10. Biophysics of metabolism and transport.

Macro transport

transport of significant amounts of material: through pipes, vessels: over longer distances

Microtransport

in small volumes: by diffusion: in smaller distances

Types of flow

Laminar (layered)
Turbulent (swirling) Flow characteristics: Velocity: [m/s] Volume flow

ideal fluids

Frictionless and incompressible fluids

Bernoulli's law

At any point of a medium (liquid or gas) flowing in a horizontal pipe, the sum of the static and throttling pressures is constant

Use of Bernoulli's law in medicine

Dynamic collapse, stenosis, aneurysm

Viscosity of gases

increases with increasing temperature

Medical implications of the Hagen-Poiseuille law

Regulation of vascular/airway tone

Blood viscosity

not constant

depends on:
flow rate (inverse proportionality)
hematocrit level (direct proportionality)
temperature (inverse proportionality)
Disease

Uniport(er)

transports a single particle species by facilitated diffusion (passive) or primary active transport (pump, ATPase)

Symporter(er)

transports two or more different particles in the same direction (typically secondary active transport,

e.g. Na+ /glucose, Na+ /K+ /2Cl symporter)

Antiport(er)

transports two different particles in opposite directions (secondary active transport, e.g. Na+ /Ca2+ exchanger (3:1), Na+ /H+ antiport)

Na+/K+ pump function

Providing energy for other transport processes, reducing osmotic pressure, membrane potential (electrogenic 3 Na+ out/2 K+ in, source of diffusion potential)

Uptake of glucose from the intestinal lumen

glucose is transported from the lumen of the intestine with the help of Na+ glucose symport by a secondary active mechanism against the glucose gradient