Calcium and Phosphate Metabolism Quiz
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Questions and Answers

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

  • Collagen Type III
  • Hydroxyapatite crystals (correct)
  • Proteoglycans
  • Glycosaminoglycans

    • Which of the following accurately describes the inorganic portion of bone?

  • Contains primarily water and collagen
  • Represents the majority of bone's organic structure
  • Is composed mostly of hydroxyapatite and other ions (correct)
  • Provides flexibility and tensile strength

    • What role do proteoglycans play in bone structure?

  • They contribute to the flexibility and resilience of the extracellular matrix (correct)
  • They account for the majority of the inorganic composition
  • They provide structural strength similar to hydroxyapatite
  • They are responsible for the mineralization of bone

    • Which statement best describes the remodeling process of bone?

    <p>Remodeling allows for adaptation and recovery from stress and damage.</p> Signup and view all the answers

    What percentage of bone is considered organic material?

    <p>33%</p> Signup and view all the answers

    Which component primarily regulates bone resorption through its action on osteoclasts?

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

    Which of the following is NOT a function of osteoblasts?

    <p>Degradation of bone matrix</p> Signup and view all the answers

    What is the primary role of osteonectin in bone physiology?

    <p>Enhances cell adhesion and modulates growth factors</p> Signup and view all the answers

    What process is primarily described by Wolff’s Law?

    <p>Bone adapts to the mechanical demands placed upon it.</p> Signup and view all the answers

    Which of the following proteins acts to regulate the differentiation of osteoclast precursors?

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

    What percentage of total body calcium resides in the skeleton?

    <p>90%</p> Signup and view all the answers

    Which of the following statements about phosphate is true?

    <p>Orthophosphate is the circulating form of phosphate in the body.</p> Signup and view all the answers

    What is the recommended daily calcium intake for postmenopausal women over 51 years of age?

    <p>1500mg</p> Signup and view all the answers

    What factor most directly influences bone diameter and growth strength?

    <p>The amount of mechanical stress applied to the bone</p> Signup and view all the answers

    Which ion is primarily involved in the intestinal absorption of phosphate?

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

    Which of the following is a consequence of non-use of bones?

    <p>Atrophy or bone loss</p> Signup and view all the answers

    How does the body respond when free ionized calcium levels are too low?

    <p>Neuronal hyper-excitability occurs.</p> Signup and view all the answers

    What phenomenon describes the reduction of stress experienced by a femur after total hip replacement?

    <p>Stress shielding</p> Signup and view all the answers

    Which of the following functions does calcium NOT serve in the body?

    <p>Regulation of plasma glucose levels</p> Signup and view all the answers

    What is the typical serum calcium concentration in plasma?

    <p>2.4-2.6mmol/L</p> Signup and view all the answers

    What happens to bone when mechanical forces are absent?

    <p>Osteoclastic activity increases</p> Signup and view all the answers

    Which hormones are primarily involved in controlling bone remodeling?

    <p>PTH and Calcitonin</p> Signup and view all the answers

    What is the result of prolonged muscle paralysis on bone density?

    <p>Decreased bone mineral density</p> Signup and view all the answers

    What role do osteocytes play in response to mechanical stress?

    <p>They release factors that promote osteoblastic activity</p> Signup and view all the answers

    What occurs around a metal implant following a hip transplant?

    <p>Loss of bone mass through resorption</p> Signup and view all the answers

    Study Notes

    Calcium and Phosphate Metabolism

    •  Calcium and phosphate metabolism are crucial for bone health and overall body function.
    • Bone is a dynamic tissue that undergoes continuous remodeling throughout life.
    • Approximately 20% of bone is undergoing remodeling at any given time.

    Bone Physiology

    • Bone's primary functions include structural support, protection of organs and soft tissues, locomotion, mineral storage, blood cell production, and endocrine regulation.
    • Bone matrix is composed of approximately 60% inorganic material, 10% water and 30% organic material.
    • The inorganic portion consists primarily of hydroxyapatite crystals, embedded within a collagen matrix. This combination provides bone's strength and facilitates regeneration.
    • Important ions, such as Na+, K+, Mg2+, CO32-, Ba2+, and Zn2+ are also present and moderate the crystallinity of bone minerals.

    Bone - Organic Portion (Osteoid)

    • Osteoid is the organic component of bone, composed predominantly of Type I collagen, making up 28% of the organic matrix.
    • The triple helix structure of collagen provides structural support and contributes to bone's mechanical properties such as flexibility and resistance to tensile forces.
    • Non-collagen structural proteins include proteoglycans, with their glycosaminoglycan core polypetides (e.g., hyaluronic acid) and organization of bone extracellular matrix and collagen fibrillogenesis. These components are crucial for organizing the bone extracellular matrix, promoting collagen fibrillogenesis, and participating in mineralization and bone formation.
    • Specialized proteins such as osteocalcin are vital for osteoblast activity and osteoclast activity. Furthermore osteonectin and osteopontin have significant effects on cell adhesion, mineralization, and bone formation.
    • Factors like RANKL and growth factors and cytokines are important for bone growth and remodeling and bone resorption regulation.

