Skeletal System

icer215's version from 2016-08-20 01:08


Question Answer
An adult bodyis made up of 206 bones
Organized in two major divisionsAxial skeleton & Appendicular skeleton
Axial skeletonRuns along the body’s midline axis. 80 bones in this division.
80 bones in this division which includeSkull, Hyoid, Auditory ossicles, Vertebral, Column, Sternum, Ribs
Appendicular skeleton126 bones in this division
126 bones in this division which includeUpper limbs, Lower limbs, Pelvic girdle, & Pectoral girdle (shoulder)
Function of skeletal systemStructural rigidity and support
Structural rigidity and supportProvides protection for our internal organs and tissues. Allow movements against the gravitational pull of the earth. Much of the support within the body comes from the spine, legs, feet, and pelvis .Framework to support the body. Maintains body shape
Bone matrixStores calcium
Calciummust be consumed through food or dietary supplements .Very important to intake calcium in early life to build a strong skeletal system


Question Answer
Bone contains99% of the total body calcium
Intestinal systemabsorbs calcium
Stored calciumis used to sustain adequate blood calcium levels
Site for calcium metabolismParathyroid hormone regulates calcium release from bone. In liver vitamin D is converted to calcidoil, kidney then converts calcidoil to calcitriol. Calcitriol is the biologically active form of vitamin D
Calcium homeostasisMechanism that maintains suitable calcium levels
Skeletal systemis crucial in protecting our vital internal organs
Skull (cranium)Protects the brain, the eye, and the middle and inner ears
Rib cageProtects the lungs, heart, and other organs
VertebraeProtects the spinal cord
PatellaProtects the knee
UlnaProtects the elbow


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Ilium and spineProtects the digestive and urogenital system and the hip
Clavicle and scapulaProtect the shoulder
Skull22 bones; 21 of them are fused together in adults
Mandible (jaw bone)is the only moveable joint in the skull with the temporal bone .In children, those bones are separated for brain and skull growth
Craniumsuperior part of the skull that protects the brain from damage
Facial bonesinferior and anterior parts of the skull that protect and support the eyes, nose and mouth
HyoidLocated inferior to the mandible. Small U-shaped bone. Only bone that does not form a joint with other bones. Holds the trachea open and forms a bony connection for the tongue muscles
Auditory ossiclesGroup of smallest bones in the body à malleus, incus, and stapes. Located in a small cavity inside the temporal bone. Transmit and amplify sound from the eardrum to the inner ear
Vertebral columnConsists of 26 vertebrae
Consists of 26 vertebrae which includeCervical (neck) ➙ 7 vertebrae, Thoracic (chest) ➙ 12 vertebrae, Lumbar (lower back) ➙ 5 vertebrae, Sacrum ➙ 1 vertebra, & Coccyx (tailbone) ➙ 1 vertebra


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SternumBreastbone, Thin, knife-shaped bone, Found along the midline of the anterior side of the thoracic region of the skeleton, Costal cartilage connects sternum to the ribs
Ribcage12 pairs of ribs with the sternum
Ribs 1-7known as “true ribs” because they are connected the thoracic vertebrae directly to the sternum through cartilage
Ribs 8-10known as “false ribs” because they are connected to the sternum through cartilage that is connected to the cartilage of the seventh rib
Ribs 11-12known as “false and floating ribs” because they have no cartilage attached to the sternum
Four types of bonesLong, Short, Flat, & Irregular
LongMajor bones of the limbs, Long structure that have greater length than width, Growth is greater than other types thus responsible for the growth of heights, Hollow medullary cavity in the center is for bone marrow storage. ex: i.e. Femur, tibia, phalanges, fibula, humerus
ShortAs long as they are wide & Cube or round shape. ex: i.e. wrist bones and tarsal bones of the foot
FlatVary in size and shape, Very thin in one direction, & Do not have medullary cavity. ex: i.e. occipital bones of the cranium
IrregularDifferent shapes than the above bones. ex: i.e. vertebrae, sacrum, and coccyx of the spine


