Week 17: (C) Pressure gradients, blood flow & peripheral resistance

Question 1

What are all blood vessels lined with?

Answer 1

a layer of endothelial cells

Question 2

What are the 3 layers of a blood vessel?

Answer 2

endothelial cells (intimal layer)
Smooth muscle cells (medial layer)
Connective tissue (adventitial layer)

Question 3

What is the emption of the capillaries?

Answer 3

just a thin layer of endothelial cells

Question 4

What provides elastin and collagen?

Answer 4

tunica media

Question 5

What pathway innervates the smooth muscle of arterioles?

Answer 5

sympathetic, allow regulation of blood flow

Question 6

What changes the venous reservoir?

Answer 6

contraction and relaxation of smooth muscle veins. altered vol of blood back to the heart known as venous return

Question 7

What are arterioles, venues and capillaries collectively known as?

Answer 7

microcirculation

Question 8

What is the lumen diameter of the capillaries?

Answer 8

~3 micrometers

Question 9

What pressures does F go to and from?

Answer 9

always from region of higher pressure to a region of lower

Question 10

What do you call the pressure exerted by a fluid called?

Answer 10

hydrostatic pressure

Question 11

What are the units of flow?

Answer 11

volume per unit time (l/min or ml/min)

Question 12

What are units of the pressure difference (deltaP)?

Answer 12

mmHg

this drives the flow

Question 13

What do we need to calculate flow rate?

Answer 13

the pressure difference between 2 points (delta P) & the resistance (R)

Question 14

What does resistance measure?

Answer 14

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

Question 15

What does blood flow through a vessel depend upon?

Answer 15

pressure gradient and vascular resistance

Question 16

What is the blood flow equation?

Answer 16

change in pressure/ resistance

Question 17

What is a pressure gradient?

Answer 17

difference in pressure between beginning and end of vessel

Question 18

What causes friction in resistance?

Answer 18

the friction between moving blood and stationary vessel wall

Question 19

If resistance increases, what must be altered to maintain flow rate?

Answer 19

pressure must increase

Question 20

What is parabolic distribution?

Answer 20

blood in contact with the epithelial wall, move slower due to increased friction (resistance). Blood flowing the centre has less resistance, flows quicker

Question 21

What 3 factors does resistance to blood flow depend upon?

Answer 21

1) viscosity of blood (n eta)
2) vessel length (L)
3) vessel radius (r)

Question 22

Why is L unimportant?

Answer 22

the length is constant

Question 23

What is the major determinant of resistance to flow along a vessel?

Answer 23

radius (r)

slight change in radius = notable change in flow

Question 24

What is the effects of a 2-fold change in radius on flow?

Answer 24

produce a 16-fold change in flow

Flow

Question 25

How to calculate mean arterial pressure?

Answer 25

= diastolic pressure + 1/3 pulse pressure

Question 26

What does arterial blood pressure fluctuate in relation to?

Answer 26

ventricular systole and diastole

Question 27

How to calculate pulse pressure?

Answer 27

systolic arterial pressure - diastolic arterial pressure.

Question 28

Why does arterial pressure not drop to zero during diastole?

Answer 28

as arterioles have a higher resistance to blood than

Question 29

How much blood enters arteries and flows to arterioles?

Answer 29

more blood enters arteries than leaves to arterioles

Question 30

what happens to arteries when heart is reeling and filling?

Answer 30

passively recoil, like a balloon exerting pressure on the blood in the arteries during diastole, pushes blood into vessels downstream. ensuring continued blood flow to organs as heart is relaxing

Question 31

Where so the arteries store excess pressure energy during systole?

Answer 31

in their stretched walls

Question 32

What does the pressure drop to on arterioles?

Answer 32

~37 mmHg

Question 33

What vessel has the slowest velocity? and why?

Answer 33

capillaries, to allow adequate time for the exchange of nutrients and waste products between the blood and cells of tissues

Question 34

What vessel has the highest cross sectional area?

Answer 34

capillaries

Question 35

What happens to the pressure in the arterioles?

Answer 35

They have high resistance so results in decreased pressure

Question 36

What the the change in mean pressure in the arterioles from~93 to ~37mmHg result in?

Answer 36

pressure drop | pressure gradient helps drive blood from the heart to the tissue capillary beds.

Question 37

What is the thick layer in arteriolar walls?

Answer 37

smooth muscle

Question 38

What type of nerves innervate the smooth muscle of arteriolar walls?

Answer 38

sympathetic

Question 39

What is the smooth muscle also sensitive to?

Answer 39

many local chemical changes and certain circulatory hormones

Question 40

What happens when contraction of the smooth muscle or arteriole occurs?

Answer 40

contraction= decreased radius, | increased resistance= decreased blood local flow= vasoconstriction

Question 41

What happens when relaxation of the arteriole occurs?

Answer 41

relaxation= increased radius, | decreased resistance= increased local blood flow= vasodilation

Question 42

What is vascular tone?

Answer 42

when the arteriolar smooth muscle displays a state of partial constriction

Question 43

What 2 factors are responsible for vascular tone?

Answer 43

1) myogenic activity | 2) sympathetic activity

Question 44

What is myogenic activity?

Answer 44

relates to the contraction initiated by smooth muscle itself, independent any external occurrence or nerve stimulation

Question 45

What is sympathetic activity (smooth muscle)?

Answer 45

increase sympathetic activity, increase contraction, vasoconstriction...decrease blood flow through vessel

Question 46

Why is vascular tone important?

Answer 46

makes it possible to decrease or increase contractile activity

Question 47

What is Poiseulle's law?

Answer 47

any change in contractility of arteriolar smooth muscle will substantially change resistance to flow in these vessels