Chapter 7 - Mass Transport and Heat Transfer in the Microcirculation

Abstract

There are five main diffusion events that take place during the process of red blood cell oxygenation within the pulmonary capillaries. The first event is known as alveolar diffusion, which is governed by Fick's laws of diffusion. The second diffusion event is the movement of the gas across the respiratory boundary, which is modeled with a partition coefficient for each of the boundaries that are included within the model. The third diffusion event is the convection and diffusion of oxygen to the red blood cell within the pulmonary capillaries. The fourth diffusion event is the diffusion of oxygen across the red blood cell membrane, which occurs approximately 100 times faster than the diffusion across the respiratory boundary. The last diffusion event is the diffusion of oxygen to hemoglobin and the kinetic association of oxygen to hemoglobin, which is modeled with a Thiele modulus. Glucose transport is also a salient transport mechanism within the microcirculation. Glucose transport is coupled to the movement of a second ion (such as sodium), where the energy gained by moving this second ion down its electrochemical gradient is used to move glucose up its concentration gradient. The critical adhesive forces that play a role in biological applications are the molecular forces, the electrostatic forces, and the capillary forces. Molecular forces are the weakest, act over the smallest range, and are sometimes transient. Electrostatic forces may arise in biological situations, if there is a net charge on one of the molecules. Capillary forces are composed of adhesion, cohesion, and surface tension.