Bone Physiology and Structure
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Questions and Answers

What characteristic differentiates trabecular bone from compact bone?

  • Trabecular bone has irregularly arranged lamellae forming trabeculae. (correct)
  • Trabecular bone is located on the exterior of bones.
  • Trabecular bone is always denser than compact bone.
  • Trabecular bone contains osteons.

    • Which type of marrow is typically found in the spaces of trabecular bone that produces blood cells?

  • Yellow bone marrow.
  • Red bone marrow. (correct)
  • Adipose tissue.
  • White bone marrow.

    • What percentage of calcium in the body is found in crystalline form within the skeleton and teeth?

  • 90%
  • 99.9%
  • 75%
  • 99% (correct)

    • Which hormone is NOT involved in the regulation of calcium and phosphate levels in the body?

    <p>Insulin.</p> Signup and view all the answers

    What effect does a decrease in free ECF calcium (Ca2+) have on neuromuscular excitability?

    <p>It increases excitability of nerves.</p> Signup and view all the answers

    How is the free calcium (Ca2+) in the extracellular fluid (ECF) primarily characterized?

    <p>It is freely diffusible.</p> Signup and view all the answers

    What happens to the permeability of excitable tissues when free Ca2+ levels increase?

    <p>Na+ permeability decreases.</p> Signup and view all the answers

    Which of the following correctly states the relationship between free calcium and its impact on the resting potential?

    <p>Lower free Ca2+ moves the resting potential closer to the threshold.</p> Signup and view all the answers

    What is the primary composition of hydroxyapatite crystals found in bone?

    <p>Calcium phosphate</p> Signup and view all the answers

    What physiological function does bone remodeling serve regarding bone strength?

    <p>Bones thicken when subjected to heavy loads</p> Signup and view all the answers

    Which cells are responsible for dissolving the hydroxyapatite crystals in bones?

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

    How often is the adult human skeleton estimated to be completely regenerated through remodeling?

    <p>Every 10 years</p> Signup and view all the answers

    What is the normal range for plasma Ca2+ concentration?

    <p>9.2 to 10.4 mg/dL</p> Signup and view all the answers

    What is the role of osteoblasts during the bone remodeling process?

    <p>They secrete osteoid to fill cavities</p> Signup and view all the answers

    Which aspect is not part of calcium homeostasis regulation?

    <p>Controlling calcium excretion through sweating</p> Signup and view all the answers

    What is the main reason old bone requires remodeling?

    <p>To replace brittle and weak organic matrix</p> Signup and view all the answers

    What is the primary function of parathyroid hormone (PTH)?

    <p>To increase plasma Ca2+ concentration.</p> Signup and view all the answers

    How does PTH primarily affect the bones?

    <p>By promoting fast Ca2+ efflux into plasma.</p> Signup and view all the answers

    What occurs in the complete absence of PTH?

    <p>Death occurs within a few days.</p> Signup and view all the answers

    Which statement best describes the role of the osteocytic-osteoblastic bone membrane?

    <p>It connects bone cells for material exchange.</p> Signup and view all the answers

    Which of the following is NOT a site of action for PTH?

    <p>Brain.</p> Signup and view all the answers

    In addition to raising plasma Ca2+ levels, what other effect does PTH have?

    <p>Lowers plasma PO43- concentration.</p> Signup and view all the answers

    How does PTH withdraw calcium from the 'bone bank'?

    <p>Through a fast efflux from the bone fluid.</p> Signup and view all the answers

    What is the immediate effect of PTH on calcium levels?

    <p>Promotion of calcium transfer from bone fluid to plasma.</p> Signup and view all the answers

    What is the function of osteoblasts in bone physiology?

    <p>They produce the organic matrix known as osteoid.</p> Signup and view all the answers

    What happens to bones without sufficient collagen fibers?

    <p>They become excessively brittle.</p> Signup and view all the answers

    Which type of bone cell is responsible for resorption of bone?

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

    What composes the osteoid found in bone tissue?

    <p>Collagen fibers embedded in a semisolid gel called ground substance.</p> Signup and view all the answers

    Compact bone is characterized by which structural feature?

    <p>An arrangement of osteons around central canals.</p> Signup and view all the answers

    What is the consequence of calcium phosphate salt deficiency in bones?

    <p>Bones become soft and bend easily.</p> Signup and view all the answers

    Where are osteocytes primarily located in the bone structure?

    <p>Embedded within the bony wall they deposited.</p> Signup and view all the answers

    What is the role of the periosteum in bone physiology?

    <p>It covers the outer surface of the bone.</p> Signup and view all the answers

    What is the primary role of PTH in relation to the kidneys?

