Question

The mechanics of blood flow in the body follows the laws of fluid dynamics for tubes with a constant diameter and length. Which statement is correct?

The flow of fluid in a tube depends upon the absolute pressure at the beginning of the tube. The rate of fluid flow in a tube will decrease if the pressure at the beginning is increased while the pressure at the end of the tube stays the same. The greater the resistance to flow in a tube, the greater the rate of flow for any given pressure difference. If both the resistance and the pressure gradient in a tube increases, the fow must also increase. The rate of flow in a tube will decrease if the resistance to flow is increased.

Answer 1

Ans - the rate of flow is decreased if resistance is increased.

Volume of blood flow is determined by five factors:

1. Pressure gradient --- Volume of blood flowing through any blood vessel is directly proportional to the pressure gradient. Pressure gradient is the pressure difference between the two ends of the blood vessel.

2. Resistance to the blood flow ---Volume of blood flow is inversely proportional to the resistance

3. Viscosity of blood ---- Volume of blood flow is inversely proportional to the viscosity

4. Diameter of blood vessels --- Volume of blood flow is directly proportional to the diameter of blood vessel. Aorta has the maximum diameter, hence maximum flow.

5. Velocity of blood flow ---Volume of blood flow is directly proportional to the velocity of blood flow.

According to Hagen-Poiseuille equation,

volume (Q) of any fluid flowing through a rigid tube is: 1.Directly proportional to pressure gradient (P1 – P2)

2.Directly proportional to the fourth power of radius (r4) 3.Inversely proportional to the length of the tube (L).

Q = K (P1 - P2) x r​​​​​​4​​​ /L

K is the constant for fluid flowing at a temperature