Anatomy of Limbs 1 - Bones Flashcards
List the mechanical properties of bone
- Cable-like flexibility and resistance to tension (because the framework is collagen and other bone proteins = osteoid)
- Pillar-like stiffness and resistance to compression conferred by impregnation of collagen with crystalline mineral (hydroxyapatite - complex calcium hydroxyphosphate)
What are the two types of bone tissue?
- Lamellar (mature)
- Woven (immature - in adults only found in repairing fractures)
Describe the arrangement of lamellar bone
- Outer hard layer of compact lamellar bone (cortical bone)
- Inner layer of interlacing struts of lamellar bone; cancellous bone (also called spongy or trabercular bone)
What is the periosteum, and what is its function?
- The outer surface of bone
- Fibrous and cellular layer
- Key roles in growth and repair (osteoblasts can develop)
- Vascular
- Good sensory nerve supply
Describe the process of bone development
- The skeleton starts to form at 6 weeks of fetal life, and growth continues until age 25
- Ossification - laying down new bone material by osteoblasts
What are the two types of ossification?
- Intramembranous
- Endochondral
What is intramembranous ossification?
- In existing vascular connective tissue
- Bone matrix deposited around collagen
- Mineralises to form woven bone
- Remodels to lamellar bone
What is endochondrial ossification?
- Within existing fetal cartilage models
- Certilage calcifies and chondrocytes die
- Periosteal osteoclasts cut channels for sprouting vessels
- Osteoblasts enter with vessels to build bone around them
How is growth in long bones continued while walking?
- As we’re growing, long bones have to support large forces as we walk (grow until mid teens)
- Bone still has to continue to grow, becoming thicker and longer
- Articulation rubs at the surface of the bone ends (disrupting terminal appositional growth)
- Solution is the shaft ossifies first, and then the epiphyses. Growth continues by ossification at a cartilage plate between them, joining the epiphyseal plates together
- Growth stops when this plate is overrun by ossification
List age-related changes in the appearance of normal bones
- In a childs wrist, epiphyses ossify in 2nd year
- Epiphyseal plates remain carilagenous until growth ceases after puberty
- Therefore, ascertain the age on X ray - cartilage appears dark so can look like a break
Describe the adaptability of bone
- Can grow without compromising its support functions
- Increases or decreases bulk and density in response to pattern of use
- Can alter its external and internal shape in response to pattern of use (remodelling)
- Can repair when fractured
What are the keys to bone growth and remodelling?
- Bone has a large blood supply (cells are never far from nutrients and O2)
- Osteocytes maintain matrix but can activate osteoblasts for new bone building
- Osteoclasts are giant cells specialised for destruction of bone matrix
Describe the growth in bone diameter
- Apposition - addition to exterior surface of bone at periosteum
- Osteoblasts and osteoclasts create ridges and grooves on bone surface
- Blood vessels align in grooves
- Osteoblasts build new osteons around vessels
- Osteoclasts remove bone from endosteal surface
Describe the process of fracture healing
- Bleeding is an important part of the process (due to damaged blood vessel)
- Haematoma becomes infiltrated by fibrous matrix, and invaded by cartilage/bone progenitors
- Woven bone remodelled to mature lamellar bone
What happens when blood calcium levels are high?
- Calcitonin released by parafollicular thyroid cells
- Breakdown of bone matrix by osteoclasts is inhibited
- Uptake of calcium into bone matrix is promoted
What happens when blood calcium levels are low?
- PTH released by chief cells of the parathyroid gland
- Osteoclast bone resorption activity promoted
- Increases calcium re-absorption by the kidneys
List the functions of bone
- Support body shape
- System of levers for muscle action
- Protection of internal organs
- Site of blood cell formation
- Mineral storage pool
Describe the structure of the long bone
- Diaphysis (shaft) - thicker, denser, compact bone, hole in the centre where marrow is found
- Epiphysis (head) - spongy bone
- Articular cartilage (joint surface)
- Holes for vessels to enter and leave (nutrient foramen - bones have a rich blood supply)
Why is the mefullary cavity and trabeculae of bone important?
- Makes the bone lighter
- Space for marrow
What is an osteon?
- Column of bone with a central canal and concentric lamellae
- Present in the compact region of lamellar bone
How do osteocytes form?
- Osteogenic stem cell
- Osteoblast (forms bone matrix)
- Osteocyte (maintains bone tissue - highly branched)
Describe the structure of osteoclasts
Large cells with a ruffled border
