Chapter 21 |Hormonal Control of Calcium
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Questions and Answers

What is the role of plasma proteins in binding with Ca2+?

  • They inhibit Ca2+ binding
  • They are less ionized at high pH
  • They are more ionized at high pH (correct)
  • They have no impact on Ca2+ binding
  • How much Ca2+ is exchanged between plasma and the stable pool of bone calcium per day?

  • 1000 mmol
  • 500 mmol
  • 7.5 mmol (correct)
  • 50 mmol
  • What regulates the distal tubular reabsorption of Ca2+ in the kidneys?

  • Brush border cells
  • Proximal tubules
  • PTH (correct)
  • Plasma proteins
  • How much of the filtered Ca2+ in the kidneys is reabsorbed?

    <p>98-99%</p> Signup and view all the answers

    What is the active form of vitamin D that is also called calcitriol?

    <p>1,25-dihydroxycholecalciferol</p> Signup and view all the answers

    How is vitamin D3 mainly produced in mammals?

    <p>By the action of ultraviolet light on 7-dehydrocholesterol</p> Signup and view all the answers

    Where does the conversion of 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol mainly occur?

    <p>In the proximal tubules of the kidneys</p> Signup and view all the answers

    Which protein transports vitamin D3 and its hydroxylated derivatives in the plasma?

    <p>Vitamin Dbinding protein (DBP)</p> Signup and view all the answers

    Which form of calcium is a vital second messenger in the body fluids?

    <p>Ionized calcium (Ca2+)</p> Signup and view all the answers

    What is the consequence of a decrease in extracellular Ca2+ in vivo?

    <p>Hypocalcemic tetany</p> Signup and view all the answers

    Why is it important to know the plasma protein level when evaluating total plasma calcium?

    <p>To understand the extent of Ca2+ binding by plasma proteins</p> Signup and view all the answers

    How do symptoms of tetany vary with changes in total calcium levels?

    <p>Increased total calcium levels worsen tetany symptoms</p> Signup and view all the answers

    Which compounds in the body contain phosphate?

    <p>ATP, cyclic adenosine monophosphate (cAMP), and many proteins</p> Signup and view all the answers

    Where is 85-90% of the total body phosphorus found?

    <p>In the skeleton</p> Signup and view all the answers

    How much phosphorus normally enters bone per kg per day?

    <p>3 mg</p> Signup and view all the answers

    What is the main site of Pi reabsorption in the kidney involving sodium-dependent Pi cotransporters?

    <p>Proximal tubule</p> Signup and view all the answers

    What is the primary action of parathyroid hormone (PTH) in calcium homeostasis?

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

    Which hormone is derived from vitamin D and plays a significant role in calcium homeostasis?

    <p>1,25-Dihydroxycholecalciferol</p> Signup and view all the answers

    What is the main function of calcitonin in calcium metabolism?

    <p>Inhibit bone resorption</p> Signup and view all the answers

    Which organs or tissues respond to changes in extracellular calcium concentrations by mobilizing, excreting, or taking up calcium?

    <p>Kidneys, bones, intestine</p> Signup and view all the answers

    What stimulates calcitonin secretion in the body?

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

    Where are the receptors for calcitonin found in the body?

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

    What is the primary source of calcitonin in mammals?

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

    In which syndrome is the plasma calcitonin level elevated?

    <p>Zollinger–Ellison syndrome</p> Signup and view all the answers

    What is the primary function of phosphorylation and dephosphorylation of proteins in the body?

    <p>To regulate cell function</p> Signup and view all the answers

    Where is the majority of filtered Pi reabsorbed in the kidneys?

    <p>Proximal tubule</p> Signup and view all the answers

    What happens to NaPi-IIa when it is inhibited by PTH?

    <p>It undergoes internalization and degradation</p> Signup and view all the answers

    Which process is stimulated by many factors that also increase Ca2+ absorption?

    <p>Pi absorption</p> Signup and view all the answers

    Which cells are responsible for bone formation?

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

    What contributes to the differentiation of osteoblasts?

    <p>Extensive growth factor regulation</p> Signup and view all the answers

    How do osteoclasts attach to bone?

    <p>Via integrins in a sealing zone</p> Signup and view all the answers

    What is the function of the periosteum?

    <p>Site of ligament attachment</p> Signup and view all the answers

    What happens to the cartilage cells at the end of long bone growth during epiphysial closure?

    <p>They secrete vascular endothelial growth factor (VEGF)</p> Signup and view all the answers

    Which hormone has the most significant impact on the width of the epiphysial plate?

    <p>Insulin-like Growth Factor I (IGF-I)</p> Signup and view all the answers

    What leads to the closure of the epiphyses in bones?

    <p>Hypertrophy of cartilage cells</p> Signup and view all the answers

    How is the 'bone age' of a young individual typically determined?

    <p>By radiographing the skeleton</p> Signup and view all the answers

    Which hormone is responsible for orderly temporal sequence closure of the epiphyses after puberty?

    <p>Growth hormone</p> Signup and view all the answers

    What is the primary function of the periosteum in relation to bone structure?

    <p>Covering and nourishing bone surfaces</p> Signup and view all the answers

    How does linear bone growth continue until epiphysial closure?

    <p>By new bone formation at the shaft ends</p> Signup and view all the answers

    What is the role of Vascular Endothelial Growth Factor (VEGF) in bone development and maturation?

    <p>It leads to vascularization and ossification</p> Signup and view all the answers

    What is determined by radiographing a young individual's skeleton in relation to bone health?

    <p>The 'bone age' based on open or closed epiphyses</p> Signup and view all the answers

    Proton pumps acidify the area to approximately pH 7.0.

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

    Pyridinolines can be measured in the urine as an index of bone resorption rate.

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

    Bone turnover rate is higher in infants than in adults.

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

    Bone remodeling involves the deposition of new bone by osteoclasts.

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

    Modeling drifts involve changes in bone shapes due to bone resorption and addition in different locations.

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

    Osteoblasts break down collagen during bone remodeling.

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

    The primary function of pyridinolines is to acidify the bone matrix.

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

    Bone resorption rate decreases with age.

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

    Bone-remodeling units involve only osteoblasts working in isolation.

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

    Osteoclasts resorb bone primarily by forming shallow depressions in the bone.

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

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