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© 2015 Pearson Education, Inc.
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The Skeletal System
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The Skeletal System Two subdivisions of the skeleton
Axial skeleton Appendicular skeleton Parts of the skeletal system Bones (skeleton) Joints Cartilages Ligaments © 2015 Pearson Education, Inc.
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Functions of Bones Support the body Protect soft organs
Skull and vertebrae protect brain and spinal cord Rib cage protects thoracic cavity organs Attached skeletal muscles allow movement Store minerals and fats Calcium and phosphorus Fat in the internal marrow cavity Blood cell formation (hematopoiesis) © 2015 Pearson Education, Inc.
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Bones of the Human Body The adult skeleton has 206 bones
Two basic types of bone tissue Compact bone Dense, smooth, and homogeneous Spongy bone Small needle-like pieces of bone Many open spaces © 2015 Pearson Education, Inc.
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Spongy bone Compact bone
Figure 5.1 Flat bones consist of a layer of spongy bone sandwiched between two thin layers of compact bone. Spongy bone Compact bone
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Classification of Bones
Bones are classified on the basis of shape, as: Long Short Flat Irregular © 2015 Pearson Education, Inc.
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Figure 5.2 Classification of bones on the basis of shape.
(c) Flat bone (sternum) (a) Long bone (humerus) (b) Irregular bone (vertebra), right lateral view (d) Short bone (talus)
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Classification of Bones
Long bones Typically 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) are long bones Examples: Femur Humerus © 2015 Pearson Education, Inc.
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Figure 5.2a Classification of bones on the basis of shape.
(a) Long bone (humerus)
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Classification of Bones
Short bones Generally cube-shaped Contain mostly spongy bone Include bones of the wrist and ankle Sesamoid bones are a type of short bone that form within tendons (patella) Examples: Carpals Tarsals © 2015 Pearson Education, Inc.
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Figure 5.2d Classification of bones on the basis of shape.
(d) Short bone (talus)
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Classification of Bones
Flat bones Thin, flattened, and usually curved Two thin layers of compact bone surround a layer of spongy bone Examples: Skull Ribs Sternum © 2015 Pearson Education, Inc.
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Spongy bone Compact bone
Figure 5.1 Flat bones consist of a layer of spongy bone sandwiched between two thin layers of compact bone. Spongy bone Compact bone
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Figure 5.2c Classification of bones on the basis of shape.
(c) Flat bone (sternum)
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Classification of Bones
Irregular bones Irregular shape Do not fit into other bone classification categories Examples: Vertebrae Hip bones © 2015 Pearson Education, Inc.
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Figure 5.2b Classification of bones on the basis of shape.
(b) Irregular bone (vertebra), right lateral view
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Concept Link © 2015 Pearson Education, Inc.
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Anatomy of a Long Bone Diaphysis Periosteum Shaft
Makes up most of bone’s length Composed of compact bone Periosteum Outside covering of the diaphysis Fibrous connective tissue membrane Perforating (Sharpey’s) fibers secure periosteum to underlying bone © 2015 Pearson Education, Inc.
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Figure 5.3a The structure of a long bone (humerus of arm).
Articular cartilage Proximal epiphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Diaphysis Distal epiphysis (a)
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Figure 5.3c The structure of a long bone (humerus of arm).
Endosteum Yellow bone marrow Compact bone Periosteum Perforating (Sharpey’s) fibers Nutrient arteries (c)
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Anatomy of a Long Bone Epiphysis Articular cartilage Ends of the bone
Composed mostly of spongy bone enclosed by thin layer of compact bone Articular cartilage Covers the external surface of the epiphyses Made of hyaline cartilage Decreases friction at joint surfaces © 2015 Pearson Education, Inc.
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Figure 5.3b The structure of a long bone (humerus of arm).
Articular cartilage Compact bone Spongy bone (b)
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Anatomy of a Long Bone Epiphyseal plate Epiphyseal line
Flat plate of hyaline cartilage seen in young, growing bone Causes lengthwise growth of a long bone Epiphyseal line Remnant of the epiphyseal plate Seen in adult bones © 2015 Pearson Education, Inc.
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Figure 5.3a The structure of a long bone (humerus of arm).
Articular cartilage Proximal epiphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Diaphysis Distal epiphysis (a)
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Anatomy of a Long Bone Marrow (medullary) cavity
Cavity inside the shaft Contains yellow marrow (mostly fat) in adults Contains red marrow for blood cell formation in infants In adults, red marrow is situated in cavities of spongy bone and epiphyses of some long bones © 2015 Pearson Education, Inc.
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Figure 5.3a The structure of a long bone (humerus of arm).
Articular cartilage Proximal epiphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Diaphysis Distal epiphysis (a)
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Bone Markings Surface features of bones Categories of bone markings
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” © 2015 Pearson Education, Inc.
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Table 5.1 Bone Markings (1 of 3).
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Table 5.1 Bone Markings (2 of 3).
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Table 5.1 Bone Markings (3 of 3).
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Microscopic Anatomy of Compact Bone
Osteocytes are situated within cavities known as lacunae Lacunae are arranged in concentric rings called lamellae Lamellae are rings situated around the central (Haversian) canal © 2015 Pearson Education, Inc.
