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Human Anatomy Skeletal System Functions • Support: body structure and shape • Protection for vital organs (brain, heart, etc.) • Movement for attached skeletal muscles – Tendons: attach muscle to bone – Ligaments: attach bone to bone • Mineral storage: calcium and phosphorus • Blood cell formation - hematopoiesis Types of Bone Compact Bone • • • • • • Very dense, stress bearing Haversian systems –basic unit of compact bone Lamellae: concentric cylinder shaped calcified structure Lacunae: small spaces containing tissue fluid Osteocytes: facilitate exchange of calcium between blood and bone Canaliculi: canals connecting the lacunae together and to the haversian canal which carries nutrients and wastes to and from the osteocytes Cancellous Bone • Light, spongy • Found at ends of long bones, ribs, sternum, hips, vertebrae, cranium • No haversian systems • Web-like arrangement • Highly vascular Classification of Bones Long bones • Found in the extremities • Act as levers • Includes: – Epiphysis • End of long bones • Covered with hyaline cartilage for articulation • Filled with cancellous bone – – – – – Diaphysis Shaft Covered with periosteum Medullary canal Compact bone • Examples: femur, tibia, fibula, humerus, radius, clavicle, metacarpals, phalanges Short Bones • Cube shaped • Allows flexible movement • Cancellous bone covered by compact bone • Examples: – Carpals – Tarsals Flat Bones • Protect vital organs and provide broad surface area for muscle attachment • Examples: – Cranial bones – Scapula – Sternum – Ribs Irregular Bones • Peculiarly shaped to provide support and protection, yet allow flexibility • Examples: – Vertebrae – Ear – Hyoid – Mandible Sesamoid Bones • Extra bones found in certain tendons • Example: – Patella Composition • Collagen: chief organic constituent (protein) • Inorganic calcium salts (Vitamin D essential for absorption of minerals i.e. calcium) • Deposition favored by – – – – a. Estrogen, testosterone b. Alkaline phosphatase c. Thyrocalcitonin d. Mechanical stress i.e. traction • Withdrawal favored by – a. Alkaline phosphatase – b. Parathormone – c. Inactivity Composition Cells • Osteoblasts: bone building, bone repairing cells in the periosteum • Osteocytes: mature bone cells within the bone matrix • Osteoclast: causes reabsorption of bone Periosteum • 1. Dense, fibrous membrane covering bone • 2. Contains blood vessels • 3. Essential for bone cell survival and bone formation • Cells that Aid in Bone Formation Osteoblast Builds new bone Mature bone cell Osteocyte Osteoclast Eats bone Bone Formation • Initially collagen fibers secreted by fibroblasts • Cartilage deposited between fibers • Skeleton fully formed by 2nd month of fetal development (all cartilage) • After 8th week of fetal development ossification (mineral matter deposited and replaces cartilage) begins • Childhood and adolescence: – ossification exceeds bone loss • Early adulthood thru middle age: – ossification equals bone loss • After age 35: – bone loss exceed ossification Fetal Skeleton 275 bones 12 weeks (6-9 inches long) Anatomy of Long Bone • Diaphysis – Shaft – Composed of compact bone • Epiphysis – Ends of bone composed mostly of spongy bone • Periosteum – outside covering of diaphysis • Endosteum – Lines medullary cavity • Arteries • Articular cartilage • Medullary cavity – Cavity inside the shaft – Contains yellow marrow (mostly fat) in adults Bone Marrow • Red bone marrow – Found in vertebrae, ribs, sternum, cranium, ends of humerus and femur – Produces: • Erythrocytes – red blood cells • Plateletes - thrombocytes – clotting cells • Some leukocytes – white blood cells • Yellow bone marrow – Found in medullary cavity of long bones – Fat storage Bone Marrow Yellow marrow • Medullary cavity of long bones • Fat storage Red marrow • Hematopoietic tissue • In all cancellous bone in children • In adults: cancellous bone of vertebrae, hips, sternum, ribs, cranial bones, proximal ends of femur and humerus • Forms RBCs, platelets, some WBCs, and destroys old RBCs and some foreign materials Divisions of the Skeletal System Axial Skeleton Forms the longitudinal axis of the body Total: 80 bones Divided into three parts: • Skull • Vertebral Column • Thorax Appendicular Skeleton • Composed of 126 bones • Includes bones of the: – Limbs (appendages) – Pectoral (shoulder) girdle – Pelvic (hip) girdle