Homeostasis and Feedback Mechanisms Quiz

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which of the following best describes the relationship between homeostasis and equilibrium?

Equilibrium and homeostasis are synonymous terms, both representing a balance that does not involve energy.

Homeostasis is a steady state that requires energy; a parameter under homeostatic control is not in equilibrium. (correct)

Homeostasis is a state of equilibrium, where no energy is required to maintain a vital parameter.

Homeostasis aims to achieve equilibrium, making them both states that require no energy.

What is the primary function of negative feedback mechanisms in maintaining a stable internal environment?

To create a positive change in the controlled variable when it is deficient.

To amplify changes in a controlled variable, leading to faster responses.

To push the controlled variable further from its mean value, temporarily.

To maintain a steady state by reversing deviations of a controlled variable from its set point. (correct)

Which characteristic is most indicative of a positive feedback loop?

It diminishes the initial stimulus.

It returns the variable to it's original set point after a disturbance.

It results in a stable, constant value for the controlled variable

It amplifies the initial stimulus, leading to further change in the same direction. (correct)

When is it most likely that a parameter is under a steady state as opposed to equilibrium?

When the parameter is held constant by the body matching actions to raise and lower the value. Signup and view all the answers

An isotonic solution placed in a cell...

...is always iso-osmotic, but may not be if it has a reflection coefficient of 0 (σ = 0). Signup and view all the answers

In a situation where a controlled variable begins to increase, what would a negative feedback loop initiate?

A series of changes aimed to reduce the controlled variable. Signup and view all the answers

Why is a positive feedback loop considered less common in physiological processes compared to negative feedback?

Positive feedback loops maintain the direction of the stimulus and can lead to instability. Signup and view all the answers

What is the membrane potential for Na+ based on the provided values?

+60 mV Signup and view all the answers

When the driving force is negative for a cation, what occurs?

Cation will enter the cell Signup and view all the answers

What is the net driving potential for diffusion calculated as?

Resting membrane potential minus equilibrium potential Signup and view all the answers

What does the equilibrium potential for Cl- equal based on the given information?

-90 mV Signup and view all the answers

Which of the following is NOT a characteristic of action potentials?

Varying duration Signup and view all the answers

What primarily determines osmotic pressure in a solution?

The concentration of impermeant solutes Signup and view all the answers

When a cell is placed in a hypertonic solution, what is the expected effect on cell volume?

The cell will shrink Signup and view all the answers

Which type of transport directly uses ATP to move substances against their electrochemical gradient?

Primary active transport Signup and view all the answers

Which statement best describes the function of an impermeant solute in a solution?

It is responsible for creating osmotic pressure. Signup and view all the answers

Which process involves the bulk intake of substances into a cell?

Endocytosis Signup and view all the answers

What is the characteristic feature of facilitated diffusion?

It involves a protein carrier. Signup and view all the answers

According to Fick’s law of diffusion, what factor does NOT affect the rate of diffusion across a cell membrane?

Type of solute Signup and view all the answers

What describes a solution that has the same osmotic pressure as the cells placed in it?

Isotonic solution Signup and view all the answers

Which example depicts secondary active transport?

SGLT1 transporter for glucose Signup and view all the answers

What is the primary factor affecting the rate of diffusion according to the provided information?

The temperature Signup and view all the answers

What happens to the transport rate in carrier-mediated transport at high solute concentrations?

It reaches a maximum and levels off Signup and view all the answers

Which coefficient is associated with the solubility of a solute in oil in the equation provided?

K Signup and view all the answers

Which is a significant clinical relevance of Tm in glucose transport in the kidney?

Glucose spillage occurs when transporters are saturated Signup and view all the answers

What does stereospecificity in carrier-mediated transport imply?

Transporters selectively bind specific isomers Signup and view all the answers

In the equation J = PA, what does 'A' represent?

The cross-sectional area through which diffusion occurs Signup and view all the answers

Which factor does NOT influence the permeability coefficient (P)?

Concentration of the solute Signup and view all the answers

What could potentially occur when carrier proteins reach their transport maximum (Tm)?

No more solute binding can occur Signup and view all the answers

Which of the following statements about diffusion is true?

