Homeostasis and Feedback Mechanisms
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Questions and Answers

What ratio of potassium ions is typically observed across a cell membrane?

  • 1:35
  • 1:1
  • 10:1
  • 35:1 (correct)

    • Which ion is the cell membrane most permeable to?

  • Sodium (Na+)
  • Calcium (Ca2+)
  • Chloride (Cl-)
  • Potassium (K+) (correct)

    • What causes the negative charge inside the cell?

  • Active transport of potassium ions
  • Influx of chloride ions
  • Leak of potassium ions via K2P channels (correct)
  • Influx of sodium ions

    • What is the electrochemical equilibrium potential?

    <p>The membrane potential at which electrical and chemical forces are equal and opposite for that ion. (B)</p> Signup and view all the answers

    If the resting membrane potential (RMP) is -70 mV and the equilibrium potential for potassium (K+) is -94 mV, what is the driving force for K+?

    <p>24 mV (A)</p> Signup and view all the answers

    A transporter that is specific for D-glucose will also recognize and transport which sugar?

    <p>D-galactose (B)</p> Signup and view all the answers

    What effect does D-galactose have on the transport of D-glucose?

    <p>It slows D-glucose transport by competing for binding sites. (B)</p> Signup and view all the answers

    The conductance of an ion channel is most directly influenced by what factor?

    <p>The probability of the channel being open. (D)</p> Signup and view all the answers

    Which type of gated ion channel responds to the change in signal molecules?

    <p>Second-messenger-gated channels (A)</p> Signup and view all the answers

    What is the primary mechanism creating the chemical gradients responsible for the resting membrane potential?

    <p>Active transport pumps, such as the Na+-K+ ATPase pump. (D)</p> Signup and view all the answers

    If the resting membrane potential is -70 mV and the equilibrium potential for an ion is +60 mV, what would be the driving force for Na+?

    <p>-130 mV (C)</p> Signup and view all the answers

    Which of the following is a characteristic of action potentials?

    <p>Stereotypical size and shape (D)</p> Signup and view all the answers

    If the equilibrium potential for calcium (Ca2+) is +120 mV, and the resting membrane potential is -70 mV, what is the driving force for Ca2+?

    <p>-190 mV (D)</p> Signup and view all the answers

    If a positively charged ion (cation) has a negative driving force, which direction will it tend to move across the cell membrane?

    <p>Into the cell (A)</p> Signup and view all the answers

    What is the equilibrium potential for chloride (Cl-) based on the provided data?

    <p>-90 mV (A)</p> Signup and view all the answers

    If the driving force for an anion is positive, in which direction will the ion move across the cell membrane?

    <p>Into the cell (C)</p> Signup and view all the answers

    What does a net driving potential of zero indicate regarding the chemical and electrical forces on an ion?

    <p>The chemical force equals the electrical force. (B)</p> Signup and view all the answers

    What is the equilibrium potential for potassium (K+) based on the provided information?

    <p>-94 mV (B)</p> Signup and view all the answers

    What does the term 'J' represent in the provided equation?

    <p>The amount of substance flowing through a unit area per unit time (A)</p> Signup and view all the answers

    Which factor is directly included within the diffusion coefficient (D)?

    <p>Size of the solute particle and viscosity of the solution (C)</p> Signup and view all the answers

    How does temperature affect the rate of diffusion?

    <p>Increased temperature increases the rate of diffusion (B)</p> Signup and view all the answers

    What is the 'transport maximum' (Tm) in carrier-mediated transport?

    <p>The point at which all binding sites are occupied (C)</p> Signup and view all the answers

    What does 'stereospecificity' in carrier-mediated transport imply?

    <p>That transport proteins have binding sites that are selective only for a specific isomer of a solute (A)</p> Signup and view all the answers

    Why does glucose sometimes appear in the urine?

    <p>Because the transport maximum of glucose is exceeded in the renal proximal tubule (B)</p> Signup and view all the answers

    Which of these is NOT a characteristic of carrier-mediated transport, based on the text provided?

    <p>Passive diffusion (A)</p> Signup and view all the answers

    What clinical significance does the text connect to stereospecificity in the renal proximal tubule?

