The Skeletal System Skeletal system includes: Skeletal system includes: –bones of the skeleton –cartilages, ligaments, and connective tissues.

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Functions of the Skeletal System 4. Blood cell production (red marrow) 5. Protection 6. Leverage (force of motion)

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The Skeletal System Skeletal system includes: Skeletal system includes: bones of the skeleton cartilages, ligaments, and connective tissues Functions of the Skeletal System 1. Support 2. Storage of minerals (calcium) 3. Storage of lipids (yellow marrow) Functions of the Skeletal System 4. Blood cell production (red marrow) 5. Protection 6. Leverage (force of motion) Classification of Bones Bone are identified by: Bone are identified by: shape internal tissues bone markings Bone Shapes 1. Long bones 2. Flat bones 3. Sutural bones 4. Irregular bones 5. Short bones 6. Sesamoid bones Long Bones Figure 61a Long Bones Are long and thin Are long and thin Are found in arms, legs, hands, feet, fingers, and toes Are found in arms, legs, hands, feet, fingers, and toes Flat Bones Figure 61b Flat Bones Are thin with parallel surfaces Are thin with parallel surfaces Are found in the skull, sternum, ribs, and scapula Are found in the skull, sternum, ribs, and scapula Sutural Bones Figure 61c Sutural Bones Are small, irregular bones Are small, irregular bones Are found between the flat bones of the skull Are found between the flat bones of the skull Irregular Bones Figure 61d Irregular Bones Have complex shapes Have complex shapes Examples: Examples: spinal vertebrae pelvic bones Short Bones Figure 61e Short Bones Are small and thick Are small and thick Examples: Examples: ankle wrist bones Sesamoid Bones Figure 61f Sesamoid Bones Are small and flat Are small and flat Develop inside tendons near joints of knees, hands, and feet Develop inside tendons near joints of knees, hands, and feet Bone Markings Depressions or grooves: Depressions or grooves: along bone surface Projections: Projections: where tendons and ligaments attach at articulations with other bones Tunnels: Tunnels: where blood and nerves enter bone Bone Markings Table 61 (2 of 2) Long Bones The femur The femur Figure 62a Long Bones Diaphysis: Diaphysis: the shaft Epiphysis: Epiphysis: wide part at each end articulation with other bones Metaphysis: Metaphysis: where diaphysis and epiphysis meet The Diaphysis A heavy wall of compact bone, or dense bone A heavy wall of compact bone, or dense bone A central space called marrow cavity A central space called marrow cavity The Epiphysis Mostly spongy (cancellous) bone Mostly spongy (cancellous) bone Covered with compact bone (cortex) Covered with compact bone (cortex) Flat Bones The parietal bone of the skull The parietal bone of the skull Figure 62b Flat Bones Resembles a sandwich of spongy bone Resembles a sandwich of spongy bone Between 2 layers of compact bone Between 2 layers of compact bone Bone (Osseous) Tissue Dense, supportive connective tissue Dense, supportive connective tissue Contains specialized cells Contains specialized cells Produces solid matrix of calcium salt deposits Produces solid matrix of calcium salt deposits Around collagen fibers Around collagen fibers Characteristics of Bone Tissue Dense matrix, containing: Dense matrix, containing: deposits of calcium salts bone cells within lacunae organized around blood vessels Characteristics of Bone Tissue Canaliculi: Canaliculi: form pathways for blood vessels exchange nutrients and wastes Characteristics of Bone Tissue Periosteum: Periosteum: covers outer surfaces of bones consist of outer fibrous and inner cellular layers Matrix Minerals 2/3 of bone matrix is calcium phosphate, Ca 3 (PO 4 ) 2 : 2/3 of bone matrix is calcium phosphate, Ca 3 (PO 4 ) 2 : reacts with calcium hydroxide, Ca(OH) 2 to form crystals of hydroxyapatite, Ca 10 (PO 4 ) 6 (OH) 2 which incorporates other calcium salts and ions Matrix Proteins 1/3 of bone matrix is protein fibers (collagen) 1/3 of bone matrix is protein fibers (collagen) Bone Cells Make up only 2% of bone mass: Make up only 2% of bone mass: osteocytes osteoblasts osteoprogenitor cells osteoclasts Osteocytes Mature bone cells that maintain the bone matrix Mature bone cells that maintain the bone matrix Figure 63 (1 of 4) Osteocytes Live in lacunae Live in lacunae Are between layers (lamellae) of matrix Are between layers (lamellae) of matrix Connect by cytoplasmic extensions through canaliculi in lamellae Connect by cytoplasmic extensions through canaliculi in lamellae Do not divide Do not divide Osteocyte Functions To maintain protein and mineral content of matrix To maintain protein and mineral content of matrix To help repair damaged bone To help repair damaged bone Osteoblasts Immature bone cells that secrete matrix compounds (osteogenesis) Immature bone cells that secrete matrix compounds (osteogenesis) Figure 63 (2 of 4) Osteoid Matrix produced by osteoblasts, but not yet calcified to form bone Matrix produced by osteoblasts, but not yet calcified to form bone Osteoblasts surrounded by bone become osteocytes Osteoblasts surrounded by bone become osteocytes Osteoprogenitor Cells Mesenchymal stem cells that divide to produce osteoblasts Mesenchymal stem cells that divide to produce osteoblasts Figure 63 (3 of 4) Osteoprogenitor Cells Are located in inner, cellular layer of periosteum (endosteum) Are located in inner, cellular layer of periosteum (endosteum) Assist in fracture repair Assist in fracture repair Osteoclasts Secrete acids and protein-digesting enzymes Secrete acids and protein-digesting enzymes Figure 63 (4 of 4) Osteoclasts Giant, mutlinucleate cells Giant, mutlinucleate cells Dissolve bone matrix and release stored minerals (osteolysis) Dissolve bone matrix and release stored minerals (osteolysis) Are derived from stem cells that produce macrophages Are derived from stem cells that produce macrophages Homeostasis Bone building (by osteocytes) and bone recycling (by osteoclasts) must balance: Bone building (by osteocytes) and bone recycling (by osteoclasts) must balance: more breakdown than building, bones become weak exercise causes osteocytes to build bone Compact Bone Figure 65 Osteon The basic unit of mature compact bone The basic unit of mature compact bone Osteocytes are arranged in concentric lamellae Osteocytes are arranged in concentric lamellae Around a central canal containing blood vessels Around a central canal containing blood vessels Perforating Canals Perpendicular to the central canal Perpendicular to the central canal Carry blood vessels into bone and marrow Carry blood vessels into bone and marrow Circumferential Lamellae Lamellae wrapped around the long bone Lamellae wrapped around the long bone Binds osteons together Binds osteons together Spongy Bone Figure 66 Spongy Bone Does not have osteons Does not have osteons The matrix forms an open network of trabeculae The matrix forms an open network of trabeculae Trabeculae have no blood vessels Trabeculae have no blood vessels Red Marrow The space between trabeculae is filled with red bone marrow: The space between trabeculae is filled with red bone marrow: which has blood vessels forms red blood cells and supplies nutrients to osteocytes Yellow Marrow In some bones, spongy bone holds yellow bone marrow: In some bones, spongy bone holds yellow bone marrow: is yellow because it stores fat WeightBearing Bones Figure 67 WeightBearing Bones The femur transfers weight from hip joint to knee joint: The femur transfers weight from hip joint to knee joint: causing tension on the lateral side of the shaft and compression on the medial side Periosteum and Endosteum Compact bone is covered with membrane: Compact bone is covered with membrane: periosteum on the outside endosteum on the inside Periosteum Figure 68a Periosteum Covers all bones: Covers all bones: except parts enclosed in joint capsules It is made up of: It is made up of: an outer, fibrous layer and an inner, cellular layer Perforating Fibers Collagen fibers of the periosteum: Collagen fibers of the periosteum: connect with collagen fibers in bone and with fibers of joint capsules, attached tendons, and ligaments Functions of Periosteum 1. Isolate bone from surrounding tissues 2. Provide a route for circulatory and nervous supply 3. Participate in bone growth and repair Endosteum Figure 68b Endosteum An incomplete cellular layer: An incomplete cellular layer: lines the marrow cavity covers trabeculae of spongy bone lines central canals Endosteum Contains osteoblasts, osteoprogenitor cells, and osteoclasts Contains osteoblasts, osteoprogenitor cells, and osteoclasts Is active in bone growth and repair Is active in bone growth and repair Bone Development Human bones grow until about