Bone Formation and Development

Anatomy Unit 3 (chap 7) Quiz 2

Intramembranous bones

form between connective tissue layers

Endochondrial bones

start as hyaline cartilage and are replaced by bone

Intramembranous Ossification

• Occurs in flat bones of the skull

• Some cells within the connective tissue become osteoblasts (bone-forming cells)

• Osteoblasts start making spongy bone around them

  • When osteoblasts are surrounded by a bony matrix, they are called osteocytes (bone cells)

Endochondrial Ossification

• Hyaline cartilage in the center of the bone starts to break down

• The periosteum forms around the developing bone and osteoblasts from the periosteum start to form spongy bone in the center and compact bone around the perimeter

  • The epiphysis stays cartilaginous and

    continues to grow

    • Growth plate (epiphyseal plate)!

  • The cartilage is eventually digested away by osteoclasts (bone reabsorbing cells), leaving the medullary cavity within the new bone

Primary ossification center

The central region

articular cartilage and epiphyseal plates

Most bones have converted to bone by birth or shortly after except in two regions:

Articular cartilage

made of hyaline cartilage, lasts forever to reduce friction at the joints

• New cartilage forms as the old wears away

Epiphyseal plates

provides vertical growth during childhood; growth is controlled by hormones and the these are converted to bone at the end of adolescence

Factors that affect bone developments

• Nutrition

• Hormonal secretion

• Physical exercise

Vitamin D

necessary for proper absorption of calcium in the small intestines

• None of this = softening and deforming of bones (Rickets)

Growth hormones

stimulate cell division at growth plates

Physical exercise

pulls on muscular attachments to bones stressing it and stimulating thickening and strength

Greenstick fracture

incomplete; the break occurs on the convex surface of the bend in the bone

Fissured fracture

incomplete, longitudinal break

Comminuted fracture

complete and fragments the bone

Transverse fracture

complete; the break occurs at a right angle to the axis of the bone

Oblique fracture

occurs at an angle, other than a right angle, to the axis of the bone

Spiral fracture

caused by excessive twisting of a bone

Reduction

Realignment of broken bone ends; this is how fractures are treated

Closed reduction

bone coaxed back into normal position by physician (no opening of the skin via surgery)

Open reduction

surgical alignment using pins and wires to secure the ends of the bones

6-8 weeks

time it takes for the healing process for simple fractures

Over 6-8 weeks

healing time for larger bones and elderly bones

Hematoma

forms because vessels rupture when the bone breaks; bone cells that have no nutrients die

Tissue repair

Osteoblasts begin to form new spongy bone, granulation tissue develops (grows new capillaries), a soft fibrocartilage callus is formed, and dead tissue and clotted blood are disposed of by phagocytes and osteoclasts

• At the end of this stage, the callus contains cartilage matrix, bony matrix, and collagen fibers to splint the bone

Bony callus forms

Osteoblasts (immature bone cells) and osteoclasts (bone cells that reabsorb bones) move in and multiply, replacing the fibrocartilage with spongy bone (bony callus).

Bone remodeling

during the next few months, the bone is remodeled to form a patch at the site of the fracture.

Fontanels (fibrous membranes)

connect skull bones instead of sutures to allow the skull to be compressed during birth and to allow …*****