Hormonal Regulation of Bone Growth
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Questions and Answers

Which hormone is primarily responsible for stimulating epiphyseal plate activity during infancy and childhood?

  • Thyroid hormone
  • Growth hormone (correct)
  • Testosterone
  • Calcitonin
  • What is the role of thyroid hormone in bone growth?

  • Directly induces growth spurts at puberty
  • Inhibits the action of growth hormone
  • Modulates the activity of growth hormone (correct)
  • Closes the epiphyseal plates
  • What effect do testosterone and estrogens have during puberty regarding bone growth?

  • Promote elongation of bones only in males
  • Induce growth spurts and lead to epiphyseal plate closure (correct)
  • Start the remodeling process of bone
  • Increase calcium absorption in the bones
  • What triggers the production of parathyroid hormone (PTH)?

    <p>Low blood calcium levels</p> Signup and view all the answers

    What is a characteristic of a displaced fracture?

    <p>Ends of the bone are out of normal alignment</p> Signup and view all the answers

    In which type of fracture is the skin penetrated?

    <p>Open (compound) fracture</p> Signup and view all the answers

    How does calcitonin function in relation to blood calcium levels?

    <p>Lowers blood calcium levels by inhibiting bone resorption</p> Signup and view all the answers

    What is the consequence of an excess or deficit of hormones on skeletal growth?

    <p>It causes abnormal skeletal growth</p> Signup and view all the answers

    What is the primary function of osteogenic cells in bone tissue?

    <p>They differentiate into osteoblasts when stimulated.</p> Signup and view all the answers

    Which layer of the periosteum contains osteogenic stem cells?

    <p>Osteogenic layer</p> Signup and view all the answers

    How does the structure of flat bones differ from that of long bones?

    <p>Flat bones consist of compact bone sandwiched between connective tissue membranes.</p> Signup and view all the answers

    What type of bone is characterized by a lack of a defined marrow cavity?

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

    Which of the following bone cells is primarily involved in the resorption of bone tissue?

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

    What primarily composes the osteoid secreted by osteoblasts?

    <p>Collagen and calcium-binding proteins</p> Signup and view all the answers

    What is the outer layer of the periosteum primarily composed of?

    <p>Dense irregular connective tissue</p> Signup and view all the answers

    Which structure covers the internal surfaces of bone?

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

    What is the primary function of osteocytes?

    <p>To maintain the bone matrix and sense mechanical stress</p> Signup and view all the answers

    What distinguishes osteoclasts from other bone cells?

    <p>They are multinucleate and specialize in bone resorption.</p> Signup and view all the answers

    Which structure serves as the basic functional and structural unit of compact bone?

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

    What role do lamellae play in the osteon structure?

    <p>They provide strength and resistance to twisting.</p> Signup and view all the answers

    How does the central canal in an osteon differ from perforating canals?

    <p>The central canal contains blood vessels and nerve fibers.</p> Signup and view all the answers

    What purpose do canaliculi serve within bone tissue?

    <p>To connect osteocytes and the central canal.</p> Signup and view all the answers

    What characteristic feature do osteoclasts possess to enhance their function?

    <p>They have ruffled borders for increased surface area.</p> Signup and view all the answers

    Which of the following structures do not contain osteocytes?

    <p>Central canal</p> Signup and view all the answers

    What is the primary structural component that provides strength to spongy bone?

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

    Which of the following is NOT a component of the organic matrix of bone?

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

    During which process does bone replace hyaline cartilage?

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

    What percentage of bone mass is made up of hydroxyapatites?

    <p>65%</p> Signup and view all the answers

    What occurs during the process of ossification?

    <p>Formation of bony skeleton</p> Signup and view all the answers

    Which of the following best describes intramembranous ossification?

    <p>Bone forms from fibrous membrane</p> Signup and view all the answers

    Which component is crucial for supplying nutrients to spongy bone?

    <p>Capillaries in endosteum</p> Signup and view all the answers

    Which stage of bone development begins in the second month of embryonic development?

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

    What is the main sequence of events in endochondral ossification?

    <p>Formation of hyaline cartilage followed by vascularization</p> Signup and view all the answers

    Which bones are formed primarily through intramembranous ossification?

    <p>Frontal and parietal bones</p> Signup and view all the answers

    What primarily controls the increase in thickness of bones during growth?

    <p>Secretion of bone matrix by osteoblasts beneath periosteum</p> Signup and view all the answers

    What occurs at the epiphyseal plate during postnatal bone growth?

    <p>Interstitial growth occurs to increase length</p> Signup and view all the answers

    How does the body adjust bone density in response to physical activity?

    <p>Stimulates more osteoblast activity leading to thicker bones</p> Signup and view all the answers

    When does the process of endochondral ossification primarily begin during development?

    <p>Late in the second month of embryonic development</p> Signup and view all the answers

    What role do osteoclasts play in the growth of bones?

    <p>Remove bone tissue from the periosteal surface</p> Signup and view all the answers

    Which factor is least likely to lead to an increase in bone thickness?

    <p>Consistent physical inactivity</p> Signup and view all the answers

    Study Notes

    Hormonal Regulation of Bone Growth

    • Growth hormone is crucial for stimulating epiphyseal plate activity during childhood.
    • Thyroid hormone regulates the activity of growth hormone, ensuring proper proportions.
    • Testosterone (males) and estrogen (females) promote adolescent growth spurts, but eventually induce closure of the epiphyseal plates, ending bone lengthening.
    • Excesses or deficits in any of these hormones can lead to abnormal skeletal growth.

