Histology Chapter 8
Bone Learning Objectives
1. What is the ground substance of bone? Which four molecules form it?
 The ground substance is noncollagenous protein which makes up 10% of bone
 Proteoglycans, multiadhesive glycoproteins, growth factors, & vitamin-K dependent proteins
2.
Prior Test Q (that I missed somehow): Which substance contributes to compressive strength of
bone and also serves as a resevoir of certain growth factors and other substances?
 proteoglycan
3.
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How would you classify osteocalcin, protein S, and matrix Gla-protein (MGP)?
These are vitamin K-dependent bone-specific proteins (part of ground substance)
Osteocalcin captures calcium and stimulates osteoclasts
Protein S assists in the removal of apoptotic cells
MGP assists in the formation of vascular calcifications
4. What growth factor is specially used to induce bone growth after surgery?
 BMP-7 is being used after surgery on large defects, fusions, and graft implantation
[think: BuMPs up your bone repair]
5. What is the immediate precursor to osteoprogenitor cells?
 Osteoprogenitor cells come from mesenchymal stem cells
6.
What do you call the angled collagen fibers passing into the bone where ligaments and tendons
attach?
 These fibers are called Sharpey’s fibers
7. How are metaphyseal nutrient arteries different from those of the epiphysis and diaphysis?
 Metaphyseal arteries arise from periostial vessels that become incorporated into the bone,
while the other arteries were originally the principal vessels of the periosteal buds
8. What is the key factor that triggers differentiation of osteoprogenitor cells?
 Core Binding Factor Alpha-1 (CBFA1) tells osteoprogenitors to become osteoblasts
9. What’s inside the matrix vesicles of osteoblasts and why do we care?
 ALP-containing matrix vesicles initiate calcification
10.
Review picture of bone cells on page 225
11. What enzyme allows for osteocytic osteolysis?
 Osteocytes release matrix metalloproteinases to degrade collagen
12. What resorption bay enzyme is used as a specific marker of osteoclast activity?
 Tartrate-resistant acid phosphatase (TRAP)
13. What transcription factors do osteoclasts exhibit initially?
 C-fos and NFкB are expressed by cells committed to becoming osteoclasts
14. What is the enzyme that decalcifies the bone?
 The first step in breakdown is decalcification by carbonic anhydrase II
15. Loss or deficiency of which enzymes can cause osteopetrosis (3)?
 Loss of carbonic anhydrase II, cathepsin K, or defective proton pumps causes osteopetrosis
16. How can you differentiate the three types of osteoporosis?
 Type I primary = post menopausal
 Type II primary = old people [there are two old people in marriage, one just hadmenopause]
 Secondary = any other cause (corticosteroids, space travel, hyperparathyroidism, etc.)
17. What are some minor vitamins that are important for healthy bones?
 Vitamin A deficiency suppresses bone growth, excess vitamin A causes fractures
 Vitamin C is needed to synthesize strong collagen
18. What does appositional growth mean? Which form of bone growth uses only this method?
 Appositional growth is the process in forming bones by which OPCs come into contact with
the initial spicules, differentiate, and then add more matrix
 This is the sole means of growth for intramembranous ossification
19. Outline the steps of endochondrall bone growth:
 Cartilage model => bony collar forms => chondrocytes hypertrophy => cartilage calcifies =>
chondrocytes die => mesenchymal cells (OPCs and hemopoietic stem cells) enter cavities =>
true bone starts to be formed => proximal secondary ossification center forms => then distal
20. List the layers starting from epiphysis and moving towards the diaphysis during ossification:
 Zone of reserve cartilage
 Zone of proliferation
 Zone of hypertrophy
 Zone of calcified cartilage (basophilic)
 Zone of resorption
 Bone (eosinophilic)
21. Which protein helps to maintain a high concentration of calcium near ossification sites?
 Osteocalcin binds extracellular Ca to engender a high concentration
22. How long does it take bone to heal? Which type of callus is formed first?
 It takes bone 6-12 weeks to heal, depending on severity and specific bone
 A soft callus of cartilage forms first, followed by a bony callus
 Trabecular bone is formed first, gradually replaced by compact bone