Fluid Dynamics: Velocity and Flow

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Questions and Answers

What is the effect of increasing the length of a tube on fluid flow according to Poiseuille's law?

Increases pressure gradient

Increases flow rate

Has no effect on flow rate

Decreases flow rate (correct)

Which factor does NOT affect the flow rate according to Poiseuille's law?

Fluid density (correct)

Pressure gradient

Tube radius

Viscosity

What condition indicates that flow is transitioning from laminar to turbulent according to Reynolds number?

Re between 1000 and 2000

Re = 2000

Re < 1000

Re > 2000 (correct)

What happens to the vascular conductance when flow becomes turbulent?

It decreases Signup and view all the answers

Which of the following best defines laminar flow?

Flow that occurs in layers Signup and view all the answers

Which statement about blood viscosity is true?

It changes depending on flow conditions Signup and view all the answers

What is the consequence of the Fahraeus-Lindqvist effect?

Decreased apparent viscosity with narrow vessels Signup and view all the answers

How does increasing the number of resistances in parallel affect total resistance in the cardiovascular system?

It decreases total resistance Signup and view all the answers

What effect does polycythemia have on blood viscosity according to the relationship outlined in the content?

Increases viscosity and increases resistance Signup and view all the answers

Which of the following factors is least likely to affect blood viscosity as described?

Diameter of the vessel Signup and view all the answers

In the context of the Fahreaus-Linqvist effect, when does viscosity decrease?

In vessels smaller than 200 um Signup and view all the answers

Which statement best describes the relationship between pressure, flow, and resistance in the cardiovascular system?

Flow increases with increased pressure and decreased resistance Signup and view all the answers

What is the significance of the Reynolds number in blood flow?

It indicates whether the flow is laminar or turbulent Signup and view all the answers

What is the primary factor that determines blood flow (Q) in the cardiovascular system?

Pressure differences between two points Signup and view all the answers

According to the law of Laplace, which condition leads to increased wall tension (T) in a blood vessel?

Increase in radius (r) Signup and view all the answers

How is the total intravascular pressure (Ptotal) calculated?

Pstatic + Pdynamic Signup and view all the answers

Which of these equations correctly represents cardiac output (CO)?

CO = SV x HR Signup and view all the answers

What is the relationship between resistance (R) and conductance (g) in blood flow?

g = 1/R Signup and view all the answers

In which part of the cardiovascular system is the blood volume normally greatest?

Venous vessels Signup and view all the answers

What component of blood pressure is primarily responsible for the movement of blood in the arteries?

Pdynamic Signup and view all the answers

Using the formula for estimating blood volume, how much blood would a 70 kg person have?

5.6 liters Signup and view all the answers

What is the primary function of the cardiovascular system?

To deliver O2 and nutrients, and remove CO2 and waste Signup and view all the answers

How is blood volume distributed within the cardiovascular system?

Most is found in the venous system, with a smaller portion in the arterial system Signup and view all the answers

What factors determine blood flow resistance according to Poiseuille's law?

Diameter of the vessel, viscosity of the blood, and length of the vessel Signup and view all the answers

Which statement about turbulent blood flow is correct?

It is commonly seen with high flow rates and irregularities in the vessel Signup and view all the answers

What is the normal hemoglobin concentration associated with the standard oxygen content in blood?

14 g/100 ml blood Signup and view all the answers

How does the Farhrus-Lindqvist effect influence blood viscosity?

It refers to a decrease in plasma viscosity with increased shear rates Signup and view all the answers

What is the significance of the law of Laplace in relation to the cardiovascular system?

It relates wall tension to pressure and vessel radius Signup and view all the answers

What is the approximate normal oxygen content in blood based on the standard hemoglobin level?

18.8 ml O2/100 ml blood Signup and view all the answers

Study Notes

Velocity, Flow, and Area

Flow (Q) is the product of velocity (v) and cross-sectional area (A): Q = v × A.
Velocity can be calculated from flow and area: v = Q/A.

Poiseuille’s Law and Resistance

Poiseuille’s experiments demonstrated that blood flow is affected by pressure gradient (ΔP), length of the vessel (L), radius of the vessel (r), and fluid viscosity (η).
Blood flow (Q) is proportional to the pressure gradient (ΔP) and the fourth power of radius (r^4), and inversely proportional to vessel length (L) and viscosity (η).
Poiseuille’s Law is mathematically expressed as: Q = (ΔPr^4π) / (ηL8).

Total Resistance in the Cardiovascular System

Total resistance is the cumulative effect of resistances in series and parallel configurations.
Increasing the number of vessels in parallel decreases total resistance.

Laminar and Turbulent Flow

Laminar flow occurs in layers, with the fastest flow in the center of the vessel; velocity profile resembles a parabolic shape.
Turbulent flow occurs when lamina breakdown, resulting in decreased vascular conductance and increased resistance to flow.
Reynold's Number (Re) indicates flow type: Re < 2000 suggests laminar flow, while Re > 2000 indicates turbulence.
Turbulence may arise at vessel bends, branch points, or stenotic valves.

Blood Viscosity

Blood is classified as a non-Newtonian fluid, exhibiting variable viscosity under different flow conditions.
The Fahraeus-Lindqvist effect describes reduced apparent viscosity when vessel diameter is less than 0.2 mm due to axial accumulation of red blood cells (RBCs).

Learning Objectives

Understand the differences in O2 content and saturation between arterial and venous blood, along with normal heart chamber pressures.
Familiarize with normal hematocrit, hemoglobin levels, and plasma electrolyte values (K+, Na+, Ca²+).
Recognize blood volume distribution in the cardiovascular system and estimate total blood volume based on body weight.
Analyze the relationship between pressure, flow, and resistance and its implications on wall tension (law of Laplace).
Distinguish between laminar and turbulent flow and factors influencing each type.
Identify factors affecting blood viscosity and the implications of the Fahraeus-Lindqvist effect.

Cardiovascular System Overview

The heart beats approximately 115,000 times daily, pumping about 7,230 liters of blood at rest.
Blood pressure peaks at about one-sixth of an atmosphere, generating roughly two watts of mechanical power.
The cardiovascular system functions as a closed-loop network supporting organ blood supply and performing essential roles like oxygen delivery, metabolic waste removal, hormone transport, immune response, temperature regulation, and fluid volume balance.

Key Hemodynamic Features

Blood volume constitutes 7-8% of body weight; estimate it using: blood volume (L) = body weight (kg) × 0.08.
Blood velocity decreases in capillaries where the cross-sectional area is maximized.

Relationships in Hemodynamics

Pressure in the system correlates with flow and resistance: P = Q × R.
Total intravascular pressure consists of static and dynamic components: P_total = P_static + P_dynamic.

Law of Laplace

Transmural pressure (ΔP) represents the difference between internal and external pressures across a vessel wall.
Wall tension (T) relates to radius and wall thickness, following the law of Laplace: T = ΔPr/h (for cylinders) and T = ΔPr/2h (for spheres).

Important Fluid Dynamics Concepts

Increased vessel radius elevates tension on vessel walls, even if pressure remains constant.
The presence of a cell-free layer at blood vessel walls enhances flow dynamics according to the Fahraeus-Lindqvist effect.
Blood viscosity, affected by hematocrit levels, influences resistance; high hematocrit (polycythemia) raises viscosity and resistance, while low hematocrit (anemia) decreases both.

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Description

Explore the principles of fluid dynamics, focusing on velocity, flow, and cross-sectional area through the equation Q = v x A. Understand Poiseuille's law and its implications on resistance in blood vessels, considering factors like pressure gradient, tube length, radius, and fluid viscosity.