1. Bone Cells & Bone Development

2. Let’s meet Bob and Claude!
Cells of Bone Tissue
Let’s meet Bob and Claude!

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

4. Osteoblasts
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

6. Osteoclasts 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. 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

9. Bone Homeostasis and Metabolism

10. Bone Metabolism (Background)
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

11. Bone Metabolism: Hormones
Parathyroid hormone (PTH) is secreted if Ca2+ levels falls
PTH gene is turned on and more PTH is secreted from gland, osteoclast activity increased
Calcitriol is a hormone that works with PTH & promotes absorption of calcium in digestive tract & blood, to prevent it from being released in the urine.

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

13. 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

14. 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

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

16. Disorders of the Skeletal System
Failure of bone calcification
Rickets
Growing children
Osteomalacia
adults

17. Herniated Disc
Ligaments of the intervertebral discs become weak or are injured, the surrounding fibrocartilage ruptures, and the material inside protrudes

18. Bunion Inflammation of the joint, bone spurs, calluses
Caused by wearing tight fitting shoes

19. Abnormal Spinal Curvatures

20. Fractures
A fracture is break in a bone

21. 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

22. 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

23. Bone Formation Osteogenesis: Ossification: bone formation
the process of replacing other tissues with bone

24. 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

25. Ossification
Chondrocytes in the center of hyaline cartilage enlarge, calcify, and die, leaving cavities in cartilage

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

27. Ossification
3. Blood vessels enter the cartilage. Spongy bone develops at the primary ossification center in the shaft where bone tissue replaces cartilage. A marrow cavity is created.

28. Ossification
4. Capillaries and osteoblasts enter the epiphyses creating secondary ossification centers

29. Ossification
5. Epiphyses fill with spongy bone (no cavity in this region of the bone). On the ends, hyaline cartilage that remains is articular cartilage.

30. Epiphyseal Plate
At the Epiphyseal plate the bone grows lengthwise as bone tissue replaces cartilage

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

32. Bone Growth
New cartilage is formed continuously on external face of articular cartilage and on the surface of the epiphyseal plate that faces the bone end (further away from medullary cavity)
Old cartilage on the internal face is broken down and replaced by bone

33. Bone Growth

34. Bone Growth Bone increases in diameter through appositional growth
Appositional growth is controlled by hormones
Osteoblasts in periosteum add bone tissue to external face of diaphysis
Osteoclasts in endosteum remove bone from inner face of diaphysis wall