The diffusion coefficient is affected by solute particle size. Signup and view all the answers

What might limit glucose transport in the renal proximal tubule?

Limited binding sites on the transport protein Signup and view all the answers

Which statement accurately describes the specificity of transporters for solutes?

Transporters may recognize and transport chemically related solutes. Signup and view all the answers

What role does D-galactose play in the transport process of D-glucose?

D-galactose inhibits the transport of D-glucose by occupying binding sites. Signup and view all the answers

Which type of ion channel responds to changes in membrane tension?

Mechanically-gated channels Signup and view all the answers

What is the primary factor that influences the conductance of an ion channel?

The probability that the channel is open Signup and view all the answers

How do chemical gradients across the cell membrane primarily form?

By the action of active transport pumps like the Na+-K+ ATPase pump Signup and view all the answers

Which ion channel type is triggered by the binding of neurotransmitters?

Ligand-gated channels Signup and view all the answers

Which of the following correctly describes the effect of increased channel opening probability?

Increased permeability and diffusion rate Signup and view all the answers

What is a characteristic of D-glucose transporters in relation to D-galactose?

They show a preference for D-glucose but can also transport D-galactose. Signup and view all the answers

What mechanism controls the opening of voltage-gated channels?

Fluctuations in membrane potential Signup and view all the answers

What mechanism allows ions to flow through a channel when it is open?

Passive transport without any energy input Signup and view all the answers

Study Notes

Homeostasis

Homeostasis is a steady state, requiring energy
Equilibrium is a state without energy consumption
A vital parameter (e.g., blood glucose) is well-regulated when in a steady state
The body carefully manages actions that lower and raise the vital parameter, maintaining a constant value

Negative Feedback

Negative feedback is the most common feedback mechanism, self-limiting
It reverses any deviation of a controlled variable from its stable point
A control system initiates a series of changes that return the factor towards its mean value, maintaining homeostasis
Key components include a stimulus initiating event, a variable, a receptor (detects change in variable), a control center (compares input to reference value), and effectors (make adjustments to the variable to return the variable to its original set point)

Positive Feedback

Positive feedback loops maintain the direction of the stimulus
The cycle tends to exaggerate deviations of the controlled variable from its stable point
Each cycle of this feedback leads to more of the same variable, possibly accelerating the process
It may cause instability and death

Electrolyte Content of Body Fluids

The table provides the electrolyte content in plasma, interstitial fluid, and intracellular fluid measured in mEq/L
The electrolytes listed include cations (sodium, potassium, calcium, magnesium) and anions (chloride, bicarbonate, sulfate, phosphate, protein).

Osmotic Pressure and Reflection Coefficient

Osmotic pressure and reflection coefficient are related
Isotonic solutions are always iso-osmotic. However, an iso-osmotic solution may not be isotonic when the reflection coefficient is 0.
Substances with a reflection coefficient of 0 move across the membrane, rapidly equilibrates between the compartments
The impermeable solutes determine the osmotic pressure and water movement

Tonicity of Solutions

Isotonic: No change in cell volume
Hypotonic: Cell swells
Hypertonic: Cell shrinks
Tonicity depends on the concentration of impermeable solutes, some solutes can permeate cell membrane

Review of Effects of Volume Changes on Osmolarity of Body Fluids

The table (Table 1) summarizes volume changes and body osmolarity following changes in body hydration

Transport Function of the Plasma Membrane

Simple diffusion follows the electrochemical gradient, through the phospholipid layer. Examples include O2, CO2, glycerol.
Facilitated diffusion follows the electrochemical gradient, through protein channels or pores. Examples include Na+, K+, H2O, fructose(GLUT5)
Primary active transport goes against the electrochemical gradient, using ATP directly. Examples include Na+-K+ ATPase, Ca++ pump
Secondary active transport goes against the electrochemical gradient, uses the electrochemical gradient created by primary active transport. Examples include Na+-glucose (SGLT1), Na+-Ca++ exchanger, Na+-amino acid exchanger
Bulk transport goes against the electrochemical gradient, includes endocytosis (bulk intake of substances) and exocytosis (bulk secretion of substances). WBC, neurotransmitters, (Ach), and hormones are examples.

