SKELETAL SYSTEM 2

• 2 TYPES OF BONE FORMATION PATTERN IN FETAL DEVELOPMENT

  1. Intramembranous ossification
  2. endochondral ossification
• bones form from pre-existing connective tissue membranes and happens at the fifth week of development in embryo

  intramembranous ossification
• Fontanels are areas of membrane that are not ossified at birth. have not yet ossified. usually closed at the age of 2.
• bones form a pre-existing cartilage model.

  Formation of cartilage ends at the end of the 4th week of embryonic development.

  Endochondral ossification
• 4 zones of the epiphyseal plate

  1. zone of resting cartilage
  2. zone of proliferation
  3. zone of hypertrophy
  4. zone of calcification
  5. closure of epiphyseal plate
• is nearest the epiphysis and contains slowly dividing chondrocytes.

  zone of resting cartilage
• chondrocytes in this zone produces new cartilage through interstitial cartilage growth.

  Chondrocytes then divide and form columns resembling a stack of plates or coins.

  zone of proliferation
• The chondrocytes produced in the zone of proliferation matures and enlarge.

  zone of hypertrophy
• is very thin and contains hypertrophied chondrocytes and calcified cartilage matrix.

  zone of calcification
• Hypertrophic chondrocytes die, and blood vessels from the diaphysis grow into areas.
• Bones stop growing once they achieve normal adult size because the epiphyseal plate has ossified and become the epiphyseal line.

  Happens approx. 12 and 25 years of age.

  closure of epiphyseal plate
• factors affecting bone growth

  1. genetic factors
  2. nutrition (vitamin d and c)
  3. hormones
• stimulates interstitial cartilage growth and appositional bone growth.

  growth hormone
• is required for normal growth of all tissues.

  a decrease in this hormone can result in a smaller individual.

  thyroid hormone
• Estrogen; females usually stop growing earlier because estrogen causes quicker closure of the epiphyseal plate than testosterone
• Estrogen and testosterone cause increased bone growth and stimulate closure of the epiphyseal plate.
• When a bone is fractured, the blood vessels in the bone surrounding the periosteum are damaged and hematoma forms.
• a localized mass of blood released from blood vessels but confined in an organ or space.

  hematoma
• is a mass of tissue that forms at a fracture site and connects broken ends of the bone.


  callus
• forms between the ends of the broken bone, as well as in the marrow cavity, If the fracture occurs in the diaphysis of a long bone.


  internal callus
• forms around the collar around the opposing ends of the bone fragments.


  external callus
• The internal and external calluses are ossified to become a woven spongy bone. through endochondral ossification.

  The result is a stronger external callus.

  callus ossification
• The woven bone is replaced to become a compact bone.


  bone remodeling