HAP Unit 4: The Skeletal System

The Skeletal System

• The skeletal system consists of bones, joints, cartilages, and ligaments.
• Functions of the skeletal system:
  • Support of the body
  • Protection of soft organs
  • Movement due to attached skeletal muscles
  • Storage of minerals and fats
  • Blood cell formation

Bones of the Human Body

• The adult skeleton has 206 bones.
• There are two basic types of bone tissue:
  • Compact bone (homogeneous, found in shafts of long bones)
  • Spongy bone (small, needle-like pieces of bone with open spaces, found in ends of long bones)

Classification of Bones

• Based on shape:
  • Long bones (e.g. femur, humerus)
  • Short bones (e.g. carpals, tarsals)
  • Flat bones (e.g. skull, ribs, sternum)
  • Irregular bones (e.g. vertebrae, hip)

Gross Anatomy of a Long Bone

• Diaphysis (shaft) composed of compact bone
• Epiphysis (ends) composed mostly of spongy bone
• Periosteum (outside covering of diaphysis) is a fibrous connective tissue membrane
• Sharpey's fibers secure periosteum to underlying bone
• Arteries supply bone cells with nutrients
• Articular cartilage covers the external surface of epiphyses
• Medullary cavity (cavity of the shaft) contains yellow marrow (mostly fat) in adults and red marrow (for blood cell formation) in infants

Bone Markings

• Surface features of bones:
  • Projections and processes (grow out from the bone surface)
  • Depressions or cavities (indentations)
• Sites of attachments for muscles, tendons, and ligaments
• Passages for nerves and blood vessels

Microscopic Anatomy of Bone

• Osteon (Haversian system) is a unit of bone
• Central (Haversian) canal carries blood vessels and nerves
• Perforating (Volkman's) canal is a canal perpendicular to the central canal, carrying blood vessels and nerves

Changes in the Human Skeleton

• In embryos, the skeleton is primarily hyaline cartilage
• During development, much of this cartilage is replaced by bone
• Cartilage remains in isolated areas (e.g. bridge of the nose, parts of ribs, joints)

Bone Growth

• Epiphyseal plates allow for growth of long bones during childhood
• New cartilage is continuously formed, and older cartilage becomes ossified
• Bones are remodeled and lengthened until growth stops

Types of Bone Cells

• Osteocytes (mature bone cells)
• Osteoblasts (bone-forming cells)
• Osteoclasts (bone-destroying cells, break down bone matrix for remodeling and release of calcium)

Bone Fractures

• A break in a bone
• Types of bone fractures:
  • Closed (simple) fracture – break that does not penetrate the skin
  • Open (compound) fracture – broken bone penetrates through the skin
• Treatment of bone fractures involves reduction and immobilization

The Axial Skeleton

• Forms the longitudinal part of the body
• Divided into three parts:
  • Skull
  • Vertebral column
  • Bony thorax

The Skull

• Two sets of bones:
  • Cranium
  • Facial bones
• Bones are joined by sutures
• Only the mandible is attached by a freely movable joint

The Vertebral Column

• Vertebrae separated by intervertebral discs
• The spine has a normal curvature
• Each vertebrae is given a name according to its location

The Bony Thorax

• Forms a cage to protect major organs
• Made-up of three parts:
  • Sternum
  • Ribs
  • Thoracic vertebrae

The Appendicular Skeleton

• Limbs (appendages)
• Pectoral girdle
• Pelvic girdle

The Pectoral (Shoulder) Girdle

• Composed of two bones:
  • Clavicle (collarbone)
  • Scapula (shoulder blade)
• These bones allow the upper limb to have exceptionally free movement

The Pelvis

• Hipbones
• Composed of three pair of fused bones:
  • Ilium
  • Ischium
  • Pubic bone
• The total weight of the upper body rests on the pelvis
• Protects several organs (e.g. reproductive organs, urinary bladder, part of the large intestine)

Joints

• Articulations of bones
• Functions of joints:
  • Hold bones together
  • Allow for mobility
• Classified functionally:
  • Synarthroses (immovable joints)
  • Amphiarthroses (slightly moveable joints)
  • Diarthroses (freely moveable joints)
• Classified structurally:
  • Fibrous joints
  • Cartilaginous joints
  • Synovial joints