    <p>The preferential transport of D-glucose over L-glucose (C)</p> Signup and view all the answers

    Why is urea considered an 'ineffective osmole'?

    <p>It rapidly equilibrates across cell membranes due to its permeability. (C)</p> Signup and view all the answers

    What primarily determines the osmotic pressure and the movement of water across a cell membrane?

    <p>The concentration of impermeant solutes. (A)</p> Signup and view all the answers

    Which term describes a solution that causes a cell to shrink?

    <p>Hypertonic (B)</p> Signup and view all the answers

    What type of transport mechanism is used by the glucose transporter (GLUT5)?

    <p>Facilitated diffusion (A)</p> Signup and view all the answers

    What is required for a substance to move across a membrane via primary active transport?

    <p>The input of energy from ATP. (D)</p> Signup and view all the answers

    How does secondary active transport differ from primary active transport?

    <p>It uses the gradient produced by primary active transport. (C)</p> Signup and view all the answers

    Which of the following uses bulk transport, specifically endocytosis?

    <p>A white blood cell ingesting bacteria. (D)</p> Signup and view all the answers

    According to Fick's Law, what directly influences the rate of diffusion across the cell membrane?

    <p>The gradient of the concentration across the membrane. (D)</p> Signup and view all the answers

    What distinguishes a system in homeostasis from one in equilibrium?

    <p>Homeostasis involves a steady state maintained through energy consumption, while equilibrium does not involve energy consumption. (C)</p> Signup and view all the answers

    Which of the following best describes how a negative feedback system functions?

    <p>It reverses deviations from a stable point, returning a variable to its original value. (A)</p> Signup and view all the answers

    How does positive feedback differ from negative feedback?

    <p>Positive feedback reinforces a stimulus; negative feedback opposes it. (A)</p> Signup and view all the answers

    What is a key characteristic of a positive feedback loop?

    <p>It creates cycles that can exaggerate deviations away from the initial value. (B)</p> Signup and view all the answers

    What is the relationship between isotonic and iso-osmotic solutions?

    <p>An isotonic solution is always iso-osmotic. (C)</p> Signup and view all the answers

    What does the reflection coefficient (σ) of a substance indicate in the context of osmosis?

    <p>The ability of a substance to exert effective osmotic pressure. (A)</p> Signup and view all the answers

    Under what circumstance might an iso-osmotic solution NOT be isotonic?

    <p>When the solute present has a reflection coefficient of 0. (B)</p> Signup and view all the answers

    Why is it important to differentiate between equilibrium and steady state in physiological systems?

    <p>Because steady state means active regulation with a constant value, while equilibrium implies no change using no energy. (C)</p> Signup and view all the answers

    Study Notes

    Homeostasis

    • Homeostasis is a steady state that involves energy consumption
    • Equilibrium is a state that does not use energy
    • A vital parameter (e.g., blood glucose) is well-regulated when in a steady state
    • The body carefully manages actions that can raise or lower the parameter value to maintain a constant value

    Negative Feedback

    • Negative feedback is the most common type of feedback mechanism
    • It reverses any deviation from a stable point
    • If a factor becomes too high or too low, a series of changes return the factor towards its mean value
    • This maintains homeostasis

    Positive Feedback

    • Positive feedback loops maintain or reinforce the stimulus
    • The cycle exacerbates deviations from a stable point
    • Repetition of this cycle can lead to instability or death

    Electrolyte Content of Body Fluids

    • Data presented includes the plasma mEq/L, interstitial fluid mEq/L, and intracellular fluid mEq/L for various electrolytes
      • Cations (Na+, K+, Ca2+, Mg2+) and Anions (Cl-, HCO3-, SO42-, PO43-, protein) are listed
      • Specific measurements are provided

    Osmotic Pressure and Reflection Coefficient

    • The relation between osmotic pressure and reflection coefficient are reviewed
    • Isotonic solution is always iso-osmotic, but an iso-osmotic solution may not be isotonic
    • Urea is freely permeable and equilibrates across compartments
    • Impermeable solute concentration determines osmotic pressure

    Tonicity of Solutions

    • Isotonic solutions cause no change in cell volume
    • Hypotonic solutions cause cell swelling
    • Hypertonic solutions cause cell shrinking
    • Tonicity depends on the concentration of impermeable solutes

