Ch. 6-5 Bone Growth

Question 1

The deposition of calcium salts - occurs during ossification, but also in other tissues

Answer 1

calcification

Question 2

• Bone replaces existing cartilage
• Most originate as hyaline cartilage

Answer 2

Endochondral ossification

Question 3

bone develops directly from mesenchyme or fibrous connective tissue

Answer 3

intramemranous ossification

Question 4

• Cartilage enlarges (outer appositional and inner interstitial growth)
• chondrocytes near the center of the shaft increase in size
• matrix is reduced to a series of small struts that begin to calcify
• enlarged chondrocytes die and disintegrate

Answer 4

First step of endochondral ossification

Question 5

• Blood vessels grow around edges of cartilage
• cells of perichondrium convert to osteoblasts
• shaft of cartilage ensheathed in superficial bone layer

Answer 5

2nd step of endochondral ossification

Question 6

• Blood vessels penetrate the cartilage and invade the central region
• Fibroblasts migrating with the blood vessels differentiate into osteoblasts and produce spongy bone at the primary ossification center
• Bone formation spreads towards both ends

Answer 6

3rd step of endochondral ossification

Question 7

• Remodeling occurs as growth continues, creating medullary cavity
• Osseous tissue of shaft becomes thicker
• Cartilage near each epiphyses replaced with bone
• Growth to increase length & diameter (2 distinct processes)

Answer 7

4th step of endochondral ossification

Question 8

Capillaries and osteoblasts migrate into epiphyses, creating secondary ossification centers

Answer 8

5th step of endochondral ossification

Question 9

• Epiphyses filled with spongy bone
• A thin cap of articular cartilage remains exposed to the joint cavity
• epiphyseal cartilage (epiphyseal plate) separates epiphysis from diaphysis

Question 10

When osteoblasts ‘catch up’ with chondrocyte production of epiphyseal cartilage, which ultimately disappears. The former location of this cartilage forms a ____ ___ detectable in x-rays

Answer 10

epiphyseal line

Question 11

Appositional Growth

(Endochondral ossification)

Answer 11

1. Cells of the inner layer of periosteum differentiate into osteoblasts and deposit superficial layers of bone matrix
2. Osteoblasts become surrounded by matrix and differentiate into osteocytes
3. Appositional growth adds a series of layers that form circumferential lamellae.

Question 12

osteoblasts differentiate within a mesenchymal or fibrous connective tissue.

Answer 12

Intramembraneous ossification

(dermal ossification)

Question 13

Flat bones of the skull

Mandible (lower jaw)

Clavicle

Answer 13

Dermal bones that result from ossification that occurs in the deeper layers of the dermis (dermal ossification)

Question 14

1. Mesenchymal cells cluster (ossification center) and start to secrete organic components of matrix.
2. As calcification occurs, mesenchymal cells differentiate into osteoblasts
3. Developing bone grows outward in smalls truts (spicules)
4. Trapped osteoblasts differentiate into osteocytes

Answer 14

First step of intramembranous ossification

Question 15

Blood vessels begin to grown into ossification areas; spicules meet and fuse toegher.

Answer 15

2nd step of intramembraneous ossification

Question 16

1. Remodeling of trapped blood vessels around spongy bone produces osteons of compact bone.
2. Connective tissue around the bone becomes organized into fibrous layer of the periosteum
3. Osteoblasts closest to surface become less active, but remain in inner layer

Answer 16

3rd (last) step of intramembraneous ossification

Question 17

The blood vessels that supply the diaphysis invade the cartilage model as endochondral ossifcation begins.

Answer 17

The Nutrient Artery and Vein

(Most bones have only one)

Question 18

The entry point for the nutrient artery and vein in the diaphysis

Answer 18

nutrient foramina

Question 19

Supply blood to the inner (diaphyseal) surface of each epiphyseal cartilage, where that cartilage is being replaced by bone

Answer 19

Metaphyseal vessels

Question 20

Blood vessels of periosteum provide blood to the superficial osteons of the shaft. During endchondral bone formation, branches of these also enter epiphyses to provide blood to secondary ossification centers

Answer 20

periosteal vessels

Question 21

The hormone ______ is synthesized in the ______ from the steroid _______, and is essential for normal calcium and phosphate ion absorption in the digestive tract.

Answer 21

1. calcitriol
2. kidneys
3. cholecalciferol (Vitamin D₃)

Question 22

Vitamins

______ is required for key enzymatic reactions in collagen snythesis, and stimulates osteoblast differentiation

______ stimulates osteoblast activity, essential in children

________ and ________ are required for the synthesis of proteins in normal bone

Answer 22

1. Vitamin C
2. Vitamin A
3. Vitamins K and B₁₂

Question 23

____ _______ is produced by the ______ gland stimulates protein synthesis and cell growth

Answer 23

Growth Hormone, pituitary

Question 24

_______ is produced by the _____ gland. It stimulates cell metabolism and increses the rate of osteoblast activity

Answer 24

thyroxine; thyroid

Question 25

at puberity, ____ and ______ hormones stimulate osteoblasts to produce bone faster than the rate at which epiphyseal cartilage expands.

Answer 25

estrogen and androgen

Question 26

\_\_\_\_\_\_\_ is released by the _____ glands, and works to increase blood calcium levels

Answer 26

1. Parathyroid hormone (PTH) 2. Parathyroid gland

Question 27

What are the three major effects of PTH?

Answer 27

1. Stimulate osteoclast activity 2. Increase intestinal absorption of calcium ions by enhancing calcitriol action 3. Decrease calcium excretion by kidneys

Question 28

\_\_\_\_\_\_\_\_\_ is produced by _____ \_\_\_\_ in the ____ gland, and decreases blood calcium concentration

Answer 28

1. calcitonin 2. parafollicular cells (C cells) 3. thyroid gland

Question 29

What are the two major functions of calcitonin?

Answer 29

1. Inhibit osteoclast activity 2. Increase rate of calcium excretion by kidneys

Question 31

Bone Repair

Answer 31

1. 1. **Fracture hematoma** forms at fracture site. Disruption fo circulation leaves a dead zone. 2. **Internal calllus** forms in medullary cavity, between broken ends of the shaft. A network of spongy boneu unites inner edges. **External callus** of cartilage and bone stabilizes outer edges Cells differentiate into chondroblasts to produce hyaline cartilage. At edges, differentiate into osteoblasts to bridge bone fragments. Broken ends temporarily stablized. 3. Osteoblasts replace central cartilage of external callus with spongy bone. Dead bone fragments are removed. 4. Osteoclasts and osteoblasts continue to remodel, and replace with living compact bone.