The Skeletal System Parts of the skeletal system

The Skeletal System • Parts of the skeletal system • Bones (skeleton) • Joints • Cartilages • Ligaments © 2012 Pearson Education, Inc.

Functions of Bones • Support the body • Protect soft organs • Skull and vertebrae for brain and spinal cord • Rib cage for thoracic cavity organs • Allow movement due to attached skeletal muscles • Store minerals and fats • Calcium and phosphorus • Fat in the internal marrow cavity • Blood cell formation (hematopoiesis) © 2012 Pearson Education, Inc.

Bones of the Human Body • The adult skeleton has 206 bones • Two basic types of bone tissue • Compact bone • Homogeneous • Spongy bone • Small needle-like pieces of bone • Many open spaces © 2012 Pearson Education, Inc.

Spongy bone Compact bone © 2012 Pearson Education, Inc. Figure 5. 1

Classification of Bones on the Basis of Shape • Bones are classified as: • Long • Short • Flat • Irregular © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Figure 5. 2

Classification of Bones • Long bones • Longer than they are wide • Shaft with heads situated at both ends • Contain mostly compact bone • All of the bones of the limbs (except wrist, ankle, and kneecap bones) • Example: • Femur • Humerus © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Figure 5. 2 a

Classification of Bones • Short bones • Generally cube-shaped • Contain mostly spongy bone • Includes bones of the wrist and ankle • Sesamoid bones are a type of short bone which form within tendons (patella) • Example: • Carpals • Tarsals © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Figure 5. 2 d

Classification of Bones • Flat bones • Thin, flattened, and usually curved • Two thin layers of compact bone surround a layer of spongy bone • Example: • Skull • Ribs • Sternum © 2012 Pearson Education, Inc.

Spongy bone Compact bone © 2012 Pearson Education, Inc. Figure 5. 1

© 2012 Pearson Education, Inc. Figure 5. 2 c

Classification of Bones • Irregular bones • Irregular shape • Do not fit into other bone classification categories • Example: • Vertebrae • Hip bones © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Figure 5. 2 b

Anatomy of a Long Bone • Diaphysis • Shaft • Composed of compact bone • Epiphysis • Ends of the bone • Composed mostly of spongy bone © 2012 Pearson Education, Inc.

Articular cartilage Proximal epiphysis Diaphysis Distal epiphysis (a) © 2012 Pearson Education, Inc. Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Figure 5. 3 a

Anatomy of a Long Bone • Periosteum • Outside covering of the diaphysis • Fibrous connective tissue membrane • Perforating (Sharpey’s) fibers • Secure periosteum to underlying bone • Arteries • Supply bone cells with nutrients © 2012 Pearson Education, Inc.

Endosteum Yellow bone marrow Compact bone Periosteum Perforating (Sharpey’s) fibers Nutrient arteries (c) © 2012 Pearson Education, Inc. Figure 5. 3 c

Anatomy of a Long Bone • Articular cartilage • Covers the external surface of the epiphyses • Made of hyaline cartilage • Decreases friction at joint surfaces © 2012 Pearson Education, Inc.

Articular cartilage Compact bone Spongy bone (b) © 2012 Pearson Education, Inc. Figure 5. 3 b

Anatomy of a Long Bone • Epiphyseal plate • Flat plate of hyaline cartilage seen in young, growing bone • Epiphyseal line • Remnant of the epiphyseal plate • Seen in adult bones © 2012 Pearson Education, Inc.

Articular cartilage Proximal epiphysis Diaphysis Distal epiphysis (a) © 2012 Pearson Education, Inc. Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Figure 5. 3 a

Anatomy of a Long Bone • Marrow (medullary) cavity • Cavity inside of the shaft • Contains yellow marrow (mostly fat) in adults • In adults, red marrow is situated in cavities of spongy bone and epiphyses of some long bones © 2012 Pearson Education, Inc.

Articular cartilage Proximal epiphysis Diaphysis Distal epiphysis (a) © 2012 Pearson Education, Inc. Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Figure 5. 3 a

Bone Markings • Surface features of bones • Sites of attachments for muscles, tendons, and ligaments • Passages for nerves and blood vessels • Categories of bone markings • Projections or processes—grow out from the bone surface • Terms often begin with “T” • Depressions or cavities—indentations • Terms often begin with “F” © 2012 Pearson Education, Inc.

Microscopic Anatomy of Compact Bone • Osteon • A unit of bone • Central canal • Opening in the center of an osteon • Carries blood vessels and nerves © 2012 Pearson Education, Inc.

Osteon (Haversian system) Lamellae Blood vessel continues into medullary cavity containing marrow Spongy bone Perforating fibers Compact bone Periosteal blood vessel Periosteum (a) © 2012 Pearson Education, Inc. Central (Haversian) canal Perforating (Volkmann’s) canal Blood vessel Figure 5. 4 a

Microscopic Anatomy of Bone • Lamellae • Rings around the central canal • Sites of lacunae • Lacunae • Cavities containing bone cells (osteocytes) • Arranged in concentric rings called lamellae © 2012 Pearson Education, Inc.

