Blood Vessels and Hemodynamics - Anatomy and Physiology
- Why is blood flow velocity slowest in the capillaries?
- The capillaries have the largest total cross-sectional area, and velocity is inversely proportional to total cross-sectional area.
- Which vessels are the main site of control of total peripheral resistance?
- The arterioles, whose smooth muscle changes their radius.
- What is the basic equation relating blood flow, pressure gradient, and resistance?
- . Flow rises with the pressure gradient and falls as resistance rises.
- A vessel's radius is halved while length and viscosity stay the same. By what factor does resistance change?
- It increases 16-fold, because .
- Which mechanisms help return venous blood to the heart against low pressure?
- The skeletal muscle pump, the respiratory pump, and one-way venous valves, aided by venous smooth muscle tone.
- Which two pressures mainly oppose each other in capillary filtration?
- Capillary hydrostatic pressure pushes fluid out; plasma colloid osmotic pressure (from proteins) pulls fluid back in.
- Which layer of a blood vessel wall contains the smooth muscle that controls diameter?
- The tunica media, which is thickest in arteries.
- An arteriole's radius doubles with the pressure gradient unchanged. By what factor does flow change?
- It increases 16-fold. Resistance falls to 1/16, so flow rises 16 times.
- What is the pulse pressure for a blood pressure of 120/80 mmHg?
- 40 mmHg. Pulse pressure is systolic minus diastolic: 120 minus 80.
- According to Poiseuille's law, how does vessel radius affect resistance?
- Resistance is proportional to , so small changes in radius cause large changes in resistance.
- Estimate the mean arterial pressure for a blood pressure of 120/80 mmHg.
- About 93 mmHg. MAP is approximately diastolic plus one-third of pulse pressure: .
- Which vessels hold the largest share of total blood volume at rest?
- The systemic veins and venules (about 60 to 65 percent), which is why they are called capacitance vessels.