Skeletal System and Joints: by Mariah, Karen, and Kaylee (Bones (Bone…
Skeletal System and Joints: by Mariah, Karen, and Kaylee
- A bone collar forms around the diaphysis of the hyaline cartilage model. A periosteum forms around the hyaline cartilage.
- Cartilage calcifies in the center of the center of the diaphysis and then develops cavities.
- Periosteal bud invades the internal cavities and spongy bone forms.
- The diaphysis elongates and the medullary cavity forms.
- The epiphyses ossifies and articular cartilage forms at the top and bottom of the bone. the epiphyseal plate forms.
- Ossification centers develop in the fibrous connective tissue membranes. Mesenchymal cells become osteoblasts.
- Osteoid is secreted from ostoblasts which calcifies.
- Immature spongy bone and periosteum form. Here mesenchyme on the bone outside becomes the periosteum.
- Compact bone replaces immature spongy bone and red bone marrow develops. Trabeculae just deep to the periosteum are remodeled and replaced with compact bone.
- A hematoma forms (bleeding).
- Fibrocartilaginous callus forms.
- bony callus forms
- bone remodeling occurs.
Mechanical Stress: this causes a positive feedback loop. The more mechanical stress the more bone needed to support it.
Calcium homeostasis: the bone maintains calcium homeostasis by bone remodeling using a negative feedback loop.
Purpose: the purpose of bone remodeling is bone homeostasis. This includes both keeping the bones strong and maintaining Ca2+ homeostasis.
Maintaing Ca2+ levels: a hormonal negative feedback loop involving parathyroid homone maintains Ca2+ homeostasis in the blood.
- There is a signal that there is a drop in blood Ca2+ levels.
- This signals the parathyroid glands to release PTH.
- PTH increases which signals the osteoclasts to degrade the bone matrix and release calcium.
- This raises the blood Ca2+ levels.
Mechanical stress: mechanical stress and gravitational forces acting on the bone drive remodeling where it is required to strengthen a bone.
- there is mechanical stress on a certain area of a bone
- this signals the osteoblasts in the bone to make more osteocytes to make the bone stronger in that area.
Types of bone growth:
- Appositional Growth: cartilage forming cells in the perichondrium secrete matrix against external face of existign cartilage. New matrix laid down on surface of cartilage. Growing outwards.
- Interstitial growth: chondrocytes witin lacunae divide and secrete new matrix expanding cartilage from within. New matrix made with cartilage interstitial growth within cartilage. Growing upwards.