1. 6
Bones and Skeletal Tissues: Part B

2. Bone Development
Bones grow and repair throughout life from 2 months into development to death.
Stages
Formation
Growth
Remodeling

3. Two Types of Ossification (bone formation)
Intramembranous ossification: during development dense irregular CT start flat bone formation (which bones were these?)
Endochondral ossification: during development and during childhood hyaline cartilage CT starts formation of long bones and other bones. (which bones were these?)
Why do we care which bones are formed which way?!

4. One brother has ACHONDROPLASTIC DWARFISM.
Which bones are growing normally? Which are not?
What does the name of the disorder tell you?

5. Intramembranous ossification of flat bones
How to make a flat bone!

6. Intramembranous ossification of flat bones
CT stem cell
Collagen fiber
Ossification center
Osteoid
Osteoblast
Early “stem” cells make a collagen sheet, or membrane.
Inside this membrane, osteoblasts form from other stem
cells
Figure 6.8, (1 of 4)

7. Intramembranous ossification
Osteoblast
Osteoid
Osteocyte
Newly calcified bone matrix
3. Osteoblasts secrete osteoid (a mix of gel and collagen fibers)
4. Calcium phosphate adds to the collagen, forming spongy bone.
5. Trapped osteoblasts become osteocytes.
Figure 6.8, (2 of 4)

8. Intramembranous ossification
CT stem cells condensing to form the periosteum
Spongy bone
Blood vessel
6. Blood vessels arrive, and more spongy bone forms
7. Nearby connective tissue becomes the periosteum cover.
Figure 6.8, (3 of 4)

9. Intramembranous ossification
Fibrous periosteum
Osteoblast
Plate of compact bone
Spongy bone
cavities contain red marrow
8. Osteoblasts change the way they lay down collagen,
and form compact bone around the spongy bone,
and below the periosteum.
9. Red marrow appears as blood cells are produced in the
marrow cavities.
Figure 6.8, (4 of 4)

10. Intramembranous ossification summary
The end product is a flat bone!
A spongy bone sandwich

11. Endochondral Ossification
Development of long bones (and parts of other bones)

12. Childhood to adolescence Week 9 Month 3 Birth
After conception
Month 3
Birth
Articular cartilage
Secondary ossification center
Spongy bone
Epiphyseal blood vessel
Area of deteriorating cartilage matrix
Epiphyseal plate cartilage
Hyaline cartilage
Medullary cavity
Spongy bone formation
Bone collar
Blood vessel of periosteal bud
Primary ossification center 1
A hyaline
cartilage “model”
of a bone forms.
Compact bone collar
forms around it
Central
cartilage area
has a planned
cell death 2
Blood vessels
enter, ostepblasts
and minerals arrive
and spongy bone
forms in diaphyses. 3 4
The epiphyses ossify. Hyaline Cartilage remains only in the epiphyseal plates and articular cartilages.
The diaphysis elongates and osteoclasts form
the marrow cavity.
In the epiphyses, cartilage
dies and spongy bone forms. 5
Figure 6.9

13. Week 9 Hyaline cartilage Bone collar
Early “bones” area actually hyaline cartilage “models”
2. The first real bone is compact osseous CT “collar” around the model to give it strength.
Bone collar
Figure 6.9, step 1

14. Area of deteriorating cartilage matrix
3. Cartilage in the center of the shaft dies and forms a cavity.
Figure 6.9, step 2

15. Primary ossification center
Month 3
4. Blood vessels invade the shaft, bringing minerals. Osteoblasts crawl along the outside of blood vessels into the shaft
5. Osteoblasts form spongy bone inside the shaft in the
Primary ossification
Center.
Spongy bone formation
Primary ossification
center
Blood vessel of periosteal bud
Figure 6.9, step 3

16. The same process occurs in the ends of the bones. Birth
Epiphyseal blood vessel
Secondary ossification center
The same process
occurs in the ends of
the bones.
Medullary cavity
Most of the spongy bone is destroyed by osteoclasts
to make way for bone marrow.
7. Secondary ossifications centers form at the ends of bone.
Figure 6.9, step 4

17. Spongy bone remains in the ends of bone. The shaft becomes filled with
Childhood to adolescence
Articular cartilage\
Hyaline cartilage CT
Spongy bone
remains in the
ends of bone.
Epiohyseal plate
Growth plate
Hyaline cartilage connective tissue
The only hyaline cartilage CT is now
at the ends of the bones and
in the epiphyseal plate.
The shaft
becomes
filled with
bone marrow
Figure 6.9, step 5

