Hormonal Regulators of Calcium-Phosphorus Balance
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Questions and Answers

Which of the following hormones is responsible for minimizing urinary excretion of calcium?

  • Calcitonin
  • Calcitriol
  • Fibroblast growth factor (FGF23)
  • Parathyroid hormone (PTH) (correct)

    • What is the effect of low serum magnesium on parathyroid hormone (PTH) production?

  • It decreases PTH production
  • It inhibits PTH secretion
  • It stimulates PTH production (correct)
  • It has no effect on PTH production

    • What is the primary source of calcitriol synthesis?

  • Kidney
  • Skin (correct)
  • Liver
  • Bones

    • Which of the following is a cause of hypercalcemia?

    <p>Primary hyperparathyroidism</p> Signup and view all the answers

    What is the role of calcitriol in calcium absorption?

    <p>It promotes the synthesis of calcium-binding protein</p> Signup and view all the answers

    What is the primary cause of hypocalcemia?

    <p>Reduced intestinal Ca absorption</p> Signup and view all the answers

    Which of the following hormones stimulates the conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D?

    <p>Parathyroid hormone (PTH)</p> Signup and view all the answers

    What is the main component of bones where phosphates are found?

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

    What is the effect of calcitriol on osteoclastic activity?

    <p>It stimulates osteoclastic activity</p> Signup and view all the answers

    Which of the following hormones plays a small role in calcium-phosphorus balance under physiological circumstances?

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

    What is the primary role of 2,3-diphosphoglycerate (2,3-DPG) in erythrocytes?

    <p>Oxygen release</p> Signup and view all the answers

    What percentage of phosphorus is found in the extracellular fluid?

    <p>1%</p> Signup and view all the answers

    What is the most common cause of hyperphosphatemia?

    <p>Acute and chronic renal failure</p> Signup and view all the answers

    What is the primary function of magnesium in the body?

    <p>ATP activation</p> Signup and view all the answers

    What percentage of magnesium is found in the extracellular fluid?

    <p>1%</p> Signup and view all the answers

    What is the role of magnesium in enzyme reactions?

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

    What is the primary function of the ionized calcium (Ca2+) in the body?

    <p>Regulating neuromuscular excitability and muscle contraction</p> Signup and view all the answers

    Which of the following statements is true about calcium in the body?

    <p>90% of calcium is found in the form of hydroxyapatite and phosphate complexes</p> Signup and view all the answers

    What is the normal range of serum calcium concentration in the body?

    <p>2.10 – 2.70 mmol/L</p> Signup and view all the answers

    What is the role of albumin in calcium homeostasis?

    <p>Binding to calcium ions to maintain a stable serum concentration</p> Signup and view all the answers

    What is the primary function of calcium in the activation of coagulation factors?

    <p>Activating clotting factors</p> Signup and view all the answers

    What is the consequence of an imbalance in calcium homeostasis?

    <p>Neuromuscular excitability and muscle contraction are impaired</p> Signup and view all the answers

    What is the proportion of calcium bound to proteins in the serum?

    <p>40% of total calcium</p> Signup and view all the answers

    What is the percentage of calcium found in the extracellular tissue (ECT)?

    <p>1% of total calcium</p> Signup and view all the answers

    What is a major obstacle for β-lactam antibiotics in reaching their targets, the PBPs, in gram-negative bacteria?

    <p>The outer membrane</p> Signup and view all the answers

    What are the protein channels in the outer membrane of gram-negative bacteria through which β-lactam antibiotics diffuse?

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

    Why can β-lactam antibiotics easily reach their targets in gram-positive bacteria?

    <p>Because the outer membrane is absent</p> Signup and view all the answers

    What type of antibiotics are penicillins, cephalosporins, carbapenems, and monobactams?

    <p>β-Lactam antibiotics</p> Signup and view all the answers

    What is the function of porins in the outer membrane of gram-negative bacteria?

    <p>To diffuse through the outer membrane</p> Signup and view all the answers

    Why are β-lactam antibiotics ineffective against bacteria that are not exposed to them?

    <p>Because the antibiotic cannot reach the target</p> Signup and view all the answers

    What is the function of β-lactamase enzymes in bacteria?

    <p>To inactivate β-lactam antibiotics</p> Signup and view all the answers

    What is the common feature among all penicillin derivatives?

