Bone Development Histology

Question 1

Bones can be formed through what two mechanisms?

Answer 1

Intramembranous ossification and endochondral ossification

Question 2

What are mesenchymal cells roles in intramembranous ossification?

Answer 2

Bone cells are differentiated directly from the mesenchymal cells to produce the osteoid

Question 3

Intramembranous ossification leads to the production of what bones?

Answer 3

Leads to the production of flat bones of the skull and bones of the face

Question 4

In what week of gestation does intramembranous ossification start?

Answer 4

Around week 8

Question 5

What happens to the mesenchymal cells in endochondral ossification?

Answer 5

Mesenchymal cells are replaced by a hyaline cartilage model

Question 6

What does the hyaline cartilage model do during endochondral ossification?

Answer 6

It initially takes the shape of the bone as well as the bones position, then the hyaline cartilage model is eroded and replaced by bone

Question 7

Endochondral ossification leads to the production of what bones?

Answer 7

Most short and long bones of the body

Question 8

During embryonic development when can one first see hyaline cartilage models?

Answer 8

6th week

Question 9

Hyaline cartilage models are present in all long bones of the limbs by what week of gestation?

Answer 9

12th

Question 10

What are the 4 steps of intramembranous ossification?

Answer 10

1. development of the ossification center
2. calcification
3. woven bone and periosteum development
4. replacement of woven bone

Question 11

During intramembranous ossification what happens during the development of the ossification center part?

Answer 11

Some of the elongated, pale-staining, mesenchymal cells cluster, differentiate into osteoprogenitor cells, and then become more rounded, while their cytoplasm changes from eosinophilic to basophilic. This basophilic change is due to changes in the cytoplasm including the addition of more rough endoplasmic reticulum. These cells have now differentiation into osteoblasts. This cluster of osteoblasts creates the ossification center as the osteoblasts secrete organic extracellular matrix known as osteoid.

Question 12

During intramembranous ossification what happens during the calcification part?

Answer 12

Calcium and other mineral salts are deposited around the framework of collagen fibers. Cells that are trapped in the calcifying osteoid are now called osteocytes and sit in lacunae.

Question 13

During intramembranous ossification what happens during the woven bone and periosteum part?

Answer 13

What is being made here is primary bone (also known as woven bone or immature bone). Additionally, the mesenchyme at the periphery of the bone condenses and forms the periosteum

Question 14

During intramembranous ossification what happens during the replacement of woven bone part?

Answer 14

The woven bone is then replaced by lamellar bone, forming compact and spongy bone. Specifically, with flat bones, spongy bone will be formed between two layers of compact bone.

Question 15

What are the six steps of endochondral ossification?

Answer 15

1. development of the fetal cartilage model
2. a bone collar forms around the diaphysis and cartilage of shaft begins to calcify
3. development of a primary ossification center in the diaphysis
4. development of secondary ossification centers
5. retention of hyaline cartilage as the articular cartilage and the epiphyseal plate
6. epiphyseal plates ossify and form epiphyseal lines

Question 16

With a H&E stain, calcified hyaline cartilage stains (a)_______, while newly formed bone stains (b)________.

Answer 16

(a) blue purple

(b) pink/red

Question 17

Hyaline cartilage is composed primarily of type (a)__ collagen, while bone is composed of primarily type (b)__collagen.

Answer 17

(a) II

(b) I

Question 18

The primary bone is (a)(eosinophilic or basophilic) and calcified cartilage is (b)(eosinophilic or basophilic)

Answer 18

(a) eosinophilic

(b) basophilic

Question 19

Does the development of secondary birth centers happen before or after birth?

Answer 19

After birth

Question 20

Secondary ossification centers are located where?

Answer 20

The epiphyses

Question 21

What does puberty signal in terms of bone development?

Answer 21

Ossification of the epiphyseal plates

Question 22

What are the five zones of the epiphyseal plate?

Answer 22

Zone 1: zone of resting/reserve cartilage
Zone 2: zone of proliferating cartilage
Zone 3: zone of hypertrophic cartilage
Zone 4: zone of calcified cartilage
Zone 5: zone of ossification

Question 23

Where is the epiphyseal plate found in a long bone?

Answer 23

Found between the epiphysis and the flared portion of the diaphysis, known as the metaphysis

Question 24

The zone of resting cartilage is closest to what part of the bone?

Answer 24

Epiphysis

Question 25

The zone of ossification is closest to what part of the bone?

Answer 25

Metaphysis

Question 26

Bones increase in width and diameter with what kind of growth?

Answer 26

Apositional

Question 27

What happens at the endosteal and periosteal surfaces during apositional growth?

Answer 27

Endosteal: osteoclasts break down bone matrix
Periosteal: osteoblasts secrete bone matrix

Question 28

What are the two controls involving bone remodeling?

Answer 28

Negative feedback loop for maintenance of calcium homeostasis and bone’s response to mechanical stress and gravity

Question 29

What percent of your bone is remodeled each year?

Answer 29

5-10%

Question 30

What two hormones are involved in bone homeostasis?

Answer 30

Calcitonin and parathyroid hormone

Question 31

What does calcitonin do?

Answer 31

Stimulates calcium salt deposits in the bone, therefore decreases blood calcium levels

Question 32

What does parathyroid hormone do?

Answer 32

Stimulates osteoclasts to degrade bone matrix and release calcium ions into the blood