Circulation Flashcards
What are some causes of turbulent flow?
Turbulent flow can occur when:
- the rate of blood flow becomes too great
- when blood flow passes by an obstruction in the vessel
- when it makes a sharp turn
- when it passes over a rough surface
Define conductance.
The measure of blood flow through a vessel for a given pressure difference.
True or False: most of the blood is located in the pulmonary circulation?
False; most of the blood is located in the systemic circulation.
Define Poiseuille’s equation?
F = (P1-P2)/R
- F = flow in ml/min
- p1 = upstream pressure
- p2 = pressure at end of segment
- R = resistance between p1 and p2
Viscosity is measuring what?
A fluid’s internal resistance
Of the three variable for determining resistance, which is the most important one?
Vessel radius
What is the function of veins?
To act as conduits for the transport of blood from venules back to the heart. Also, they serve as a major reservoir of extra blood.
In laminar flow, the velocity is greatest where?
The center
Systolic pressure
The highest arterial pressure during a cardiac cycle. Measured after systole.
Why is blood about 3 times more viscous than water?
Because of its large numbers of suspended red blood cells.
What is the function of the capillaries?
To exchange fluid nutrients, nutrients, electrolytes, hormones, and other substances between the blood and interstitial fluid.
What percentage of blood in the systemic circulation is located in the veins?
64%
what is the range of pressures exhibited by the pulmonary arteries?
25 mmHg- 8mmHg
Name 2 of the 3 functional principles of the circulatory system.
- Rate of blood flow to each tissue of the body is almost always precisely controlled in relation to the tissue need
- The cardiac output is controlled mainly by the sum of all local tissue flows
- Arterial pressure regulation is generally independent of either local blood flow control or cardiac output control
What is the range of pressures for systemic capillaries?
35 mmHg- 10 mmHg
How are conductance and resistance related?
Conductance is the exact reciprocal of resistance.
1/R
The tendency for turbulent flow increases in _______ proportion to the diameter of the vessel?
Direct
For turbulent flow to occur in some regions, the Re should be above what value?
200-400 Re
What is Laminar flow?
When blood flows at a steady rate through a long, smooth blood vessel, it flows in stream lines, with each layer of blood remaining the same distance from the vessel wall. Also, the central most portion of the blood stays in the center of the vessel.
How would you measure resistance
It must be indirectly calculated from the measurements of blood flow and pressure.
- Resistance = pressure/ (volume/time)
- given in peripheral resistance units (PRUs)
Flow is _____ proportional to pressure difference but ______ proportional to resistance?
Directly, inversely
How is cardiac output controlled by the sum of all local tissue flows?
The heart responds to the demands of the tissues. It often, also, needs help in the form of special nerve signals to help it pump the required amounts of blood.
What is turbulent flow?
When blood flows in all directions in a disorganized fashion. It is non-layered flow and produces much more resistance than laminar flow.
The systemic arterial pressure drops to 0mmHg by the time it reaches the termination of the _____.
Vena cava
What percentage of blood is located in the heart and lungs?
16%
What formula would you use to determine the velocity of blood flow?
v = F/A
- v = velocity
- F = volume of blood flow
- A = vascular cross-sectional area
When would you see the peripheral resistance drop to as low as 0.2 PRU?
In conditions when the vessels are greatly dilated.
What is the viscosity of blood at a normal hematocrit?
3
What is blood pressure?
The force exerted by the blood against any area of the vessel wall
Polycythemia _______ viscosity?
Increases
Define blood flow autoregulation.
The ability of each tissue to adjust its vascular resistance and to maintain normal blood flow during changes in arterial pressure between approximately 70 and 175 mmHg.
In regards to the velocity of blood flow, what is the relationship between velocity and vascular cross-sectional area?
The velocity of blood flow (v) is inversely proportional to vascular cross-sectional area (A)
Arterioles, capillaries, venules, and veins are arranged in ______ ?
Series
if the mean pulmonary arterial pressure is 16mmHg, the mean left atrial pressure is 2mmHg, and cardiac is normal at 100mL/sec, what is the total pulmonary vascular resistance?
16mmHg-2mmHg = 14mmHg
14mmHg / 100mL/sec = 0.14
= 0.14 PRU
Define pressure gradient
The pressure between the two ends of a vessel.
