Bones Flashcards
Functions of bones (4)
- Weight bearing/ support
- Protection (e.g. skull for brain, vertebrae for spinal cord, ribcage for lungs and other internal organs)
- Mineral store (if not enough minerals are supplied through diet, the body depends on storage, malnutrition is the leading cause of lack of minerals)
- Blood formation (red bone marrow)
Compact bone (cortical bone)
Found near the cortical (hard) bone area, made up of osteons; concentric cylinders of bone tissue with a central vascular canal
Spongy bone (trabecular bone)
- Typically found at ends of long bone, highly vascular and contains red marrow often
- Sponge- like
- Also called cancellous, trabecular bone or diploe
- Less dense than compact bone
- Network of lamellated trabeculae (rod-like tissue with a specific mechanical function) filled with bone marrow
- no Harversion systems present!
- Orientation of trabeculae reflect main directions of mechanical forces
Medullary Cavity
Found near shaft and filled with bone marrow
2 membranes found in bone
periosteum and endosteum
Osteons/ Haversian systems
-Under the microscope, osteons can be seen on bone
Osteons are made of sheets of bone (concentric rings)
Compact bone organised in circular structures (osteons/ Harvasian systems
Central Harvasian canal and horizontal perforating
- Harvasian canals surround blood vessels and nerve cells and communicate with osteocytes
- Osteocytes and concentric rings of bone matrix (lamellae) are found around it
Volkmann’s canals
transmit blood vessels from periosteum into the bone and communicate with Harvasian canals
Different types of bone (6)
- Sutural bone, e.g. in the suture joints in the cranium (skull)
- Irregular bone, e.g. vertebrae
- Long bone, e.g. femur
- Sesamoid bone: patella (kneecap), usually in hands or feet and regions with high frictions
- Short bone, e.g. carpal (in the wrist)
- Flat bone, e.g. frontal or scapula (shoulder blade)
What are the 2 different bone formation types? (ossification)
- Endochondral (most common type including long bone growth, growth from hyaline cartilage)
- Intramembranous (flat bones of skulls, mandible/jaw bone, maxilla/upperjaw, clavicles/collarbones)
Describe endochondral ossification process
- Bone first as a “cartilage” model first
- Blood vessels invade cartilage
- Cartilage replaced with bone
- Cartilage remains in the epiphyseal growth plate
Growth plate eventually ossifies
Describe intramembranous ossification process
- no cartilaginous phase
- most direct way of forming bone
- Mesenchymal cells develop into osteoprogenitor cells that mature into osteoblasts that start depositing bone
- Residual mesenchymal cells develop blood vessels & bone marrow
- This bone formation also occurs in adult cortical bone
What 3 types of cells make up the bone?
- osteoblasts
- osteocytes
- osteoclasts
What are the main components of the bone
- cells
- ECM (extracellular matrix)
What is the component of ECM in the bone?
~45% hydroxyapatite crystals (complex form of calcium phosphate)
~35% Collagen (Type I)
~20% Water
What two components give bone its strength?
- Minerals (hydroxyapatite):
- Makes bones stiff and able to support structures
- High strength under compression (like concrete) - Collagen
- Gives bone flexibility and reduces risk of fracture
High strength under tension
What 2 functions of the bone give it its dynamic nature?
- fracture healing
- mechanical adaptation
Osteoblasts (what are they? what’s their function?)
- Immature bone cells created from osteopregenitor cells in periosteum and endosteum.
- Function: produces bone matrix (unmineralised matrix= osteoid) and initiates calcification (mineralises it)
- Become osteocytes once surrounded by matrix
- derived from the mesenchymal lineage, and that their differentiation is regulated by specific regulatory molecules.
Osteocytes (what are they? what’s their function?)
- Mature bone found inside lacunae (small cavity within bone matrix)
- Numerous processes found in canaliculi (little network which connect cells in a network to communicate)
- Canaliculi connect lacunae to each other
- Function: not well understood, may maintain bone matrix & sense mechanical forces and adaptation
Describe properties of ECM (4)
- mainly made up of minerals, collagen and water
- Modified type 1 collagen fibres
- strongly cross linked and has large gaps within fibrils for hydroxyapatite crystals
- orientation of fibres reflects orientation of mechanical forces
Describe 3 main bone disorders of remodelling and their causes
- Osteoporosis (resorption>formation): trabecular network is less spongy, more breakable and bone becomes weaker over time, can easily cause femur fractures)
- Paget’s disease (resorption/formation): renewal and repair of bone doesn’t happen very well causing deformation and weakness, can cause loss of hearing
- Osteopetrosis (formation> resorption): no resorption happens (no renewal), make bone abnormally dense, can cause short stature
What mechanical loads affect the bone mass?
- Weightlessness (such as in astronauts) or extended bed rest can cause significant bone loss
- Higher bone material density in athletes maintains an increased bone mass due to excessive training (BMD)
Osteoclasts (what are they and what is their function?)
Multinucleate cells derived from monocytes/macrophages Found on bone surface Large cells with ‘ruffled border’ Function: resorb bone matrix Howship’s lacunae – resorption pits derived from the haemopoietic lineage
