Biology 322 Human Anatomy Histology of the Skeletal System

Recall: SYSTEMS are composed of one or more organs, all serving a common function ORGANS are composed of one or more types of tissues, all serving a common function TISSUES are composed of one or more types of cells and their products, all serving a common function

Organs of skeletal system = Like all organs, these contain four types of tissue: However: Two types of specialized connective tissues predominate: each of which is surrounded by dense irregular connective tissue:

Two types of specialized connective tissue predominate:

Cartilage: Function

Cartilage: Also: Forms

Cartilage: Young cells = Actively forming new extracellular matrix Mature cells = Maintain and repair extracellular matrix Extracellular Matrix

Cartilage: Three types: All three types:

Hyaline Cartilage:

Elastic Cartilage:

Fibrous Cartilage:

Bone: Young cells = Actively forming new extracellular matrix Mature cells = Maintain and repair extracellular matrix Located in Third cell type = Reabsorb extracellular matrix

Bone tissue: Extracellular matrix: Fibers: Ground substance Bone tissue constantly remodeling itself:

Two forms of bone tissue:

Lamellar Bone:

Both trabecular and lamellar bone: Osteocytes have lost ability to divide so Osteoblasts at edges

Both trabecular and lamellar bone: Osteocytes have These extensions of osteocytes

Two types of bone formation ("osteogenesis") for growth, remodeling, and repair:

Bones (organs) grow by both intramembranous and endochondral osteogenesis: Average age (years) at completion of ossification: Scapula Clavicle Os coxa Vertebrae - 25 Sacrum Sternum - body manubrium Humerus, radius, ulna Femur, tibia, fibula

Bones repair fractures by both intramembranous and endochondral osteogenesis:

Bone tissue is constantly remodelling itself to adjust to different physical and biochemical demands placed upon it. Old bone is destroyed by osteoclasts and new bone is produced by osteoblasts and osteocytes. Example: If you have a cast on your arm, the bones will become smaller since they are not being stressed and more bone tissue is removed than is synthesized. But: When the cast is removed and the bones again subjected to stress, they will become larger again.

Bone remodelling regulated by many hormones: Growth hormone stimulated osteoblast activity & collagen synthesis Thyroid hormone stimulates osteoblast activity & collagen synthesis; stimulates formation of ossification centers Testosterone stimulates osteoblast activity & bone growth Progesterone stimulates osteoclast activity & bone loss Estrogen stimulates osteoblast activity & bone growth