Week 5 - Bone Physiology Flashcards
What is included in the skeletal system?
Bones
Cartilage
Joints
Ligaments
Other connective tissues
What are the functions of the skeletal system?
• Support against gravity
• Leverage for muscle action
• Protection of soft internal organs
• Storage of:
Calcium, phosphorous
Fat
• Blood cell production
How are bones classified by their shape?
Flat bones
• Internal & external table
separated by diploë
Long bones
• Longer than they are wide
Short bones
• width≈length
Irregular bones
• Complex shapes
Sutural bones
• Between skull bones
Sesamoid bones
• Small, develop in tendons
What are the features of a typical long bone?
Diaphysis (shaft) - compact (dense) bone, medullary cavity
Epiphyses (ends) - Trabecular (spongy) bone
Articular cartilage
What is bone (osseus) tissue made from?
Ground substance - Two thirds of bone matrix. Minerals, predominantly crystals of hydroxyapatite Ca10(PO4)6(OH)2 with other calcium salts and ions.
Protein - One third of bone matrix. Most abundant protein type I collagen fibres.
Bone cells - Only 2% of bone mass
How are Osteocytes created?
• Mesenchymal stem cells => => osteoblasts => osteocytes
What is an osteoblast?
An immature bone cell that secretes matrix proteins.
What is an osteocyte?
Mature bone cell that maintains the bone matrix.
What is an osteoclast?
A multinucleate cell that secretes acids and enzymes to dissolve bone matrix.
Describe the microscopic structure of compact bone?
Osteon - Basic functional unit, columnar, strong in long axis. Several ostensibly in compact bone.
Central Canal - tunnel for blood vessels
Lamellae - Concentric layers of matrix
Lacunae - contains osteocytes
Describe the microscopic features of trabecular (spongey) bone
No Osteons
Trabecular - arches, rods, plates of bone. Branching network, strong in many directions.
Red marrow - Between trabecular. Forms red blood cells, provides nutrients to osteocytes.
Yellow bone marrow - Found in medullary cavity, stores fat.
What is periosteum?
Membrane outside bone consisting of:
Outer(fibrous) layer - Collagen fibres continuous with bone, ligaments, tendons, joint capsule.
Inner (cellular) layer
also contains lymphatic vessels and nerves
What is endosteum?
Membrane lining bone which has an incomplete cellular layer. Lines of medullary cavity, central canals and trabeculae.
What are three types of bone formation and growth?
Intramembranous ossification - flat bone formation
Endochrondral ossification - formation from cartilage model
Appositional bone growth - growth in width.
What are the steps of intramembranous ossification?
- Mesenchymal cells differentiate into osteoblasts.
- Ossification forms spicules of bone.
- Trabecular bone formed.
- Remodeled into compact bone
What happens in endochronal ossification?
- Chondrocytes within calcifying matrix enlarge then die
- Osteoblasts cover the shaft in a thin layer of bone
- Blood vessels and osteoblasts penetrate to form a primary ossification centre
- Primary ossification centre enlarges.
- Secondary ossification centres formed at epiphyses.
What happens in appositional bone growth?
Bone deposited by osteoblasts which pushes the other bone outwards
What is needed for normal bone growth?
Minerals - calcium, phosphate
Vitamins - Vitamin D3 and others
Hormones - Growth hormone, sex hormones, thyroid hormone, others
What occurs in bone remodelling?
Continuous breakdown and reforming of bone tissue - resorption by osteoclasts, formation by osteoblasts
Adaptation to loading - osteocytes detect forces in bone
Calcium homeostasis - 99% of calcium stored in bones. Hormones control storage/release
. PTH stimulates bone resorption to release calcium.
. Calcitonin stimulates bone formation to store calcium.
What occurs during fracture repair?
- Bleeding and formation of clot (fracture hematoma).
- Formation of external callus (cartilage) and internal callus (spongy bone).
- External callus replaced by bone. Internal callus united broken ends
- Initial swelling eventually remodelled.
