Physiology: Flow Down Gradients

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Questions and Answers

According to Poiseuille's Law, how does decreasing the radius of a blood vessel by half affect the resistance to blood flow?

Resistance increases by a factor of 16.

Explain how the body uses Poiseuille's Law to control blood flow to tissues, mentioning at least two specific mechanisms.

The body controls blood flow by adjusting pressure in large vessels and by changing the radius of small vessels. Increased pressure raises flow, while increasing radius lowers resistance, raising flow.

Explain in your own words the relationship between flow, gradients, and resistance in a system. How does changing each parameter affect the others?

Flow is directly proportional to the gradient and inversely proportional to the resistance. Increasing the gradient increases flow, while increasing resistance decreases flow. Changes in flow can affect the gradient if the system is not at equilibrium.

Identify two factors, other than radius, that affect flow in Poiseuille's Law, and describe how increasing each of these factors would influence flow rate.

Two factors are pressure difference and viscosity. Increasing the pressure difference between two points increases flow rate. Increasing viscosity decreases flow rate. Signup and view all the answers

How does Poiseuille's Law apply to airflow in the respiratory tract, and provide a specific example of a respiratory condition where this law is relevant?

Poiseuille's Law applies to airflow by describing how flow is affected by pressure difference, airway radius, airway length, and air viscosity. Asthma where airway constriction reduces the radius, decreasing airflow to the lungs, is one example. Signup and view all the answers

Consider a scenario where the resistance to flow in a system increases. Describe two possible compensatory mechanisms the system might employ to maintain a constant flow rate.

The system could increase the gradient to overcome increased resistance and maintain flow. Another compensatory mechanism involves reducing the flow to match the changes in resistance and gradient. The system will attempt to balance these factors to maintain homeostasis. Signup and view all the answers

What is the significance of understanding 'flow down gradients' in the context of physiological systems, and why is it important for understanding clinical cases?

Understanding flow down gradients is crucial because it explains how substances move within the body, driving essential processes like nutrient delivery, waste removal, and signal transduction. In clinical cases, disruptions in these gradients can lead to disease states, thus understanding them is vital for accurate diagnosis and effective treatment. Signup and view all the answers

If a section of a garden hose is lengthened, what variable in Poiseuille's Law changes, and how does this change impact the overall water flow through the hose?

The length (l) variable changes. Increasing the length of the hose decreases the overall water flow through the hose. Signup and view all the answers

Differentiate between the roles of gradients and resistances in determining the rate of flow within a physiological system. Provide examples to highlight your point.

Gradients act as the driving forces that initiate and maintain flow, while resistances oppose flow, acting as a 'brake'. For instance, blood pressure gradients drive blood flow, while blood vessel constriction creates resistance. Similarly, concentration gradients drive diffusion, while membrane permeability acts as resistance. Signup and view all the answers

If the energy gradient between points A and B doubles, but the resistance to flow also doubles, how will the flow rate change? Explain your answer.

The flow rate will remain the same. Because Flow = Gradient / Resistance, doubling both the gradient and the resistance results in no net change in the flow rate. Mathematically, if original values are G and R, then Flow = G/R. The new flow = 2G/2R = G/R, which is the original flow. Signup and view all the answers

Based on Mary’s presentation, which physico-chemical law is most directly related to the increased capillary refill time observed in her right foot? Explain how this law applies in this specific clinical context.

Poiseuille's Law. Reduced blood flow due to narrowed vessels (atherosclerosis from diabetes) increases resistance, slowing capillary refill. Signup and view all the answers

Explain how diabetes mellitus can lead to the observed differences in temperature and color between Mary's right and left feet. Reference specific vascular changes associated with diabetes.

Diabetes causes microvascular and macrovascular complications. Atherosclerosis reduces blood flow to the right foot, causing coolness and pallor. The left foot has better circulation, hence normal temperature and color. Signup and view all the answers

Mary's loss of sharp/dull sensation in her right foot is likely related to diabetic neuropathy. Briefly explain the mechanism of how chronic hyperglycemia contributes to nerve damage and sensory deficits.