Name the 2 factors for determining blood flow.
- Pressure difference between the two ends of a vessel (pressure gradient)
- Impediment to blood flow through the vessel (resistance)
What is the overall blood flow of an adult at rest in mL/min?
5000 mL/min ( = cardiac output)
How would you measure the conductance for vessels arranged in parallel?
Take the sum of conductance of each parallel pathway.
Blood flows with greater resistance when _____ currents occur?
Eddy
Diastolic pressure
The lowest arterial pressure. it is measured when the heart is relaxed (diastole).
The tendency for turbulent flow increase in _______ proportion to velocity of blood flow
Direct
When would you see the peripheral resistance rise to as high as 4 PRU?
In conditions when the vessels are strongly constricted
Name the three major variables that determine resistance.
- vessel radius
- blood viscosity
- vessel length
Turbulence will occur in a straight vessel when the Re rises above this value?
2000 Re
If you remove a parallel circuit (amputation of limb) what effects will this have on conductance, blood flow, and resistance?
- Total vascular conductance will decrease
- Blood flow will decrease
- Total peripheral resistance increases
The greater the viscosity, the ______ the resistance?
Greater
What percentage of blood is located in the systemic circulation?
84%
______ flow causes murmurs?
Turbulent
What is the function of arterioles?
They act as control conduits through which blood is released into the capillaries.
The tendency for turbulent flow increases in _______ proportion to the density of the blood?
Direct
Why is pulmonary circulation arterial pressures much lower than systemic circulation arterial pressures?
Because the blood only has to travel to the lungs where it will pick up oxygen via the capillaries and return oxygenated blood to the heart.
Conductance is directly proportional to ________?
Diameter4
Anemia ______ viscosity?
Decreases
Define vascular resistance
Impediment to blood flow through the vessel.
Name some circulations that are arranged in parallel with each other.
Brain
kidney
muscle
gastrointestinal
skin
coronary circulation
Name the functional components of circulation.
- Arteries
- Arterioles
- Capillaries
- Venules
- Veins
What is the definition of cardiac output?
The amount of blood pumped into the aorta by the heart each minute.
What is the function of venules?
To collect blood from the capillaries and gradually coalesce into progressively larger veins.
How is blood flow expressed?
It is usually expressed as mL/min or L/min
How doe the total resistance of branched vessels compare to that of any single blood vessel?
The total resistance of branched blood vessels is significantly lower than any single blood vessel.
What term would be applicable if the hematocrit was 60-70?
Polycythemia
What is the function of the arteries?
To transport blood under high pressure to the tissues.
Pulse pressure
The difference between systolic and diastolic pressure.
You can measure blood pressure 2 ways, what are they?
With a mercury manometer OR with electronic transducers
How would you calculate the resistance of all systemic circulation? What is the actual value?
Cardiac output (mL/sec) / Pressure difference from systemic arteries to systemic veins
= (100mL/sec) / (100mmHg) = 1 PRU
In systemic circulation arterial pressure ranges from _____ mmHg(systolic) to _____ mmHg(diastolic).
120,80
How is the rate of blood flow to each tissue of the body precisely controlled in relation to need of the tissue?
This is done by the microvessels. They continuously monitor the needs of tissue, such as O2 availability, CO2 accumulation, and tissue waste product accumulation. They act on local blood vessels, dilating or constricting them, to control local blood flow precisely to that level required for the tissue activity.
What is the prime determinant of blood viscosity?
The hematocrit
What is the cardiac output of and adult at rest in mL/min?
5000 mL/min
The tendency of blood flow increases in _______ proportion to the viscosity of the blood?
Inverse
Blood vessels branch extensively to form _______ circuits that supply blood to many organs and tissues of the body?
Parallel
How is arterial pressure regulated independently of local blood flow and cardiac output control?
Nervous reflexes kick in if arterial pressure falls below 100mmHg to kick start a series of circulatory changes to raise the pressure back to normal.
Those changes include:
- increasing the force of heart pumping
- constrict large venous reservoirs
- increase arterial pressure by constricting most of the arterioles throughout the body
- kidneys (hours /days later)
How can flow through a vessel be calculated?
Flow through a vessel can be calculated by Ohms law (Poiseuille equation)
What are normal hematocrit values for men and women?
42 for men, 38 for women
