Bone Structure and Function
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Questions and Answers

What is the primary function of bone in the body?

  • To regulate body temperature
  • To produce blood cells
  • To act as a reservoir for proteins
  • To support the body and protect internal organs (correct)

    • Which type of collagen is an important component of osteoid?

  • Type I collagen (correct)
  • Type II collagen
  • Type IV collagen
  • Type III collagen

    • What is the role of osteocalcin in bone development?

  • To generate matrix vesicles
  • To bind PO4- ions
  • To bind Ca2+ ions (correct)
  • To regulate osteoblast activity

    • How do osteocytes communicate with adjacent cells?

    <p>Through a network of long dendritic processes</p> Signup and view all the answers

    What is the role of osteoclasts in bone development?

    <p>To locally erode bone matrix</p> Signup and view all the answers

    What is the result of high concentrations of Ca2+ and PO4- ions in the bone matrix?

    <p>Formation of hydroxyapatite crystals</p> Signup and view all the answers

    What is the primary function of the periosteum?

    <p>To mediate bone growth and remodeling</p> Signup and view all the answers

    What type of fibers bind the periosteum to the bone matrix?

    <p>Type I collagen fibers</p> Signup and view all the answers

    Which cells are present in regions of periosteum adjacent to bone?

    <p>Osteoprogenitor cells and osteoblasts</p> Signup and view all the answers

    What is the endosteum composed of?

    <p>A thin layer of active and inactive osteoblasts</p> Signup and view all the answers

    Where are osteoblasts required for bone growth?

    <p>In both the periosteum and endosteum</p> Signup and view all the answers

    What is the purpose of the canaliculi in the osteon?

    <p>To allow all cells to communicate with the central canal</p> Signup and view all the answers

    What type of bone tissue is characterized by small bony trabeculae or spicules?

    <p>Cancellous bone</p> Signup and view all the answers

    What is the function of osteoclasts and osteoblasts in bone remodeling?

    <p>To remodeled woven bone into lamellar bone</p> Signup and view all the answers

    What is the organization of lamellae in compact bone?

    <p>Concentrically around small central canals</p> Signup and view all the answers

    What is the term for the small, knobby, bulbous ends of long bones?

    <p>Epiphyses</p> Signup and view all the answers

    What is the term for the immature bone tissue formed during osteogenesis or repair?

    <p>Woven bone</p> Signup and view all the answers

    Which type of ossification is responsible for the formation of bones in the skull and jaws?

    <p>Intramembranous ossification</p> Signup and view all the answers

    What is the initial cavity in the diaphyses of fetal long bones formed from?

    <p>Enclosure of the cartilage within a collar of woven bone</p> Signup and view all the answers

    What is the role of periosteal osteoblasts and vasculature in primary ossification centers?

    <p>To enter the initial cavity and promote bone growth</p> Signup and view all the answers

    What is the location of the cartilage in the epiphyseal growth plate?

    <p>Between the primary and secondary ossification centers</p> Signup and view all the answers

    What is the characteristic of bone formation in all bones except those of the skull and jaws?

    <p>Endochondral ossification</p> Signup and view all the answers

    What is the function of the zone of proliferation in the growth plate?

    <p>Chondrocytes undergo mitosis</p> Signup and view all the answers

    What occurs in the zone of hypertrophy?

    <p>The most mature chondrocytes swell up and undergo apoptosis</p> Signup and view all the answers

    What is the result of the events in the zone of cartilage calcification?

    <p>Spaces are created in the matrix that are invaded by osteoblasts and vasculature</p> Signup and view all the answers

    What is the role of osteoblasts in the zone of ossification?

    <p>Lay down woven bone</p> Signup and view all the answers

    What is the result of appositional bone growth?

    <p>The bone circumference increases</p> Signup and view all the answers

    What is the main function of osteoclasts and osteoblasts in bone remodeling?

    <p>To change the size and shape of bones according to mechanical stress</p> Signup and view all the answers

    What is the initial stage of bone repair after fracture or other injury?

    <p>Activation of periosteal fibroblasts to produce a soft callus of fibrocartilage-like tissue</p> Signup and view all the answers

    What is the purpose of bone remodeling?

    <p>To change the size and shape of bones according to mechanical stress</p> Signup and view all the answers

    What is the final stage of bone repair after fracture or other injury?

    <p>Remodeling of lamellar bone to produce stronger bone</p> Signup and view all the answers

    What is the function of periosteal fibroblasts in bone repair?

    <p>To produce an initial soft callus of fibrocartilage-like tissue</p> Signup and view all the answers

    What is the primary function of calcium in the body?

    <p>To maintain proper blood calcium levels</p> Signup and view all the answers

    Which hormone stimulates osteoclasts to elevate calcium levels in blood?

    <p>Parathyroid hormone (PTH)</p> Signup and view all the answers

    What is the result of inadequate dietary calcium intake?

    <p>Mobilization of calcium from bone</p> Signup and view all the answers

    Which cells are involved in maintaining proper blood calcium levels?

    <p>All three major bone cells</p> Signup and view all the answers

    What is the effect of calcitonin on osteoclast activity?

    <p>Inhibition of osteoclast activity</p> Signup and view all the answers

    Study Notes

    Bone Structure and Function

    • Bone is a type of connective tissue that provides support to the body, protects internal organs, and acts as the body's calcium reservoir.

