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Questions and Answers
What is the primary function of Parathyroid Hormone (PTH)?
What is the primary function of Parathyroid Hormone (PTH)?
How does an increase in extracellular calcium concentration affect PTH secretion?
How does an increase in extracellular calcium concentration affect PTH secretion?
What role do mitochondria and the endoplasmic reticulum (ER) play in calcium regulation?
What role do mitochondria and the endoplasmic reticulum (ER) play in calcium regulation?
Which statement correctly describes the effect of low extracellular calcium levels on PTH secretion?
Which statement correctly describes the effect of low extracellular calcium levels on PTH secretion?
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What is the composition of Parathyroid Hormone (PTH)?
What is the composition of Parathyroid Hormone (PTH)?
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What percentage of bone is composed of organic materials?
What percentage of bone is composed of organic materials?
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Which mineral is primarily responsible for the structural strength of bone?
Which mineral is primarily responsible for the structural strength of bone?
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What is the primary function of collagen in bone?
What is the primary function of collagen in bone?
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Which ion is not typically found in the inorganic portion of bone?
Which ion is not typically found in the inorganic portion of bone?
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How much of the bone's dry weight is made up of inorganic materials?
How much of the bone's dry weight is made up of inorganic materials?
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What type of collagen is most abundant in bone?
What type of collagen is most abundant in bone?
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Which statement best describes the role of proteoglycans in bone?
Which statement best describes the role of proteoglycans in bone?
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What role does osteocalcin play in bone physiology?
What role does osteocalcin play in bone physiology?
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Which statement about osteoclasts is accurate?
Which statement about osteoclasts is accurate?
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What is the function of RANKL in the context of bone health?
What is the function of RANKL in the context of bone health?
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Which protein is known for modulating growth factor activity and cell adhesion in bone?
Which protein is known for modulating growth factor activity and cell adhesion in bone?
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What process is primarily responsible for the degradation of proteins in bone?
What process is primarily responsible for the degradation of proteins in bone?
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Under what condition do osteoblasts differentiate into osteocytes?
Under what condition do osteoblasts differentiate into osteocytes?
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What is a consequence of Wolff’s Law on bone structure?
What is a consequence of Wolff’s Law on bone structure?
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What type of proteins are sialoproteins, and what is their significance in bone?
What type of proteins are sialoproteins, and what is their significance in bone?
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How do osteoblasts respond to parathyroid hormone (PTH)?
How do osteoblasts respond to parathyroid hormone (PTH)?
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What primarily controls the growth in diameter of bones?
What primarily controls the growth in diameter of bones?
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What is the likely consequence of prolonged immobilization of bones?
What is the likely consequence of prolonged immobilization of bones?
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What phenomenon occurs around a metal implant after a total hip replacement?
What phenomenon occurs around a metal implant after a total hip replacement?
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What is the result of the absence of mechanical forces on bone?
What is the result of the absence of mechanical forces on bone?
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What do osteocytes release in response to mechanical stress?
What do osteocytes release in response to mechanical stress?
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Which hormones are primarily involved in regulating when bone remodeling occurs?
Which hormones are primarily involved in regulating when bone remodeling occurs?
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What happens to the bones of astronauts due to spending extended periods in space?
What happens to the bones of astronauts due to spending extended periods in space?
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How does mechanical stress influence where bone remodeling occurs?
How does mechanical stress influence where bone remodeling occurs?
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What is the relationship between mechanical stress and piezoelectricity in bone?
What is the relationship between mechanical stress and piezoelectricity in bone?
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What can heavy usage of bones lead to?
What can heavy usage of bones lead to?
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What condition can lead to falsely low total calcium levels due to low albumin?
What condition can lead to falsely low total calcium levels due to low albumin?
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What does corrected calcium aim to estimate in a patient's blood?
What does corrected calcium aim to estimate in a patient's blood?
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Which of the following factors increases the ionized calcium level when pH decreases?
Which of the following factors increases the ionized calcium level when pH decreases?
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What is the effect of alkalosis on calcium binding in blood?
What is the effect of alkalosis on calcium binding in blood?
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Which hormone is NOT involved in calcium homeostasis?
Which hormone is NOT involved in calcium homeostasis?
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What correction factor is used in the corrected calcium formula for a serum albumin of 4.0 g/dL?
What correction factor is used in the corrected calcium formula for a serum albumin of 4.0 g/dL?
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How does a 0.1 decrease in pH affect ionized calcium levels?
How does a 0.1 decrease in pH affect ionized calcium levels?
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What system is NOT part of calcium homeostasis?
What system is NOT part of calcium homeostasis?
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In the context of calcium transport, what happens during acidosis?
In the context of calcium transport, what happens during acidosis?
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What is the total calcium measurement primarily affected by low albumin levels?
What is the total calcium measurement primarily affected by low albumin levels?
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Study Notes
Calcium and Phosphate Metabolism
- Calcium and phosphate metabolism are essential for maintaining healthy bone
- Bone is 60% inorganic, 10% water and 30% organic materials.
- Bone is constantly remodeled throughout life
Bone Physiology
- Bones provide structural support
- Protect internal organs and soft tissues
- Allow locomotion
- Serve as a mineral storage site
- Produce blood cells
- Are involved in endocrine regulation
Bone - Inorganic Portion (67%)
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Consists of hydroxyapatite crystals (Ca10(PO4)6(OH)2) embedded in collagen matrix
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Accounts for 60-70% of bone's dry weight
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Provides structural strength to bone
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Facilitates bone regeneration
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Other ions present, such as Na+, K+, Mg2+, CO32-, Ba2+, and Zn2+, regulate the crystallinity of bone minerals
Bone - Organic Portion (aka osteoid) (33%)
- Contains collagen proteins, primarily type I, which form ligaments and tendons
- Composed of triple helix structure
- Providing structural support and contributing to the mechanical properties of bone (flexibility, resistance to tensile forces)
- Contains type III and IV collagen
- Also contains non-collagen structural proteins, such as proteoglycans (macromolecules with core polypeptides and glycosaminoglycans like hyaluronic acid), sialoproteins (highly glycosylated and sulphated phosphoproteins), and other bone-specific proteins (e.g., osteocalcin, osteonectin, osteopontin, RANKL) involved in bone formation, cell adhesion and mineralization
Bone Remodeling
- Osteoclasts dissolve bone, these are large multinucleated cells
- Osteoblasts produce bone, respond to factors like PTH, CT, Vitamin D, growth factors, and cytokines and produce collagen
- Osteoblasts that become encased in bone become osteocytes
Bone Cells
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Osteoblasts:
- Involved in bone formation
- Synthesize matrix proteins (e.g., type I collagen, osteocalcin)
- Participate in mineralization
- Regulate osteoclast production via RANKL
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Osteoclasts:
- Break down bone (bone resorption)
- Degrade matrix proteins via enzymes
- Acidify the bone environment
Bone Remodeling (Diagram)
- The diagram illustrates the complex interplay between osteoblasts and osteoclasts in bone remodeling, highlighting the roles of proteins like RANKL and OPG, and various factors influencing this process.
Wolff's Law
- Bone adapts to the forces and stresses placed upon it, growing or remodeling in response.
- Appositional growth in bone diameter is controlled by the amount of mechanical stress and gravity.
- Heavy bone usage leads to heavy bone, conversely, non-use leads to bone loss.
- Astronauts lose bone density during prolonged space travel.
Piezoelectricity
- Bone generates an electric charge in response to applied mechanical stress.
- This electrical activity stimulates osteoblastic activity, leading to bone growth and increased density.
Hormones PTH and Calcitonin
- Control whether and when bone remodeling occurs.
- Mechanical stresses dictate where remodeling occurs, high stress areas grow/remodel.
Phosphate
- Found in bone, ATP, cAMP, proteins, and regulates cell function
- Total body phosphate is 500-800g (85%-90% in skeleton)
- Plasma phosphate is 3-4.5 mg/dL (0.9-1.3mM)
- Circulates as orthophosphate (PO4)
- Filtered by kidney, 85% reabsorbed, 15% excreted as urinary buffer, Absorbed in the intestine by sodium transporter.
Calcium
- Total calcium in the body is 1100g (90% in skeleton)
- Plasma calcium is 2.2-2.6 mmol/L
- Calcium functions include nerve and muscle excitability, neurotransmission, excitation-contraction coupling in muscle, enzyme cofactor, second messenger function, fertilisation, and mitosis.
Body Requirements
- Calcium requirements vary by age. Pregnant and lactating women need more calcium.
Plasma Calcium Regulation
- Plasma calcium is tightly regulated (5%) at 2.4mM (9.4 mg/dL).
- 1.2mM of plasma calcium is the free ionized calcium
- 9% of plasma calcium is complexed to anions.
- 41% is calcium to protein.
- Low ionized calcium = Neuronal hyper-excitability
- High ionized calcium = Neuronal depression
Total Calcium Measurement
- Low albumin levels can cause calcium levels to appear falsely low.
- Corrected calcium provides a more accurate reflection of calcium status by adjusting for albumin levels.
Calcium Transport in the Blood
- Ionized calcium fraction depends on pH.
- Protein binding decreases as pH decreases in alkalosis.
- Protein binding increases in acidosis.
- pH affects free ionized calcium concentration
Calcium Homeostasis
- Bone, kidney, and intestine are the three major systems involved in calcium homeostasis.
- Parathyroid hormone (PTH), calcitonin, and vitamin D are hormones critical in regulating this system.
Intracellular and Extracellular Calcium
- Intracellular calcium levels are tightly regulated at 10⁻⁷M
- Extracellular calcium levels are tightly regulated at 10⁻³M
- The ratio of intra to extra cellular calcium is 1:10,000 and is crucial for cellular functions
- The diagram has various transporters for Calcium: Na+/Ca2+ Exchanger, Ca2+ ATPase, and various channels
Parathyroid Hormone (PTH)
- Produced by the parathyroid glands
- Regulates blood calcium levels primarily by increasing calcium in the extracellular fluid (ECF)
- Low calcium in the ECF stimulates PTH secretion
- PTH increases calcium resorption from bone, reabsorption by the kidney and calcium absorption in the intestines
PTH on Bone
- PTH initially causes an increase in bone formation (briefly)
- It promotes bone resorption over a longer duration by influencing osteoclast activity.
PTH on Kidney and Intestine
- PTH indirectly stimulates calcium absorption in the intestine through vitamin D activation.
- PTH increases calcium reabsorption in the kidney
Regulation of PTH secretion
- Calcium sensing receptors on chief cells regulate PTH secretion.
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Description
Test your knowledge on calcium and phosphate metabolism, essential components of bone health. This quiz covers the anatomical and physiological roles of bones, their inorganic and organic compositions, and the importance of minerals in bone structure and function.
