Bone Remodeling

Bone Growth

• focus on growth taking place at the epiphyseal plate and this growth added length to the diaphysis which pushes the epiphyses further away

• about the length

• ends late adolescents and early adulthood
  - nose and lower jaw continue through life
  - at this point, any bone alterations that take place is the result of an injury or the result of bone remodeling

• Cartilage grows at the articular cartilage

• Cartilage is replaced by bone under articular cartilage

• cartilage grows above the epiphyseal plate

• cartilage is replaced by bone under the epiphyseal plate

Bone Remodeling

• Bone remolding: process where we are adding new bone to existing bone or making the bone thicker and stronger, or taking bone away, possibly making bone more brittle and weaker, but does not change its length
  - does change its mass/density
  - about the thickness

• Has articular cartilage and epiphyseal plate like bone growth

• bone gets resorbed (process where tissues or substances are broken down and absorbed back into the body)

• then bone is added by appositional growth

• Bone is then again resorbed

• can occur throughout the lifespan
  ex: prenatally, during early childhood and adolescence, and during adulthood

Factors that allow us to influence bone remodeling

• primarily regulated either by hormones that regulate blood calcium concentrations or mechanical stress

Bone Remodeling is the constant turn-over of bone

• bone remodeling refers to the turnover of bone
  - turnover of bone meaning adding new bone and taking away bone

• bone is dynamic, 5-7% of bone mass recycled per week
  - bones are changing on a weekly bases, dynamic, living tissue

Bone Deposition

• make bone, forming new bone

• the balance between bone resorption and bone deposition is bone remodeling

• you would hope that bone deposition is greater then bone resorption because this would result in thickening and strengthening of the bones

• you break down bone faster then you rebuild new bone

• osteoblasts build new bone cells
  - these osteoblasts lay down collagen and and later mineralize that collagen thus forming new bone
  - helps make bone stronger and more resilient to stress so our bones will last our lifespan

• formed by osteoblasts and there is a important nutrition component related to that as it relates to vitamins and minerals

Bone Deposition (repair)

• occurs after injury or for additional strength

• factors that influence bone deposition:
  - Vitamin C: collagen synthesis
  - Scurvy: vitamin C deficiency
  - when you don’t produce enough collagen and the collagen you do have starts to break down (since collagen is everywhere this means you start to fall apart)
  - this is not limited to bone, but all connective tissue would be impacted by this
  - having excess vitamin C does not make bones stronger as opposed to having the right amount of vitamin C
  - Vitamin D: calcium absorption
  - Fat soluble vitamin that plays a critical role in calcium absorption in the small intestine
  - Vitamin D is added into milk in order to promote absorption of calcium and strong bones
  - having adequate vitamin D means your going to have more calcium to put the deposit into bones than if you have inadequate vitamin D
  - Vitamin A: balance deposit & resorption minerals: calcium, phosphorous, and magnesium
  - vitamin A effects the balance of deposition and resorption
  - you can have to much or to little vitamin A
  - with vitamin A having just the right amount does help with the balance of deposition and resorption (having just the right amount of vitamin A is a broad range)
  - when having the right amount of vitamin A you enhance deposition relative to resorption
  - when you go outside the perfect amount of vitamin A zone, the pattern reverses and you favor resorption

• you need to have minimum amounts of these vitamins in order for your bones to be healthy

Bone resorption

• taking bone away, breaking down bone

• the balance between bone resorption and bone deposition is bone remodeling

• osteoclasts break down bone, they break down collagen and then soluablize the mineral
  - osteoclast cells have the same lineage as macrophages, they raise blood calcium levels or remove necrotic debree

• thought to be derived from macrophages
  - macrophages are technically a connective tissue cell, a hematepoetic stem cell
  - does mean that the clasts are not derived directly from osteoprogenitor cells

• “scrubbing bubbles” make groves in the bone
  - collagen is broken down and release and solubilize the mineral
  - this causes blood calcium levels to raise

• lysosomal enzymes: (aka lysosimes)

• enzymes that break down proteins (in this case that includes collagen)
  - digest organic matrix such as
  - collagen: since it is made up of amino acids and amino acids are organic

• once collagen is broken down, then you begin to release the hydroxyapatite (which is not soluble because it is a crystal and it requires hydrochloric acid LEFT OFF AT 15:13
  

Hydroxyapatite

• Hydroxyapatite is a crystal form of these mineral salts
  - calcium phosphates are the most abundant

• Hydroxyapatite is what makes bone hard and is essential to the health and well being of bones, if you do not have adequate calcium, the bones will be soft and bow

• other nutritional components:
  - minerals
  - calcium
  - phosphorus
  - magnesium

• other minerals in lesser quantities