Lamella Osteocyte (b) © 2012 Pearson Education, Inc. Canaliculus Lacuna Central (Haversian) canal Figure 5. 4 b

Osteon Lacuna © 2012 Pearson Education, Inc. (c) Central canal Interstitial lamellae Figure 5. 4 c

Formation of the Human Skeleton • In embryos, the skeleton is primarily hyaline cartilage • During development, much of this cartilage is replaced by bone • Cartilage remains in isolated areas • Bridge of the nose • Parts of ribs • Joints © 2012 Pearson Education, Inc.

Bone Growth (Ossification) • Epiphyseal plates allow for lengthwise growth of long bones during childhood • New cartilage is continuously formed • Older cartilage becomes ossified • Bone replaces cartilage through the action of osteoblasts © 2012 Pearson Education, Inc.

Bone Growth (Ossification) • Bones are remodeled and lengthened until growth stops • Bones are remodeled in response to two factors • Blood calcium levels • Pull of gravity and muscles on the skeleton • Bones grow in width (called appositional growth) © 2012 Pearson Education, Inc.

Bone starting to replace cartilage Bone collar Hyaline cartilage model In an embryo © 2012 Pearson Education, Inc. Figure 5. 5, step 1

Hyaline cartilage New center of bone growth Medullary cavity Invading Growth blood in bone vessels length In a fetus © 2012 Pearson Education, Inc. Figure 5. 5, step 2

Articular cartilage Spongy bone New bone forming Epiphyseal plate cartilage Growth in bone width Invading blood vessels New bone forming Epiphyseal plate cartilage In a child © 2012 Pearson Education, Inc. Figure 5. 5, step 3

Bone growth Bone grows in length because: 1 Cartilage grows here. 2 Cartilage is replaced by bone here. 3 Cartilage grows here. 4 Cartilage is replaced by bone here. © 2012 Pearson Education, Inc. Bone remodeling Growing shaft is remodeled as: Articular cartilage Epiphyseal plate 1 Bone is resorbed here. 2 Bone is added by appositional growth here. 3 Bone is resorbed here. Figure 5. 6

Types of Bone Cells • Osteocytes—mature bone cells • Osteoblasts—bone-forming cells • Osteoclasts—giant bone-destroying cells • Break down bone matrix for remodeling and release of calcium in response to parathyroid hormone • Bone remodeling is performed by both osteoblasts and osteoclasts © 2012 Pearson Education, Inc.

Bone Fractures • Fracture—break in a bone • Types of bone fractures • Closed (simple) fracture—break that does not penetrate the skin • Open (compound) fracture—broken bone penetrates through the skin • Bone fractures are treated by reduction and immobilization © 2012 Pearson Education, Inc.

Repair of Bone Fractures • Hematoma (blood-filled swelling) is formed • Break is splinted by fibrocartilage to form a callus • Fibrocartilage callus is replaced by a bony callus • Bony callus is remodeled to form a permanent patch © 2012 Pearson Education, Inc.

Hematoma External callus New blood vessels Internal callus (fibrous tissue and cartilage) 1 Hematoma forms. © 2012 Pearson Education, Inc. Bony callus of spongy bone Healed fracture Spongy bone trabecula 2 Fibrocartilage callus forms. 3 Bony callus forms. 4 Bone remodeling occurs. Figure 5. 7

Developmental Aspects of the Skeletal System • At birth, the skull bones are incomplete • Bones are joined by fibrous membranes called fontanels • Fontanels are completely replaced with bone within two years after birth © 2012 Pearson Education, Inc.

Parietal bone Frontal bone of skull Mandible Occipital bone Clavicle Scapula Radius Ulna Humerus Femur Tibia Ribs Vertebra Hip bone © 2012 Pearson Education, Inc. Figure 5. 34

Skeletal Changes Throughout Life • Fetus • Long bones are formed of hyaline cartilage • Flat bones begin as fibrous membranes • Flat and long bone models are converted to bone • Birth • Fontanels remain until around age 2 © 2012 Pearson Education, Inc.

Skeletal Changes Throughout Life • Adolescence • Epiphyseal plates become ossified and long bone growth ends • Size of cranium in relationship to body • 2 years old—skull is larger in proportion to the body compared to that of an adult • 8 or 9 years old—skull is near adult size and proportion • Between ages 6 and 11, the face grows out from the skull © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Figure 5. 35 a

Skeletal Changes Throughout Life • Curvatures of the spine • Primary curvatures are present at birth and are convex posteriorly • Secondary curvatures are associated with a child’s later development and are convex anteriorly • Abnormal spinal curvatures (scoliosis and lordosis) are often congenital © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Figure 5. 18

Skeletal Changes Throughout Life • Osteoporosis • Bone-thinning disease afflicting • 50 percent of women over age 65 • 20 percent of men over age 70 • Disease makes bones fragile and bones can easily fracture • Vertebral collapse results in kyphosis (also known as dowager’s hump) • Estrogen aids in health and normal density of a female skeleton © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Figure 5. 36

© 2012 Pearson Education, Inc. Figure 5. 37