Systemic Circulation

Question 1

Vessels are primarily composed of which four things?

Answer 1

• endothelial cells
• elastin
• vascular smooth muscle
• collagen

Question 2

How is compliance determined?

Answer 2

change in volume / change in pressure (looks at how pressure changes in relation to a given change in volume)

Question 3

Does a less compliant (more stiff) vessel have a larger or smaller pulse pressure?

Answer 3

A stiffer vessel has a larger pulse pressure

Question 4

What are the primary differences in composition between an artery and a vein?

Answer 4

• arteries have elastic lamina
• arteries have more VSM
• arteries have less connective tissue (adventitia)

Question 5

Rank the compliance properties of the arterial wall components (collagen vs. elastic lamina vs. smooth muscle)

Answer 5

in order of decreasing compliance…

elastic lamina > VSM > collagen

Question 6

What are the implications of veins lacking an elastic layer?

Answer 6

Because of this, veins act as passive bags and can fill with blood but cannot squeeze back down as effectively as arteries.

Question 7

In which layer are the vasa vasorum found?

Answer 7

in the tunica adventitia

Question 8

Where is the most common place to find a continuous capillary?

Answer 8

in connective tissues

Question 9

Where are fenestrated capillaries most commonly found?

Answer 9

in the kidneys and intestines

Question 10

Where are discontinuous (sinusoidal) capillaries most commonly found?

Answer 10

in the liver, bone marrow, and spleen - all allow a lot of things to enter/leave via wide spaces in capillaries

Question 11

The higher the ___________ ratio, the greater the control of vessel diameter and blood flow.

Answer 11

wall thickness to lumen diameter

Question 12

Which vessels have the highest wall thickness to lumen diameter ratio and what is the implication?

Answer 12

arteriole and pre-capillary sphincters; this means they have the greatest control over vessel diameter and blood flow

Question 13

How much of our blood volume is sitting in our veins, on average?

Answer 13

~64%

Question 14

If capillaries have the largest total CSA, why do they have such a small blood volume?

Answer 14

This is because they are so short and physically cannot hold a lot of blood volume.

Question 15

Why does the aorta have such a small blood volume?

Answer 15

Blood is never held in the aorta, as it is rapidly being pumped out through the systemic circulation to other areas of the body.

Question 16

Which vessels have the lowest total resistance and why?

Answer 16

capillaries because they have the largest total cross sectional area

Question 17

Where does the largest drop in arterial pressure occur?

Answer 17

in the resistance vessels, primarily the arterioles (we use up most of the pressure generated by the LV to get blood through the resistance vessels)

Question 18

What does pulse pressure represent?

Answer 18

the force of contraction of the heart (difference b/t systolic and diastolic pressures)

Question 19

The average pressure existing in the aorta and proximal arterial system during one cardiac cycle.

Answer 19

Mean Arterial Pressure (MAP)

Question 20

Is MAP determined more by systolic or diastolic pressure?

Answer 20

diastolic

Question 21

Is there a pulse pressure in the capillaries and veins?

Answer 21

no!

Question 22

Why does pulse pressure widen in vessels farther from the heart?

Answer 22

decrease in compliance, as well as Bernoulli’s principle (decreased velocity=increased pressure)

Question 23

Why does a patient with an LVAD not have a pulse?

Answer 23

The device is continuously circulating blood around the body, so there is no need for pulsatility to pump the blood through the circulation.

Question 24

Explain the hydraulic filtering of the aorta and how this relates to its compliance.

Answer 24

-The volume ejected from the LV during systole is temporarily stored by distention of the elastic component of the aorta (compliant vessel); after systole ends, the distended aortic wall recoils and acts as a secondary (Windkessel) pump to maintain constant flow during diastole

Question 25

How does the aorta remodel itself with aging?

Answer 25

compliance decreases due to less elastin and more collagen

Question 26

What happens with a less compliant aorta in terms of work?

Answer 26

A stiffer aorta has to do more cardiac work to pump a sufficient volume of blood; more work=greater O2 consumption=larger energy requirements

Question 27

Are arteries more or less compliant than veins?

Answer 27

less compliant; this is why arteries are resistance vessels and veins are capacitance vessels

Question 28

How are pulse pressure and pressure pulse related?

Answer 28

a larger pulse pressure corresponds to a faster pressure pulse

Question 29

How does the velocity of propagation of the pressure pulse change with compliance?

Answer 29

decreased compliance (stiffer vessel) corresponds to an increased velocity of propagation