1. Bone Homeostasis: Remodeling and Repair By: Haley Drayer

2. What does Homeostasis mean?
According to the medical dictionary the word homeostasis means, “the maintenance of relatively stable internal physiological conditions (as in body temperature or the pH of blood) in higher animals under fluctuating environmental conditions.”
This term can be applied to bones and the way they remodel and repair themselves to get back to the normal structure after a fracture.
Na+ and K+ pump

3. Bones seem lifeless, but did you know?
Bone is a dynamic and active tissue
Small-scale changes in bone architecture occur continually
Every week we recycle 5%-7% of our bone mass
Up to ½ gram of Ca2+ may enter or leave the adult skeleton everyday
Spongy bone (internal layer of bone) is replaced every 3-4 years
Compact bone (external layer of bone) is replaced every 10 years

4. What would happen if these facts weren’t true?
When bone remains in place for long periods the calcium crystallizes and becomes more brittle sometimes causing fractures.

5. Bone Remodeling
Bone remodeling consists of bone deposit and bone removal.
Bone deposit and bone removal are done with the help of remodeling units.
Osteoclasts= large cells that break down bone matrix
Osteoblasts= bone-forming cells
In a healthy young adult the total bone mass should remain constant
This means that the rates of bone deposit and removal are equal.
Some parts of bone are remodeled more often than others and at different rates.

6. Bone Deposit
Bone deposit occurs whenever bone is injured or the bone needs to be stronger.
Proteins, vitamin C, vitamin D, vitamin A, calcium, phosphorus, magnesium, manganese, etc…
Pg. 188 old book.

7. Bone Resorption or Removal
Major contributor in this process is the osteoclast
Osteoclasts move along a bone surface, digging grooves called resorption bays as they break down the bone matrix.
The part of the osteoclast that touches the bone is highly folded to form a ruffled membrane that clings tightly to the bone, sealing off the area of bone destruction.
Osteoclasts may phagocytize the deminerialized matrix and dead osteocytes.

8. Control of Remodeling pg. 189-190
Hormonal Mechanism
Parathyroid Hormone
Calcitonin
Homeostatic Imbalance
Response to mechanical stress

9. Fractures
Despite their remarkable strength, bones are susceptible to fractures, or breaks
Young ages:
Sports injuries, automobile accidents,, and falls, etc…
Old ages:
Most fractures are due to bones thinning and weakening

10. Types of Fractures Fractures may be classified into four categories:
Position of the bone ends after the fracture
Nondisplaced
Displaced
2. Completeness of the break
Complete
Incomplete
3. Orientation of the break
Linear
Transverse
If the bone ends penetrate the skin
Open
Closed

11. Fractures
Fractures can be classified by the location of the fracture, the external appearance, and/or the nature of the break.
A fracture is treated by reduction.
Reduction is the realignment of bone
Closed Reduction is when the bone ends are coaxed into position by the physicians hands.
Open Reduction is when the bone ends are secured together surgically with pins or wires.
After a broken bone is realigned, it is immobilized either by a cast or traction to allow the healing process to begin

12. Bone Repair
A simple fracture dealing with small or medium sized bones in young adults may take six to eight weeks to heal.
A fracture dealing with longer bones, larger bones, weight-bearing bones, and bones of elderly could be a longer healing process

13. First Stage of Bone Repair
Hematoma Formation
When a bone breaks, blood vessels in the bone, periosteum, and surrounding tissues, are torn and hemorrhage.
As a result, a hematoma (or mass of clotted blood) forms at the fractured site
Bone cells die because they are not getting the nutrition they need
The tissue at the site becomes swollen, painful, and inflamed

14. Second Stage of Bone Repair
Fibrocartilaginous Callus Formation
Within a few days, capillaries grow into the hematoma
Phagocytic cells invade the area and begin cleaning up the debris
Fibroblasts and osteoblasts invade fracture site and begin reconstructing bone
Fibroclasts produce collagen fibers that span the break and connect the broken bone ends
Osteoblasts begin forming spongy bone
This all helps to form the mass of repair tissue otherwise known as the fibrocartilaginous callus and this splints the broken bone

15. Third Stage of Bone Repair
Bony Callus Formation
Within a week, new bone trabeculae begin to appear in the fibrocartilaginous callus and gradually convert it to a bony (hard) callus of spongy bone.
Bony callus formation continues until a firm union is formed about two months later

16. Fourth Stage of Bone Repair
Bone Remodeling
Bone remodeling begins during the formation of the bony callus and continues for several months after the bony callus is remodeled.
The excess material is removed and compact bone is laid down to reconstruct the shaft walls.
The final structure of the remodeled areas resembles that of the original unbroken bony region.

17. Bone Repair Video