Hyperglycemia leads to the accumulation of advanced glycation end-products (AGEs) and activation of the polyol pathway, causing oxidative stress and nerve damage, resulting in neuropathy. Signup and view all the answers

Considering Mary's symptoms, which clinical finding is least likely to be solely due to vascular changes associated with diabetes? Explain your reasoning.

Loss of sharp/dull sensation. While ischemia can contribute, diabetic neuropathy is a more direct and common cause of sensory loss. Signup and view all the answers

Based on the provided images of arterioles and elastic arteries from a patient with Type II diabetes, describe the key structural differences compared to those from a patient without vascular disease, and explain how these differences contribute to Mary's diminished peripheral pulses.

Diabetic vessels show thickened basement membranes and narrowed lumens. This reduces vessel elasticity and increases resistance, diminishing pulse strength distally. Signup and view all the answers

According to Poiseuille's Law, what single factor has the most significant impact on resistance to fluid flow in a tube, and why?

The radius of the tube is the most important determinant of resistance because resistance is inversely proportional to the fourth power of the radius. Signup and view all the answers

What are three conditions under which Poiseuille's Law may not be entirely accurate in describing fluid flow?

Poiseuille's Law isn't exact when tubes are branched, irregularly shaped, flexible, or when fluid flow becomes turbulent. Signup and view all the answers

A scientist measures the pressure drop across a rigid tube and the resulting flow rate. How could they determine the resistance to flow using a variant of Ohm's Law?

Resistance can be determined by dividing the pressure drop by the flow rate (Resistance = Pressure Drop/Flow Rate). Signup and view all the answers

Explain how Fick's Law relates to the movement of oxygen from the alveoli in the lungs to the blood.

Fick's Law describes the rate of oxygen diffusion from the alveoli to the blood as proportional to the concentration gradient, surface area, and permeability, and inversely proportional to membrane thickness. Signup and view all the answers

State Fick's Law in equation form, defining each of the terms.

$F = k \cdot \frac{A(C_A - C_B)}{t}$, where $F$ is flow/flux, $k$ is a constant related to permeability and solubility, $A$ is surface area, $C_A - C_B$ is the concentration gradient, and $t$ is membrane thickness. Signup and view all the answers

How do the properties of a substance (molecular size and solubility) affect the constant '$k$' in Fick's Law?

The constant '$k$' increases when the substance is a smaller molecule or has better solubility in the membrane. Signup and view all the answers

According to Fick's Law, how would increasing the thickness of a membrane affect the rate of diffusion across it, assuming all other factors remain constant?

Increasing the membrane thickness would decrease the rate of diffusion. Signup and view all the answers

Describe how tissue structure has adapted to optimize diffusion according to Fick's Law.

Tissues have adapted to minimize the thickness of the diffusion barrier, as flux is very slow over distances greater than 0.1 mm. Signup and view all the answers

How does a large difference in concentration affect flow/flux, all other things being equal?

A larger difference in concentration will increase flow/flux. Signup and view all the answers

In the context of Fick's Law, how would an increase in the surface area available for diffusion (A) affect the overall flow (F) across a membrane?

An increase in the surface area available for diffusion ($A$) would lead to a proportional increase in the flow ($F$) across the membrane, assuming all other factors remain constant. Signup and view all the answers

According to Ohm's law, if the voltage across a membrane increases while the resistance remains constant, what happens to the current and why?

The current increases because current is directly proportional to voltage, as described by the equation $I = \frac{V}{R}$. Signup and view all the answers

Explain how an increased number of ion channels in a cell membrane affects the resistance to ion flow, and consequently, the current, assuming the voltage remains constant?