    <p>The presence of a thiazolidine-β-lactam ring</p> Signup and view all the answers

    What is the result of modifying the R side chain in penicillins?

    <p>Altered pharmacologic properties and antibacterial spectra of activity</p> Signup and view all the answers

    What is the purpose of combining penicillins with β-lactamase inhibitors?

    <p>To expand the number of bacterial species susceptible to penicillins</p> Signup and view all the answers

    What determines the antibacterial activity of penicillins?

    <p>The presence of a thiazolidine-β-lactam ring</p> Signup and view all the answers

    What is the characteristic of members within a class of penicillins?

    <p>Similar pharmacokinetic properties and spectra of activity</p> Signup and view all the answers

    Which type of bacteria is susceptible to natural penicillins?

    <p>Gram-positive bacteria (Staphylococcus aureus)</p> Signup and view all the answers

    What is the effect of pumps, penicillinases, and porins working together?

    <p>A dramatic change in susceptibility to antibiotics</p> Signup and view all the answers

    Which Streptococcus species is susceptible to natural penicillins?

    <p>Streptococcus pyogenes</p> Signup and view all the answers

    What is the antimicrobial activity of natural penicillins against Neisseria meningitidis?

    <p>Highly susceptible to natural penicillins</p> Signup and view all the answers

    Which of the following bacteria is susceptible to natural penicillins?

    <p>Streptococcus pyogenes</p> Signup and view all the answers

    What is the antimicrobial activity of natural penicillins against Listeria monocytogenes?

    <p>Highly susceptible to natural penicillins</p> Signup and view all the answers

    Which of the following is NOT susceptible to natural penicillins?

    <p>Escherichia coli</p> Signup and view all the answers

    What is the antimicrobial activity of natural penicillins against Clostridia species?

    <p>Variable susceptibility to natural penicillins</p> Signup and view all the answers

    What is the main function of efflux pumps in some bacteria?

    <p>To transport antibiotics back out to the environment</p> Signup and view all the answers

    What is the main difference between extended-spectrum penicillins and natural penicillins?

    <p>Their activity against enteric gram-negative rods</p> Signup and view all the answers

    What is the function of penicillins?

    <p>To inhibit cell wall synthesis</p> Signup and view all the answers

    What is the role of β-lactamases in bacteria?

    <p>To degrade β-lactams before they reach the PBPs</p> Signup and view all the answers

    What is the effect of β-lactam antibiotics on bacteria that do not produce peptidoglycan?

    <p>They are not effective in inhibiting the growth of these bacteria</p> Signup and view all the answers

    What is the primary benefit of adding a β-lactamase inhibitor to an extended-spectrum penicillin?

    <p>Improved resistance to β-lactamase</p> Signup and view all the answers

    Why do β-lactam antibiotics need to successfully navigate around certain pitfalls to be effective?

    <p>Because they can be blocked by efflux pumps, β-lactamases, and other mechanisms</p> Signup and view all the answers

    What is the main difference between aminopenicillins and natural penicillins?

    <p>Their spectrum of activity against enteric gram-negative rods</p> Signup and view all the answers

    What is a characteristic of β-lactam antibiotics?

    <p>They are a heterogeneous group of compounds</p> Signup and view all the answers

    What is the effect of adding a β-lactamase inhibitor to an aminopenicillin?

    <p>Increased resistance to β-lactamase</p> Signup and view all the answers

    What is the result of β-lactams binding to PBPs with low affinity?

    <p>The β-lactams are unable to inactivate the PBPs</p> Signup and view all the answers

    What is the primary mechanism of action of penicillins?

    <p>Inhibition of cell wall synthesis</p> Signup and view all the answers

    What is the main difference between antistaphylococcal penicillins and natural penicillins?

    <p>Their activity against staphylococcal bacteria</p> Signup and view all the answers

    What is the primary benefit of using extended-spectrum penicillins?

    <p>Improved activity against enteric gram-negative rods</p> Signup and view all the answers

    What is the primary energy source utilized to power processes such as active transport of nutrients and generation of ATP?

    <p>Proton motive force</p> Signup and view all the answers

    Where is the energy stored in the process of generating a proton gradient?

    <p>Between the interior and exterior of the cell</p> Signup and view all the answers

    What is the process by which bacteria utilize DNA information to synthesize an RNA molecule?

