Flashcards in Chapter 15 - Guyton Deck (24):
Equation for vascular distensibility.
vascular distensibility = increase in volume / (increase in pressure x original volume)
Why are veins more distensible than arteries?
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)
Equation for vascular compliance.
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)
What is the difference between distensibility and compliance?
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.
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.
What mechanism allows the systemic circulation to accommodate extra blood when necessary, such as after a transfusion?
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
Two major factors affect the pulse pressure (difference between systolic and diastolic pressure):
1) the stroke volume output of the heart and 2) the compliance (total distensibility) of the arterial tree
How would arteriosclerosis affect pulse pressure?
it will rise because the arteries are much less compliant
The relationship between velocity of pulse pressure and compliance is _________ related.
inversely, the greater the compliance of each vascular segment, the slower the velocity
What is damping?
progressive diminution of the pulsations in the
periphery (caused by resistance X compliance)
Is the mean arterial pressure closer to the diastolic or systolic pressure?
mean pressure is closer to diastolic during the cardiac cycle (60% of the diastolic and 40% of the systolic)
What is central venous pressure?
pressure in the right atrium
How will weakness of the heart affect central venous pressure?
it will increase (decreased ability to pump blood to right ventricle and pulmonary circulation so more blood accumulates in right atrium)
Factors that can increase venous return and thus increase right atrial pressure.
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
While standing still, gravitational pressure would result in the venous pressures to be ________ in the legs than in arms.
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?
valves; this is the venous pump or muscle pump action to propel blood back to the heart
What causes varicose veins?
incompetent venous valves
More than 60 per cent of all the blood in the circulatory system is usually in the _____.
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
Specific blood reservoirs?
spleen, liver, large abdominal veins, venous plexus beneath the skin, heart, lungs
The red pulp of the spleen is a special reservoir that contains large quantities of concentrated:
red blood cells
Normal right atrial pressure
0 mm Hg (atmospheric pressure around the body)
What could increase right atrial pressure to as much as 20-30 mmHg (very abnormal conditions)?
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
Weakness of the heart elevates/depresses the right atrial pressure.