18. Childhood to adolescence
Week 9
Month 3
Birth
Childhood to adolescence
Articular cartilage
Secondary ossification center
Spongy bone
Epiphyseal blood vessel
Area of deteriorating cartilage matrix
Epiphyseal plate cartilage
Hyaline cartilage
Medullary cavity
Spongy bone formation
Bone collar
Blood vessel of periosteal bud
Primary ossification center 1
Cartilage
model
Bone grows
In diaphyses 2
Blood enters
bone 3
Bone grows
In epiphyses. Cartilage
Dies back throughout bone. 4
Bone tissue continues
To grow. Cartilage only
At ends of bone and in
Growth plates. 5
Figure 6.9

19. Types of bone GROWTH (length and width)
Age birth - 21, bone grows in length.
Age , bone can grow in width and repair
Increases the thickness or density of bone

20. How does a bone grow in length?
The cartilage cells in the epiphyseal plate multiply in spurts, die, and are quickly replaced by bone. There are 5 zones in each epiphyseal plate:
Resting zone (cartilage connects to epiphysis)
Proliferation zone (multiplication of chondrocytes)
3. Hypertrophic zone (growth of chondrocytes)
4. Calcification zone (invasion of mineral salts)
5. Ossification zone (osteoblasts lay down collagen which combines with mineral salts= osteoid)

21. Growth in the length of long bones occurs at epiphyseal plate
Resting zone
Proliferation zone
Cartilage cells undergo
mitosis. 1
Hypertrophic zone
Older cartilage cells
enlarge. 2
Calcification zone
Matrix becomes calcified;
cartilage cells die; matrix
begins deteriorating. 3
Calcified cartilage
spicule
Osteoblast depositing
bone matrix
Ossification zone
New bone formation is
occurring.
Osseous tissue
(bone) covering
cartilage spicules 4
Figure 6.10

22. Hyaline cartilage model of an entire developing long bone, pre-birth

23. Primary and secondary ossification centers form in the hyaline cartilage model
bone
epiphysis
metaphysis
diaphysis
Cartilage tissue does NOT turn into bone tissue,
it dies and is REPLACED by bone tissue

24. Chondrocytes in the epiphyseal plate mutlipy, and lengthen the bone.
New cartilage grows, lengthening bone
Cartilage tissue does NOT turn into bone, it dies and is REPLACED by bone tissue.

25. To prevent the bone from becoming too wobbly, the cartilage dies, and is replaced by bone. Lengthening is accelerated during puberty by estrogen and testosterone.
Older cartilage is
Replaced by bone,
strengthening bone

26. The processof of bone lengthening continues until hormone levels rise quite high in the late teens.

27. By age 21 the increased amounts of estrogen and testosterone STOP bone growth and the growth plate dies and is replace by bone.
Growth from birth
to the end of puberty
In utero
birth
18ish
21ish

28. Growth in the length of long bones occurs at epiphyseal plates
Resting zone
Proliferation zone
Cartilage cells undergo
mitosis. 1
Hypertrophic zone
Older cartilage cells
enlarge. 2
Calcification zone
Matrix becomes calcified;
cartilage cells die; matrix
begins deteriorating. 3
Calcified cartilage
spicule
Osteoblast depositing
bone matrix
Ossification zone
New bone formation is
occurring.
Osseous tissue
(bone) covering
cartilage spicules 4
Figure 6.10

29. Which x ray is from a child, and which from an adult? Why?

30. Bones can widen for additional strength and repair throughout life
But a diet rich in protein; vitamins C, D, and A; calcium; phosphorus; magnesium; and manganese is necessary.

31. Bone responds to USE!
A bone grows or remodels in response to forces or demands placed upon it
We know this because:
Handedness (right or left handed) results in bone of one upper limb being thicker and stronger than the other
Curved bones are thickest where they are most likely to buckle, and so the body grew extra bone.
Large, bony projections grow where heavy, active muscles attach

32. Load here (body weight)
BONE SHAPE
depends on the
forces placed upon it
Figure 6.13

33. Trabecular patterns in femur

34. Calcium and Phosphate are stored in bone matrix, but….
Calcium is also necessary for
Transmission of nerve impulses
Muscle contraction
Blood coagulation Calcium?
Nerve cells
Cell division
How does calcium get from the bone matrix to where it is needed?

