Bone Health Flashcards
What are the 3 main components of bone = connective tissue?
- Cells ( osteoclasts, osteoblasts, osteocytes)
- Protein fibres
- Ground substance: Viscous fluid with proteoglycans cross linked by protein fibres
What are the 3 main protein fibres?
Collagenous = bundles of collagen fibrils to strengthen the tissue
Reticular - join connective tissue to other tissues
Elastic - made of elastin fibres for stretch
What are the main functions of bone?
1: Mechanical - protection, rigid stability of the limbs, act as levers
2: Mineral storage - storage of minerals e.g Ca2+ and phosphate, bone marrow for haematopoesis
What are the 2 main types of bone?
Cortical hard bone = mechanical functions
Cancellous spongy bone = lattice of trabeculae, large SA so is very metabolically active
What is appositional growth?
How bone grows by osteoblast activity
It is the deposition of new matrix on the exisiting surface
What are the 2 main types of bone formation?
Intramembranous ossification: From fibrous membranes
Endochondral ossification: From hyaline cartilage
Describe the process of intra membranous ossification
- Osteoblasts can form ossification centres
- Osteoblasts can secrete ECM, Ca2+ to harden the matrix
- Osteoid forms along with the periosteum
- Osteoid forms around blood vessels to create spongy bone
- Spongy bone crowds the blood vessels to condense into red marrow
- Spongy bone is remodelled to be covered by a thin layer of cortical bone
Describe the process of endochondral ossification
- Mesenchymal stem cells -> chondrocytes
- Perichondrium forms
- Perichondrium becomes infiltrated with blood vessels, cells and osteoblasts
- Osteoblasts can convert the perichondrium -> periosteum
What blood vessels supply the bone?
Nutrient arteries
Periosteal arteries
Metaphyseal arteries
Perforating arteries, anastamose with branches of the nutrient arteries to supplY the marrow space
What are Haversian canals?
What are Volkman canals?
Central canals of the bone lying parallel to the bone axis, they contains lymphatics, nerves and vasculature
Volkman canals connect the haversian canals and are perpendicular to the bone axis.
Where are osteoblasts and osteocytes derived from?
What other cells do they give rise to?
Osteoprogenitor cells ( mesenchymal stem cells) Myoblasts, fibroblasts, adipocytes
What are osteocytes?
Major cells of the bones
They are supportive cells that maintain the bone matrix
What are the main functions of osteoblasts?
- Form the organic matrix by depositing ECM, collagen and special proteins ( osteoclastin and osteonectin)
- Mineralisation via deposition of hydroxypatite between the collagen fibrils
Describe mineralisation
- Osteoblasts remove ions e.g Ca2+ and phosphate from the mitochondria and cytoplsm and release these onto the organic matrix
- They have vesicles to concentrate the ions until hydroxyapatite forms
- The crystals have nucleation sites allowing for more apatite crystals to form
What are the main components of the organic matrix?
88% Type 1 collagen
10% proteins : Osteocalcin + osteonectin
1-2% : Glycosaminoglycans and lipids
