Pressure Gradients, Blood Flow and Peripheral Resistance

Question 1

Major vessel types and features of each

Answer 1

Arteries - low resistance, act as pressure reservoirs for maintaining blood flow
Arterioles - major sites of resistance, regulate arterial pressure
Capillaries - site of exchange between blood and tissues
Veins - low resistance vessels for blood return to heart

Question 2

3 layers and basic structure of a blood vessel wall

Answer 2

adventitial layer - connective tissue, collagen and elastin
medial layer - smooth muscle radial around lumen
intimal layer - endothelial cells

Question 3

units for blood flow, pressure gradient and resistance

Answer 3

F = flow rate of blood (l/min)
deltaP = pressure gradient (mmHg)
R = resistance of blood vessels (mmHg.l/min)

Question 4

which type of pressure does flow rate depend on more

Answer 4

pressure difference not absolute pressure

Question 5

define resistance

Answer 5

a measure of how difficult it is for blood to flow between two points at any given pressure difference
friction impeding flow

Question 6

relationship between flow, pressure and resistance

Answer 6

F = deltaP/R

Question 7

where in a blood vessel is resistance highest

Answer 7

at the edge

Question 8

describe the effect on blood flow of an increase or decrease in resistance

Answer 8

increase in resistance leads to decreased flow and vice versa

Question 9

what 3 factors dictate resistance and which is important

Answer 9

viscosity of the blood
vessel length
vessel radius (most important)

Question 10

what is Poiseuille’s equation

Answer 10

flow rate = pi.deltaP.r^4 / 8.viscosity.vessel length

Question 11

mean arterial pressure

Answer 11

93mmHg

Question 12

how to calculate pulse pressure

Answer 12

systolic pressure - diastolic pressure

Question 13

how to calculate mean arterial pressure

Answer 13

diastolic pressure + 1/3 pulse pressure

Question 14

why is 1/3 used when calculating mean arterial pressure

Answer 14

time in systole and time in diastole are a 1:2 ratio

Question 15

why is diastolic arterial pressure not 0 mmHg

Answer 15

there is still pressure within the circulatory system due to elastic recoil of arterial walls and blood in the vessels

Question 16

explain how arteries act as pressure reservoirs

Answer 16

walls contain lots of elastin and collagen, expand and hold energy - between beats passively return maintaining flow

Question 17

why are arterioles the major resistance vessels

Answer 17

due to their small diameter
small radius = large resistance

Question 18

which nerves innervate the smooth muscle found in the walls of arterioles
what are they also sensitive to

Answer 18

sympathetic
also sensitive to chemical changes and hormones