Histology Lecture 6 - Bone Development

Question 1

What is appositional bone growth?

Answer 1

Outwards from the surface

Question 2

What are the two types of appositional bone growth?

Answer 2

De novo and cartilage calcification

Question 3

Describe the process of cartilage calcification –> bone.

Answer 3

Hyaline chondrocytes undergo hypertrophy. This causes O2 and nutrient deficiency, and the die. Macrophages infiltrate and phagocytize things. Angiogenesis brings in osteogenic cells –> osteoblasts to lay down bone.

Question 4

What are the two mechanisms of bone organ formation?

Answer 4

Intramembranous ossification and endochondral ossification.

Question 5

What is intramembranous ossification? Which bones form this way?

Answer 5

Bone organ formation that occurs directly from within the mesenchyme (stem cells present in the ECM). This is a type of appositional growth. Forms the flat bones of the skull, facial bones, part of the jaw, and clavicles (the dermal bones).

Question 6

Is collagen eosinophilic or basophilic? So what color does it stain?

Answer 6

It is eosinophilic and stains red in H&E. In Mallory Trichrome the acidophilic parts stain blue-green.

Question 7

Is cartilage usually eosinophilic or basophilic? What color is that?

Answer 7

Eosinophilic - red

Question 8

What is endochondral ossification?

Answer 8

Bone organ formation via hyaline cartilage templates.

Question 9

What bones form via endochondral ossification?

Answer 9

Axial and perpendicular bones.

Question 10

Summarize endochondral ossification.

Answer 10

1. Fetal hyaline cartilage model forms
2. Cartilage calcifies and a periosteal bone collar forms around diaphysis (where appositional growth will occur for girth)
3. Primary ossification center forms in diaphysis
4. Secondary ossification centers form in epiphyses
5. . Bone replaces cartilage (except for articular surface and epiphyseal plates)
6. Epiphyseal plates ossify and form epiphyseal lines.

Question 11

How does the epiphyseal plate form?

Answer 11

The remaining hyaline cartilage between the diaphysis and epiphyses forms the plate.

Question 12

Name the cell zones within the epiphyseal plate.

Answer 12

1. Resting zone w/ stem cells
2. Proliferation zone (where chondrocyte mitosis happens)
3. Hypertrophic zone
4. Calcification zone
5. Erosion zone
6. Ossification zone

Question 13

What are interstitial lamellae?

Answer 13

The old osteons that have been degraded partially during remodeling.

Question 14

What does the antiobiotic tetracycline do to new bones/teeth?

Answer 14

It preferentially binds to new mineral deposits.

Question 15

Is calcified cartilage basophilic or acidophilic?

Answer 15

Basophilic (from the calcium-phosphate-hydroxyl groups)

Question 16

How does decalcified bone stain in H&E?

Answer 16

RED (acidophilic)

Question 17

By what type of bone growth is the bone collar formed?

Answer 17

De novo

Question 18

What are the diagnostic features of osteoclasts?

Answer 18

BIG, and multinucleate.

Question 19

How do you tell the difference between osteogenic cells and osteoblasts?

Answer 19

Osteogenic cells are flattened, look more like fibroblasts, and osteoblasts are more cuboidal.