Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Anatomy and Physiology Chapter 8: Skeletal Tissues

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Functions of Bone Support—bones form the framework of the body and contribute to the shape, alignment, and positioning of body parts; ligaments help hold bones together (Figure 8-1) Protection—bony “boxes” protect the delicate structures they enclose Movement—bones with their joints constitute levers that move as muscles contract Mineral storage—bones are the major reservoir for calcium, phosphorus, and other minerals Hematopoiesis—blood cell formation is carried out by myeloid tissue 2

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Types of Bones Structurally, there are five major types of bones (Figure 8-2)  Long bones—cylindrical  Short bones—boxlike  Flat bones—broad, sheetlike  Irregular bones—various shapes  Sesamoid bones—seedlike 4

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Types of Bones Size, shape, and appearance of bones vary to meet the various needs served Bones vary in the proportion of compact and cancellous (spongy) bone  Compact bone—dense and solid in appearance  Cancellous bone—characterized by open space partially filled with a lattice of thin branched structures supporting soft tissue 6

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Types of Bones Parts of a long bone (Figure 8-3)  Diaphysis Main shaft of a long bone Hollow, cylindrical shape and thick compact bone Function—to provide strong support without cumbersome weight  Epiphyses Both ends of a long bone; made of cancellous bone filled with marrow Bulbous shape Function—to provide attachments for muscles and give stability to joints 7

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Types of Bones Parts of a long bone (cont)  Articular cartilage Layer of hyaline cartilage that covers the articular surface of epiphyses Function—to cushion jolts and blows 9

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Types of Bones Parts of a long bone (cont)  Periosteum Dense, white fibrous membrane that covers bone Attaches tendons firmly to bones Contains cells that form and destroy bone Contains blood vessels important in growth and repair Contains blood vessels that send branches into bone Essential for bone cell survival and bone formation 10

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Types of Bones Parts of a long bone (cont)  Medullary (or marrow) cavity Dense, white fibrous membrane that covers bone Attaches tendons firmly to bones Contains cells that form and destroy bone Contains blood vessels important in growth and repair  Endosteum—thin fibrous membrane that lines the medullary cavity 11

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Types of Bones Parts of a flat bone  Inner portion is cancellous bone covered on the outside with compact bone Cranial flat bones have an internal and external table of compact bone and an inner cancellous region called the diploe (Figure 8-4) Bones are covered with periosteum and lined with endosteum, as in a long bone Other flat bones, short bones, and irregular bones have features similar to the cranial bones  Spaces inside the cancellous bone of short, flat, irregular and sesamoid bones are filled with red marrow 12

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Bone Tissue Most distinctive form of connective tissue Extracellular components are hard and calcified Rigidity of bone allows it to serve its supportive and protective functions Tensile strength nearly equal to that of cast iron at less than one third the weight 14

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Bone Tissue Composition of bone matrix  Inorganic salts Hydroxyapatite—crystals of calcium and phosphate contribute to bone hardness Slender needlelike crystals are oriented to most effectively resist stress and mechanical deformation Magnesium, sodium, sulfate, and fluoride are also found in bone 15

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Bone Tissue Composition of bone matrix (cont)  Organic matrix Composite of collagenous fibers and an amorphous mixture of protein and polysaccharides called ground substance Ground substance—secreted by connective tissue cells Adds to overall strength of bone and gives some degree of resilience to bone 16

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Microscopic Structure of Bone Compact bone (Figure 8-5)  Contains many cylinder-shaped structural units called osteons, or Haversian systems (Figure 8-6)  Osteons surround central (osteonal or Haversian) canals that run lengthwise through bone and are connected by transverse (Volkmann) canals Living bone cells located in these units Constitute the structural framework of compact bone 17

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Microscopic Structure of Bone Compact bone (cont)  Osteons permit delivery of nutrients and removal of waste products  Structures that make up each osteon Lamellae  Concentric—cylinder-shaped layers of calcified matrix around the central canal  Interstitial—layers of bone matrix between the osteons; left over from previous osteons  Circumferential—few layers of bone matrix that surround all the osteons; run along the outer circumference of a bone and inner circumference (boundary of medullary cavity) of a bone 20

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Microscopic Structure of Bone  Structures that make up each osteon (cont) Lacunae—small spaces containing tissue fluid; bone cells are located between hard layers of the lamella Canaliculi—ultra-small canals radiating in all directions from the lacunae and connecting them to each other and to the central canal Central (osteonal or Haversian) canal—extends lengthwise through the center of each osteon and contains blood vessels and lymphatic vessels 21

