6-2. Ossification and Bone Growth

Question 1

Ossification

Answer 1

the process by which bone forms in the body

Question 2

models

Answer 2

fibrous membranes and hyaline cartilege in the embryonic skeleton shaped like bones

Question 3

Ossification begins around the __ week and __ eventually replaces most of the embryonic skeleton.

Answer 3

8; bone tissue

Question 4

What are the two types of bone formation?

Answer 4

intramembranous ossification

endochondral ossification

Question 5

Intramembranous ossification

Answer 5

when a bone develops from a fibrous membrane

Question 6

What bones form from intramembranous ossification?

Answer 6

clavicles and cranial bones in skull

Question 7

What bones form from endochondral ossification?

Answer 7

all bones except for the clavicles and cranial bones in the skull

Question 8

Endochondral ossification

Answer 8

when a bone develops from hyaline cartilage models

Question 9

Primary Ossification Center

Answer 9

blood vessels penetrate the perichondrium midway along shaft of cartilage model at this region

Question 10

What are the steps of endochondral ossification, at the primary ossification center?

Answer 10

1. Blood vessels penetrate the perichondrium midway along shaft of cartilage model at the primary ossification center. This stimulates the underlying cells to become osteoblasts and converts the perichondrium to periosteum.
2. Osteoblasts secrete osteoid that encases the shaft of the model in a bone collar.
3. Changes occur in the cartilage in the center of the shaft, resulting in calcification. The osteocytes die since nutrients can’t diffuse across the membrane, leaving cavities that merge to eventually form the medullary cavity.
4. The periosteal collar thickens and lengthens in the shaft, but the cartilage model continues to grow rapidly at its epiphysis.

Question 11

What are the steps of endochondral ossification, at the secondary ossification center?

Answer 11

shortly after birth, blood vessels enter the epiphyses, and osteoblasts begin to lay down bone there

Question 12

The primary ossification center is located ___.

Answer 12

midway along the shaft of the cartilage model

Question 13

The secondary ossification center is located ___.

Answer 13

the epiphyses

Question 14

When secondary ossificaiton is complete, hyaline cartilage remains: ___.

Answer 14

at the tips of long bones as articular cartilage

at the junction of the diaphysis and epiphysis, forming the epiphysial plate

Question 15

During infancy and youth, ___ bones grow in length, and ___ bones grow in thickness. Most bones stop growing during ___.

Answer 15

long; all; adolescence

Question 16

What happens during appositional growth (growth in thickness)?

Answer 16

1. osteoblasts beneath the periosteum add new bone tissue to the outer surface, producing a thicker and stronger bone
2. at the same time, osteoblasts on the endosteal surface remove the bone lining the medullary cavity, to prevent it from becoming too heavy

Question 17

What allows the diaphysis of long bones to continue growing in length?

Answer 17

the epiphysial plate

Question 18

What happens during bone growth in length?

Answer 18

1. cartilage cells on the epiphysial side of the plate divide quickly, increasing the thickenss fo thep late and pushing the epiphysius further from the diaphysis
2. the older chondrocytes that have been pushed closer to the shaft enlarge, and the surrounding matrix calcifies, causing the cells to die and be replaced with spongy bone.
3. the epiphyseal plate remains a constant thickness - the rate of cartilage growth is balanced by replacement with bony tissue

Question 19

epiphyseal plate closure

Answer 19

cartilage cells in the plate are all replaced by bone and growth in length stops

Question 20

Epiphyseal plate closure happens at __ yrs in females and __ in males.

Answer 20

18; 21

Question 21

What are some factors affecting bone growth?

Answer 21

diet
hormones
exercise
aging

Question 22

What diet is most conducive to bone growth?

Answer 22

rich in protein, calcium, phosphorus, Mg and Mn, plus vitamins A, C, and D

Question 23

growth hormone

Answer 23

most important stimulus of bone growth during childhood released from pituitary gland.

Question 24

Too little growth hormone results in ___; too much results in ____

Answer 24

pituitary dwarfism; gigantism

Question 25

What are the roles of sex hormones in bone growth?

Answer 25

• promote the “growth spurt” seen in puberty
• masclinization/feminization of skeleton
• cause the epiphyseal plate to close

Question 26

calcitonin

Answer 26

produced by the thyroid gland, accelerates calcium uptake by the bones - when levels are high, causes the excess to be deposited in bones

Question 27

parathyroid hormone

Answer 27

released from the parathyroid glands when blodo calcium levels are low - stimulates osteoclasts to break down bone matrix, releasing calcuim from bones

Question 28

When calcium levels are too high, ___ is produced.

Answer 28

calcitonin

Question 29

When calcium levels are too low, ___ is produced

Answer 29

PTH (parathyroid hormone)

Question 30

How does exercise help bone growth?

Answer 30

stimulates bone growth, causing mineral salts to be laid down making bones thicker and stronger. Bone grows in response to the demands made on it.

Question 31

What happens to bones as we age?

Answer 31

calcium is lost from bones; there is also a decrease in protein production, leading to fewer collagen fibers and making bones brittle

Begins at age 30-40 in women and 60 in men

Question 32

bone remodeling

Answer 32

in the adult skeleton, old bone is continually being removed (resorption) by the osteoclasts and replaced with new bone by the osteoblasts

Question 33

Spongy bone on surface is remodeled into ___ early in life.

Answer 33

compact bone

Question 34

Worn and injured bone is ____.

Answer 34

actively replaced

Question 35

The distal end of the femur is remodeled every ___.

Answer 35

5-10 years

Question 36

What is blood calcium essential for?

Answer 36

maintained in a narrow range of 9-11 mg/dl. Essential for muscle contraction, nerve impulse contraction, and blood clotting