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Explore the composition of organs and tissues in the skeletal system, focusing on cartilage and bone, along with the process of bone remodeling. Discover how bones repair fractures and adapt to physical demands. Learn about hormonal regulation of bone remodeling.
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Biology 322Human 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:
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:
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:
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 - 18-20 Clavicle - 23-31 Os coxa - 18-23 Vertebrae - 25 Sacrum - 23-25 Sternum - body - 23-25 - manubrium - 30-35 Humerus, radius, ulna - 17-20 Femur, tibia, fibula - 18-22
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