Homeostasis and Feedback Mechanisms
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Questions and Answers

What does the permeability coefficient (P) represent in the context of diffusion?

  • The solubility of the substance in oil (correct)
  • The amount of substance that flows per unit area and time
  • The thickness of the membrane through which diffusion occurs
  • The diffusion rate based on temperature and viscosity

    • At what point does the transport maximum (Tm) occur in carrier-mediated transport?

  • When the diffusion coefficient becomes constant
  • When the temperature is near absolute zero
  • When the concentration gradient reverses
  • When all binding sites on the carrier proteins are occupied (correct)

    • Which of the following factors does NOT directly affect the rate of diffusion according to Fick's law?

  • Thickness of the membrane (∆X)
  • Size of the particle (K) (correct)
  • Viscosity of the solution (D)
  • Concentration difference (∆C)

    • What is the role of stereospecificity in carrier-mediated transport?

    <p>To ensure only the natural isomer is recognized and transported by the transporter (D)</p> Signup and view all the answers

    How does an increase in temperature affect the rate of diffusion?

    <p>It generally increases the rate of diffusion (C)</p> Signup and view all the answers

    Which of the following best describes competition in carrier-mediated transport?

    <p>Different solutes compete for binding to a single transporter (D)</p> Signup and view all the answers

    What is a consequence of Tm-limited glucose transport in the kidney?

    <p>Excess glucose is excreted in the urine when levels increase (C)</p> Signup and view all the answers

    What happens to the transport rate as solute concentrations increase towards saturation?

    <p>The transport rate levels off and becomes constant (A)</p> Signup and view all the answers

    What is the primary role of potassium ions (K+) in generating electrical gradients across the cell membrane?

    <p>They leak out of the cell, creating a negative charge that attracts them back. (A)</p> Signup and view all the answers

    What does the Nernst equation specifically describe regarding ion movement?

    <p>The balance between electrical and chemical forces for each ion. (C)</p> Signup and view all the answers

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

    <p>+24 mV towards the inside of the cell (C)</p> Signup and view all the answers

    Which statement best describes the movement of ions relative to the equilibrium potential?

    <p>Ions diffuse towards their equilibrium potential, adjusting the Em towards that value. (C)</p> Signup and view all the answers

    What can be inferred about the permeability of a cell membrane to ions during normal conditions?

    <p>The opening of ion channels does not significantly change ion concentrations. (B)</p> Signup and view all the answers

    Which statement best describes homeostasis?

    <p>Homeostasis is a steady state that consumes energy. (D)</p> Signup and view all the answers

    What is the primary function of negative feedback in physiological processes?

    <p>To maintain stability by reversing deviations. (A)</p> Signup and view all the answers

    In which of the following situations would positive feedback most likely occur?

    <p>Increasing uterine contractions during childbirth. (A)</p> Signup and view all the answers

    What distinguishes a steady state from equilibrium in physiological terms?

    <p>A steady state actively maintains specific values, while equilibrium indicates no energy use. (C)</p> Signup and view all the answers

    Which characteristic accurately describes positive feedback mechanisms?

    <p>They tend to exaggerate deviations from stable points. (D)</p> Signup and view all the answers

    Which condition must be true for an iso-osmotic solution to be considered isotonic?

    <p>It must have a reflection coefficient greater than 0. (C)</p> Signup and view all the answers

    What role do reflection coefficients (σ) have in osmotic pressure?

    <p>They indicate the permeability of solutes through a membrane. (A)</p> Signup and view all the answers

    How does the body use energy in maintaining homeostatic balance?

    <p>Through the constant regulation of vital parameters. (B)</p> Signup and view all the answers

    Which type of solution will cause a cell to swell due to water movement?

    <p>Hypotonic solution (D)</p> Signup and view all the answers

    What primarily determines the osmotic pressure of a solution?

    <p>Concentration of impermeant solute(s) (A)</p> Signup and view all the answers

    Which type of transport requires energy to move solutes against their electrochemical gradient?

    <p>Primary active transport (D)</p> Signup and view all the answers

    Which of the following processes is not classified as bulk transport?

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

    Which process uses a protein carrier but does not directly use ATP?

    <p>Secondary active transport (C)</p> Signup and view all the answers

    What is the role of urea in relation to cell membranes?

    <p>Permeable solute that does not affect cell volume (D)</p> Signup and view all the answers

    Which of the following solutes can move through protein channels in facilitated diffusion?

    <p>Water (D)</p> Signup and view all the answers

    Which factor does NOT affect the rate of diffusion across the cell membrane?

    <p>Cell size (A)</p> Signup and view all the answers

    Based on the provided information, what is the equilibrium potential for calcium ions (Ca2+)?

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

    What occurs during an absolute refractory period?

    <p>Inactivation gates of Na+ channels are closed, preventing a new action potential. (B)</p> Signup and view all the answers

    Which of the following accurately describes the propagation of an action potential along an axon?

    <p>Action potentials regenerate as they travel down the axon. (B)</p> Signup and view all the answers

    What distinguishes the relative refractory period from the absolute refractory period?

    <p>Greater inward current can elicit an action potential during the relative refractory period. (C)</p> Signup and view all the answers

    Which factor does NOT directly influence the conduction velocity of action potentials?

    <p>External temperature (D)</p> Signup and view all the answers

    What best explains the characteristic all-or-none response of action potentials?

    <p>Only stimuli that reach the threshold will result in an action potential. (A)</p> Signup and view all the answers

    During which phase of an action potential is the membrane potential closer to the K+ equilibrium potential?