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Figure 5.4a Microscopic structure of compact bone.
Spongy bone Perforating (Volkmann’s) canal Osteon (Haversian system) Blood vessel continues into medullary cavity containing marrow Lamellae Blood vessel Compact bone Central (Haversian) canal Perforating (Sharpey’s) fibers Periosteum Periosteal blood vessel (a)
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Microscopic Anatomy of Bone
Central (Haversian) canal Opening in the center of an osteon Runs lengthwise through bone Carries blood vessels and nerves Osteon (Haversian system) A unit of bone containing central canal and matrix rings © 2015 Pearson Education, Inc.
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Figure 5.4b Microscopic structure of compact bone.
Lamella Osteocyte Canaliculus Lacuna Central (Haversian) canal (b)
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Figure 5.4c Microscopic structure of compact bone.
Osteon Interstitial lamellae Lacuna Central (Haversian) canal (c)
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Microscopic Anatomy of Bone
Canaliculi Tiny canals Radiate from the central canal to lacunae Form a transport system connecting all bone cells to a nutrient supply Perforating (Volkmann’s) canal Canal perpendicular to the central canal Carries blood vessels and nerves © 2015 Pearson Education, Inc.
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Figure 5.4b Microscopic structure of compact bone.
Lamella Osteocyte Canaliculus Lacuna Central (Haversian) canal (b)
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Bone Components Organic parts of the matrix make bone flexible
Calcium salts deposited in the matrix make bone hard © 2015 Pearson Education, Inc.
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Bone Formation and Growth
Ossification Process of bone formation Occurs on hyaline cartilage models or fibrous membranes Long bone growth involves two major phases © 2015 Pearson Education, Inc.
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New center of bone growth New bone forming Epiphyseal plate cartilage
Figure 5.5 Stages of long-bone formation in an embryo, fetus, and young child. Articular cartilage Hyaline cartilage Spongy bone New center of bone growth New bone forming Epiphyseal plate cartilage Growth in bone width Medullary cavity Bone starting to replace cartilage Invading blood vessels Growth in bone length New bone forming Bone collar Hyaline cartilage model Epiphyseal plate cartilage In an embryo In a fetus In a child
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Bone Formation and Growth
Two major phases of ossification in long bones Osteoblasts Bone-forming cells Cover hyaline cartilage model Enclosed cartilage is digested away, opening up a medullary cavity © 2015 Pearson Education, Inc.
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Bone Formation and Growth
By birth, most cartilage is converted to bone except for two regions in a long bone: Articular cartilages Epiphyseal plates New cartilage is formed continuously on external face of these two cartilages Old cartilage is broken down and replaced by bony matrix © 2015 Pearson Education, Inc.
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Figure 5.6 Growth and remodeling of long bones.
Bone growth Bone remodeling Bone grows in length because: Growing shaft is remodeled as: Articular cartilage Cartilage grows here. 1 Epiphyseal plate Cartilage is replaced by bone here. 2 Bone is resorbed here. 1 Cartilage grows here. 3 Bone is added by appositional growth here. 2 Cartilage is replaced by bone here. 4 Bone is resorbed here. 3
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Bone Formation and Growth
Bones grow in length and width Appositional growth Growth in diameter Controlled by hormones such as growth hormone Epiphyseal plates are converted to bone during adolescence Growth in length ends © 2015 Pearson Education, Inc.
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Bone Remodeling Bones are lengthened until growth stops
Bones are remodeled throughout life in response to two factors: Blood calcium levels Pull of gravity and muscles on the skeleton © 2015 Pearson Education, Inc.
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Bone Remodeling Parathyroid hormone (PTH)
Released when blood calcium levels are low Activates osteoclasts (bone-destroying cells) Osteoclasts break down bone and release calcium ions into the blood Hypercalcemia (high blood calcium levels) prompts calcium storage to bones © 2015 Pearson Education, Inc.
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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 © 2015 Pearson Education, Inc.
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Bone Fractures Bone fractures are treated by reduction and immobilization Closed reduction: bones are manually coaxed into position by physician’s hands Open reduction: bones are secured with pins or wires during surgery © 2015 Pearson Education, Inc.
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Repair of Bone Fractures
Hematoma (blood-filled swelling) is formed Fibrocartilage callus forms Cartilage matrix, bony matrix, collagen fibers splint the broken bone Bony callus replaces the fibrocartilage callus Osteoblasts and osteoclasts migrate in Bone remodeling occurs in response to mechanical stresses © 2015 Pearson Education, Inc.
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Figure 5.7 Stages in the healing of a bone fracture.
Hematoma External callus Bony callus of spongy bone New blood vessels Internal callus (fibrous tissue and cartilage) Healed fracture Spongy bone trabecula Hematoma forms. 1 Fibrocartilage callus forms. 2 Bony callus forms. 3 Bone remodeling occurs. 4
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Common Types of Fractures
Comminuted: bone breaks into many fragments Compression: bone is crushed Depressed: broken bone portion is pressed inward Impacted: broken bone ends are forced into each other Spiral: ragged break occurs when excessive twisting forces are applied to a bone Greenstick: bone breaks incompletely © 2015 Pearson Education, Inc.
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Table 5.2 Common Types of Fractures.
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