Musculoskeletal system
Functions of the skeletal system
Support
Protection
Movement assistance
Mineral homeostasis
Blood cell production
Red bone marrow
Haemopoiesis: produces RBC, WBC, and platelets
In a newborn all bone marrow is red
Made of adipocytes, macrophages and fibroblasts
Most bone marrow close to the axial skeleton is red
Calcium and phosphorus reserve
Needed for conduction and muscle contraction
Need P for ATP and cell membranes etc
Muscles attach to musculoskeletal system
joints between bones allow movement, because the muscles pull on the joints
Structure of a bone
Epiphysis
Metaphysis
Diaphysis
The ends of a bone: top=proximal, bottom=distal
covered in articular cartillage- needs support with plates of compact bone at the edge before the cartillage
Made of spongy bone, contains red bone marrow
Inbetween section
Apply pressure outwards when pressure is applied to bone
Middle section of bone
Doesn't need support, but needs a thick wall
Tension/compression run parallel to the wall of the bone (run vertical)
Endosteum lines internal surfaces
Made of compact bone
has nutrient blood vessels running through it
Still spongy bone but fuses with compact bone of diaphysis
Little holes on the surface of the bone are nutrient foramen and allow blood vessels to run in/out of bone
Spongey bone has trabeculae- spider-web folds that are covered in endosteum
Where there is cartillage, there is no periosteum
Bone wall
Endosteum
Compact bone between endosteum and periosteum
Periosteum
Thin, fibrous layer lining internal cavity
Fibrous sheath surrounding bone
medullary cavity
Space in the middle, in the epiphysis= red bone marrow, in the diaphysis= yellow bone marrow
Bone cells
Osteoprogenitor / osteogenic cell
Osteoblast
Osteocyte
Osteoclast
Unspecialised bone stem cells
Bone building cells, synthesize collagen fibres + things for extracellular matrix of bone
Found: within lacunae in bone- communicate with neighbour cells through canaliculi
Very big, formed by fusion of monocytes, have a ruffled boarder
Found: bone surface, periosteum, endosteum, central canals of compact bone
Normally dormant, supply developing bone with bone-forming cells
Made from osteogenic cells and become osteocytes in the extracellular matrix
Found: under periosteum or endosteum
When they are present = active
Bone tissue maintenance, exchange nutrients and waste with blood, maintain extracellular matrix
Main bone tissue cells
Found in places where bone resorption (breakdown of bone ex matrix) occurs
Secrete acid and enzymes, dissolves mineral and organic parts of bone
Compact bone tissue
Strongest form of bone tissue
found beneath the periosteum
bulk of diaphysis
Composed of osteons
each osteon is a concentric lamellae arranged around a central canal
Concentric lamellae: circular plates of mineralised extracellular matrix, surrounding small blood vessels and nerves in the central canal
Collagen fibres (Type I)
Thickest and strongest form of collagen
Bad at resisting compression, but
good at resisting tension
Primary osteons: formed around an existing blood vessel on bone surface when the bone is growing and laying new bone tissue
1) osteoblasts in the active periosteum put down new bone, forming ridges
2) bone grows and ridges fuse to form a tunnel around the blood vessel, and line the tunnel with endosteum
3) osteoblasts in the endosteum build concentric lamellae onto the tunnel walls, filling it in
4) bone keeps growing outwards as the osteoblasts in the periosteum build new circumferential lamellae
Secondary osteons: created inside existing bone
1) osteoclasts bore their way through existing bone (cutting cone area) and create a tunnel through the bone
2) osteoblasts move in and line the tunnel wall, forming a new active endosteum and depositing osteoid (organic matrix) onto tunnel walls. The osteoid layer is hardened forming lamella, and a blood vessel can grow in the tunnel
3) osteoblasts deposit many layers of concentric lamellae onto tunnel walls, filling it in. Some osteoblasts get trapped and become osteocytes
Lamellae are thin layer tissue plates
4) tunnel is reduced to Haversian canal size, and the osteoblasts die or become osteogenic cells
Synovial joints
Articular cartilage
Protects ends of bones that make the joint
Chondorcytes: nourished only by diffusion, build and maintain cartilage live in lacunae
specialised hyaline cartilage
PG (proteoglycan) content increases from surface zone to deep zone, and then back to low in the calcified cartillage
Articular capsule
Fibrous layer
Synovial membrane
Surrounds synovial joint, connecting the ends of the bones in the joint
Must be loose to allow the joint to move, but tight enough to protect against too much movement
dense irregular and regular connective tissue
loose connective tissue with elastic fibres
made of interlacing bundles of white collagen fibres
Badly vascular, very innervated (has nerves, hence pain when sprains happen)
Synovial fluid
viscous, lookes like egg whites
redues friction. absorbs shocks, supplies oxygen and nutrients