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What are the functions of the skeletal system?
- 1. Support: structural support for entire body by providing framework for attachment of other tissues
- 2. Storage of minerals and lipids: 99% of the body's Ca2+ is stored in bones, yellow bone marrow are stores of lipids
- 3. Blood cell production: RBC and WBC are produced in red bone marrow
- 4. Protection: surrounds soft tissues and organs (ribs protect the heart and lungs)
- 5. Leverage: bones act as levers that change the magnitude and direction of forces generated by skeletal muscles
What is bone tissue made up of?
- 1.Bone tissue is supporting connective tissue
- 2. Matrix: collagen fibers and calcium salts
- 3. Cells: Osteocytes, osteoblasts, osteoprogenitors, and osteoclasts
What are the 4 types of cells found in bone tissue?
- 1. Osteoprogenitor cells: mesenchymal cells that divide to produce daughter cells that differentiate into osteoblasts, found in cellular layer of periosteum or in the endosteum
- 2. Osteoblasts: produce new bone matrix through ossification, mature into osteocytes
- 3. Osteocytes: mature osteoblasts that live in lacuna, have cytoplasmic extensions that travel through canaliculi to communicate with other osteocytes
- 4. Osteoclasts: remove and recycle bone matrix, large cells with 50+ nuclei
What are the membranes that cover bones and what are their functions?
- 1. Periosteum: wraps around the outside of the bone, has a fibrous superficial layer and a cellular deep layer, isolates bone from surrounding tissues, provides route for nervous and circulatory supply, participates in bone regrowth and repair
- 2. Endosteum: Incomplete cellular layer that lines the medullary cavity of the bone, consists of a simple flattened layer of osteoprogenitor cells
How is compact bone constructed?
- 1. Osteon: basic functional unit, osteocytes are arranged in concentric circles around a central canal
- 2. Collagen fibers: form a spiral that adds strength and resiliency
- 3. Interstitial lamellae: fills the space between osteons
How is spongy bone constructed?
- 1.Trabeculae: network of supporting bundles of fibers, no capillaries, nutrients reach the osteocytes by diffusion through canaliculi
- 2. Red bone marrow: blood cell formation
- 3. Yellow bone marrow: adipose tissue
What are the differences between compact and spongy bone?
- 1. Compact bone: located in the diaphysis, osteons are aligned the same, parallel to the bone shaft, very strong along the axis of alignment
- 2. Spongy bone: located in the epiphysis where bones are not heavily stressed/stress arrives from many directions, much lighter than compact bone
What are the 3 methods for bone growth?
- 1. Endochondrial Ossification: Hyaline cartilage converts to bone during development, epiphyseal cartilage continues to allow bone growth through puberty until ostoblasts produce bone tissue faster than chodroblasts produce cartilage tissue, creates epiphyseal line in adult bones
- 2. Appositional growth: Bones get thicker/increase in diameter
- 3. Intramembranous ossification: dermal tissue (cutaneous membrane) converts to form flat bones of the skull, mandible and clavicle
How are nerves and blood delivered to bone tissue?
- 1. Nutrient artery and vein: blood vessels that supply the diaphysis, enter bone through nutrient foramina, form canals and extend along shaft into osteons
- 2. Metaphyseal vessels: supply blood to inner (diaphyseal) surface of epiphyseal cartilage, where that cartilage is being replaced by bones
- 3. Periosteal vessels: blood vessels from the periosteum provide blood to superficial osteons of the shaft
What are the factors that increase the density of the bone?
- 1. Exercise!: when bone is stressed, mineral crystals generate electrical field that attracts osteoblasts to stimulate bone healing, heavily stressed bones become thicker and stronger
- 2. Hormones: calcitonin and PTH/calcitriol have oppositional effects to maintain bone homeostasis, GH stimulates protein synthesis and cell growth, at puberty sex hormones stimulate osteoblasts
- 3. Nutrients: Vitamin C required for collagen synthesis, Vitamin D3, Vitamin A stimulates osteoblast activity, Vitamin K and Vitamin B12 for synthesis of protein in normal bone