Skull, thorax, and vertebral column

80 Bones

Form Longitudinal Axis of Body

Bones of limbs and girdles that attach them

to the axial skeleton

126 bones

Support

Storage of Minerals (calcium and phosphate, most abundant minerals in body, approx. 2-4 lbs.)

98% stored in bones

Blood cell production (all formed elements of blood)

Protection (organs and delicate tissue surrounded by bone)

Leverage (acts as levers with skeletal muscle to move body)

Flat bones- Thin, roughly parallel bones

Sutural Bones- Wormian- Irregular Bones formed between  cranial bones)

Long Bones - Relatively long and slender, limb bones

Irregular bones- complex shapes, vertebrae, pelvic bones, facial bones.

Sesamoid bones- Small, flat, shaped like a sesame seed. Developed in tendons of hands, knees, and feet.

Short bones- Small and boxy (wrist bones)

Also known as bone markings

External and internal features related to functions

Elevations/projections for ligament and tendon attachment

Depressions/grooves/tunnels for blood vessels or nerves to lie alongside or penetrate

Tubercle- Small rounded projection

Tuberosity- Small, rough projection; may occupy broad area.

Long Bone Features

Epiphysis (expanded ends)

Mostly spongy bone (trabecular bone)

-Network of struts and plates

-Resists forces from various directions, directs body weight to diaphysis and joints.

Outer covering of compact bone (strong, organized bone)

Articular cartilage- Avascular, recieves resources from synovial fluid

-Covers portions of epiphysis that forms articulations

Metaphysis-connects epiphysis to shaft

Diaphysis (shaft)- contains medullary cavity filled with marrow

-Red bone marrow (red blood cell production)

-Yellow bone marrow (adipose storage)

Bone growth and maintenance requires extensive blood supply.

-Nutrient artery/vein (one per bone) 

Has nutrient foramen (tunnel providing access to marrow cavity)

-Metaphyseal artery/vein

Carries blood to and from metaphysis, connects to epiphyseal arteries/veins

Osteocytes

Mature bone cells that cannot divide

Most numerous bone cell type

Maintain protein and mineral content of adjacent matrix

-Dissolve matrix to release minerals

-Rebuild matrix to deposit minerals

Occupy lacunae

-Seperated by layers of matrix (lamellae)

-Connected with canaliculi

Osteoblasts (blast, precursor)

-Produce new bony matrix (osteogenesis, ossification)

Begins with release of proteins and other organic compounds to produce unmineralized matrix (osteoid)

Then assists in depositing calcium salts to convert osteoid to bone

Become osteocytes once surrounded by bony matrix

Osteoprogenitor cells

Mesenchymal (stem) cells that differentiate to become osteoblasts

Important in fracture repair

Locations-

Inner lining of periosteum

Lining endosteum in medullar cavity

Lining passageways containing blood vessels

Osteoclasts (clast, break)

Remove/remodel bone matrix

Giant cells w/ 50+ nuclei, derived from same stem cells as macrophages

Release acids and proteolytic enzymes to dissolve matrix and release stored minerals (Osteolysis, loosening)

Collagen fibers account for approx 1/3 bone weight, calcium phosphate accounts for 2/3 bone weight

Calcium phosphate interacts with calcium hydroxide to form crystals of hydroxyapatite, which provides bone strength

Functional unit is osteon

Organized concentric lamellae around a central canal

-Osteocytes(in lacunae) lie between lamellae

-Central canal contains small blood vessels

Canaliculae connect lacunae with each other and central canal

-Strong along its length

Periosteum (outermost layer) 

Compact bone (outer bone tissue layer)

Circumferential lamellae (Outer and inner surfaces of compact bone)

Interstitial lamellae

-Fills spaces between osteons

Osteons

-Contain central canals(Parallel to bone structure)

-Connected by perforating canals(Perpendicular)

Spongy bone (innermost layer)

-Located where bones are not heavily stressed

-Lamellae form struts and plates (trabeculae)creating an open network (creates open network, reduces bone weight, no blood vessels in matrix, recieve nutrients through canaliculi open to trabeculae surfaces)

Two layers

-Two layers, Fibrous outer layer and cellular inner layer

Functions:

Isolates bone from surrounding tissue

Route for blood and nerve supply

Actively participate in bone growth and repair

Perforating fibers

Created by osteoblasts in periosteum cellular layer

Strongly connects tendons, ligaments, and joint capsules to bone through periosteum

Incomplete cellular layer lining medullar cavity

Covers spongy bone and lining central canals

Consists of simple layer of osteoprogenitor cells

Where incomplete, osteoclasts and osteoblasts remodel matrix

Increases bone diameter but does not form original bones

Osteoprogenitor cells differentiate into osteoblasts that add bone matrix under periosteum, adds successive layers of circumferential lamellae. Trapped osteoblasts become osteocytes

Deeper lamellae is recycled and replaced by osteons

Osteoclasts remove matrix at inner surface to enlarge medullar cavity.