Pressure, Flow and Resistance Flashcards
In which types of organisms is diffusion alone sufficient to deliver oxygen and nutrients and remove waste products?
In single-celled and simple multi-cellular organisms.
What process is used to transport substances around the body in complex multicellular organisms?
Bulk flow.
bulk flow definition
Transport within blood or air due to pressure differences
passive diffusion definition
Movement down a concentration gradient
transport of gases require what 2 things?
both bulk flow and passive diffusion
How does diffusion differ from bulk flow?
Bulk flow moves large quantities of substances (like oxygen, O₂) from one location to another through a system, as shown in the image with the lungs and respiring tissue.
Diffusion moves individual molecules (like oxygen and carbon dioxide) from areas of higher concentration to areas of lower concentration across membranes, as shown in the diagram.
What determines the rate of diffusion between air and blood?
The rate of diffusion is driven by:
The concentration (or partial pressure) difference (C₁ - C₂).
What limits the rate of diffusion?
The rate of diffusion is limited by:
The thickness (T) and surface area (A) of the diffusion barrier.
The solubility and molecular weight (MW) of the substance.
What is the formula for the rate of diffusion according to Fick’s Law?
What is the formula for the rate of diffusion according to Fick’s Law?
What physical properties influence the permeability of a substance during diffusion?
The physical properties of the diffusion barrier and the diffusing substance influence the permeability of the substance.
Why is diffusion too slow over large distances?
Diffusion is too slow over large distances, so FLOW is required to transport substances around the body.
What does Ohm’s Law state?
Where:
I = current
V = voltage
R = resistance
What does Darcy’s Law describe?
Darcy’s Law describes the relationship between flow, pressure difference, and resistance:
Where:
𝑃1−𝑃2 = pressure difference
R = resistance to flow
What is the alternate form of Darcy’s Law?
How are flow and pressure difference (P₁ - P₂) related?
Flow and pressure difference (P₁ - P₂) are proportional to each other.
If P₁ > P₂, flow occurs from a region of high pressure to a region of low pressure.
What determines resistance to flow according to Poiseuille’s Law?
Where:
L = Length of the tube
r = Radius of the tube
V = Viscosity of the fluid
What is the combined equation for flow when Darcy’s Law and Poiseuille’s Law are combined?
How is flow related to vessel radius?
How is resistance related to vessel radius?
Why does a small change in vessel radius cause a large change in resistance and flow?
How can arterioles adjust their radius?
Arterioles can adjust their radius through vasoconstriction (constriction) or vasorelaxation (relaxation), which affects their resistance.
What happens during vasoconstriction?
During vasoconstriction:
The arteriole radius decreases, resulting in increased resistance.
what are 5 examples of vasoconstrictor stimuli
Noradrenaline (SNS)
Adrenaline
Angiotensin II (RAAS)
Vasopressin (ADH)
Pressure
What happens during vasodilation?
During vasodilation:
The arteriole radius increases, resulting in reduced resistance.
what are 4 examples of vasodilator stimuli
Adrenaline
Atrial natriuretic peptide
Histamine
Flow
What is the state of arterioles at rest?
At rest, arterioles are partially constricted.
How does viscosity affect blood flow?
The thicker the fluid, the higher the viscosity, and the higher the resistance.
Red cell mass and plasma proteins make blood very viscous, which reduces flow.
How does blood compare to water in terms of viscosity?
Blood is 3-4 times thicker than water, which would alone reduce the flow
What is significant about blood being a non-Newtonian fluid?
Since blood is a non-Newtonian fluid, it behaves differently from simple fluids, and the usual relationship between viscosity and flow does not apply in the same way.
What is laminar flow?
Laminar flow occurs when viscous drag at the sides of the tube slows the fluid, so the fastest movement (flow) happens in the center of the tube. This effect becomes more apparent as the radius of the tube becomes smaller.
What happens to cells in laminar flow?
In laminar flow, cells tend to align in the fastest-moving fluid, a phenomenon known as axial streaming.
How does laminar flow affect viscosity in small vessels?
In small vessels, laminar flow effectively reduces viscosity, which is known as the Fåhraeus-Lindqvist effect.
What is the size comparison between red blood cells and capillaries?
Red blood cells = 7 μm.
Capillaries = 6 μm.
Why can red blood cells pass easily through capillaries despite the size difference?
Red blood cells are very deformable and can slip easily through the capillaries, allowing them to pass through despite their size difference.
How does the viscosity of blood in capillaries compare to plasma?
The viscosity of blood in capillaries is similar to plasma because red blood cells are able to pass through easily.
Why is high viscosity in blood important?
High viscosity (e.g., from a high red blood cell count) can lead to:
Increased total peripheral resistance (TPR)
Increased mean arterial pressure (MAP), which may contribute to hypertension.
What causes turbulent flow?
Turbulent flow can occur when:
There is high velocity,
Sharp edges or branch points are present, especially in large tubes.
These factors can disrupt laminar flow, leading to turbulence.
What effect does turbulence have on resistance?
Turbulence significantly increases resistance in the blood vessels.
What health issues can turbulence cause?
Narrowed heart valves causing high velocity blood flow leads to murmurs.
Narrowed airways causing high velocity airflow leads to wheezing.
What additional damage can turbulence cause?
Turbulence can also cause:
Damage to the vessel wall,
Activation of clotting mechanisms.
How does flow behave in flexible tubes compared to rigid tubes?
Flow increases more gradually with pressure, as shown by the green line representing flow autoregulation (e.g., cerebral circulation).
Passive distention occurs with pressure, causing a rapid increase in flow, as shown by the red line (e.g., pulmonary circulation).
In rigid tubes (blue line), flow increases linearly with pressure.
How do resistances to flow combine in series and parallel?