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

    What is the term used to describe the energy stored in the proton gradient?

    <p>Potential energy</p> Signup and view all the answers

    What is the term used to describe the flow of protons down the gradient?

    <p>Proton flow</p> Signup and view all the answers

    What is the primary function of RNA polymerase in bacterial cells?

    <p>To synthesize mRNA</p> Signup and view all the answers

    Where does the process of transcription occur in bacterial cells?

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

    What is the purpose of harnessing energy from fuel consumption in bacterial cells?

    <p>To generate ATP</p> Signup and view all the answers

    What is required to add a single amino acid to a growing protein?

    <p>The energy of three or four nucleoside triphosphates</p> Signup and view all the answers

    What is the role of bacterial enzymes in protein production?

    <p>To transcribe template bacterial genes into RNA</p> Signup and view all the answers

    What is the significance of the difference between bacterial and human cellular components in protein production?

    <p>It makes protein production in bacteria amenable to inhibition by antibiotics</p> Signup and view all the answers

    What is the purpose of acquiring raw materials in protein production?

    <p>To synthesize new proteins</p> Signup and view all the answers

    What is the role of RNA in protein production?

    <p>To translate RNA into protein</p> Signup and view all the answers

    What is the significance of the human body as a 'country' for bacteria?

    <p>It is a source of resources for bacterial growth</p> Signup and view all the answers

    What is the role of template bacterial genes in protein production?

    <p>To transcribe template bacterial genes into RNA</p> Signup and view all the answers

    What is the result of inhibiting protein production in bacteria?

    <p>Bacteria are inhibited from replacing old worn-out parts and building new bacteria</p> Signup and view all the answers

    What is the precursor of THF that humans readily absorb from their diet?

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

    Which enzyme is responsible for replicating the bacterial chromosome?

    <p>DNA polymerase</p> Signup and view all the answers

    What is the result of twisting one end of the DNA while holding the other end fixed?

    <p>Increased supercoiling</p> Signup and view all the answers

    What is the role of topoisomerase in DNA replication?

    <p>Regulating supercoiling</p> Signup and view all the answers

    What is the number of nucleotide pairs per helical turn in a relaxed DNA structure?

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

    What is the consequence of having a chromosome composed of helical DNA?

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

    What is the role of dihydropteroate synthase in THF synthesis?

    <p>Synthesizing dihydropteroate</p> Signup and view all the answers

    Why is the THF synthesis pathway an attractive target for antimicrobial compounds?

    <p>Because most bacteria are unable to synthesize THF</p> Signup and view all the answers

    Study Notes

    Hormonal Regulators of Ca-P Balance

    • Parathyroid hormone (PTH) is a polypeptide hormone synthesized and secreted by chief cells of the parathyroid glands.
    • Decreased Ca2+ and low serum magnesium stimulate PTH secretion.
    • PTH increases blood Ca concentration in three ways:
      • Minimizes urinary excretion of Ca by increasing reabsorption in renal tubules.
      • Stimulates conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D (calcitriol) in kidneys.
      • Mobilizes Ca and P from bones with calcitriol.

    Calcitriol

    • Calcitriol is a vitamin D-derived hormone synthesized in the skin from 7-hydroxycholesterol via UV radiation.
    • Calcitriol promotes synthesis of calcium-binding protein essential for Ca and P absorption in small intestinal cells.
    • Together with PTH, calcitriol stimulates osteoclastic activity, releasing Ca and P from bones.

    Calcium

    • 99% of body's total calcium is bound in bones and teeth, mainly in the form of hydroxyapatite and phosphate complexes.
    • 1% of calcium is found in the extracellular fluid (ECF), predominantly in the form of free, ionized Ca2+ (50%) and bound Ca (50%).
    • Serum concentration of total calcium is maintained between 2.10-2.70 mmol/L.

    Phosphates

    • Most phosphorus in the body exists in the form of phosphates, with 85% found in bones.
    • Phosphates in soft tissues are bound in numerous organic compounds, including nucleic acids and phospholipids of cell membranes.
    • Phosphates play a key role in energy metabolism of cells and release of O2 in tissues.

    Hyperphosphatemia and Hypophosphatemia

    • Hyperphosphatemia is usually due to increased intake, decreased renal excretion, and redistribution from ICF to ECF.
    • Acute and chronic renal failure is the most common cause of hyperphosphatemia.

