V4

• Many organs, such as the lungs, liver and kidney, are organized to enable the rapid exchange of molecules between the blood and the tissue.

• In addition, various levels of biological organization can be explained by the rates of transport or molecules from their sources to their sites of delivery

• Alterations in transport processes are important factors in several diseases, such as artherosclerosis, cancer and kidney diseases

• Understanding the transport is important for the characterization and operation of several devices and the development of new therapies

• Random molecular motion

• Transport across concentration gradients

• Movement of molecules from high to low concentration regions

-> The net movement of a substance from a region of high to a region of low concentration

->Molecules are in a constant motion due to thermal energy (Albumin’s average speed is 6m/s)

->Molecules are constantly colliding and changing directions (Random walks)

>Molecules initially placed in one location tend to spread out over time —-> Diffusion

• Random movement of particles suspended in a fluid resulting from fast collisions by molecules in the fluid

• A molecule collides around about a billion times per second, resulting in random motions

• The collision frequency depends on the size and shape of particle, velocity of the liquid, temperature, mean free path, etc.

• Random walk: net molecular motion arising from random collisions

• Movement of molecules resulting from the bulk movement of a fluid

• Fluid movement resulting from the application of forces (gravity, pressure, shearing forces

The transport of material between a boundary surface and a moving fluid or between two immiscible moving fluids separated by a mobile interface

• Free convection: Gradients inside the fluid: Temperature, density, concentration differences

• Forced convection: Movement of fluid under the influence of external forces (pressure difference), Laminar or turbulent

Convection = Movement of large mass of particles in the same direction through the fluid

Diffusion = Movement of single particles and transfer of particle’s momentum and energy to other particles in the fluid