Chapter 6: Skeletal System: Bones and Bone Tissue

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five major functions of skeletal system
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1. support – strong bone sutied for bearing weight. cartilage provides firm yet flexible support. ligaments are strong bands of fibrous connective tissue that attach to bone 2. protection – protects organs 3. movement – muscles attach to bones via tendons 4. storage – mineral in blood are taken into bone and stored. if blood levels of these minerals decrease, minerals released from bone 5. blood cell production – bones contain cavities filled w/ red bone marrow which gives rise to blood cells and platelets
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three types of cartilage
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hyaline – precursor of most bones in the body fibrocartilage elastic cartilage
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chondroblasts
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cells that produce cartilage matrix
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chondrocyte
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when cartilage surrounds a chondroblast, it becomes a _______, a rounded cell that occupies a space called a lacunae within the matrix
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perichondrium
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Dense irregular connective tissue membrane covering cartilage. blood vessels penetrate outer layer, but do not enter the cartilage matrix
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articular cartilage
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cartilage covering the ends of bones where they come together to form joints. has no perichondrium
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appositiional growth
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type of cartilage growth. chondroblasts in the perichondrium add new cartilage to the outside of the existing cartilage. chondroblasts lay down new matrix and add new chondrocytes to the outside of the tissue
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interstitial growth
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type of cartilage growth where chondrocytes within the tissue divide and add more matrix between the existing cells.
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bone matrix
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composed of 35% organic and 65% inorganic material
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hydroxyapatite
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the inorganic calcium phosphate in bone
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function of collagen fibers in bone
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gives bone flexible strength (like steel bars)
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function of mineral matrix in bone
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gives bone weight-bearing strength
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osteoblasts
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bone-forming cells; produce collagen and proteoglycans
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ossification
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formation of bone by osteoblasts
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osteocyte
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term for an osteoblast once it becomes surrounded by bone matrix
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lacunae
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small cavities in the bone or cartilage that hold individual bones or cartilage cells
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canaliculi
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spaces occupied by the osteocyte cell processes
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osteoclasts
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responsible for the reabsorption or breakdown of bone. large cells that contain several nuclei.
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ruffled border
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areas where the plasma membrane of osteoclasts contacts the bone matrix
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osteochondral progenitor cells
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stems cells that can become osteoblasts or chondroblasts – located in inner layer of perichondrium and inner layers of connective tissue that covers bone (periosteium/endosteum)
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woven bone
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immature bone present during fetal development or in the early stages of bone repair (after a fracture); collagen fibers are randomly distributed and have crisscross pattern
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bone remodling
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process of removing old bone and adding new bone
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lamellar bone
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mature bone that is organized into thin sheets or layers approximately 3-7 micrometers thick called lamellae. collagen fibers lie parallel to one another but at an angle to the collagen fibers in adjacent lamellae
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spongy bone
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consists of interconnecting rods or plates of bone called trabeculae; the spaces are filled with bone marrow and blood vessels
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trabeculae
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supporting bundles of bony fibers in cancellous (spongy) bone; oriented along the lines of stress within the bone
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compact bone
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dense and thick bone matrix; lamellae are oriented around blood vessels that enter the bone
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central canal
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The hollow center of an osteon, also known as a Haversian canal. The central canal contains blood vessels, lymphatic vessels, and nerves. Bone is laid down around the central canal in concentric rings called lamellae.
