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Exchange and transport

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Question 27

The table below compares the pressures of a capillary with the surrounding tissue fluid:

PropertyCapillaryTissue fluid
Hydrostatic pressure4.8 kPa0.20 kPa
Oncotic pressure3.8 kPa0.05 kPa

The net movement of fluid between the capillary and tissue fluid depends on the net driving force (JvJ_vJv​):

Jv=(Pc−Pi)−σ(πc−πi) J_v = (P_c - P_i) - \sigma(\pi_c - \pi_i) Jv​=(Pc​−Pi​)−σ(πc​−πi​)

Where:

  • PcP_cPc​ = capillary hydrostatic pressure
  • PiP_iPi​ = tissue fluid hydrostatic pressure
  • πc\pi_cπc​ = capillary oncotic pressure
  • πi\pi_iπi​ = tissue fluid oncotic pressure
  • σ\sigmaσ = reflectance factor (varies between 0 for totally permeable and 1 for totally impermeable)
a.

In a particular tissue, the reflectance factor (σ\sigmaσ) was found to be 0.80. Use this information and the data in the table to calculate a value for the net driving force, JvJ_vJv​, and predict the direction of fluid movement.

[4]
b.

Suggest the effect of a liver disease that reduces the synthesis of plasma proteins on the net driving force (JvJ_vJv​) and explain how this affects the volume of tissue fluid formed.

[3]

Exchange and transport Questions

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