5.2 Pressure & flow in the systemic circulation

Question 1

What is ‘diastolic’ arterial pressure?

Answer 1

when blood doesn’t flow into arteries

elastic recoil - to maintain pressure (prevent pressure drop)

Question 2

What is ‘pulse pressure’? when does it change?

Answer 2

Difference between systolic & diastolic pressure

decreases with increasing resistance & capacitance (e.g. arterioles –> capillaries)

Question 3

How do you calculate mean arterial pressure from systolic, diastolic & pulse pressure?

Answer 3

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

Question 4

What is the approximate time is systole & diastole?

Answer 4

systolic: 0.3s
diastolic: 0.55s

Question 5

what is ‘total peripheral resistance’?

Answer 5

total of all arteriole resistance on the body
inversely proportional to total body blood flow demand

(demand increase, TRP decreases)

Question 6

How does elastic nature of arteries act to reduce arterial pressure fluctuation between systole & diastole?

Answer 6

in systole: elastin in aorta & elastic arteries stretch to smooth out pressure increase (not rapid increase)

diastole: elastic arteries release energy stored to smooth blood flow

‘Windkessel’ effect

Question 7

What is ‘systolic’ arterial pressure?

Answer 7

pressure in arteries when blood flow into it

aorta + elastic arteries stretch to smooth out pressure wave

Question 8

What is the role of arterioles?

Answer 8

resistance vessels along with pre-capillary sphincters
control volume of blood entering the capillaries
arterioles have a high resistance due to small lumen

Question 9

What are pre-capillary sphincters?

Answer 9

a band of smooth muscles controlling flow into capillaries

Question 10

Define vasoconstriction

Answer 10

constriction of (peripheral) arteries to increase blood pressure

Question 11

define vasodilation

Answer 11

relaxation of arteries allow a greater volume of blood flowing through at any one time (rate), decreases blood pressure

Question 12

What is vasomotor tone?

Answer 12

tonic contraction of smooth muscles (basic sustained contraction)

Question 13

Which factors increase vasomotor tone?

Answer 13

autonomic SNS

through release of NA acting on alpha 1-GPCR - leading to Ca2+ contraction (IP3, SR, Ca2+, CaM, MLCK) - vasoconstriction

Question 14

Which factors decrease vasomotor tone?

Answer 14

increase vasodilatation (trying to increase vasodilation)
metabolically active tissues produce vasodilator metabolites (e.g. H+, CO2, K+, Adenosine, Lactate)

decrease vasomotor tone causes vasodilation

Question 15

What removes metabolic factors? Effects?

Answer 15

increased blood supply
gradually dominated by SNS
return to vasomotor tone

Question 16

What does vasodilator metabolites achieve?

Answer 16

local control of blood flow

Question 17

What is reactive hyperaemia?

Answer 17

increase in blood flow after a brief period of ischaemia (e.g. arterial occlusion - maybe from blood pressure cuff)

Question 18

What is venous return?

Answer 18

blood flow back to right atrium from body

Question 19

What is central venous pressure?

Answer 19

blood volume determined by: cardiac output, body metabolic demand, back pressure (pressure opposing flow e.g. round bends)
depends on return of blood from body, pumping of heart, gravity & muscle pumping (out via heart - cardiac output)

Question 20

What is the range for central venous pressure and where is it measured?

Answer 20

-10 to +10mmHg

measured in the great veins

Question 21

What is autoregulation?

Answer 21

an example of homeostasis e.g. reactive hyperaemia - when blood flow becomes excessive after a brief ischaemia to try and adequately reperfuse the tissue before any damage from ischaemia

Question 22

What are the 3 broad factors affecting vasomotor tone?

Answer 22

1. hormones (systemic)
2. myogenic (local) e.g. acute contraction in violent coughing to present sudden increase in pressure
3. endothelial factors (local) - from arterial endothelium