1-1. The lungs always receive more blood flow than any other organ because 100% of the cardiac output always passes through the lungs.
1-2. False. Flow through any vascular bed depends on its resistance to flow and the arterial pressure. As long as this pressure is maintained constant (a critical point), alterations in flow through any individual bed will have no influence on flow through other beds in parallel with it.
1-3. A leaky aortic valve will cause a diastolic murmur. Normally, the aortic valve is closed during diastole when there is a large reverse pressure difference between the aorta and left ventricle.
1-4. False. Slowing conduction through the AV node will have no effect on the heart rate but will increase the interval between atrial and ventricular excitation. The heart rate is normally slowed by decreases in the rate of action potential initiation by pacemaker cells in the SA node.
1-5. The blood flow rate through the lungs (Q̇L) must equal the cardiac output (CO) because of the way the cardiovascular system is arranged. Q̇L is equal to the pressure drop across the lungs (ΔPL) divided by the resistance to flow through the lungs (RL).
(b) According to Poiseuille's equation,
With other factors constant
Thus doubling the radius with exercise increases flow 16-fold over that at rest. Therefore,
1-7. Significant blood loss has a profound negative effect on cardiac pumping because there is not enough blood left to fill the heart properly. This results in decreased cardiac output because of Starling's law of the heart. The consequence of decreased cardiac pumping ability is a lessened pressure difference between arteries and veins. Because of the basic flow equation, less ΔP causes less flow through the systemic organs. Interstitial homeostasis is compromised when there is abnormally low blood flow through capillaries. Improper interstitial conditions impair nerve function and cognitive ability in the brain and cause weakness in skeletal muscles.
1-8. Norepinephrine is the normal sympathetic neurotransmitter substance, so the same cardiovascular effects that normally accompany activation of sympathetic nerves should be predicted. These include increased heart rate, increased forcefulness of cardiac contraction, arteriolar constriction, and venous constriction.
1-9. Arteriolar and venous constriction would be expected because the sympathetic nerve effects on these vessels are normally mediated via α-receptors. There would be no direct effects on the heart expected because the sympathetic effects on the heart are mediated by β-receptors.