    <p>Increases reabsorption of Ca2+ and promotes vitamin D activation</p> Signup and view all the answers

    How does PTH indirectly affect the absorption of Ca2+ and PO43- in the intestine?

    <p>By activating vitamin D through stimulation of hydroxylase in the kidney</p> Signup and view all the answers

    What are the two sites where vitamin D undergoes activation in the body?

    <p>Liver and kidneys</p> Signup and view all the answers

    What triggers the secretion of PTH from the parathyroid glands?

    <p>Decrease in plasma concentration of free Ca2+</p> Signup and view all the answers

    What is the active form of vitamin D referred to as?

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

    Calcitonin is secreted from which gland?

    <p>Thyroid gland</p> Signup and view all the answers

    Which of the following statements about the function of vitamin D is true?

    <p>Vitamin D increases intestinal absorption of Ca2+ and PO43-.</p> Signup and view all the answers

    What biochemical alterations are required for vitamin D to become biologically active?

    <p>Addition of two hydroxyl groups</p> Signup and view all the answers

    Study Notes

    Bone Physiology

    • Bone is a dynamic connective tissue comprising cells and osteoid, an organic matrix that provides structure.
    • Osteoblasts are responsible for producing the organic matrix, which includes collagen fibers embedded in a gel-like ground substance.
    • Calcium phosphate crystals within the osteoid harden the bone, giving it the strength to support body weight.
    • Osteogenesis imperfecta leads to brittle bones due to a lack of collagen, resulting in excessive fragility.
    • Rickets is characterized by soft bones due to inorganic salt deficiency.
    • Three primary bone cells:
      • Osteoblasts: Secrete osteoid.
      • Osteocytes: Retired osteoblasts residing within the bone they deposited.
      • Osteoclasts: Macrophages that resorb bone tissue.

    Bone Structure

    • Compact Bone: Dense outer layer consisting of organized osteon units; characterized by concentric lamellae and central canals for blood vessels.
    • Trabecular Bone: Also known as spongy bone, found internally, lacks osteons, and contains irregularly arranged lamellae and macroscopic spaces filled with marrow.
    • Trabecular bone spaces are either filled with red marrow (blood cell production) or yellow marrow (fat storage).

    Calcium Regulation and Hormonal Control

    • Approximately 99% of body calcium (Ca2+) resides in the skeleton and teeth, with small amounts in soft tissues and the extracellular fluid (ECF).
    • Only free ECF calcium is biologically active and subject to regulation.
    • Calcium homeostasis is governed by three main hormones: parathyroid hormone (PTH), calcitonin, and vitamin D.

    Regulation of Plasma Calcium

    • Normal plasma Ca2+ concentration ranges from 9.2 to 10.4 mg/dL.
    • Vital for neuromuscular excitability; adjustments in plasma Ca2+ levels can dramatically affect nerve and muscle functions.
    • Ca2+ influences membrane permeability to Na+, affecting excitability.

    Bone Remodeling

    • Bone resorption (by osteoclasts) and deposition (by osteoblasts) occur simultaneously, allowing continual remodeling.
    • Remodeling adjusts bone strength and shape according to stress and prevents brittleness from aging bone.
    • Osteoclasts dissolve bone crystals with hydrochloric acid, while osteoblasts fill cavities with new osteoid.

    Calcium Balance and PTH Function

    • PTH is crucial for maintaining both calcium homeostasis and balance by acting on bone, kidneys, and intestines.
    • It releases calcium from bones, increases kidney absorption, and enhances intestinal absorption through vitamin D activation.
    • Essential for life; absence of PTH leads to fatal hypocalcemia.

    Vitamin D Activation

    • Vitamin D is necessary for calcium absorption and is acquired via diet or synthesized from skin exposure to sunlight.
    • Requires conversion in the liver and kidneys to become active (1,25-(OH)2-vitamin D3 or calcitriol).
    • Vitamin D enhances the absorption of calcium and phosphate from the intestine.

    Calcitonin

    • Secreted by parafollicular cells in the thyroid gland, acting to lower plasma calcium levels when they rise.

    Feedback Mechanism

    • PTH secretion is tightly regulated by plasma free Ca2+ levels, typically increasing when Ca2+ is low and decreasing when Ca2+ is high, establishing a negative feedback loop.

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    Description

    Explore the dynamic nature of bone as a connective tissue, including its cells and structure. This quiz covers the roles of osteoblasts, osteocytes, and osteoclasts, as well as conditions like osteogenesis imperfecta and rickets. Test your knowledge on compact and trabecular bone!

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