Figure 3

Modelling and simulation of CO ₂ transport. (A) Reference topology based on a cylinder-within-tubes arrangement (R. Moenickes, O. Richter and R. Pirow, in preparation). A sector piece was removed to show the alternation of concentric hollow cylinders of tissue (gray) and hemolymph (red, green, blue). (B) Simplified topology with only one tissue layer. This topology is applied in the compartment model. (C) Compartment model of the relevant transport processes. CO₂ is excreted from the tissue compartment of length dL into the inner and outer hemolymph (HL) lacuna at rates of (1-φ)F_Ex and φF_Ex. Hemolymph leaving the inner HL lacuna at a volume-flow rate is distributed between the outer HL lacuna and the carapace HL lacuna. From these compartments CO₂ diffuses across cuticular barriers into the medium, which flows at a rate of . Indicated are the CO₂ partial pressures (P_hi, P_ho, P_hc, P_m) and flow velocities (ν_b, ν_f, ν_m) in the hemolymph lacunae and the medium. P_in is the inspiratory P_CO2. (D) Simulation results for the uncatalyzed and catalyzed hydration of CO₂ for an animal exposed to normal conditions (ambient pH = 8.0, ambient P_CO2 = 0.035 kPa). Acid-base variables are shown for the medium and hemolymph lacunae in relation to the exchange coordinate.