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