    Control of Remodeling

    • Parathyroid hormone (PTH) is released by the parathyroid glands in response to low blood calcium levels.
      • PTH stimulates osteoclasts to resorb bone, releasing calcium into the bloodstream.
      • This process continues until calcium levels reach homeostasis.
    • Calcitonin is produced by the parafollicular cells of the thyroid gland in response to high blood calcium levels.
      • Calcitonin inhibits osteoclast activity, decreasing bone resorption and lowering blood calcium levels.

    Bone Repair

    • Fractures are classified based on the position of bone ends, completeness of the break and whether the skin is penetrated.
      • Position:
        • Nondisplaced: Bone ends remain in their normal position.
        • Displaced: Bone ends are out of alignment.
      • Completeness:
        • Complete: Break extends through the entire bone.
        • Incomplete: Break does not extend through the entire bone.
      • Skin Penetration:
        • Open (compound): Skin is penetrated by the fractured bone.
        • Closed (simple): Skin is not penetrated.

    Gross Anatomy: Long Bone

    • Membranes:
      • Periosteum: Double-layered membrane covering the external surface of bone, excluding joints.
        • Fibrous layer: Outer layer composed of dense irregular connective tissue with Sharpey's fibers that secure to bone matrix.
        • Osteogenic layer: Inner layer containing osteogenic stem cells that give rise to most bone cells.
      • Endosteum: Delicate connective tissue membrane lining the internal bone surface.
        • Contains osteogenic cells.

    Gross Anatomy: Flat Bone

    • Flat, irregular, and short bones have thin plates of spongy bone covered by compact bone.
    • Compact bone is sandwiched between periosteum and endosteum.
    • Bone marrow is scattered throughout the spongy bone; there is no defined marrow cavity.

    Microscopic Anatomy of Bone: Cells

    • Osteogenic cells: Mitotically active stem cells in periosteum and endosteum.
      • Differentiate into osteoblasts.
    • Osteoblasts: Bone-forming cells that secrete osteoid, an unmineralized bone matrix composed of collagen and calcium-binding proteins.
      • Collagen makes up 90% of bone protein.
    • Osteocytes: Mature bone cells housed in lacunae that maintain bone matrix and act as stress sensors.
    • Osteoclasts: Giant, multinucleate cells derived from hematopoietic stem cells.
      • Involved in bone resorption.
      • Reside in depressions called resorption bays, featuring ruffled borders for enhanced enzyme degradation of bone.

    Microscopic Anatomy of Compact Bone

    • Osteon (Haversian system): Structural unit of compact bone.
      • Elongated cylinder running parallel to the long axis of the bone, acting as weight-bearing pillars.
      • Composed of lamellae, rings of bone matrix containing collagen fibers oriented in different directions for stress resistance.
    • Canals and canaliculi:
      • Central (Haversian) canal: Runs through the core of the osteon, containing blood vessels and nerve fibers.
      • Perforating (Volkmann’s) canals: Perpendicular to central canal, lined with endosteum.
      • Lacunae: Small cavities housing osteocytes.
      • Canaliculi: Hairlike canals connecting lacunae to each other and to the central canal.

    Microscopic Anatomy of Spongy Bone

    • Spongy bone is organized along lines of stress for optimal resistance.
    • Trabeculae: Irregular lattice-like bony struts that resist stress.
      • Contain irregularly arranged lamellae and osteocytes interconnected by canaliculi.
      • No osteons are present in spongy bone.
    • Capillaries in the endosteum supply nutrients to spongy bone.

    Chemical Composition of Bone

    • Organic Component: One-third of organic bone matrix is osteoid, secreted by osteoblasts.
      • Osteoid is composed of ground substance and collagen fibers, granting bone flexibility and tensile strength.
    • Inorganic Component:
      • Hydroxyapatites (mineral salts): Account for 65% of bone mass.
        • Tiny calcium phosphate crystals located in and around collagen fibers, responsible for bone hardness and resistance to compression.

    Bone Development

    • Ossification (osteogenesis): Bone tissue formation.
      • Embryonic ossification: Begins during month 2 of development.
      • Postnatal ossification: Continues until early adulthood.
      • Bone remodeling and repair: Lifelong processes.

    Embryonic Bone Growth

    • Endochondral ossification: Bone formation by replacing hyaline cartilage.
      • Responsible for formation of most bones in the body, except for some skull bones and clavicles.
      • Requires breakdown of hyaline cartilage prior to ossification.
      • Starts at the primary ossification center in the shaft of long bones.
    • Intramembranous ossification: Bone formation directly from fibrous membranes.
      • Forms flat bones of the skull and the clavicle.

    Postnatal Bone Growth

    • Longitudinal growth: Occurs at the epiphyseal plate, allowing bones to lengthen.
    • Appositional growth: Bones increase thickness by adding bone matrix on the external surface.
    • Bone growth ceases during adolescence, except for slow, continued growth of some facial bones throughout life.

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    Description

    This quiz covers the essential hormones responsible for bone growth and remodeling. It explores the roles of growth hormone, thyroid hormone, and sex hormones in skeletal development during various life stages. Additionally, it examines the mechanisms of calcium homeostasis and the impact of parathyroid hormone and calcitonin on bone health.

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