    Cells and Matrix Components of Bone

    • Osteoblasts differentiate from osteoprogenitor cells and secrete osteoid, which allows matrix mineralization to occur.
    • Osteoid components include type I collagen, osteocalcin, and matrix vesicles with enzymes generating PO4-.
    • High concentrations of Ca2+ and PO4- ions cause formation of hydroxyapatite crystals, which gradually calcify the entire matrix.
    • Osteocytes differentiate from osteoblasts and become enclosed within matrix lacunae, maintaining the matrix and detecting mechanical stresses on bone.
    • Osteocytes communicate with adjacent cells via a network of long dendritic processes that extend through the matrix via narrow canaliculi radiating from each lacuna.
    • Osteoclasts are formed by fusion of several blood monocytes and locally erode bone matrix during osteogenesis and bone remodeling.

    Periosteum

    • A layer of dense connective tissue on the outer surface of bone
    • Bound to bone matrix by bundles of type I collagen called perforating (or Sharpey) fibers
    • Regions adjacent to bone are rich in osteoprogenitor cells and osteoblasts
    • Mediates much bone growth and remodeling through osteoprogenitor cells and osteoblasts

    Endosteum

    • A thin layer of active and inactive osteoblasts
    • Lines all internal surfaces within bone
    • Osteoblasts in endosteum are required for bone growth

    Types of Bone

    • Dense bone beneath the periosteum is called compact bone
    • Deep to compact bone are small bony trabeculae or spicules of cancellous (or spongy) bone

    Bone Structure

    • Long bones of the limbs have both compact and cancellous bone in epiphyses (knobby, bulbous ends) and diaphysis (intervening shaft)

    Immature Bone

    • Woven bone is formed during osteogenesis or repair and has a calcified matrix with randomly arranged collagen fibers

    Bone Remodeling

    • Osteoclasts and osteoblasts remodel woven bone into lamellar bone with new matrix deposited in distinct layers with parallel collagen bundles

    Lamellar Bone

    • Compact and cancellous bone are both types of lamellar bone
    • Most lamellar bone consists of lamellae organized concentrically around small central canals containing blood vessels and nerves, called an osteon or Haversian system
    • Osteocytic lacunae occur between the lamellae, with canaliculi radiating through the lamellae, allowing all cells to communicate with the central canal

    Osteogenesis

    • Bones of the skull and jaws develop through intramembranous ossification, where osteoblasts differentiate directly from mesenchyme progenitor cells.
    • In contrast, all other bones form through endochondral ossification, involving osteoprogenitor cells surrounding and invading hyaline cartilage models in the embryo.
    • Primary ossification centers in fetal long bones develop when chondrocytes die after being enclosed by a collar of woven bone, creating an initial cavity.
    • Periosteal osteoblasts and vasculature then enter this cavity, marking the beginning of primary ossification.
    • Secondary ossification centers develop later, within the epiphyses, with the cartilage of the epiphyseal growth plate situated between the primary and secondary ossification sites.

    Bone Elongation During Childhood

    • Growth plates consist of an interrelated series of developing zones that enable bone elongation during childhood

    Zones of Growth Plate Development

    • Reserve Zone: most distal zone, composed of typical hyaline cartilage that serves as a "resting" zone
    • Proliferation Zone: adjacent to reserve zone, chondrocytes undergo mitosis and appear stacked within elongated lacunae
    • Hypertrophy Zone: most mature chondrocytes swell up, compress the matrix, and undergo apoptosis, located closer to the primary ossification center
    • Zone of Cartilage Calcification: spaces created in the matrix by apoptosis are invaded by osteoblasts, osteoclasts, and vasculature from the primary center
    • Zone of Ossification: woven bone is initially laid down by osteoblasts and remodeled into lamellae bone

    Bone Growth and Development

    • Appositional bone growth increases the circumference of a bone through osteoblast activity at the periosteum
    • Enlargement of the medullary marrow cavity accompanies appositional bone growth

    Bone Growth and Remodeling

    • Bone growth occurs throughout life, with continuous turnover of cells and matrix through the activities of osteoblasts and osteoclasts.
    • Lamellae and osteons are temporary structures that are constantly replaced and rebuilt in a process of bone remodeling.
    • Bone remodeling allows bones to change size and shape according to changes in mechanical stress.

    Bone Repair

    • Bone repair after fracture or injury involves the activation of periosteal fibroblasts to produce an initial soft callus of fibrocartilage-like tissue.
    • The soft callus is gradually replaced by a hard callus of woven bone.
    • The hard callus is soon remodeled to produce stronger lamellar bone.

    Calcium Homeostasis

    • Calcium (Ca2+) is a crucial ion for all cells, and its levels are maintained through bone storage and mobilization.
    • When dietary calcium is sufficient, Ca2+ is stored in bone.
    • When dietary calcium is deficient, Ca2+ is mobilized from bone.

    Bone Cell Activity

    • Maintenance of proper blood calcium levels involves the activity of osteoblasts, osteoclasts, and osteocytes.
    • Subtle paracrine interactions among bone cells and other cells regulate this process.

    Hormonal Regulation

    • Parathyroid hormone (PTH) indirectly stimulates osteoclasts, increasing calcium levels in the blood.
    • Calcitonin inhibits osteoclast activity, decreasing blood calcium levels.

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    Description

    Learn about bone as a type of connective tissue, its components, and its role in the body. Explore osteoblasts, osteoid, and matrix mineralization.

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