Fick's Law of Diffusion

Fick's Law relates diffusive flux to the gradient of concentration across a membrane.
J = P × (ΔC/ΔX). More precisely written as J = (K×D×ΔC)/ΔX where J is the flux, P is permeability coefficient, K is partition coefficient, D is diffusion coefficient, ΔC is concentration difference and ΔX is the thickness of the membrane

Saturation in Carrier-Mediated Transport

Carrier proteins have a limited number of binding sites for solutes
At low solute concentrations, the rate of transport increases as more binding sites are available
At high concentrations, the rate of transport levels off (transport maximum or Tm)

Stereospecificity in Carrier-Mediated Transport

Binding sites on transport proteins are stereospecific (stereoselective)
This means the transporter for glucose, in the kidney, recognizes and transports the natural isomer, D-glucose, but not L-glucose.

Competition in Carrier-Mediated Transport

Binding sites for transported solutes are specific, but they may also recognize and bind chemically related solutes
D-galactose may compete with D-glucose for binding sites, reducing glucose uptake

Ion Channel Characteristics

Conductance (g) of a channel depends on the probability that it is open, the higher the probability, the higher its conductance. Conduction speeds up the rate of diffusion.
Ion channel gates are controlled by sensors: voltage-gated channels respond to changes in membrane potential, ligand-gated channels respond to changes in ligands (hormones, neurotransmitters), second-messenger-gated channels respond to changes in signaling molecules, and mechanically-gated channels respond to changes in membrane tension.

Mechanisms Responsible for the Resting Membrane Potential

Chemical gradients are generated by active transport pumps (e.g., Na+/K+ ATPase)
Selective permeability of the membrane, particularly to potassium (K+) ions, creates a negative intracellular charge
Electrical gradients arise from potassium leak (K2P channels) which attracts potassium ions back into the cell, opposing the chemical gradient
Electrochemical equilibrium develops when the electrical and chemical forces balance for each ion species

Equilibrium Potential

The equilibrium potential is the membrane potential where the diffusive forces (chemical gradient) equal the electrical forces(electrical charges).
The ion always diffuses in a direction that brings the membrane potential toward its equilibrium potential.
The overall current flow of the ion is directly proportional to the net force and conductance of the membrane for the ion.

Driving Force for Diffusion: Equilibrium Potential vs. RMP

A cell's resting membrane potential (RMP) affects the diffusion of ions based on the driving force of the ion's equilibrium potential.
The net driving force is the difference between the RMP and the ion's equilibrium potential.

Characteristics of Action Potentials

Action potentials are stereotyped (specific size and shape) for a given cell type
They propagate down the entire length of the axon without decrement
They are all-or-none responses, requiring a certain threshold to initiate

Refractory Periods

Absolute refractory period is the time where no stimulus can cause another AP to occur. Inactivation gates of Na+ channels are responsible.
Relative refractory period is the time after the ARP, when an AP can fire but only if a larger than usual stimulus is applied. Higher K+ conductance is present during this period.

Propagation of Action Potentials

Action potentials propagate along a nerve or muscle fiber by the spread of local currents, from active regions to inactive regions
APs are initiated in the axon's initial segment (hillock)and propagated down the axon by local current spread

Factors Affecting Conduction Velocity in Nerves

Factors that influence nerve conduction velocity include myelination (myelinated nerves conduct faster), axon diameter (wider axons conduct faster), and temperature (warmer temperatures conduct faster)

Receptors, Signaling Pathways, and Messengers

Receptors include ligand-gated ion channels (e.g., GABA, acetylcholine), G protein-coupled receptors (e.g., acetylcholine, peptides), enzyme-linked receptors (e.g., insulin, growth factors), and nuclear receptors (e.g., steroid hormones)
Signaling pathways involve second messengers (e.g., cAMP, DAG, IP3).
Note: information about neurotransmitter pathways, second messengers, and associated receptors

Good Study Habits

Good study habits are important to optimize understanding and retention
Consistently cultivating good study habits leads to better comprehension, improved performance, and reduced stress.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your understanding of homeostasis and feedback mechanisms with this quiz. Explore the concepts of equilibrium, negative feedback loops, and positive feedback in physiological processes. Challenge yourself with questions that delve into these critical biological principles.