Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings BIOLOGY OF HUMAN AGING CHAPTER 5 The Skeletal System

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Function of Bones  Support – form the framework that supports the body and cradles soft organs  Protection – provide a protective case for the brain, spinal cord, and vital organs  Movement – provide levers for muscles  Mineral storage – reservoir for minerals, especially calcium and phosphorus  Blood cell formation – hematopoiesis occurs within the marrow cavities of bones

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Bone Textures  Compact bone – dense outer layer  Spongy bone – honeycomb of trabeculae filled with yellow bone marrow

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Structure of Long Bone  Long bones consist of a diaphysis and an epiphysis  Diaphysis  Tubular shaft that forms the axis of long bones  Composed of compact bone that surrounds the medullary cavity  Yellow bone marrow (fat) is contained in the medullary cavity

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Structure of Long Bone  Epiphyses  Expanded ends of long bones  Exterior is compact bone, and the interior is spongy bone  Joint surface is covered with articular (hyaline) cartilage  Epiphyseal line separates the diaphysis from the epiphyses

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Structure of Long Bone Figure 6.3

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Compact Bone  Haversian system, or osteon – the structural unit of compact bone  Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen  Haversian, or central canal – central channel containing blood vessels and nerves

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Structure of Bone: Compact Bone  Osteocytes – mature bone cells  Lacunae – small cavities in bone that contain osteocytes  Canaliculi – hairlike canals that connect lacunae to each other and the central canal

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Structure of Bone: Compact Bone Figure 6.6a, b

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Composition of Bone: Organic  Osteoblasts – bone-forming cells  Osteocytes – mature bone cells  Osteoclasts – large cells that resorb or break down bone matrix

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Composition of Bone: Inorganic  Mineral salts  Sixty-five percent of bone by mass  Mainly calcium phosphates  Responsible for bone hardness and its resistance to compression

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Bone Development  Osteogenesis and ossification – the process of bone tissue formation, which leads to:  The formation of the bony skeleton in embryos  Bone growth until early adulthood  Bone thickness, remodeling, and repair

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Control of Remodeling  Hormonal mechanism maintains calcium homeostasis in the blood

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Hormonal Mechanism  Rising blood Ca 2+ levels trigger the thyroid to release calcitonin  Calcitonin stimulates calcium salt deposit in bone  Falling blood Ca 2+ levels signal the parathyroid glands to release PTH  PTH signals osteoclasts to degrade bone matrix and release Ca 2+ into the blood

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Hormonal Mechanism Figure 6.12

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Skeletal Cartilage  Three types – hyaline, elastic, and fibrocartilage

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Hyaline Cartilage  Provides support, flexibility, and resilience  Is the most abundant skeletal cartilage  Is present in these cartilages:  Covers the ends of long bones  Costal – connects the ribs to the sternum  Nasal – supports the nose

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Elastic Cartilage  Similar to hyaline cartilage but contains elastic fibers  Found in the external ear

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Fibrocartilage  Highly compressed with great tensile strength  Contains collagen fibers  Found in menisci of the knee and in intervertebral discs

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Growth of Cartilage  Interstitial – lacunae-bound chondrocytes inside the cartilage divide and secrete new matrix, expanding the cartilage from within  Calcification of cartilage occurs  During normal bone growth  During old age

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Bones and Cartilages of the Human Body Figure 6.1

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Age-related changes Loss of calcium from the bone (more in female than male) Collegen fibers decreases Gradual increase of inorganic salts in the bone matrix (bone may become brittle and fracture easily Medullary cavity of long bones become enlarged due to bone resorption Decrease ability of bone withstanding stress with aging (due to loss of collegen fibers) bones become thinner Bone formation vs. bone resorption Hormonal imbalance (parathyroid hormone and calcitonin Joints become thinner and signs of deterioration may appear Restriction of movement of joints Calcification of costal cartilage Changes in the fibrocartilage that forms the intervertebral discs The center of each disc is known as nucleus pulposus (gradual loss of water and cells) Formation of lipofucin and calcification of the discs and other degenerative processes may occur Deformity of the vertebral column or poor posture

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Age-related Dysfunction Bursitis Tumors of bone Arthritis: Osteoarthritis Rheumatoid arthritis Gouty arthritis

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Osteoporosis  Group of diseases in which bone reabsorption outpaces bone deposit  Spongy bone of the spine is most vulnerable  Occurs most often in postmenopausal women  Bones become so fragile that sneezing or stepping off a curb can cause fractures