L8.1 Blood Pressure

Question 1

what is blood pressure?

Answer 1

the force exerted on the walls of the blood vessels

Question 2

how can blood pressure be measured?

Answer 2

can be measured indirectly using sphygmomanometer:

• inflatable cuff with pressure gauge
• cuff compresses brachial artery
• measures systolic and diastolic pressure

Question 3

describe the sounds heard by the sphygmomanometry.

Answer 3

sound can not be heard when: no blood is flowing or blood is flowing smoothly (laminar)
sound is heard when blood is flowing turbulently: partially collapsed artery

Question 4

how does the sphygmomanometry effect blood flow

Answer 4

• cuff is inflated (cuff pressure > arterial pressure)
• artery is completely blocked
• no sound
• cuff pressure is reduced until first sound is heard: systolic pressure (=highest pressure in artery); blood passes through turbulently when arterial pressure transiently > cuff pressure
• no sound heard when cuff pressure < diastolic pressure
• last sound heard is diastolic pressure

Question 5

what are some other measures of pressure?

Answer 5

pulse pressure:
- difference between systolic and diastolic pressure
- indicator of stroke volume- amount of blood pumped out of the ventricle with every beat
mean arterial pressure:
- average blood pressure in the arteries
- closer to diastole because heart spends longer in diastole

Question 6

what is the mean arterial pressure formula?

Answer 6

mean arterial pressure = diastolic pressure + 1/3 pulse pressure

important: MAP is used by the body to regulate blood pressure, not systolic or diastolic pressure

Question 7

what are the factors that rate of blood flow is dependent on?

Answer 7

the rate at which blood flows through the circulatory system is dependent on:
- the activity of the heart (cardiac output)
- the resistance to blood flow (vessel diameter)
the heart has to generate enough pressure to overcome resistance to blood flow

Question 8

blood flow is _____ proportional to the pressure gradient

Answer 8

blood flow is DIRECTLY proportional to the pressure gradient
(increased pressure gradient = increase in flow)

Question 9

blood flow is _____ proportional to cardiovascular resistance

Answer 9

blood flow is INVERSELY proportional to cardiovascular resistance
(increase in resistance = decreased in flow)

Question 10

what is the formula for blood flow?

Answer 10

flow = pressure gradient / resistance

Question 11

what is the resistance to blood flow controlled by?

Answer 11

• blood viscosity (thickness)
• vessel length
• vessel diameter
  (blood viscosity and vessel length remain constant)

Question 12

describe the effect of vessel radius (diameter) on cardiovascular resistance

Answer 12

increase the radius = increase blood flow

Question 13

how do we measure resistance in the entire circulatory system?

Answer 13

total peripheral resistance = amount of resistance in circulatory system

Question 14

define pressure gradient

Answer 14

difference in pressure between beginning and end of a vessel

• contraction of heart gives pressure to the blood
• pressure in cardiovascular system decreases from arteries to veins
• blood flows from high pressure to low pressure

Question 15

how do we measure pressure gradient in the entire circulatory system?

Answer 15

pressure in arteries minus pressure in veins

mean arterial pressure (MAP) - central venous pressure (CVP)

Question 16

what is the mean arterial pressure formula?

Answer 16

mean arterial pressure = cardiac output x total peripheral resistance

Question 17

describe arteriolar radius

Answer 17

total peripheral resistance is controlled by blood vessel radius

• radius of the arterioles can be increased or decreased
• arterioles are the major resistance vessels

Question 18

describe how to control arteriolar radius

Answer 18

• sympathetic nervous system: generalised vasoconstriction through a1 receptors
• hormones

Question 19

describe how local metabolic changes control arteriolar diameter

Answer 19

local metabolic changes in a tissue control arteriolar diameter and allows blood flow to meet the needs to the tissue
e.g. during exercise an increase in metabolism stimulates the dilation of local arterioles

exercise -> increase tissue metabolism –> increase O2, increase CO2, increase H+ –> arterioles dilate –> decrease resistance = increase blood flow –> increase O2 and nutrients supplied to metabolising tissue

Question 20

describe the effects of the parasympathetic system on the heart and how this effects blood pressure

Answer 20

decrease HR, decrease CO, decrease blood pressure

Question 21

describe the effects of the sympathetic system on the heart and how this effects blood pressure

Answer 21

increase HR and increase contractile strength (which increases stroke volume), the increase in HR and stroke volume increases CO thus increasing blood pressure

Question 22

describe the effects of the sympathetic system on the arterioles and how this effects blood pressure

Answer 22

increase vasoconstriction, increase TPR, increase blood pressure

Question 23

describe the effects of the sympathetic system on the veins and how this effects blood pressure

Answer 23

increase venous return, increase stroke volume, increase CO, increase blood pressure