How does flow relate to pressure difference and total resistance in the simple model?
What happens to the pressure of the fluid as it flows through an artery?
As the fluid flows through an artery (modeled as a resistor), the pressure drops from a region of high pressure (P₁) on the left to a region of lower pressure (P₂) on the right. This causes the pressure to decrease as the fluid flows from left to right.
How is total resistance in the simple model calculated?
How is the total resistance calculated in the simple model?
What does the total pressure drop depend on in the simple model?
The total pressure drop is the sum of the individual pressure drops across the resistances in series and parallel:
pressure drop across RA = PX
pressure drop across RB = PY
How does the nephron model represent resistance?
the nephron is represented with 2 regions:
region A - total resistance RA = R1+ R2, where R1 is the afferent arteriole and R2 is the efferent arteriole
region b - total resistance RB = 1/ [1/r3 + 1/r4), where R3 and R4 represent the peritubular capillaries.
What is the structure of the cardiovascular system?
The cardiovascular system is a single circulation with two pumps in series:
The right ventricle pumps deoxygenated blood to the lungs.
The left ventricle pumps oxygenated blood to the systemic tissues.
How is the pulmonary vasculature characterized?
The pulmonary vasculature has:
Low resistance,
Low pressure (~16 mmHg), and
It is in series with the systemic vasculature.
What is the role of the systemic vasculature?
The systemic vasculature has:
High resistance,
High pressure (~92 mmHg), and
It is mostly in parallel with the vascular structures of the brain, GI tract, and muscles.
What is the flow relationship between the right and left ventricles?
The flow out of the RV must match the flow out of the LV.
Cardiac output (CO) is the same for both ventricles (~5 L/min
What is venous return and how does it relate to flow into the right ventricle (RV)?
The venous return (~5 L/min) must match the flow into the RV, ensuring the same volume as the flow out of the LV.
What determines filling pressure and what is it also known as?
Filling pressure is determined by Central Venous Pressure (CVP) and is also known as PRELOAD.
What does resistance to flow refer to and how is it related to the left heart?
Resistance to flow is known as Total Peripheral (Systemic) Resistance (TPR), which determines the pressure load on the left heart and is referred to as AFTERLOAD.
How is cardiac output (CO) calculated?
Cardiac output (CO) is the product of Stroke Volume (SV) and Heart Rate (HR):
What are the two levels of control for organ blood flow?
The two levels of control are:
Changing perfusion pressure will change blood flow.
Blood flow through each organ/tissue can be regulated independently because they are in parallel with each other.
How can blood flow through individual organs or tissues be regulated independently?
Blood flow can be regulated independently by selective regulation of vascular resistance in the target organ.
What is perfusion pressure and how is it different from MAP?
Perfusion pressure refers to the pressure of the blood within the individual tissues, NOT the mean arterial pressure (MAP).
How is Mean Arterial Pressure (MAP) calculated?
CO = Cardiac output
TPR = Total peripheral resistance
What are the two levels of control for MAP?
Flow control (the pump): Regulated by heart rate (HR) and stroke volume (SV).
Resistance control: Regulated by arteriolar radius.
How can blood flow through one tissue be reduced without changing MAP or blood flow through other tissues?
This can be achieved by increasing the vascular resistance (e.g., RA) in the tissue of interest. This will reduce the flow to that tissue while maintaining MAP and blood flow to the other tissues.
What happens when vascular resistance increases in a tissue?
When vascular resistance increases (e.g., in tissue 1, shown as RA increases), the total flow to that tissue decreases. To maintain MAP, cardiac output (CO) will decrease, which reduces flow through all tissues, but the relative flow to other tissues remains the same.
How does MAP remain constant when resistance is increased in one tissue?
By adjusting cardiac output (CO) downward in response to increased resistance in one tissue, MAP is maintained, even as flow to the affected tissue is reduced.
How can blood flow through one tissue be greatly increased without significantly changing MAP?
To greatly increase blood flow through one tissue without significantly changing MAP, total peripheral resistance (TPR) can be selectively reduced in that tissue while cardiac output (CO) is increased to maintain blood pressure.
How is blood flow adjusted during exercise to increase flow to specific tissues?
What happens to CO and TPR during exercise?
During exercise:
Cardiac output (CO) is increased to supply more oxygen to the tissues.
Total peripheral resistance (TPR) is decreased in certain tissues, such as muscles, to allow more blood to flow through.
How is blood flow distributed at rest?
At rest (with a total cardiac output of 5L/min):
Brain (RA): 700 ml/min (14% of total blood flow)
Kidneys (RB): 1000 ml/min (20% of total blood flow)
Muscles (RC): 1000 ml/min (20% of total blood flow)
Other organs: Share the remaining 2300 ml/min (46% of total blood flow)
How does blood flow distribution change during moderate exercise?
During moderate exercise (with a cardiac output of 10L/min, doubled from rest):
Brain: Partial constriction, still receives 700 ml/min (7% of total blood flow).
Kidneys: Strong constriction, reduced to 300 ml/min (3% of total blood flow).
Muscles: Strong dilation, receives 6000 ml/min (60% of total blood flow).
Other organs: The remaining 3000 ml/min is shared by other organs (30% of total blood flow).
What is the relationship between arterial radius and resistance?
As arteries branch into arterioles, their radius decreases, which increases resistance. Small changes in radius result in significant changes in resistance and pressure (P₁ - P₂).
If R1 = 1 and R2 = 10 - what are the total resistances of A and B?
When R2 is changed to 10, does A or B show the largest percentage change in total resistance?
If the pressure/voltage difference is maintained constant, by how much does flow/current change when R2 is changed to 10?
If R2 was an artery, how much would its diameter have to change in order for its resistance to be increased from 1 to 10?
