Human Anatomy Skeletal System Functions Support body structure

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 Osteocyte Osteoclast Builds new bone Mature bone cell Eats bone

Bone Formation • Initially collagen fibers secreted by fibroblasts • Cartilage deposited between fibers • Skeleton fully formed by 2 nd month of fetal development (all cartilage) • After 8 th 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