by enzymatically eroding mineralized bone and releasing the minerals. Osteoclast activity is stimulated by parathormone in response to serum calcium levels and inhibited by calcitonin.

Bone is continually remodeled by new bone deposition and mineralization by active osteoblasts and selective resorption by osteoclasts.

1. 011-001
2. 011-002
3. 011-003
4. 011-004
5. 011-005
6. 011-006
7. 011-007
8. 011-008
9. 011-009
10. Also see below

1. Sheets of mesenchymal cells condense as bone-forming membranes. This process is known as intramembranous ossification and results in the formation of flat bones.

2. Endochondral ossification involves the transformation of previously formed cartilage into long bones and permits elongation and thickening of the bone during fetal development and childhood growth. Hyaline cartilage develops from immature mesenchymal tissue and assumes the approximate shape of the bone. The cartilage model is subsequently transformed into bone by osteoid deposition and mineralization.

• Osteomalacia is the failure of newly developed osteoid to mineralize with an increased tendency of bone fractures. Osteomalacia in growing children leads to a disease called rickets and produces permanent skeletal deformities.

• Osteoporosis involves the thinning of bones and especially prevalent among the elderly. The bones are more fragile and prone to fracture. Fracture of the femur neck is common in osteoporotic patients.

Slide 13	Bone: cross ground section of masserated bone
	High magnification Fig 013-001: Ground section of bone Fig 013-002: Ground section of bone Fig 013-003: Ground section of bone Fig 013-004: Ground section of bone
a

Slide 14	Bone: longitudinal ground section of masserated bone
	Fig 014-001: Ground section of bone High magnification
a

Slide 11	Bone development: longitudinal section through the head of a rabbit's femur
	Low magnification High magnification Low magnification Low magnification Low magnification
a