Increasing the number of ion channels decreases resistance. According to Ohm's law ($I = \frac{V}{R}$), with constant voltage, a decrease in resistance leads to an increase in current. Signup and view all the answers

How does the charge of a particle and the voltage gradient across a membrane influence the movement of the particle across the membrane?

Opposite charges attract, and like charges repel. A positively charged particle will move towards a more negative area, and vice versa, 'down' the voltage gradient. Signup and view all the answers

Describe the relationship between the permeability of a membrane to a charged particle, the voltage gradient, and the resulting current flow.

Higher membrane permeability allows more charged particles to flow, leading to a greater current, given a constant voltage gradient. Lower permeability restricts flow, reducing the current. Signup and view all the answers

Why is the concept of voltage across a cell membrane considered a form of potential energy?

Voltage represents the energy stored by separating charges. This stored energy can do work, such as moving charged particles across the membrane. Signup and view all the answers

Given a scenario where a cell membrane has a high concentration of positive ions on one side and a lower concentration on the other, describe how this concentration difference contributes to the voltage across the membrane.

The unequal distribution of ions creates a charge separation, leading to a voltage. The side with more positive ions will be more positive relative to the other side, establishing an electrical potential difference. Signup and view all the answers

Explain why the electric field generated by separated charges across a membrane declines rapidly as the distance from the membrane increases?

The electric field declines rapidly due to the nature of electrostatic forces. The effect of individual charges diminishes quickly with distance. Signup and view all the answers

Using Ohm's law, explain what would happen to the current if the resistance of a cell membrane suddenly increased due to the blocking of ion channels, assuming the voltage remains constant?

According to Ohm's law ($I = \frac{V}{R}$), if the resistance (R) increases and the voltage (V) remains constant, the current (I) will decrease. Signup and view all the answers

In biological systems, why is it important that overall positive and negative charges are balanced in physiological compartments, even though local charge separations create membrane potentials?

Overall charge balance is essential for maintaining electrochemical stability and preventing uncontrolled electrical activity. Local charge separations create localized potentials for specific functions. Signup and view all the answers

Describe how the concepts of voltage, current, and resistance, as described by Ohm's law, apply to the movement of ions across a cell membrane during an action potential.

During an action potential, changes in ion channel permeability alter membrane resistance, causing changes in ion flow (current) driven by the voltage gradient across the membrane. This dynamic interplay underlies the action potential. Signup and view all the answers

How do cells specialized for transporting large amounts of solutes adapt their structure to enhance this process?

They increase the number of transporters and develop structural features that maximize the surface area to volume ratio. Signup and view all the answers

Explain how manipulating concentration gradients is crucial for bodily functions, providing at least one specific example.

Concentration gradients drive many essential processes, such as nutrient absorption facilitated by transporters, and waste removal, with the cell maintaining these gradients through metabolism and active transport. Signup and view all the answers

Describe a scenario where the saturation of protein transporters could impact solute flux, and what the likely result of this would be.

When protein transporters are saturated, the rate of solute flux decreases because there are not enough transporters to bind additional solute, so, the amount of substance crossing the membrane remains constant even if the substance's concentration increases. Signup and view all the answers

Under what circumstances might the rate of diffusion become a critical factor in physiological function, leading to disease?

Diffusion rate becomes critical when physiological demands exceed the capacity of diffusion, such as during high metabolic activity or in conditions where barriers to diffusion are increased (e.g., edema, fibrosis), leading to impaired delivery of oxygen or nutrients to tissues. Signup and view all the answers

Considering Fick's Law, how does an increase in the thickness of a membrane affect the rate of diffusion across it, assuming all other factors remain constant?

An increase in membrane thickness decreases the rate of diffusion because the distance a molecule must travel increases, thus reducing flux ($J = -D (dC/dX)$). Signup and view all the answers

Flashcards

Flow

Movement of a substance from point A to point B in a system.

Energy Gradient

The difference in energy between two points that drives flow.