    Bone - Inorganic Portion

    • Hydroxyapatite crystals, (Ca10(PO4)6(OH)2) are the key inorganic component of bone, accounting for approximately 60-70% of its dry weight. These crystals are embedded in the collagen matrix, providing bone with its robust structural strength and facilitating bone regeneration.
    • Other ions, such as sodium (Na+), potassium (K+), magnesium (Mg2+), carbonate (CO32-), barium (Ba2+), and zinc (Zn2+), also regulate the properties of bone minerals.

    Bone Cells

    • Osteoblasts: Responsible for bone formation. They synthesize and secrete matrix proteins, including Type I collagen and osteocalcin, and contribute to mineralization. Osteoblast activity is crucial in bone formation. Osteoclasts also play a key role in bone resorption.
    • Osteoclasts: Primarily responsible for bone resorption. They degrade proteins in bone matrix via enzymes and acidification.

    Bone Remodeling

    • Osteoclasts dissolve bone matrix, and osteoblasts create new bone tissue. This interplay determines the growth and maintenance of bone tissue.
    • Osteoblasts have receptors for hormones, cytokines, and growth factors for bone production and increase bone growth/strength.
    • When osteoblasts become encased in bone matrix they differentiate into osteocytes.

    Wolff's Law and Response to Bone Remodeling

    • Bone remodels in response to the forces and stresses placed on it. This principle underlies how bone adapts to physical demands.
    • Growth in bone diameter is directly related to the mechanical forces and gravity.
    • Heavy use of heavy bones leads to increase bone density, while inadequate use leads to bone loss (atrophy).
    • Spaceflight, paralysis, or prolonged immobilisation can cause significant bone loss due to reduced bone stress.
    • Bone adapts to the stresses placed on it – if stressed a lot, it will grow thicker and denser. If not stressed, it will become thinner and weaker.

    Controlling Bone Remodeling

    • Hormones like parathyroid hormone (PTH) and calcitonin regulate bone remodeling, dictating when and where remodeling occurs.
    • Mechanical stress dictates where remodeling is necessary, with high stress areas experiencing appositional growth.

    Calcium and Inorganic Phosphate

    • Important elements for structure & function of bone tissue.
    • Total body calcium is approximately 1100g (90% in skeleton) and plasma calcium is 2.2-2.6 mmol/L.
    • Calcium is present in bones, ATP, blood proteins, etc., where it regulates cell function, muscle & nerve function, enzyme co-factors, as well as second messenger for fertilization and mitosis regulation.
    • Phosphate is also present in bone as well as found in ATP, other crucial blood components, where it acts to regulate cell function. The total body phosphate range is approximately 500-800g and 3-4.5 mg/dl in plasma.

    Body Requirements

    • Calcium requirements vary with age. Pregnant and lactating women need higher calcium intake.

    Regulation of Plasma Calcium

    • Plasma calcium is tightly regulated within a narrow range (2.4 mM, 9.4 mg/dl) with 50% of this being ionized calcium.
    • Protein-bound calcium component comprises about 41%.
    • The ionized fraction depends on pH; protein binding decreases as pH decreases.
    • pH 7.45 (alkalosis) increases calcium binding and decreases ionized fraction, while pH 7.35 (acidosis) decreases calcium binding and increases ionized fraction.
    • Correct calcium levels are crucial for proper neuronal function.

    Total Calcium Measurement

    • Incorrect measurement can occur due to low albumin levels (i.e., malnutrition).
    • Corrected calcium measurements adjust for albumin level variations to provide a more accurate assessment of calcium status.

    Calcium Transport in the Blood

    • Ionized calcium is tightly regulated.
    • The ionized fraction depends on the blood pH.
    • Lower blood pH (acidosis) increases ionized calcium, while higher blood pH (alkalosis) decreases ionized calcium.

    Calcium Homeostasis

    • Calcium homeostasis is maintained by bone, kidney, and intestine via absorption and excretion, regulated by parathyroid hormone (PTH) and calcitonin.
    • Vitamin D is important to regulate gut calcium absorption.

    Regulation of PTH Secretion

    • Calcium sensing receptors on chief cells regulate PTH secretion.
    • When calcium levels are low, PTH secretion increases in order to increase calcium reabsorption and minimize calcium loss through excretion.
    • When calcium is high, PTH secretion decreases to limit calcium reabsorption.

    PTH on Bone

    • PTH regulates bone function to maintain Calcium balance.
    • Briefly, PTH will stimulate bone formation, but the long-term effect is stimulating bone resorption.

    PTH on Kidney and Intestine

    • PTH indirectly impacts calcium absorption in the gut via Vitamin D activation.
    • PTH has direct impact on the kidneys to increase calcium reabsorption.

    Kidneys and Calcium Excretion/Reabsorption

    •  The kidneys play a role in calcium reabsorption/excretion.

    Calcium Homeostasis

    • Calcium homeostasis is complex and regulated by multiple systems: bone, intestine, kidneys, and hormones (PTH, Calcitonin, Vitamin D).
    • These systems function in coordination to maintain calcium levels, supporting various critical cellular functions.

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    Calcium and Phosphate Metabolism Lecture VIII PDF

    Description

    This quiz covers the essential aspects of calcium and phosphate metabolism and their role in bone health. Explore the dynamic nature of bone tissue, its physiology, and the composition of bone matrix. Test your understanding of the organic and inorganic components of bone.

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