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Human physiology > Lecture 10: Overview of circulation > Flashcards

Lecture 10: Overview of circulation Flashcards

1
Q

Velocity of blood flow is _____ proportional to vascular cross-sectional area

A

Inversely

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2
Q

Overall blood flow of an adult at rest is

A

5000 mL/min = Cardiac output

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3
Q

Three major variables that determine resistance and which one is most important

A

Vessel radius (most important)
Blood viscosity
Vessel length

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4
Q

Prime determinant of blood viscosity is the

A

Hematocrit

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5
Q

If arterial pressure falls below 100 mm Hg, nervous reflexes:

A

Increase force of heart pumping
Constrict large venous reservoirs
Generally constrict most of the arterioles throughout the body (increase arterial pressure)
Kidneys may later play important role in pressure control

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6
Q

Eddy currents

A

Blood flows with greater resistance when eddy currents occur

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7
Q

Examples of circulations arranged in parallel

A 
Brain
Kidney
Muscle
GI
Skin
Coronary circulation
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8
Q

% volume of blood in arteries

A

13

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9
Q

Flow is ______ proportional to pressure difference but ______ proportional to resistance

A

Flow is directly proportional to pressure difference but inversely proportional to resistance

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10
Q

For blood vessels arranged in parallel, the total resistance to blood flow is expressed as

A

1/Rtotal = 1/R1 + 1/R2 +1/R3 ……

Therefore, the total resistance is far less than the resistance of any single blood vessel

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11
Q

Amputation of limb, removal of kidney removes a parallel circuit. What is the effect

A

Reduces total vascular conductance
Reduces total blood flow
Increases total peripheral vascular resistance

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12
Q

Laminar flow

A 
Streamline flow
Blood flows at steady rate
Blood vessel is long and smooth
Blood flows in streamlines (layers)
Velocity of blood in center is greater than on the outer edges
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13
Q

Two main factors controlling blood flow

A

Pressure difference between the two ends of a vessel (pressure gradient)
Impediment to blood flow through the vessel (resistance)

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14
Q

Conductance is ______ proportional to vessel diameter

A

Directly

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15
Q

When Re rises above 2000

A

Turbulent flow will occur even in a straight vessel

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16
Q

Poiseuilles law/equation

A 
F = (Pi*(P1-P2)*r^4) / 8nl
F- rate of blood flow mL/min
P-pressure
r- radius of vessel
l- length of vessel
n- blood viscosity
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17
Q

Turbulent flow

A

Non-layered flow
Creates murmurs
Produces more resistance than laminar flow

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18
Q

When cardiac output is normal at 100mL/sec the total pulmonary vascular resistance is

A

14/100 or 0.14 PRU

19
Q

Functional principles of the circulatory system

A

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 the local tissue flows
Arterial pressure regulation is generally independent of either local blood flow control or cardiac output control

20
Q

When vessels are greatly dilated, total peripheral resistance may

A

Drop to 0.2 PRU

21
Q

Ohms law (Poiseuille equation)

A 
F=(P1 - P2)/R
F- flow in mL/min
P1- upstream pressure
P2- pressure at end of segment
R- resistance b/w P1 and P2
22
Q

% volume of blood in systemic arterioles and capillaries

A

7

23
Q

% volume of blood in heart and lungs

A

16

24
Q

Blood viscosity

A

The property of blood to adhere to vessel walls and to eachother

  • based on the number, shape and size of RBCs
  • Viscosity ensures laminar flow of blood in vessels
25
Q

The largest pressure drop in the circulatory system occurs where

A

In the arterioles because they have the highest resistance

26
Q

Total conductance for vessels arranged in parallel is

A

The sum of the conductance of each parallel pathway

27
Q

Rate of blood flow in entire circulatory system is

A

100ml/sec

28
Q

% volume of blood in veins

A

64

29
Q

Resistance of the entire systemic circulation (total peripheral resistance) is

A

100/100 or 1 PRU (peripheral resistance unit)

30
Q

Mean left atrial pressure averages

A

2 mm Hg

31
Q

% volume of blood in systemic circulation

A

84

32
Q

Conductance definition and equation

A

The measure of blood flow through a vessel for a given pressure difference
Conductance = 1/resistance

33
Q

Blood flow autoregulation

A

The ability of each tissue to adjust its vascular resistance and to maintain normal blood flow through changes in arterial pressure between approximately 70 and 175 mm Hg

34
Q

Turbulent flow occurs when

A

Flow is too great
Blood passes an obstruction with the vessel
Blood has to make a sharp turn
Blood passes over rough surface

35
Q

When Re rises above 200-400:

A

Turbulent flow will occur in some regions of a vessel

36
Q

Pressure difference from systemic arteries to systemic veins is

A

100 mm Hg

37
Q

Tendency for turbulent flow increases

A

In direct proportion to velocity of blood flow
In direct proportion to diameter of vessel
In direct proportion to density of the blood
Inversely to the viscosity of the blood

38
Q

Mean pulmonary arterial pressure averages

A

16 mm Hg

39
Q

A fourfold increase in vessel diameter can have what effect on blood flow

A

Increase flow by as much as 256x

40
Q

Velocity of blood flow equation

A

V=F/A
F- volume of blood flow
A- vascular cross-sectional area

41
Q

Resistance equation

A

R= 8nl / Pi x R^4
n- viscosity of blood
l- length of vessel
r^4- radius of vessel to the fourth power

42
Q

In conditions when vessels are strongly constricted, total peripheral resistance may

A

Rise to 4 PRU

43
Q

Reynolds number equation

A 
RE=(V x D x p) / n
V-mean velocity of blood flow in cm/sec
D- vessel diameter in cm
p- density
n- viscosity (in pose)- blood viscosity is normally 1/30 poise

Human physiology (16 decks)

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