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Unit 5: The Skeletal System Ch. 7 General Organization 206 bones* Axial Skeleton – down the center Skull Cranium – 8 Facial – 14 Middle Ear - 6 Vertebral Column Cervical – 7 Thoracic – 12 Lumbar – 5 Sacrum, Coccyx Thoracic Cage 12 pairs 7 true ribs 5 False Ribs 2 floating ribs Appendicular Skeleton – the appendages Pectoral Girdle Scapula – 2 Clavicle – 2 Upper Limbs Humerus – 2 Radius – 2 Ulna – 2 Carpals – 16 Metacarpals – 10 Phalanges – 28 Pelvic Girdle Coxal – 2 Lower Limbs Femur – 2 Patella – 2 Tibia – 2 Fibula – 2 Tarsals – 14 Metatarsal 10 Phalanges - 28 Types of Bones Long – cartoon bone Short – boxy or cube-like Vertebrae, many facial bones Sesamoid – found in joints for stability Ribs, scapula, sternum Irregular – variety of shapes Carpals, tarsals Flat – platelike Expanded ends Longer than wide Humerus, femur, finger bones Patella (knee cap) Wormian (sutural) – extra bones in skull where cranial bones meet Bone Structure: Macroscopic Structure – Long bone Epiphyses – expanded ends Articular Cartilge – hyaline; protection in joints Diaphysis – shaft Medullary Cavity – hollow portion containing marrow Periosteum – outer covering Endosteum – inner covering Types of bone Compact – dense for strength outer Osteons Spongy – light, airy inner Reduce weight Trabeculae Bone Structure: Microscopic – Compact Osteon – Repeating unit Osteonic (Haversion Canal) Central Blood vessels, nerves Lamellae – concentric circles of matrix Osteocytes – mature bone cells Bullseye Lacunae Canaliculi Transverse (perforating/ Volkmann’s) Canal Connects osteonic canals Bone Structure: Spongy - cancellous Trabeculae – bony plates Osteocytes found here Bone Growth and Development Skeletal Formation Animation Ossification – formation of bone Osteoblast – deposit solid mineral matrix Turn into osteoclasts – mature bone cells Endochondral Bone Formation Most common; arise from hyaline cartilage Periosteum forms; deposit bone underneath – outside of bone first Primary ossification center – center of diaphysis Ossification moves towards ends Secondary Ossification Center – Epiphyses Mainly spongy bone develops Bone Growth and Development Epiphyseal Disk – growth plate Area between the two ossification centers that remains cartilage Does not ossifiy until adulthood 4 layers of cells Cartilage cells continue to divide, mature, ossify and die Move toward ends of bone Intramembranous Ossification – bone formation between two sheets of connective tissue Generally in flat bones of skull Factors Affecting Bone Growth Diet – what you eat Minerals such as calcium, phosphates Vitamin D – needed for proper absorption of calcium Rickets/ osteomalacia – lack of vit. D; soft bones Dehydrocholesterol – inactive form; activated by sunlight in the skin Vitamin A & C Vit. A – bone resorption Vit. C – collagen synthesis Hormones – chemical messengers from glands Human Growth Hormone – pituitary; stimulates growth of epiphyseal disk Lack causes retardation in development Dwarfism, gigantism, achondroplasia, acromegaly Thyroid hormone – thyroid; replace cartilage with bone Male and Female Sex Hormones Physical Stress – exercise Tug of tendons cause bones to thicken and strengthen Skeletal Functions: Support and Protection Body Movement – lever actions 1st class – EF, F, RF 2nd class – F, RF, EF Mandible 3rd Class – F, EF, RF Triceps Bicep Blood Cell Formation – Hematopoiesis Marrow – hematopoietic tissue Found in medullary cavity of long bones (young); spongy bone spaces (older) Red – blood cell formation Yellow – fat storage Can be converted back and forth as needed Skeletal Functions: Hemocytoblast – blood stem cell Erythrocyte – red blood cell Leukocyte – white blood cell Thrombocyte – platelet Inorganic Salt Storage Electrolytes needed for a variety of physiological functions Ca++ needed for nerve impulse conduction, skeletal muscle contraction Negative Feedback Blood Ca levels too high: Thyroid releases Calcitonin osteoblast activity; deposit calcium in bone Blood Ca levels too low: Parathyroid release parathyroid hormone Osteoclast activity; dissolve bone, release minerals into blood