Lecture 9
Skeletal System
T. Irving 01/07/97; revised A.Howard 02/14/00

Goals of this section

1. Describe the structure of a long bone and its growth and development
2. List at least 4 structures of the skeleton
3. List and state a function for the major bones of the axial skeleton
4. List and state a function for the bones of the appendicular skeleton
5. Classify joints and give an example of each type

Skeleton

• Bone is a living tissue
• Bones start off collagenous
• Differentiates into compact bone and spongy bone
• Spaces in spongy bone contain red bone marrow (blood cell production)
• Long bones contain yellow bone marrow (fat storage)

Cells in the skeletal system

• Bone produced from cells called osteoblasts
• Osteoblasts get isolated in lacunae arranged around Haversian Canals and are then called osteocytes
• Haversian canals contain blood vessels and nerves
• Matrix consists of collagen plus phosphorus and Ca salts
• Bones constantly being built up and torn down in adults:
• Osteoclasts "eat" bone
• Osteoblasts build up

Skeleton has 6 functions

1. Support body against gravity
2. Protect soft body parts
3. Produce blood cells
4. Store phosphorous and Ca²⁺
5. Provide sites for muscle attachment
6. Permit flexible body movements

Segments of the Skeleton:

• Axial skeleton: skull, ribs, sternum, vertebrae
• Appendicular skeleton: Pectoral and pelvic girdles and appendages
  

Skull

• Cranium composed of 8 bones joined tightly together in adults by fibrous joints
• In infants. some bones not fully formed, fuse by about 16 months
• There are an additional 11 bones that form the face and jaw.
• Jaw is called the mandible

Vertebral Column (backbone)

• Extends from the skull to the pelvis
• Not straight but curved - strength and resiliency
• Form a canal down the middle where the spinal cord passes
• Disks of connective tissue are interleaved between vertebrae
• Absorbs shock of walking running etc.
• Allows motion between vertebrae so we can bend and twist etc.

Ribs

• Join thoracic vertebrae at the back
• All but two pairs of them join the sternum at the front by way of cartilage
• Flexibility
• The last two pair are "floating"
• Men & women have same number of ribs

Joints

• Fibrous joints - join plates in skull - immovable
• Cartilaginous joints - between vertebrae and the pelvis are slightly movable
• Most joints are freely movable synovial joints
  • Bones held together by ligaments forming an opening or capsule
  • Joint capsule lined by synovial membrane which produces synovial fluid
  • Lubricates the joint
  • May also contain bursa or fluid filled sacs
  • pieces of cartilage called menisci
  • Hinge joints
    • e.g. knee and elbow
    • Allow motion in one direction
  • Ball and socket joints
    • e.g. femur to hipbone and humerus to scapula
    • Allow motion in all directions

 Arthritis

• Synovial joints may get arthritis
• Rheumatoid arthritis results in inflammation of synovial membrane;
  Appears to be an autoimmune reaction
• Osteoarthritis
  • Normal complaint of old-age
  • Cartilage at end of bones deteriorates so that rough ends of bone come in contact