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Jointswhere bones connect which allows for movements and provides mechanical support
Structural classificationSynovial joint, Cartilaginous joint, & Fibrous joint
Synovial jointWeakest type but most common joint tissue type, Joint capsule enchasing the joint and synovial fluid within the joint, & Helps cushion and protect the joints. ex: i.e. shoulder, hips, knees, elbow
Cartilaginous jointConnects by fibrocartilage & Less mobile than synovial joint. ex: i.e. intervertebral discs of the spinal column
Fibrous jointLeast mobile, Contains dense connective tissue, & Doesn’t allow movement between the bones that form the joint. ex: i.e. sutures of the skull, syndemoses
SynarthroisisLittle or no mobility
AmphiarthrosisSlightly more mobile
DiarthrosisFreest mobility
EndoskeletonExternal, hard case on the surface of the organism, More protective because it covers the muscles and other soft tissues, & Acellular – does not grow as the organism grows (arthropods periodically shed their exoskeletons). Support the body & Allow for movement through contraction of muscles. Ex: shells of crabs
ExoskeletonHard and mineralized structure within the soft tissue of organisms, Less protective and usually under the muscles and soft tissues, & Grows smoothly and evenly and does not shed. Support the body & Allow for movement through contraction of muscles. Ex: human skeleton


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Bone’s hardnesscomes from inorganic components. Ex: Calcium, phosphate and hydroxide ions form hydroxyapatite crystals
Bone’s flexibilitycomes from organic components. Ex: Collagen, glycoproteins and other peptides
Mineralsare also stored in bone. Ex: Sodium, magnesium and potassium
Osteons (Haversian systems)Bony matrix units. Encircles a Haversian canal, a central microscopic channel, which is surrounded by lamellae, circles of bony matrix
Spaces between the matrixis called lacunae
Interconnected by canaliculiwhich are small canals for the exchange of nutrients and wastes with the Haversian canals
Mature bone cellscalled osteocytes. Housed in lacunae.
Osteocytesmaintenance of bone


Question Answer
These contain blood vesselsnerve fibers and lymph
OsteoclastsLarge cells with many nuclei (multinucleated), Precursors circulate in the blood and bone marrow,Fusion of the precursors produce mature osteoclasts, Found on the surface of the bone and at sites of injured, unnecessary, and old bone, Reabsorb (breakdown of) bone, &Balance between osteoblasts and osteoclasts is crucial in skeletal system
OsteoblastsCuboidal and columnar shape with central nucleus on the bone surface, Responsible for forming new bone, Found in periosteum and endosteum, the growing portions of bone, Do not divide, & Synthesize and secrete the collagen matrix and calcium salts
OsteocytesInside of the bone (lacuna), surrounded by bone tissue, Have long braches, Maintain the mineral concentration of the matrix, Secrete enzymes, Senses mechanical strain on the bone, & Secrete growth factors and activate the lining cells or stimulate the osteoblasts
Osteoprogenitor (osteogenic) cellsFound in deep layers of periosteum and the marrow, Only bone cells that can divide, & Develop into osteoblasts by differentiating
Cartilage StructureSofter and flexible connective tissue. Consists of chondrin. Firm but flexible matrix & Secreted by chondrocytes. Provide extra flexibility and resilience in bodies. Does not have blood and lymphatic vessels (avascular) and is not innervated either


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Three types of cartilageElastic cartilage, Hyaline cartilage, & Fibrocartilage
Elastic cartilageYellow cartilage. Found in the outer ear and in the epiglottis
Hyaline cartilageTransparent, Found on many joint surfaces like larynx, trachea, and bronchi, Covered by perichondrium that contains vessels to supply nutrition, Stiff but flexible, Reduces friction between bones
FibrocartilageWhite fibrous tissue, Only type that consists of type I collagen, Found in the pubic symphysis, Resistance to compression, Limited relative movement, Prevents bone to bone contact
LigamentsConnective tissue that connects bone to bone, Hold structure together for stability, Similar to a shock absorber, More random organization, Weaving pattern, made of collagen
TendonsConnective tissue that connects muscle to bone, Can withstand tension, Similar to an anchor point, Organized, Long axis direction, made of collagen