Cell Membrane Transport Mechanisms
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Questions and Answers

What is the primary function of the sodium-potassium pump in cells?

  • Facilitating ion channel activity
  • Stimulating glucose uptake
  • Regulating cell volume (correct)
  • Supporting protein synthesis

    • Which type of cells are responsible for the most potent primary active transport of hydrogen ions?

  • Beta cells
  • Intercalated cells
  • Acidophilic cells
  • Parietal cells (correct)

    • How is hydrochloric acid formed in the stomach?

  • From the release of bile salts
  • By combining sodium and potassium ions
  • Through the conversion of glucose
  • From the interaction of hydrogen ions and chloride ions (correct)

    • What happens if the sodium-potassium pump fails in cells?

    <p>Cell lysis or bursting</p> Signup and view all the answers

    Which glucose transporter is primarily found in muscle and adipose tissue?

    <p>GLUT4</p> Signup and view all the answers

    What primarily limits the rate of facilitated diffusion?

    <p>Weak binding force of receptors causing dissociation</p> Signup and view all the answers

    According to the Nernst equation, what does the variable EMF represent?

    <p>The electromotive force (voltage) between two sides of the membrane</p> Signup and view all the answers

    What is the effect of membrane electrical potential on ion diffusion?

    <p>Positive charge attracts negative ions while repelling positive ions</p> Signup and view all the answers

    What is the significance of Vmax in facilitated diffusion?

    <p>It signifies the upper limit of the diffusion rate despite increased concentration</p> Signup and view all the answers

    In the context of diffusion, what does the term 'thermal motion' refer to?

    <p>The kinetic energy causing molecules to move randomly</p> Signup and view all the answers

    Which of the following is true regarding the Nernst equation for univalent ions?

    <p>It calculates the EMF required to balance a concentration difference</p> Signup and view all the answers

    What happens to the rate of facilitated diffusion as the concentration of the diffusing substance continues to increase?

    <p>It eventually plateaus at maximum transport capacity</p> Signup and view all the answers

    What role does the carrier protein play in facilitated diffusion?

    <p>It facilitates the movement of molecules and undergoes conformational changes</p> Signup and view all the answers

    What is the osmotic pressure equivalent to a concentration of 1 milliosmole per liter?

    <p>19.3 mmHg</p> Signup and view all the answers

    What is the calculated osmotic pressure for a 300 milliosmolar concentration?

    <p>5790 mmHg</p> Signup and view all the answers

    What is the average actual osmotic pressure of body fluids?

    <p>5500 mmHg</p> Signup and view all the answers

    How does the actual osmotic pressure of body fluids compare to the calculated value?

    <p>It is about 0.93 times the calculated value.</p> Signup and view all the answers

    What is measured as osmolarity rather than osmoles per kilogram of water?

    <p>Osmolar concentration</p> Signup and view all the answers

    Which mechanism allows substances to be transported against a concentration gradient?

    <p>Active transport</p> Signup and view all the answers

    What happens to the net charge during each cycle of the sodium-potassium pump?

    <p>One positive charge is moved from the cell interior to the exterior.</p> Signup and view all the answers

    Which of the following substances is typically NOT actively transported through cell membranes?

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

    What role do calcium ions play in membrane excitability?

    <p>They act as stabilizers, decreasing membrane excitability.</p> Signup and view all the answers

    How do local anesthetics affect sodium channel activity?

    <p>They make it harder for sodium channels' activation gates to open.</p> Signup and view all the answers

    What happens when the safety factor for nerve impulses is reduced below 1.0?

    <p>Nerve impulses begin to fail along anesthetized nerves.</p> Signup and view all the answers

    What effect does a high extracellular fluid calcium ion concentration have on sodium ion permeability?

    <p>It decreases sodium ion permeability.</p> Signup and view all the answers

    What is a consequence of reduced excitability due to higher calcium ion concentrations?

    <p>Decreased likelihood of generating action potentials.</p> Signup and view all the answers

    What role does the sodium ion play in co-transport mechanisms?

    <p>It acts as a coupling mechanism for transporting substances together.</p> Signup and view all the answers

    Which of the following statements best describes counter-transport?

    <p>It requires simultaneous transport of sodium and hydrogen ions in opposite directions.</p> Signup and view all the answers

    In which part of the body is sodium-hydrogen counter-transport particularly important?

    <p>Proximal tubules of the kidneys.</p> Signup and view all the answers

    What is the main function of sodium-glucose co-transporters?

    <p>To facilitate the absorption of glucose in the intestinal and renal epithelial cells.</p> Signup and view all the answers

    Which of the following best describes primary active transport?

    <p>It utilizes ATP to move ions against their concentration gradient.</p> Signup and view all the answers

    How does co-transport differ from active transport?

    <p>Co-transport harnesses energy from an electrochemical gradient.</p> Signup and view all the answers

    What substance is commonly co-transported with sodium in the intestinal tract?

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

    Which of the following is NOT a type of transport mentioned?

    <p>Simple diffusion.</p> Signup and view all the answers

    Study Notes

    Facilitated Diffusion

    • Facilitated diffusion rates increase with higher concentrations of the diffusing substance, reaching a maximum rate (Vmax).
    • Binding forces of receptors are weak; thermal motion causes molecules to detach and cross the membrane.
    • The rate of transport is limited by how quickly the carrier can return to its initial state.

    Nernst Potential

    • The electrical difference required to balance a concentration gradient for univalent ions can be calculated with the Nernst equation:
      EMF (in millivolts) = ±61 log C1/C2.
    • EMF indicates the voltage difference across a membrane due to ion concentration differences.

    Osmotic Pressure

    • A concentration of 1 milliosmole per liter corresponds to an osmotic pressure of 19.3 mmHg.
    • The calculated osmotic pressure of body fluids averages 5500 mmHg, but the actual value is about 0.93 times this.

    Active Transport

    • Active transport moves ions or molecules against concentration gradients and includes sodium, potassium, calcium, and other ions.
    • Maintains cell volume: without the sodium-potassium pump, cells could swell excessively and rupture.
    • Parietal cells are specialized for hydrogen ion transport to form hydrochloric acid in the stomach.

    Transport Mechanisms

    • Co-transport involves a carrier protein that transports sodium and another substance together into a cell.
    • Sodium-glucose co-transporters in the intestines and kidneys facilitate glucose absorption linked to sodium transport.

    Sodium-Potassium Pump

    • The pump is electrogenic, moving one positive charge outside for each cycle, contributing to the membrane potential difference.
    • It plays a critical role in maintaining cell volume and membrane potential.

    Inhibition of Membrane Excitability

    • Increased extracellular calcium reduces sodium permeability and membrane excitability, acting as a stabilizer.
    • Local anesthetics reduce excitability by blocking sodium channel activation gates, lowering nerve impulse transmission when the safety factor drops below 1.0.

    Transport Functions

    • Facilitated diffusion and active transport mechanisms are essential for nutrient absorption in the gastrointestinal system and kidney function.
    • The interaction between sodium and hydrogen ions regulates pH and maintains cellular acidity, particularly in renal and gastric systems.

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    Description

    Explore the different mechanisms of transport across cell membranes, including facilitated diffusion and active transport. Understand the principles of osmotic pressure and the Nernst potential, as well as their relevance in biological systems. This quiz covers key concepts essential for understanding cellular physiology.

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