    Transport Function of the Plasma Membrane

    • Simple Diffusion: Follows electrochemical gradient; through phospholipid layer
    • Facilitated Diffusion: Follows electrochemical gradient; requires a protein carrier
    • Primary Active Transport: Against electrochemical gradient; Uses ATP directly
    • Secondary Active Transport: Against electrochemical gradient; Uses the electrochemical gradient produced by primary active transport
    • Bulk Transport: Against electrochemical gradient; Endocytosis and exocytosis
    • Examples of substances transported using each method are given*

    Fick's Law of Diffusion

    • Relates diffusive flux to concentration gradient across a membrane
    • Factors affecting the rate of diffusion are:
      • Permeability coefficient
      • Partition coefficient
      • Diffusion coefficient
      • Thickness of the membrane
      • Cross-sectional area
      • Concentration difference

    Saturation in Carrier-Mediated Transport

    • Carrier proteins have a limited number of binding sites for solutes.
    • At low concentrations, transport rate increases steeply
    • At high concentrations, transport rate levels off (transport maximum) at the point where all binding sites are occupied

    Stereospecificity in Carrier-Mediated Transport

    • Binding sites for solutes on transport proteins are stereospecific.
    • Glucose transporter recognizes and transports only D-glucose and not L-glucose
    • The difference between D and L is displayed*

    Competition in Carrier-Mediated Transport

    • Binding sites are specific, but related solutes can be transported
    • D-galactose can inhibit the transport of D-glucose

    Ion Channel Characteristics

    • Conductance depends on the probability that the channel is open, the higher the probability, the higher the conductance/permeability.
    • Gates on ion channels controlled by different types of sensors:
      • Voltage-gated channels
      • Ligand-gated channels
      • Second-messenger-gated channels
      • Mechanically-gated channels

    Mechanisms Responsible for the Resting Membrane Potential

    • Chemical gradients generated by active transport pumps
    • Selective membrane permeability (more permeable to potassium ions)
    • Electrical gradients (create negative intracellular charge)
    • Electrochemical equilibrium

    Equilibrium Potential

    • The equilibrium potential for an ion is the membrane potential at which the diffusive force is exactly balanced by the electrical force
    • The overall current flow of an ion directly relates to the net force and conductance

    Driving Force for Diffusion

    • How driving forces affect ion diffusion across the cell membrane
    • Driving force is calculated by taking the resting membrane potential minus the cell's equilibrium potential for a given ion
    • When the result is negative, ions flow into the cell, if the result is positive, ions flow out of the cell*
    • Examples of ions (Na+, Cl+, K+, Ca 2+) driving force are displayed graphically

    Characteristics of Action Potentials

    • Stereotypical size and shape
    • Non-decremental propagation
    • All-or-none response
    • Examples of action potentials are given to demonstrate this concept*

    Refractory Periods

    • Absolute refractory period: no new action potential is possible, due to inactivation gates in Na+ channels.
    • Relative refractory period: a new AP can be generated, but only with a larger stimulus due to the hyperpolarizing after-potential

    Propagation of Action Potentials

    • Action potentials are propagated down a nerve or muscle fiber by local currents
    • The action potentials start at the initial segment/hillock of the axon, and propagate down the axon by spread of local currents

    Factors Affecting Conduction Velocity in Nerves

    • Myelination, axon diameter, temperature affect the speed of conduction
    • A table comparing faster and slower conduction factors is shown*

    Different Receptors, Signaling Pathways, and Messengers

    • Various receptors and signaling pathways described and categorized
    • Different receptor types and signaling pathways are mentioned with examples of their ligands.*
    • For each, Second Messengers and what effect they have are given*

    Good Study Habits

    • Consistent study schedule
    • Note-taking
    • Study breaks
    • Organized workspace
    • Prioritized tasks
    • Distraction-free environment
    • Peer study groups
    • Periodic review sessions

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    Physiology Block 1 Review SPRING 2025 PDF

    Description

    Test your understanding of homeostasis, negative feedback, and positive feedback mechanisms in the human body. Learn how these processes regulate vital parameters such as blood glucose and the role of electrolytes in body fluids. Assess your knowledge on maintaining stability and the consequences of feedback loop failures.

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