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

    What initiates an action potential in a neuron?

    <p>The initial segment of the axon, near the cell body. (A)</p> Signup and view all the answers

    What happens to the action potential as it travels down the length of an axon?

    <p>It maintains its shape and size due to regeneration. (B)</p> Signup and view all the answers

    Study Notes

    Homeostasis

    • Homeostasis is a steady state, not equilibrium
    • It maintains a stable internal environment by using energy
    • A vital parameter (like blood glucose) is regulated, but not in equilibrium.
    • The body carefully balances actions that lower the vital parameter with actions that raise it, keeping the value constant.

    Negative Feedback

    • Negative feedback is the most common feedback mechanism
    • It reverses any deviation from a stable point.
    • If a factor becomes excessive or deficient, negative feedback returns the factor to a mean value.
    • This maintains homeostasis.
    • This involves a series of changes.

    Positive Feedback

    • Positive feedback is less common than negative feedback
    • It maintains the direction of the stimulus, possibly accelerating it.

    Electrolyte Content of Body Fluids

    • Lists various electrolytes and their concentrations in plasma, interstitial fluid, and intracellular fluid.

    Osmotic Pressure and Reflection Coefficient

    • Examines the relation between osmotic pressure and reflection coefficient.
    • Iso-osmotic solution has equal solute concentrations in each compartment however, it may not be isotonic.
    • Osmolarity of compartment 1 and 2 in the example provided changed during the process.
    • Urea is freely permeable, and equilibrates quickly between compartments.

    Tonicity of Solutions

    • Isotonic solutions do not cause a change in cell volume.
    • Hypotonic solutions cause cell swelling.
    • Hypertonic solutions cause cell shrinkage.

    Transport Function of the Plasma Membrane

    • Summarizes different types of membrane transport
    • Includes examples of substances transported by each method (e.g., simple diffusion, facilitated diffusion, primary active, secondary active, bulk transport).

    Fick's Law of Diffusion

    • Relates diffusive flux to the gradient of the concentration across the membrane
    • Factors affecting diffusion rate across a membrane are: permeability coefficient, partition coefficient, diffusion coefficient, thickness of the membrane, cross-sectional area and the difference in concentration.
    • Temperature has an effect on the diffusion rate.

    Saturation in Carrier-Mediated Transport

    • Carrier proteins have a limited number of binding sites.
    • At low solute concentrations, the rate of transport increases as concentration increases
    • At high solute concentrations, transport levels off (transport maximum, Tm).
    • Clinical significance: Tm-limited glucose transport in the kidneys.

    Stereospecificity in Carrier-Mediated Transport

    • Binding sites on carrier proteins are specific, recognizing only certain isomers.
    • The transporter for glucose is specific for the D-isomer.

    Competition in Carrier-Mediated Transport

    • Related substrates can compete for binding sites on a transporter.
    • D-galactose inhibits glucose transport by occupying glucose receptor sites.

    Ion Channel Characteristics

    • Conductance depends on the probability of a channel being open
    • Gate control mechanisms include voltage-gated, ligand-gated, second messenger-gated and mechanically-gated channels.

    Mechanisms Responsible for the Resting Membrane Potential

    • Chemical gradients from active transport pumps, (Na+ -K+ ATPase pump).
    • Selective membrane permeability.
    • Electrical gradients.

    Equilibrium Potential

    • The membrane potential at which the net movement of an ion across a membrane is zero.
    • The ion diffuses in a direction that brings the membrane potential toward its equilibrium potential
    • The overall current is directly proportional to The net force and conductance.
    • The Em moves towards the equilibrium potential of the most permeable ion.

    Driving Force for Diffusion: Equilibrium Potential vs. RMP

    • The driving force for an ion is the difference between the membrane potential and the equilibrium potential.
    • The driving force affects the direction of ion movement across the membrane.

    Characteristics of Action Potentials

    • Stereotypical: Size and shape are consistent for a given cell type
    • Propagation: Action potentials are propagated down the entire length of the axon without decrement
    • Active or All-or-none response: A signal above the threshold level is required for an action potential to be produced.

    Action Potential sequence

    • Depolarization
    • Repolarization
    • Hyperpolarization

    Refractory Periods

    • Absolute Refractory Period: No new action potential can be generated, regardless of stimulus strength.
    • Relative Refractory Period: A stronger stimulus is needed to generate an action potential.

    Propagation of Action Potentials

    • Action potentials propagate along the nerve axon due to the spread of local currents from active to inactive areas.
    • APs are initiated in the axon hillock near the nerve cell body and then propagated down the axon through local current spreads.

    Factors Affecting Conduction Velocity in Nerves

    • Factors such as myelination, axon diameter, and temperature influence conduction velocity.

    Different Receptors and Signaling Pathways

    • Describes different types of receptors (ligand-gated ion channels, G protein-coupled receptors, enzyme-linked receptors, nuclear receptors).
    • Provides details about the signaling pathways and 2nd messenger involved for each receptor type.

    Good Study Habits

    • Good study habits involve consistent and effective practices to optimize understanding and retention of information.
    • Examples include having a consistent schedule, active note-taking, study breaks, an organized workspace, prioritizing tasks, a distraction-free environment, peer study groups and periodic review sessions.

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    Related Documents

    Physiology Block 1 Review SPRING 2025 PDF

    Description

    This quiz covers essential concepts of homeostasis, including negative and positive feedback mechanisms that maintain stable internal conditions. It also discusses the electrolyte content of body fluids and the roles of osmotic pressure. Test your understanding of how the body regulates vital parameters through feedback systems.

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