Chapter 15 - Guyton

Question 1

Equation for vascular distensibility.

Answer 1

vascular distensibility = increase in volume / (increase in pressure x original volume)

Question 2

Why are veins more distensible than arteries?

Answer 2

the walls of the arteries are far stronger than those of the veins, given increase in pressure causes about eight times as much increase in blood in a vein as in an artery of comparable size (remember its the opposite for pulmonary arteries and veins)

Question 3

Equation for vascular compliance.

Answer 3

vascular compliance = increase in volume / increase in pressure (total quantity of blood that can be stored in a given portion of the circulation for each millimeter of mercury pressure rise)

Question 4

What is the difference between distensibility and compliance?

Answer 4

A highly distensible vessel that has a slight volume may have far less compliance than a much less distensible vessel that has a large volume because compliance is equal to distensibility times volume.

Question 5

Enhancement of ___________ tone, especially to the veins, reduces the vessel sizes enough that the circulation continues to operate almost normally even when as much as 25 per cent of the total blood volume has been lost.

Answer 5

sympathetic

Question 6

What mechanism allows the systemic circulation to accommodate extra blood when necessary, such as after a transfusion?

Answer 6

delayed compliance (stress-relaxation), a vessel exposed to increased volume at first exhibits a large increase in pressure, but progressive delayed stretching of smooth muscle allows the pressure to return back to normal over a period of minutes to hours

Question 7

Two major factors affect the pulse pressure (difference between systolic and diastolic pressure):

Answer 7

1) the stroke volume output of the heart and 2) the compliance (total distensibility) of the arterial tree

Question 8

How would arteriosclerosis affect pulse pressure?

Answer 8

it will rise because the arteries are much less compliant

Question 9

The relationship between velocity of pulse pressure and compliance is _________ related.

Answer 9

inversely, the greater the compliance of each vascular segment, the slower the velocity

Question 10

What is damping?

Answer 10

progressive diminution of the pulsations in the

periphery (caused by resistance X compliance)

Question 11

Is the mean arterial pressure closer to the diastolic or systolic pressure?

Answer 11

mean pressure is closer to diastolic during the cardiac cycle (60% of the diastolic and 40% of the systolic)

Question 12

What is central venous pressure?

Answer 12

pressure in the right atrium

Question 13

How will weakness of the heart affect central venous pressure?

Answer 13

it will increase (decreased ability to pump blood to right ventricle and pulmonary circulation so more blood accumulates in right atrium)

Question 14

Factors that can increase venous return and thus increase right atrial pressure.

Answer 14

increased blood volume, increased large vessel tone throughout the body with resultant increased peripheral venous pressures, and dilation of the arterioles, which decreases the peripheral resistance and allows rapid flow of blood from the arteries into the veins

Question 15

While standing still, gravitational pressure would result in the venous pressures to be ________ in the legs than in arms.

Answer 15

higher

Question 16

While ambulating, why would the venous pressure in the leg be +20 mm Hg instead of the normal +90 mm Hg in an individual who is standing due to gravitational pressure?

Answer 16

valves; this is the venous pump or muscle pump action to propel blood back to the heart

Question 17

What causes varicose veins?

Answer 17

incompetent venous valves

Question 18

More than 60 per cent of all the blood in the circulatory system is usually in the _____.

Answer 18

veins, for this reason and also because the veins
are so compliant, it is said that the venous system
serves as a blood reservoir for the circulation

Question 19

Specific blood reservoirs?

Answer 19

spleen, liver, large abdominal veins, venous plexus beneath the skin, heart, lungs

Question 20

The red pulp of the spleen is a special reservoir that contains large quantities of concentrated:

Answer 20

red blood cells

Question 21

Normal right atrial pressure

Answer 21

0 mm Hg (atmospheric pressure around the body)

Question 22

What could increase right atrial pressure to as much as 20-30 mmHg (very abnormal conditions)?

Answer 22

serious heart failure or after massive transfusion of blood, which greatly increases the total blood volume and causes excessive quantities of blood to attempt to flow into the heart from the peripheral vessels

Question 23

Weakness of the heart elevates/depresses the right atrial pressure.

Answer 23

elevates

Question 24

What could cause the right atrial pressure to drop sub-atmospheric (-3 to -5 mm Hg)?

Answer 24

heart beating with exceptional vigor or when a significant blood volume is lost (hemorrhage)