age 25 Human bones grow until about age 25 Osteogenesis: Osteogenesis: bone formation Ossification: Ossification: the process of replacing other tissues with bone Ossification The 2 main forms of ossification are: The 2 main forms of ossification are: intramembranous ossification endochondral ossification Endochondral Ossification Ossifies bones that originate as hyaline cartilage Ossifies bones that originate as hyaline cartilage Most bones originate as hyaline cartilage Most bones originate as hyaline cartilage Endochondral Ossification Growth and ossification of long bones occurs in 6 steps Growth and ossification of long bones occurs in 6 steps Endochondral Ossification: Step 1 Chondrocytes in the center of hyaline cartilage: Chondrocytes in the center of hyaline cartilage: enlarge form struts and calcify die, leaving cavities in cartilage Figure 69 (Step 1) Endochondral Ossification: Step 2 Figure 69 (Step 2) Endochondral Ossification: Step 2 Blood vessels grow around the edges of the cartilage Blood vessels grow around the edges of the cartilage Cells in the perichondrium change to osteoblasts: Cells in the perichondrium change to osteoblasts: producing a layer of superficial bone around the shaft which will continue to grow and become compact bone (appositional growth) Endochondral Ossification: Step 3 Blood vessels enter the cartilage: Blood vessels enter the cartilage: bringing fibroblasts that become osteoblasts spongy bone develops at the primary ossification center Figure 69 (Step 3) Endochondral Ossification: Step 4 Figure 69 (Step 4) Remodeling creates a marrow cavity: Remodeling creates a marrow cavity: bone replaces cartilage at the metaphyses Endochondral Ossification: Step 5 Capillaries and osteoblasts enter the epiphyses: Capillaries and osteoblasts enter the epiphyses: creating secondary ossification centers Figure 69 (Step 5) Endochondral Ossification: Step 6 Figure 69 (Step 6) Endochondral Ossification: Step 6 Epiphyses fill with spongy bone: Epiphyses fill with spongy bone: cartilage within the joint cavity is articulation cartilage cartilage at the metaphysis is epiphyseal cartilage Appositional growth: Appositional growth: compact bone thickens and strengthens long bone with layers of circumferential lamellae Endochondral Ossification PLAY Figure 69 (Step 2) Endochondral Ossification Epiphyseal Lines Figure 610 Epiphyseal Lines When long bone stops growing, after puberty: When long bone stops growing, after puberty: epiphyseal cartilage disappears is visible on X-rays as an epiphyseal line Remodeling The adult skeleton: The adult skeleton: maintains itself replaces mineral reserves Remodeling: Remodeling: recycles and renews bone matrix involves osteocytes, osteoblasts, and osteoclasts Functions of Calcium Calcium ions are vital to: Calcium ions are vital to: membranes neurons muscle cells, especially heart cells Calcium Regulation Calcium ions in body fluids: Calcium ions in body fluids: must be closely regulated Homeostasis is maintained: Homeostasis is maintained: by calcitonin and parathyroid hormone which control storage, absorption, and excretion Calcitonin and Parathyroid Hormone Control Bones: Bones: where calcium is stored Digestive tract: Digestive tract: where calcium is absorbed Kidneys: Kidneys: where calcium is excreted Calcitonin Secreted by C cells (parafollicular cells) in thyroid Secreted by C cells (parafollicular cells) in thyroid Decreases calcium ion levels by: Decreases calcium ion levels by: inhibiting osteoclast activity increasing calcium excretion at kidneys Figure 616 (1 of 9) The Major Types of Fractures Potts fracture Potts fracture The Major Types of Fractures Comminuted fractures Comminuted fractures Figure 616 (2 of 9) The Major Types of Fractures Transverse fractures Transverse fractures Figure 616 (3 of 9) The Major Types of Fractures Spiral fractures Spiral fractures Figure 616 (4 of 9) Figure 616 (5 of 9) The Major Types of Fractures Displaced fractures Displaced fractures Figure 616 (6 of 9) The Major Types of Fractures Colles fracture Colles fracture Figure 616 (7 of 9) The Major Types of Fractures Greenstick fracture Greenstick fracture Figure 616 (8 of 9) The Major Types of Fractures Epiphyseal fractures Epiphyseal fractures Figure 616 (9 of 9) The Major Types of Fractures Compression fractures Compression fractures

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