Physiology-2

Physiology-2 - Transport Mechanisms Diffusion: D iffusion-...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Transport Mechanisms Diffusion: Diffusion- the movement of molecules from one location to another solely as a result of their random thermal motion. the amount of material crossing a surface in a unit of time is known as a flux . o The one way-flux of glucose from compartment 1 to compartment 2, in a cell is dependent on concentration. o At a short time, some of the glucose molecules that have entered compartment 2 will randomly move back into compartment 1. The magnitude depends upon the concentration of glucose in compartment 2 at any time. Net flux is the difference b/w the two one-way fluxes. (Vector addition) When two compartments fluxes are in equal magnitude but in opposite direction the system has reached diffusion equilibrium . o There are 3 fluxes: 2 one way fluxes and the net flux. o The net flux always proceeds from higher to lower concentrations . 4 Factors that affect the magnitude of the net flux: o Temperature: greter kinetic speed and greater collision o Mass of the molecule: larger mass has slower speeds o Surface Area: the greter the surface area b/w two reagons, the greater space available for diffusion. o Medium through wich the molecules are moving: molecules move faster in air than water. The diffusion times increase in proportion to the square of the distance over which the molecules diffuse. o Few seconds for a millimetres, Millions of years for a meter. o Diffusion only works for close proximities o The heart does the rest of the transportation. o Cells must have a small volume/surface area ratio because it would take too longs for materials to reach the cell organelles. The rate at which a substance diffuses across a plasma membrane can be measured by monitoring the rate at which its intracellular concentration approaches diffusion equilibrium with the ECF (assume ECF is constant). o The net flux J, is calculated by: J = PA(C o – C i ) Where (Co – Ci) is the difference in concentration A is the surface area of the membrane P is the membrane permeability coefficient (experimental) o The greater the P (mpc), the bigger the net flux. Pages 96-114, 45-48, 394-397
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Transport Mechanisms o Membranes slow down diffusion, and is due to the hydrophobic interior of its lipid bi-layer. In lipid bilayers: o Non-polar molecules dissolve in the nonpolar regions of the membrane occupied by the fatty acid chains of the membrane phospholipids o Increasing the lipid solubility of a substance by decreasing the number of polar or ionized groups it contains, will increase the number of molecules dissolved in the membrane lipids. o Oxygen, carbon dioxide, fatty acids, and steroid hormones diffuse rapidly through the lipid portions of membranes. o
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 12/06/2009 for the course PHGY 209 taught by Professor Wechsler during the Spring '07 term at McGill.

Page1 / 11

Physiology-2 - Transport Mechanisms Diffusion: D iffusion-...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online