1. BONE CELLS & BONE DEVELOPMENT Directed Notes 

2. Osteogenic cells  osteoblast  osteocyte

3. BONE CELLS: Osteoprogenitor (Osteogenic) Cells
Embryonic cells that divide to produce osteoblasts
Are located in inner endosteum
Assist in fracture repair

4. Osteoblasts not yet calcified to form bone
Immature bone producing cells that secrete matrix compounds
not yet calcified to form bone
Osteoblasts surrounded by osseous tissue become osteocytes

5. Osteocytes Mature bone cells that maintain the bone matrix
Do not divide
OSTEON = one unit of bone tissue

6. SUMMARY
Osteogenic cells  osteoblast  osteocyte

7. Osteoclasts = “break bone”
Breaks down bone
Dissolve bone matrix and release stored minerals which is taken up by the blood
Causes osteoporosis
(loss of bone tissue) if
bone is unable to repair

8. the process of replacing other tissues with bone
Osteogenesis:
bone formation
Ossification:
the process of replacing other tissues with bone

9. Produces bones such as mandible and clavicle
The 2 main forms of ossification:
1) Intramembranous ossification
( dermal ossification)
occurs in the dermis
Produces bones such as mandible and clavicle
2) *Endochondral ossification
Bone replaces cartilage
Most bones formed this way
Observed easily in long bones

10. ENDOCHONDRAL OSSIFICATION
STEP 1)
 Chondrocytes in the center of hyaline cartilage enlarge, calcify, and die, leaving cavities in cartilage

11. STEP 2)
Blood vessels grow around the edges of the cartilage and cells begin to change to osteoblasts
Produces layer of superficial bone around shaft which becomes compact bone

12. Blood vessels enter the cartilage
STEP 3)
Blood vessels enter the cartilage
spongy bone develops at the primary ossification center in the shaft where bone tissue replaces cartilage
 creates a marrow cavity

13. STEP 4)
 Capillaries and osteoblasts enter the epiphyses creating secondary ossification centers

14. On the ends; hyaline cartilage that remains is ARTICULAR CARTILAGE
STEP 5)
Epiphyses fill with spongy bone and there is no cavity in this region of the bone
On the ends; hyaline cartilage that remains is
ARTICULAR
CARTILAGE

15. * At the Epiphyseal plate
(between the diaphysis and epiphysis) the bone grows lengthwise as bone tissue replaces cartilage

16. become Epiphyseal Lines
Epiphyseal Plates
become Epiphyseal Lines
When long bone stops growing,
after puberty, epiphyseal cartilage disappears at the growing epiphyseal plate and an epiphyseal line is visible on X-rays.

17. BONE CELLS & BONE DEVELOPMENT BONE METABOLISM Directed Notes 
But first let’s see if this helps…
Bob and Claude???

18. Bone Metabolism Bone stores 99% of total calcium in body
Calcium ions involved with many body systems
nerve & muscle cell function
blood clotting
enzyme function in many biochemical reactions

19. Bone Homeostasis/Metabolism

20. Details…Details… that you don’t have to know…
 G-protein activates
adenylate cyclase to
convert ATP to
cAMP in the cytosol
G proteins
(guanine nucleotid
-binding proteins)
Proteins involved in transmitting
chemical signals outside the cell,
and causing changes inside the cell
They communicate signals from
many hormones,
neurotransmitters,
and other signaling factors

21. Bone Metabolism Background only…
The thyroid gland is located in the front of the neck and wraps around the trachea; has a shape that is similar to a butterfly formed by two wings (lobes) and helps to regulate metabolism

22. Bone Metabolism Hormones
*Parathyroid hormone (PTH) is secreted if Ca+2 levels falls
PTH gene is turned on and more PTH is secreted from gland
osteoclast activity increased
kidneys retain Ca+2 so it is not all lost in urine and
produces calcitriol
*Calcitriol is a hormone that works with PTH & promotes absorption of calcium in digestive tract & blood

23. Bone Metabolism Hormones
*Calcitonin is a hormone that produces the opposite effects:
if calcium level gets too high
less absorption in the digestive tract,
increased excretion by the kidneys,
movement of calcium from the blood into the bones
inhibits osteoclast activity
increases bone formation by osteoblasts

24. Important Bone Metabolism Vitamins
Vitamin A:
Necessary for osteoclast activity
Vitamin C:
Needed to build durable bone matrix (osteoid)
Vitamin D:
Calcitriol is formed from vitamin D

25. Bone Homeostasis Bone Tissue and Exercise
Pull on bone by skeletal muscle and gravity is mechanical stress.
Lack of mechanical stress results in bone loss
reduced activity while in a cast or bedridden person
Weight-bearing exercises build bone mass

26. Osteoporosis Prevention (or decrease in severity)
Calcium supplements, weight-bearing exercise, & hormone replacement therapy (including a form of calcitonin)
behavior when young may be most important factor!

27. Bone Remodeling Ongoing process
Osteoclasts secrete enzymes and acids to break down bone
This releases calcium and other minerals of bone for resorption by blood
Osteoblasts rebuild osteons

28. Bone Remodeling
Continual remodeling of bone matrix along lines of mechanical stress
The distal femur is fully remodeled every 4 months

29. Fracture Repair A fracture is break in a bone STAGE 1 Inflammation)
Repair starts with formation of fracture hematoma: damaged blood vessels produce clot, bone cells die
new capillaries grow into damaged area
STAGE 2 Repair)
Callus (healing tissue) formation:
fibroblasts lay down collagen fibers
chondroblasts produce cartilage to span the broken areas of the bone

30. Fracture Repair Bone Formation: Bone remodeling:
osteoblasts secrete spongy bone that joins the broken areas of bone
lasts 3-4 months
Bone remodeling:
compact bone replaces the spongy in the callus
surface is remodeled back to normal shape

31. Video Clip Principles of Fracture Healing