PowerPoint Presentation Hole’s Human Anatomy and Physiology, 9/e Shier, Butler, and Lewis

Skeletal System – Bone Growth

Bone Growth and Development Before six weeks of development the skeleton is cartilage. Osteogenesis is bone formation. Ossification is bone replacing existing tissue.  Calcification is the process of depositing calcium salts into tissues. 

Bone Growth and Development The skeletal system begins to form during the 8th week of prenatal development. Some bones originate within sheets of connective tissue (intramembranous bones). Some bones begin as models of hyaline cartilage that are replaced by bone (endochrondral bones).

Stages of Intramembranous Ossification

Stages of Intramembranous Ossification

Stages of Intramembranous Ossification

Stages of Intramembranous Ossification

Intramembranous Bones Broad, flat skull bones are intramembranous bones. During osteogenesis layers of primitive, connective tissue supplied with blood vessels appear at the site of future bone.

Intramembranous Bones Cells differentiate into osteoblasts (bone- building cells) which deposit spongy bone. Osteoblasts become osteocytes when surrounded by bony matrix in lacunae.

Intramembranous Bones Connective tissue on the surface of the bone forms the periosteum. Osteoblasts on the inside of the periosteum deposit compact bone over spongy bone. This process is called intramembranous ossification.

Endochondral Ossification

Endochondral Bones Begins in the second month of development Hyaline cartilage forms a model of the bone during embryonic development. Cartilage degenerates, periosteum forms. Periosteal blood vessels and osteoblasts invade the bone forming a primary ossification center in the diaphysis. Secondary ossification centers develop in the epiphyses.

Endochondral Bones Osteoblasts form spongy bone in the space occupied by cartilage. Osteoblasts become osteocytes when bony matrix surrounds them.

Endochondral Bones Osteoblasts beneath the periosteum deposit compact bone around spongy bone. A band of cartilage remains between the diaphysis and epiphyses as the epiphyseal disk.

Endochondral Bones Growth of long bones occurs along four layers of cartilage in the epiphyseal disk. First Layer: resting cells that do not grow. Second Layer: young mitotic cells. Third Layer: older cells that enlarge. Fourth Layer: dead cells and calcified intercellular substances.

Growth in Bone Width

Growth in Bone Width

Growth in Bone Width

Blood and Lymphatic Supply

Bone Homeostasis After bone formation, osteoclasts and osteoblasts continue to remodel the bone. Resorption and deposition are regulated to keep bone mass constant.

Nutrition and Bone Development Vitamin D is necessary to absorb calcium in the small intestine. Vitamin D deficiency leads in rickets in children and osteomalacia in adults.

Nutrition and Bone Development Vitamin A is necessary for osteoblast and osteoclast activity. Vitamin C is necessary for collagen synthesis.

Hormones and Bone Growth Hormone (GH) stimulates epiphyseal cartilage cell division. Deficiency of GH: pituitary dwarfism. Excess GH: pituitary gigantism in children and acromegaly in adults.

Hormones and Bone Thyroid hormone stimulates cartilage replacement in the epiphyseal disks. Sex steroids promote formation of bone tissue close the epiphyseal disk.

Physical Factors Affecting Bone Physical stress stimulates bone growth. Weight bearing exercise stimulates bone tissue to thicken and strengthen (hypertrophy). Lack of exercise leads to bone wasting (atrophy).

Life-Span Changes Calcium levels fall through life and the skeleton loses strength. Osteoclasts outnumber osteoblasts.

Life-Span Changes By age 35, everyone loses bone mass. Women lose bone mass faster between menopause and age seventy. Trabecular bone is lost before compact bone.