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osteon
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The unit of combact bone, also called a Haversian system. Osteons are essentially long cylinders of bone; the hollow center is called the central canal, and is where blood vessels, nervs, and lymphatic vessels are found. Compact bone is laid down around the central canal in rings (lamellae). cut in cross section it resembles a bullseye
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haversian system
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A unit of compact bone consisting of a tube (haversian canal) with the laminae of bone that surrounds it
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three types of lamellae
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concentric – circular layers of bone matrix that surround a common central canal circumferential – thin plates that extend around the bone (outer surfaces of central canal) interstitial – between osteaons; remnants of concentric or circumferential lamellae that were partially removed during bone remodling
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volkmann’s canals aka perforating canals
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channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal
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four basic bone shapes
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1. long bone – longer than they are wide (upper and lower limbs) 2. short bone – round or nearly cubed-shaped (wrist bone and ankle bone) 3. flat bone – relatively thin, flattened shape and usually curved (skull bones, ribs, sternum, shoulder blades) 4. irregular bone – does not fit readily into the other 3 categories (vertebrae and facial bones)
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diaphysis
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the shaft of a long bone
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epiphysis
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the end of a long bone (knobby ends); develops from a center of ossification distinct from the diaphysis
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epiphyseal plate
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cartilaginous area at the ends of long bones where lengthwise growth takes place in the immature skeleton; separates the epiphysis from the diaphysis
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medullary cavity
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cavity within the shaft of the long bones; filled with bone marrow
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red marrow vs. yellow marrow
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red – site of blood cell formation yellow – mostly adipose tissue
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periosteum
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a dense fibrous membrane covering the surface of bones (except at their extremities) and serving as an attachment for tendons and muscles;
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endosteum
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vascular membrane that lines the inner surface of long bones
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sinuses
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air filled spaces inside flat and irregular bones that are lined with mucous membranes
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intramembranous ossification
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takes place in connective tissue membranes; begins when mesenchymal cells in the membrane become osteochondral progenitor cells
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center of ossification
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A location in a developing bone where osteoblasts produce and secrete bone matrix
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fontanels
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a soft, membrane-covered space between the bones at the front and the back of a newborn’s skull
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endochondral ossification
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the most common bone formation process, which involves the replacement of hyaline cartilage (developed by mesenchyme) with bone, occurs in postcranial skeleton (except clavicle) and in bones of cranial base 1. mesenchyme condenses to form hyaline cartilage precursor 2. A bone collar forms around the circumference of cartilage model–this is periosteal bone 3. At primary center of ossification (forms first): cartilage matrix becomes calcified, erodes and forms spicules; then, bone forms on spicules 4. Ossification repeats in secondary centers of ossification in epiphyses
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bone collar
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the osteoblasts produce compact bone on the surface of the cartilage model.
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calcified cartilage
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Cartilage tissue in which inorganic calcium salts are deposited in the matrix, which occurs prior to replacement by osseous tissue, and sometimes in aging cartilage.
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bone growth
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only occurs via appositional growth; new bone on the surface of older bone or cartilage
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zone of resting cartilage
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anchors growth plate to bone
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zone of proliferation
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2nd region of epiphyseal plate; made of a column of flattened cells. Region of rapid proliferation of chondroblasts from isogenous group. Actively makes cartilage via intersititial growth
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zone of hypertrophy
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chondrocytes mature and enlarge
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zone of calcification
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is very thin and contains hypertrophied chondrocytes and calcified cartilage matrix. The hypertrophied chondrocytes die, and blood vessels from the diaphysis grow into the area.
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growth at articular cartilage
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Increases size of bones with no epiphyses: e.g., short bones; chondrocytes near the surface of the articular cartilage similar to those in zone of resting cartilage
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factors affecting bone growth
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1. nutrition – vitamin d is necessary for the normal absorption of calcium from the intestines; vitamin c is necessary for collagen synthesis by osteoblasts 2. hormones – growth hormone stimulates cartilage growth and appositional bone growth, thyroid hormone necessary for growth of all tissues including cartilage; estrogen and testosterone stimulate bone growth.
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bone remodling
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converts old woven bone to new lamellar bone. is involved in bone growth, changes in bone shape, adjustment of bone to stress, bone repair, and calcium ion regulation in the body. causes the diameter of the medullary cavity to increase as the bone increases in length and width
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interstitial lamellae
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the areas between osteons that are fragments of older osteons that have been partially destroyed during bone rebuilding or growth
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hematoma
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localized mass of blood released from blood vessels, but confined in an organ or space; usually forms a clot that stops the bleeding; adjacent tissue to the bone fracture site dies
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callus formation
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osteoclasts digest into the hematoma as bone stem cells differentiate into osteoblasts and chondrocytes
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callus ossification
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during bone repair callus replaced by woven, cancellous bone through endochondral ossification
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calcium homeostasis
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minerals are deposited in the skeleton and withdrawn when they are needed for other purposes; depends on a balance btwn dietary intake, urinary and fecal loses, and exchanges btwn osseous tissue

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