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Microscopic Structure of Bone Cancellous bone—also called spongy bone or trabecular bone (Figure 8-6)  No osteons in cancellous bone; instead, it has trabeculae  Nutrients are delivered and waste products removed by diffusion through tiny canaliculi  Lattice of bony branches (trabeculae) are arranged along lines of stress to enhance the bone’s strength (Figure 8-7) 22

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Microscopic Structure of Bone Cancellous bone (cont)  Blood supply Bone cells receive blood supply from the bone marrow in the internal medullary cavity of cancellous bone Blood vessels from the periosteum become incorporated into the bone and serve nutrient needs of cells by way of transverse (Volkmann) canals, connected with vessels in the central canals of osteons 24

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Microscopic Structure of Bone Types of bone cells  Osteoblasts (Figure 8-8) Bone-forming cells found in all bone surfaces Small cells synthesize and secrete osteoid, an important part of the ground substance Collagen fibrils line up in osteoid and serve as a framework for the deposition of calcium and phosphate 25

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Microscopic Structure of Bone Types of bone cells  Osteoclasts (Figure 8-8) Giant multinucleated cells Responsible for the active erosion of bone minerals Contain large numbers of mitochondria and lysosomes  Osteocytes—mature, nondividing osteoblasts surrounded by matrix and lying within lacunae (Figure 8-9) 27

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Bone Marrow Type of soft, diffuse connective tissue; called myeloid tissue Site for the production of blood cells Found in the medullary cavities of long bones and in the spaces of spongy bone 29

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Bone Marrow Two types of marrow occur during a person's lifetime (Figure 8-10)  Red marrow Found in virtually all bones in an infant’s or child’s body Functions to produce red blood cells  Yellow marrow As an individual ages, red marrow is replaced by yellow marrow Marrow cells become saturated with fat and are no longer active in blood cell production 30

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Bone Marrow Main bones in an adult that still contain red marrow include the ribs, bodies of the vertebrae, humerus, pelvis, and femur Yellow marrow can change to red marrow during times of decreased blood supply, such as anemia, exposure to radiation, and certain diseases 32

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Regulation of Blood Calcium Levels Skeletal system serves as a storehouse for about 98% of body calcium reserves  Helps maintain constancy of blood calcium levels Calcium is mobilized and moves into and out of blood during bone remodeling During bone formation, osteoblasts remove calcium from blood and lower circulating levels During breakdown of bone, osteoclasts release calcium into blood and increase circulating levels 33

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Regulation of Blood Calcium Levels Skeletal system (cont)  Homeostasis of calcium ion concentration essential for the following: Bone formation, remodeling, and repair Blood clotting Transmission of nerve impulses Maintenance of skeletal and cardiac muscle contraction 34

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Regulation of Blood Calcium Levels Mechanisms of calcium homeostasis (Figure 8-11)  Parathyroid hormone Primary regulator of calcium homeostasis Stimulates osteoclasts to initiate breakdown of bone matrix and increase blood calcium levels Increases renal absorption of calcium from urine Stimulates vitamin D synthesis 35

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Regulation of Blood Calcium Levels Mechanisms of calcium homeostasis (cont)  Calcitonin Protein hormone produced in the thyroid gland Produced in response to high blood calcium levels Stimulates bone deposition by osteoblasts Inhibits osteoclast activity Far less important in homeostasis of blood calcium levels than is parathyroid hormone 37

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Regulation of Blood Calcium Levels Mechanisms of calcium homeostasis (cont)  Other mechanisms Growth hormone (GH)—increases bone growth, thus reducing blood calcium Serotonin—inhibits osteoblast activity, thus increases blood calcium 38

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Development of Bone Osteogenesis—development of bone from small cartilage or membrane model to adult bone Intramembranous ossification (Figure 8-13)  Occurs within a connective tissue membrane  Flat bones begin when groups of cells differentiate into osteoblasts  Osteoblasts are clustered together in ossification center 39

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Development of Bone Intramembranous ossification (cont)  Osteoblasts secrete matrix material and collagenous fibrils  Large amounts of ground substance accumulate around each osteoblast  Collagenous fibers become embedded in the ground substance and constitute the bone matrix  Bone matrix calcifies when calcium salts are deposited  Trabeculae appear and join in a network to form spongy bone  Appositional growth occurs by adding osseous tissue 41

