CTB4: Blood pressure and flow

Question 1

Define compliance

Answer 1

The ability to distend in response to applied pressure

Question 2

Define resistance

Answer 2

The ability to oppose a change

Question 3

Large elastic arteries are ______

Answer 3

conduits

Question 4

Muscular arteries and arterioles have smooth muscle which provides ______ to blood flow

Answer 4

resistance

Question 5

What do veins ability to be highly compliant mean they are able to do?

Answer 5

allows them to act as reservoirs of blood as they are responsible for capacitance

Question 6

What does capacitance mean?

Answer 6

Storing blood volume

Question 7

Make the appropriate connections between the following:
Vein, capillaries, small arteries, large arteries
and
distribution, exchange, capacitance, resistance

Answer 7

Vein = capacitance
Capillaries = exchange
Small arteries = resistance
Large arteries = distribution

Question 8

What is the main aortic pressure in healthy humans?

Answer 8

~90 mmHg

Question 9

Why does pressure fall across circulation?

Answer 9

Due to viscous (frictional) pressure losses

Question 10

Where does the large fall in mean blood pressure occur? What is the percentage drop?

Answer 10

Between large arteries and small arteries/arterioles

- approximately 50-70% drop

Question 11

What is the mean pressure in capillaries?

Answer 11

25-30 mmHg, depending on the organ

Question 12

When does blood pressure fall further?

Answer 12

As blood travels into the veins and back to the heart

Question 13

What are the greatest systolic and diastolic pressures?

Answer 13

systolic: 120mmHg
diastolic: 80mmHg

Question 14

Which system operates at a lower pressure: pulmonary or systemic?

Answer 14

Pulmonary

Question 15

What are the lowest systolic and diastolic pressures?

Answer 15

systolic: ~25mmHg
diastolic: ~10mmHg

Question 16

The magnitude of oscillation in pressure (pulse pressure) is _____ in the smaller arteries and arterioles

Answer 16

damped

Question 17

What causes the major drop in pressure after the large arteries?

Answer 17

<0.5mm internal diameter of small muscular arteries

Question 18

What are the two types of blood flow?

Answer 18

Laminar

Turbulent

Question 19

Describe Laminar blood flow

Answer 19

– velocity of the fluid is constant at every point and particles move in straight lines without interfering with one another.

Question 20

Describe Turbulent blood flow

Answer 20

– velocity of the fluid differs at various points and particles flow irregularly while generating whirlpool regions.

Question 21

When does blood flow not exhibit laminar properties, when it usually does?

Answer 21

At branching points of vessels or when encountering vascular occlusion when they display turbulent flow

Question 22

What are the two forced endothelial cells lining the interior of blood vessels experience?

Answer 22

Cylindrical strain

Shear stress

Question 23

Describe cylindrical strain

Answer 23

– vessel wall distention by transmural pressure

Question 24

Describe shear stress

Answer 24

– adhesive force between blood and surface of the blood vessel

Question 25

What is shear rate? | What is the equation for this?

Answer 25

the rate at which layers of fluid move past one another. Shear stress is calculated as follows: Shear stress = shear rate x viscosity

Question 26

If resistance can not be overcome, what happens?

Answer 26

Blood flow would not be maintained

Question 27

What does resistance of a tube depend on?

Answer 27

``` Fluid viscosity (η) Tube length (L) Inner radius of tube (r) ```

Question 28

Which variables of resistance remain constant?

Answer 28

Viscosity & tube length usually remain constant, making inner radius the main determinant of vascular resistance

Question 29

What is Poiseulles's equation for resistance?

Answer 29

R= 8Lη/πr^4

Question 30

Halving the radius does what to the resistance?

Answer 30

Increases the resistance by 16x

Question 31

How can mean blood pressure be calculated?

Answer 31

Cardiac output x Resistance

Question 32

How can mean blood pressure be calculated?

Answer 32

Stroke volume x Heart rate

Question 33

List the 5 ways resistance in regulated

Answer 33

- Myogenic theory - Vascular injury - Endothelial chemicals - Systemic circulating hormones - Autonomic nervous system

Question 34

How can pressure be regulated by the Myogenic theory?

Answer 34

stretch-sensitive ion channels allow smooth muscle fibres to contract when pressure increases

Question 35

How can pressure be regulated by vascular injury?

Answer 35

damage to the vessel walls stimulates the release of serotonin from platelets which causes vasoconstriction

Question 36

How can pressure be regulated by endothelial chemicals?

Answer 36

the endothelium releases both vasorelaxants (nitric oxide and prostacyclin) and vasoconstrictors (endothelins and thromboxane)

Question 37

How can pressure be regulated by systemic chemicals?

Answer 37

vasodilation can be caused by kinins and atrial natriuretic peptide while vasoconstriction can be caused by vasopressin, noradrenaline and angiotensin II

Question 38

How can pressure be regulated by the autonomic nervous system?

Answer 38

the sympathetic and parasympathetic branches can increase or decrease heart rate respectively. The sympathetic nervous system causes increased contraction force and vasoconstriction which increases BP whilst the parasympathetic nervous system decreases heart rate and cardiac output to lower BP.

Question 39

What are Baroreceptors

Answer 39

Stretch receptors found in the aortic arch and carotid sinuses which help regulate blood pressure

Question 40

Where are low pressure baroreceptors found?

Answer 40

On the vena cava and the right atrium

Question 41

How can mean systemic arterial pressure be calculated?

Answer 41

Cardiac output x Total peripheral resistance

Question 42

What are the two readings blood pressure is measured by? When do these take place?

Answer 42

- Systolic blood pressure – during cardiac contraction | - Diastolic blood pressure – resting pressure between heartbeats

Question 43

What is the difference between systolic blood pressure and diastolic blood pressure known as?

Answer 43

Pulse pressure

Question 44

Is blood pressure usually measured on right or left arm?

Answer 44

Left | Otherwise it can be taken on other extremities

Question 45

What are segmental pressures?

Answer 45

Blood pressure redaings taken from different extremities

Question 46

What can segmental pressure readings help do?

Answer 46

Help identify arterial occlusion or blockage along a limb

Question 47

What is the mean blood pressure value usually?

Answer 47

approximately DBP + 1/3PP

Question 48

What is the Windkessel effect?

Answer 48

The damping of blood pressure as blood leaves the heart and enters the aorta before the blood already within them can leave

Question 49

What does the Windkessel effect help maintain? How?

Answer 49

constant flow and reduces The fluctuation of blood pressure over the cardiac cycle Possibly due to arterial compliance

Question 50

Why does blood pressure increase with age?

Answer 50

The arterial compliance is reduced as arteries become stiffer, which reduces the Windkessel effect and increases blood pressure