    Magnesium

    • 60% of magnesium is bound in bone to hydroxyapatite crystals, almost 40% is in muscle and soft tissue cells, and only about 1% is in the extracellular fluid.
    • Magnesium is the second most important intracellular cation after potassium, necessary for ATP activation.
    • Magnesium is a cofactor of more than 300 enzymes, catalyzing reactions using ATP.

    Factors Affecting β-Lactam Antibiotics

    • β-Lactam antibiotics cannot kill bacteria if they cannot reach their targets, the PBPs (penicillin-binding proteins)
    • Gram-negative bacteria have a protective outer membrane that β-lactams must breach through porins, protein channels in the outer membrane
    • Some bacteria produce efflux pumps that transport β-lactams out of the periplasmic space
    • β-Lactamases can degrade β-lactams before they reach the PBPs
    • Some bacteria produce PBPs that do not bind β-lactams with high affinity
    • The absence of peptidoglycan in some bacteria makes them unaffected by β-lactams

    β-Lactam Antibiotics

    • The four major classes of β-lactam antibiotics are penicillins, cephalosporins, carbapenems, and monobactams
    • All β-lactam antibiotics exert their action by binding to PBPs
    • β-Lactamases are enzymes that cleave β-lactam antibiotics, inactivating them

    Penicillins

    • Consist of a thiazolidine ring attached to a β-lactam ring modified by a variable side chain
    • The thiazolidine-β-lactam ring is required for antibacterial activity, while the side chain can be modified to produce different penicillin derivatives
    • Classes of penicillins include natural penicillins, antistaphylococcal penicillins, aminopenicillins, and extended-spectrum penicillins
    • Some penicillins are combined with β-lactamase inhibitors, expanding their antibacterial spectrum

    Natural Penicillins

    • Have moderate activity against aerobic gram-positive bacteria and anaerobic bacteria
    • Have poor activity against aerobic gram-negative bacteria and most atypical bacteria
    • Active against Streptococcus pyogenes, viridans group streptococci, some Streptococcus pneumoniae, some enterococci, Listeria monocytogenes, Neisseria meningitidis, and some Haemophilus influenzae

    Extended-Spectrum Penicillins

    • Active against even more enteric gram-negative rods and Pseudomonas aeruginosa
    • The addition of a β-lactamase inhibitor to an extended-spectrum penicillin extends its activity to most enteric gram-negative bacilli

    Protein Production in Bacteria

    • Protein production in bacteria is a process that involves the synthesis of proteins using DNA, RNA, and amino acids.
    • The process requires energy from nucleoside triphosphates, which is stored in the form of a proton motive force.
    • The proton motive force is generated by the flow of protons down a gradient between the interior and exterior of the cell.

    Transcription

    • Transcription is the process by which DNA is used to synthesize messenger RNA (mRNA).
    • The enzyme RNA polymerase is used by bacteria to accomplish transcription.
    • Tetrahydrofolate (THF) is required for the synthesis of nucleotides during transcription.

    Tetrahydrofolate Synthesis

    • Bacteria synthesize THF from para-aminobenzoate (PABA) and dihydropterin pyrophosphate.
    • The enzymes dihydropteroate synthase and dihydrofolate reductase are involved in the synthesis of THF.

    DNA Replication

    • DNA polymerase is responsible for replicating the bacterial chromosome.
    • Other enzymes, such as topoisomerases, are also required for DNA replication.
    • Topoisomerases regulate supercoiling, or twisting, of the DNA molecule.

    Supercoiling of DNA

    • Supercoiling occurs when the double helix structure of DNA is twisted, resulting in additional stress on the DNA molecule.
    • This stress is accommodated by the formation of supercoils.

    Protein Synthesis

    • Protein synthesis in bacteria requires raw materials such as RNA, amino acids, and energy-containing nucleoside triphosphates.
    • The energy of three or four nucleoside triphosphates is required to add a single amino acid to a growing protein.
    • Bacterial enzymes are used to translate RNA into protein.
    • Protein production in bacteria is amenable to inhibition by antibiotics due to differences in bacterial components compared to human cells.

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    Description

    This quiz covers the main hormonal regulators of calcium-phosphorus balance in the body, including parathyroid hormone, calcitriol, fibroblast growth factor, and calcitonin.

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