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

Osteoblast Osteocyte Osteoclast Eats bone Builds new bone Mature bone cell Cells that Aid in Bone Formation

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

275 bones 12 weeks (6-9 inches long) Fetal Skeleton

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