Cellular Bone Formation

Two types of cells that work together to alter your bones in response to different environmental factors?

- Osteoclasts - Osteoblasts

2. Describe how you would identify an osteoblast vs. and osteoclast vs. an osteocyte.

1. osteoblast: single nucleus 2. osteoclast: multi nucleus 3. osteocyte: has dendtries

Apoptosis

AKA "cell suicide" Not a pathologic state, it is the natural way that the body eliminates cells that are not needed Certain carefully regulated genes within the cell are activated causing the cell to disintegrate The factors that regulate apoptosis are currently under investigation possibly related to estrogens or interleukins Medications are being developed that could modify apoptosis as a potential treatment for osteoporosis

5. Explain some advantages and disadvantages to autograft bone

Advantages: Has the full triad Disadvantages: -Donor site complications -Expensive -MSC quantity and quality are unpredictable

OSTEOBLASTS

Build bone Come from the Mesenchymal Stem Cell (MSC) lineage Secrete the RANKL that activates the activity of the osteoclast precursor (macrophage)• Once finished building bone, 3 basic actions can happen them: 1. Some become surrounded with their own matrix and differentiate into osteocytes 2. Others will remain on the surface of the new bone and differentiate into lining cells 3. The rest undergo apoptosis ("cell suicide") and disintegrate

4. Describe the 3 elements necessary for new bone or tissue formation.

Cells, Signals, Scaffolds

OSTEOCLASTS

Come from the Hematopoietic Stem Cell (HSC) lineage Resorb bone Make and secrete digestive enzymes that break up or dissolve (resorb) the bone mineral/tissue Once finished resorbing bone, they undergo apoptosis (aka: programmed cell death, cell suicide)

Osteocytes

Come from the osteoblast (MSC lineage) Live within the bone and have long branching arms (dendrites) which allow them to contact each other, as well as to the lining cells on the bone surface Form a communication network throughout the bony structure to sense changes, like mechanical strain, and respond by directing cellular activity Can secrete growth factors which activate the lining cells, causing them to re-up and resume osteoblastic activity or to stimulate the osteoblast activity in general

Lining Cells

Former osteoblasts which have become flat and pancake-shaped Line the entire surface of the bone and come in contact with osteocyte dendrites Protect the bone from chemicals in the blood which dissolve crystals (such as pyrophosphate) Have receptors for hormones and factors that initiate bone remodeling (activate osteoclasts) Regulate the passage of calcium in and out of bone Can re-up and resume osteoblastic activity

1. What is an osteoclast? Osteoblast? Osteocyte?

Osteoclast: resorb bone Osteoblast: build bone Osteocyte: Live within the bone and have long branching arms (dendrites) which allow them to contact each other, as well as to the lining cells on the bone surface

3. Explain the role of signals in the bone formation process.

growth factors aka cytokines ( control cell migration (chemotaxis), cell division (proliferation), and cell specialization (differentiation)