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Development of Bone Endochondral ossification (Figure 8-14)  Most bones begin as a cartilage model with bone formation spreading essentially from the center to the ends  Periosteum develops and enlarges to produce a collar of bone  Primary ossification center forms (Figure 8- 15)  Blood vessel enters the cartilage model at the midpoint of the diaphysis 42

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Development of Bone Endochondral ossification (cont)  Bone grows in length as endochondral ossification progresses from the diaphysis toward each epiphysis (Figure 8-16)  Secondary ossification centers appear in the epiphysis, and bone growth proceeds toward the diaphysis  Epiphyseal plate remains between the diaphysis and each epiphysis until bone growth in length is complete 45

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Development of Bone Endochondral ossification (cont)  Epiphyseal plate is composed of four layers (Figures 8-17 and 8-18) “Resting” cartilage cells—point of attachment joining the epiphysis to the shaft Zone of proliferation—cartilage cells undergoing active mitosis, which causes the layer to thicken and the plate to increase in length Zone of hypertrophy—older, enlarged cells undergoing degenerative changes associated with calcium deposition Zone of calcification—dead or dying cartilage cells undergoing rapid calcification 47

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Development of Bone Endochondral ossification (cont)  Epiphyseal plate can be a site for bone fractures in young people (Figure 8-19)  Long bones grow in both length and diameter (Figure 8-20) 50

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Bone Remodeling Primary osteons develop within early woven bone (Figure 8-21)  Conelike or tubelike space is hollowed out by osteoclasts  Osteoblasts in the endosteum that lines the tube begin forming layers (lamellae) that trap osteocytes between layers.  A central canal is left for the blood and lymphatic vessels and nerves  Primary osteons can be replaced later by secondary osteons in a similar manner 53

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Bone Remodeling Bones grow in length and diameter by the combined action of osteoclasts and osteoblasts  Osteoclasts enlarge the diameter of the medullary cavity  Osteoblasts from the periosteum build new bone around the outside of the bone Mechanical stress, as from physical activity, strengthens bone 55

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Bone Remodeling Fracture—break in the continuity of a bone Fracture healing (Figure 8-22)  Fracture tears and destroys blood vessels that carry nutrients to osteocytes  Vascular damage initiates repair sequence  Callus—special repair tissue that binds the broken ends of the fracture together  Fracture hematoma—blood clot occurring immediately after the fracture, which is then resorbed and replaced by callus 56

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Cartilage Characteristics  Avascular connective tissue  Fibers of cartilage are embedded in a firm gel  Has the flexibility of firm plastic  No canal system or blood vessels 58

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Cartilage Characteristics (cont)  Chondrocytes receive oxygen and nutrients by diffusion  Perichondrium—fibrous covering of the cartilage  Cartilage types differ because of the amount of matrix present and the amounts of elastic and collagenous fibers 59

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Cartilage Types of cartilage (Figure 8-23)  Hyaline cartilage Most common type Covers the articular surfaces of bones Forms the costal cartilages, cartilage rings in the trachea, bronchi of the lungs, and the tip of the nose Forms from special cells in chondrification centers, which secrete matrix material Chondrocytes are isolated into lacunae 60

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Cartilage Types of cartilage (cont)  Elastic cartilage Forms external ear, epiglottis, and eustachian tubes Large numbers of elastic fibers confers elasticity and resiliency  Fibrocartilage (fibrous cartilage) Occurs in pubic symphysis and intervertebral disks Small quantities of matrix and abundant fibrous elements Strong and rigid 62

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Cartilage Function of cartilage  Tough, rubberlike nature permits cartilage to sustain great weight or serve as a shock absorber  Strong yet pliable support structure  Permits growth in length of long bones 63

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Cartilage Growth of cartilage  Interstitial or endogenous growth Cartilage cells divide and secrete additional matrix Seen during childhood and early adolescence while cartilage is still soft and capable of expansion from within  Appositional or exogenous growth Chondrocytes in the deep layer of the perichondrium divide and secrete matrix New matrix is deposited on the surface, thereby increasing its size Unusual in early childhood, but once initiated, continues throughout life 64

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Cycle of Life: Skeletal Tissues Skeleton fully ossified by mid-twenties  Soft tissue may continue to grow— ossifies more slowly Adults—changes occur as a result of specific conditions  Increased density and strength result from exercise  Decreased density and strength result from pregnancy, nutritional deficiencies, and illness 65

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Cycle of Life: Skeletal Tissues Advanced adulthood—apparent degeneration  Hard bone matrix replaced by softer connective tissue  Exercise can counteract degeneration 66