Support and Movement

Chapter 38

Skeletal system

– Supports and protects the body

– Transmits mechanical forces generated by muscles

• Endoskeletons

– Chordates (Vertebrate)– Internal skeleton that can grow– Consists of calcium-impregnated tissue

• Cartilage• Bone

FunctionThe integrated action of joints, bones, and skeletal muscles

produces obvious movements such as walking and running.The main functions of the Musculoskeletal system are:• Provides support and shape of the body.• Makes blood cells (bone marrow).• Stores nutrients include calcium, phosphorus and other

minerals .• Movement, voluntary.• Protection for vital organs such as the brain, heart and

lungs.

Axial & appendicular skeleton

Axial & appendicular skeleton

Three special types of cells• OSTEOCLASTS are responsible for bone resorption (breaking

down). They come from the bone marrow. Break down bone• OSTEOBLASTS are bone forming cells. They come from the

bone marrow. Produce bone. • They produce the matrix collagen& other protein. • They control calcium and mineral deposition. • Found on the surface of the new bone. • OSTEOCYTES mature bone cells. Come from osteoblasts. • Some of the osteoblasts turn into osteocytes then osteocytes get

surrounded by new bone.

Osteoblast Osteoblast

Osteocyte Osteocyte

Osteoclast Osteoclast

• Long bone

– Thin outer shell of compact bone

– Inner spongy bone

– Central cavity with bone marrow

Typical long bone

Structure of a Typical Long BoneParts of the long bone:• Periosteum: outside layer of white fibers(ct) around the

bone, which is capable of producing fresh layer of bone.• Diaphysis: long bone shaft. • Epiphysis: ends between the growth plate and the nearest

joint • Metaphysis: in children, disk of cartilage between the

epiphysis and the diaphysis, this is where most of the bone growth is taking place.

• Bone marrow: fat in a central cavity (yellow).• Articular cartilage: joints.

• Endochondral bone formation

• Long bones– Develop from cartilage templates

• Intramembranous bone Development

– Develop from a noncartilage connective tissue model

Bone Growth: Two Ways During childhood, bones form.

A process stimulated by growth hormone, to lengthen. 

• In adult bones continue to grow in density& thickness.

• 1- Intramembranous bone development:

• Flat bones develop from a non-cartilage.

• From connective tissue.

• E.g. skull bones.

Endochondral bone development

• Long bone is formed, in a process called an endochondral ossification, where cartilage is replaced by bone :

• 10 ossification center: in the center of diaphysis there is a collar of periosteum, part with a bone marrow cavity within it.

• 20 ossification center: on both ends of the shaft there is cartilagenous discs, that cartilage which will later be formed into the epiphysis.

Joints• The bones join together to form

joints or articulations.

• The end of each bone is covered by a tough, smooth shiny substance called cartilage.

• The cartilage-coated bone-ends are kept apart by a thin film of fluid that lubricates the joints.