Skeletal System

Macroscopic Features

Diaphysis: Mid part of the bone.

Epiphysis: Each end of a long bone. Usually part of the joint between that bone and others.

Compact bone: Found on the outside. Very strong and dense.

Spongy bone: Found inside the bone. Very porous and light.

Red Marrow: Found in most bones of young, only found in the pelvis and sternum of adult humans. Makes blood.

Yellow Marrow: High content of adipocytes. Stores energy in the form of fat.

Periosteum: Connective tissue sheath that helps nourish and repair the bone.

Microscopic Features
Osteocytes: Bone cells
  • Osteoclasts: Osteocytes that have differentiated into cells that dissolve calcium salts (Bone eaters).
  • Osteoblasts: Osteocytes that have differentiated into cells that lay down calcium salts (Bone makers).

Lacunae: Small pits that bone cells wall themselves into (the center of the concentric rings in the picture to the right)

Canaliculi: Small channels through the bone matrix through which osteocytes link to each other and blood supply.

Long Bone Growth
1) The bone starts as a cartilage model.
2) A primary ossification center appears in the diaphysis of the bone. This is an area of active osteoblasts laying down bone.
3) Secondary ossification centers appear in both epiphyses.
4) These ossification centers grow until they meet and a small line of cartilage remains called the epiphyseal plate.
5) The remaining growth of the diaphysis occurs at the epiphyseal plate.
6) The bone is done growing when these plates are ossified.

Injury and Repair

1) A broken bone usually will break blood vessels causing a hematoma (bleeding around the injury).
2) A sort of blood clot (known as a callus) forms to stabilize the bone and bone fragments.
3) Osteoblasts work to regrow bone.
4) Osteoclasts breakdown the various bone fragments that are out of place.
5) The bone will usually have a thickening (bump) at the site of injury. This serves as reinforcement to protect the bone from a similar future injury.
6) Over many years, osteoclasts will slowly dissolve this thickening down if the area is unstressed.

Types of Movement

Refer to Text Pg. 152


Types of Joints

Hinge (elbow, knee) 1 degree of freedom (usually extension/flexion).

Saddle Joint (base of thumb) 2 degrees of freedom.

Ball-and-socket (shoulder, hip) allows rotation and circumduction.

Suture (plates of bone in the skull) allow little to no movement.