35. How does calcium move from bone to blood (resorption)?
When calcium and phosphate are needed elsewhere in body..
Osteoclasts digest bone using
Lysosomal enzymes (to digest proteins)
Acids (to convert calcium salts into soluble forms)
Bone minerals and proteins are returned to blood
About 1% of minerals flow through blood to other needy tissues. The rest resides in bone.
Minerals and protein
Back to blood

36. What processes correct low blood calcium?
1. Falling blood
Ca2+ levels
4. Calcium is
released from bone
into blood
Thyroid
gland
2. Parathyroid glands release parathyroid hormone into blood.
Parathyroid
glands
3. PTH stimulates
osteoclasts to
digest bone.
PTH
Figure 6.12

37. Hormonal Control of Blood Ca2+
1. As blood calcium levels drop
2. Parathyroid glands sense low Ca++, release PTH into blood
3. PTH travels through blood to bone, and stimulates osteoclasts to degrade bone matrix, releasing Ca2+ into the blood
4. SOLUTION! Blood Ca2+ levels raised to normal, and organ receive enough calcium to function

38. Hypocalcemia: Abnormally low blood calcium
Abnormally LOW blood calcium leads to HIGHLY excitable neurons causing skeletal and cardiac muscle spasms

39. Even excessive sweating can lead to dangerously low blood calcium
Even excessive sweating can lead to dangerously low blood calcium. If not corrected quickly it can be fatal.

40. HYPER calcemia Abnormally HIGH blood calcium
-taking antacids (contain calcium carbonate) -release of too much PTH (osteoclasts overwork) -immobility of the patient (calcium leaves bones)

41. Signs and symptoms of hypercalcemia
UNDER excitable neurons and confusion, coma, under performing muscles, heart stops beating.

42. Common Types of Fractures

43. Classification of bone fractures Nondisplaced—ends retain normal position Displaced—ends out of normal alignment

44. Completeness of the break Complete—broken all the way through Incomplete—not broken all the way through

45. Orientation of the break to the long axis of the bone: Linear—parallel to long axis of the bone Transverse—perpendicular to long axis of the bone

46. Whether or not the bone ends penetrate the skin: Compound (open)—bone ends penetrate the skin Simple (closed)—bone ends do not penetrate skin skin

47. Comminuted: Shattered Compression: Crushed
Table 6.2

48. Epiphyseal: cartilage separates from bone
Spiral: bone twists
Epiphyseal: cartilage separates from bone
Table 6.2

49. Depressed: compacts spongy bone
Greenstick: bone does not break all the way through
Table 6.2

50. Stages in the Healing of a Bone Fracture
Hemostasis and inflammation
Torn blood vessels hemorrhage
Hematoma (clot) forms
Inflammation causes swollen, painful, red area (as in skin)
Hematoma .

51. Stages in the Healing of a Bone Fracture
Fibrocartilage forms
Phagocytic cells clear debris
Fibroblasts secrete collagen fibers to connect bone ends

52. Stages in the Healing of a Bone Fracture
Bony callus formation
Osteoblasts form spongy bone until firm union occurs in ~2 months
Compact bone forms on the surface
Figure 6.15, step 3

53. Stages in the Healing of a Bone Fracture
Bone remodeling
Osteoclasts remodel and smooth the bone approximating the original shape
Healed fracture

54. Bony callus of spongy bone
Hematoma
External callus
Bony callus of spongy bone
Internal callus (fibrous tissue and cartilage)
New blood vessels
Healed fracture
Spongy bone trabecula 1
A hematoma forms. 2
Fibrocartilaginous callus forms. 3
Bony callus forms. 4
Bone remodeling occurs.
Figure 6.15

55. Homeostatic Imbalances: Rickets
Due to Vitamin D deficiency or insufficient dietary calcium in children leads to bowed and weak bones

56. Homeostatic Imbalances: Osteporosis
In adults, low bone calcium due to lack of estrogen, calcium or vitamin D deficiency, immobility, thyroid disease, and diabetes can cause loss of bone mass

57. Vertebrae collapse and compress
Spongy bone of spine and neck of femur becomes porous and more susceptible to fracture
Vertebrae collapse and compress
Figure 6.16

58. Osteoporosis: Treatment and Prevention
Diet with sufficient calcium
Weight-bearing exercise throughout life