BL Bone Flashcards
What are the two sections of the skeleton?
What are each section comprised of?
Axial - skull
- vertebrate
- ribs/thoracic cage
Appendicular - upper limbs
- shoulder girdle
- lower limbs
- pelvic girdle
Why is bone a living tissue?
Contains blood vessles
Made out of various cells, proteins, mineral etc.
Can repair and remodel
Functions of bone
- mechanical: protection, framework + levers in movement
- synthetic: haemopoiesis
- metabolic: mineral storage, fat storage (yellow bone marrow) + acid base homeostasis
Outline the two types of bone
Cancellous bone - forms a network of bony columns calls trabeculae, spaces filled by bone marrow
Compact bone - forms the external surface of bone
what are the two types of ossification?
Endochondral ossificaion
Intra-membranous ossification
Outline endochondral ossification
Formation of long bones from cartilage template
- Continued lengthening at epiphyseal plates
- appositional growth - growth at the edges
Outline intra-membranous ossification
Formation of bone from clusters of mesenchymal stem cells in the centre of the bone > flat bones
Interstitial growth - growth in the middle
What are epiphyseal plates?
Part of the long bone where bone growth occurs
What do mesenchymal stem cells develop into?
Connective tissue
Blood vessels
Lymphatic tissues
Bones
What type of growth occurs in endochondral ossification?
Appositional growth - growth at edges
What type of growth occurs at intra-membranous ossification?
Interstitial growth - growth in the middle
How do flat bones develop?
Directly from mesenchymal tissue
By intra-membranous ossification
How do long bones develop?
Require cartilage template to develop
By endochondral ossification
Outline bone remodelling
Reabsorption:
- osteoclasts breakdown old bone
- uses acid to dissolve minerals
Formation:
1- osteoblasts lay down osteoid (collagen 1), enzymes and ground substance
2- osteoblasts change osteoid pH»_space; deposition of hydroxyapatite
3- mineralisation occurs
4- osteoid turns into bone tissue
5- osteoblasts become trapped within bone lamellae»_space; becomes osteocytes
Outline the process of bone formation
1- osteoblasts lay down osteoid (collagen 1), enzymes and ground substance
2- osteoblasts change osteoid pH»_space; deposition of hydroxyapatite
3- mineralisation occurs
4- osteoid turns into bone tissue
5- osteoblasts become trapped within bone lamellae»_space; becomes osteocytes
What is the cement line?
Where osteoid meet existing bone
Outline the conversion of cancellous bone to cortical bone
1- MSC convert into osteoblasts that line recently formed trabeculae
2- osteoid laid down
3- mineralisation occurs
4- 1-3 repeat
5- central MSC convert into blood vessels, lymph vessels + nerves
Similarities and differences between cancellous and cortical bone
Similarities:
- consist of concentrically arranged lamellae with osteoblasts between structures + osteocytes in lacunae
Differences:
- compact bones have osteons, Haversian canals + Volkman canals
- compact bone is a ‘solid continuous mass’
- spongy bone is a ’3D network of regular trabeculae’
What do osteoblasts use to create bone matrix?
Extracellular components:
Collagen
Enzymes
Ground substance
Calcium
Phosphorus
What are responsible for bone reabsorption?
Osteoclasts - secrete collagenase + acids to break down bone matrix
What is periosteum?
Tough fibrous vascular connective tissue layer attached to external surface of bone
What are the two steps in bone remodelling?
1- cutting cone - osteoclasts make a wide tunnel in the bone
2- closing cone - osteoblasts make a smaller tunnel of cortical bone
What factors effect bone stability?
- activity of osteocytes, osteoblasts + osteoclasts
- nutrition: vitamin D3, C, K + B12
How does the vitamin D3 affect bone stability?
Produces calcitriol - needed for calcium absorption
How does vitamin C affect bone stability
Synthesis of collagen
Osteoid - collagen I
How does do vitamin K and B12 affect bone stability?
Synthesis of bone proteins
How many bones are there in the body?
How is it spread between the two skeletons?
206
Axial - 80
Appendicular - 126
How are bones involved in acid base homeostasis?
Absorbs or releases alkaline salts to help regulate blood pH
Compare the structure of immature and mature bones
- immature: osteocytes in random arrangements
- mature: oestocytes arranged in concentric lamellae of osteons
Haversian canal vs Volkman canal
- Haversian canals run through osteons
- Volkmann’s canal connect Haversian canals
