Q42 — The Starling Equation and Capillary Fluid Exchange
Human bodies have different types of capillaries that differ in wall structure, depending on the function of the organ they are located in.
Oncotic pressure is a pressure driven by proteins in the solution.
Below is the Starling equation, which governs the fluid exchange across capillaries:
$$J_v = K_f\left((P_c - P_i) - \sigma(\pi_c - \pi_i)\right) \qquad (1)$$
where,
| Symbol | Meaning |
|---|---|
| $K_f$ | filtration coefficient |
| $P_c$ | capillary hydrodynamic pressure |
| $P_i$ | interstitial hydrodynamic pressure |
| $\pi_c$ | capillary oncotic pressure |
| $\pi_i$ | interstitial oncotic pressure |
| $\sigma$ | reflection coefficient |
When Jv is positive, there is a net fluid movement out of the capillary (filtration); when Jv is negative, there is a net fluid movement into the capillary (absorption).
In a simple model, Pc is influenced by arterial and venous pressures, and can be summarized by the following formula:
$$P_c = \frac{0.2 P_a + P_v}{1.2} \qquad (2)$$
where Pa and Pv are arterial and venous pressures, respectively.
On your answer sheet, indicate “T” for true statements and “F” for false ones.
Question reproduced from IBO 2024, Theoretical Exam Part B, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF