Skeletal System

dynamic tissue

continually being formed and brocken down

Two subdivisions of the skeleton

axial: central

appendicular: arms+legs

Compact bone

cortical “solid bone”

Spongy bone

cancellous/trebecular “holey”

spaces contain RBM

no osteon but include lacunae (osteocytes inside) and canaliculae

Bone Function

Support

Protection

Motion

Mineral Homeostasis

Blood Cell Production: hemopoiesis in RBM

Triglyceride Storage: energy storage in YBM

Types of bones

Long Bone

Short Bone

Flat Bone

Irregular Bone

Diaphysis

medullary cavity contains YBM

Epiphysis

distal and proximal ends

Metaphysis

Neck of bone

Articular cartilage

Hyaline, covers epiphysis, repair minimal, friction

Periosteum (gurth)

Outside covering, forms new bone thickness/diameter only, protection, nourish, attachment; Sharpey Fibers, secure periosteum to bone

Medullary Cavity

Hollow cylinder of diaphysis; fatty YBM adults (contains RBM in infants)

Endosteum

Thin membrane that lines medullary cavity; single layer of bone forming cells

central/ haversian canal

blood vessels, nerves, lymphatics (up and down)

volksman canal

perforating canals connect with those of medullary cavity (right to left)

concentric lamellae

(tree) rings; layers of hard calcified matrix

lacunae

lakes containing osteocytes

canaliculae

radiating from lacunae (little canals)

finger-like proj from osteocytes, connect all bone cells to a nutrient supply

diffusion is slow so canal system vital to pass nutrients, oxygen to osteocytes and carry waste away

Ossification

bone formation

begins with osteogenic cells from mesenchyme

remodel and repair

resorption by osteoclasts and deposition by osteoblasts

Blood Calcium functions

muscle contraction

nerve stimulation/conduction

blood clotting

bone density: Wolff’s Law; increase stress to bone leads to increased osteoblast bone deposition

Calcium Homeostasis

negative feedback loops:

parathyroid hormone: if blood Ca+2 decreases, stimulates increased osteoclasts activity and decreased loss of Ca+2 in urine; leads to increased Ca+2 blood

calcitonin: causes decreased osteoclast activity and increased -blast and -cyte; grab calcium out of blood and deposits as bone

comminuted

bone breaks into many fragments

compression

bone is crushed

depressed

broken bone portion is pressed inward

impacted

broken bone ends are forced into each other

spiral

ragged break occurs when excessive twisting forces are applied to a bone

greenstick

bone breaks incompletely, much in the way a green twig breaks

parathyroid hormones

secreted by the parathyroid glands; promotes bone resorption by osteoclasts; enhances recovery of calcium from urine; promotes formation of the active form of vitamin D

Calcitonin

Secreted by the thyroid gland; inhibits bone resorption by osteoclasts