Chapter 14 Overview Of The Circulation: Pressure, Flow And Resistance Flashcards
What is the function of arterioles?
They act as control conduits of the tissue blood flow. They have strong muscular walls which can contract to completely obliterate the tissue perfusion or dilate to increase blood flow.
Distribution of blood in the heart?
7%
Distribution of blood volume in arteries?
13%
Distribution of blood in arterioles and capillaries?
7%
Distribution of blood in veins, venules, and venous sinuses?
64%
Distribution of blood in pulmonary circulation?
9%
What is the velocity of blood flow in the aorta?
33cm/ sec
What is the velocity of blood flow in the capillary beds?
0.3mm/ second
What is the normal BP in aorta?
100mmHg
Blood pressure in the large arteries?
120 mmHg
Blood pressure in vena cave?
0 mmHg
Pressure at the arterioler end ?
35 mmHg
Blood pressure at the venous end ?
10 mmHg
Average functional blood pressure of vascular beds ? 17 mmHg
Blood pressure at the glomerular capillary bed ?
60 mm hg
Systolic and diastolic pressure of the pulmonary arteries?
25 mmHg and 8 mmHg
Mean pulmonary artery pressure?
16 mmHg
Blood pressure in pulmonary capillary bed?
7 mmHg
What are the basic principles of circulatory function?
1) Local blood flow to most tissues are controlled according to the tissue need. It is orchestrated by the local arterioles along with nervous and hormonal control of tissue perfusion.
2) Cardiac output is the sum of all the local tissue flows.
3) arterial pressure regulation is generally independent of either local blood flow control or cardiac output control: whenever the arterial pressure falls below 100 mmHg, a barrage of nervous reflexes will increase the force of heart pumping, cause contraction of the large venous blood reservoir by increasing diastolic volume, cause generalized constriction of arterioles to increase intra- arterial blood pressure.
Ohm’s law of blood flow:
F= delta P/ vascular resistance.
Delta P= ( P1-P2)
The blood flow is directly proportional to delta P and inversely proportional to vascular resistance.
What is the blood flow in total circulation in a min ( cardiac output) at rest?
5000 ml/ min.
What is the difference between laminar flow and turbulent flow of blood in the blood vessels?
In laminar blood flow: the center most layer of blood column flows faster than the progressively outermost layers with highest velocity.
Turbulent flow occurs when laminar flow is obscureed by intra vessel obstructions, which will cause the blood flow to develop whirlpools called Eddy currents increasing the resistance to blood flow.
What are the causes of turbulent flow?
Too great flow rate, obstruction in a vessel, when the flow takes a sharp turn, when it passes over a rough surface.
The whirlpools occurs during turbulent flow of blood are called?
Eddy currents
What is the measure of the tendency for turbulent blood flow?
Reynold’s number abbreviated as Re.
Re= v.d.p/ n
V= velocity of blood flow in CM per second
d= Vessel diameter in CM.
P= density of the blood in Grams/mL
n= viscosity of the blood in poise
Normal viscosity of the blood?
1/30 poise
Normal density of the blood?
1060 kg/ M^3
What is the Raynold’s number threshold for turbulent flow to occur?
200 to 400 in large arteries and it will die away
The rate of blood flow through the entire circulatory system is equal to ____ and what is it in normal human being?
Cardiac output and is 100 ml/ seconds in normal human.
What is the pressure difference between the systemic arteries to the systemic veins?
100 mmHg
What is the total peripheral resistance of the entire systemic circulation?
The rate of blood flow of the entire circulatory system= 100 ml/sec
The pressure difference of systemic arteries and veins= 100 mmHg
Therefore, the total peripheral resistance of the entire circulation= 100/100 or 1 PRU.
What is the maximum peripheral resistance increase of the systemic circulation in generalized vasoconstriction?
4 PRU.
What is the peripheral resistance decrease of the systemic circulation in generalized vasodilation?
0.2 PRU
What is the normal pulmonary vascular resistance?
0.14 PRU
Because the average pulmonary arterial pressure= 16 mmHg
The left atrial pressure during normal cardiac output= 2 mmHg
Therefore the net pressure gradient of the pulmonary circulation= 14 mmHg.
Hence, pulmonary vascular resistance= 14 mmHg/ 100 mL/ second or 0.14 PRU.
Conductance of blood flow in a vessel is equal to ____?
It is the reciprocal of the vascular resistance or 1/ resistance
The conductance of blood flow through a vessel increase in proportion to _____?
Fourth power of the diameter of the vessel.
For example at a pressure gradient of 100 mmHg the blood conductance through a vessel with a diameter of 2 mm increase to 16 ML/ min.
While though a vessel with a diameter of 4 mm increases to 256 ML/ min.
What is the significance of the vessel diameter fourth power law?
In muscular arterioles a small change in arterioler diameter ( normal range 4 micrometers to 25 micrometers) can increase or decrease the blood flow to the fourth power of it’s diameter.
What is the normal hematocrit level?
Males = 42 or 42% of the blood volume
In females= 38%
A significant reduction in hematocrit concentration is called anemia. A significant increase is called polycythemia
Poiseuille equation of blood flow ?
F= pi. Pressure gradient. r^4/ 8nl
Pi.r^4= diameter of the vessel
Pressure gradient= pressure at one end of the vessel - the other end pressure.
n = viscosity of the blood
l = length of the vessel
What is blood flow autoregulation?
The ability of each tissue to adjust it’s arterioler vascular resistance in response to changes in arterial blood pressure between 70 and 175 mmHg is called blood flow autoregulation.
Explain pressure flow relationship in passive elastic vascular beds?
When the arterial pressure increases it not only increases the force that push the blood through the artery but also decreases vascular resistance by stretching the elastic walls of the artery. Conversely, a fall in BP will lead to reduction in blood flow and increase in vascular resistance due to collapse of the elastic arterial wall. When the pressure falls below the critical closing pressure the flow through the vessel completely ceases due to the collapse of the vessel wall.
Explain the Law of Laplace for vascular wall tension?
Wall pressure (T) for a thin walled tube is proportional to the transmural pressure gradient ( ∆P) times the radius of the blood vessel (r) divided by its wall thickness (h).
T = ∆P. (r/).
∆P = intravascular pressure Pi- extravascular pressure Pt.
What enables large elastic blood Vessel Wall to withstand high transmural pressure gradient?
The support of collagen fibrous bands.
What is vascular sheer stress?
It is the frictional force or drag exerted by the blood flow on the endothelial cells. It is directly proportional to the flow velocity and viscosity of the blood and inversely proportional to the radius cubed.
