4. Membrane Transport Mechanisms Flashcards
What is the distribution of water in the body?
60% of body water
1/3 of water is ECF, 2/3 is ICF
75% of ECF is interstitial, 25% is plasma
What are the main ions in ECF?
Cation - Na+
Anion - Cl-
What can pass through membranes?
Hydrophobic molecules (gases, vey small uncharged polar molecules) can pass easily
Can water and urea pass through membranes?
Yes as they are small uncharged polar molecules however not as easily as gases
What cannot pass through the membrane?
Large charged polar molecules, ions and charged polar molecules
How do some molecules such as water, urea and ions pass through capillary walls?
Pass through fenestrations
What is passive movement?
No energy, down concentration gradient
What is active transport?
Movement against concentration gradient, requires ATP
What is vesicular transport?
Molecules move in vesicles
Active process
Includes pinocytosis and phagocytosis
What is flux?
Describes how fast a solute moves
Number of moles crossing unit area of membrane per unit time (moles/cm^2/s)
Rate of flow of uncharged solute due to diffusion is directly proportional to…
Rate of change of concentration with distance in direction of flow
What happen when concentration gradient of substance is 0?
System must be in equilibrium and net flux will be 0
How dies the thickness of the membrane affect flux?
Thicker membrane, flux is slower
What is diffusion proportional to/inversely proportional to?
Proportional to surface area of barrier
Inversely proportional to its thickness
Describe the diffusion of 2 solutes
Each substance diffuses down its own concentration gradient, independent of concentration gradients of other substances
What is facilitated diffusion?
Move from high to low through protein channel
Passive
What are gated channels and how do they work?
Proteins that only open in presence of stimulus
Stimulus usually different to transported molecule
Ion gated or voltage gated
What is active transport?
Pump against concentration
Uses protein pump
Requires ATP
How are large molecules transported?
Exocytosis
Endocytosis
Requires ATP, vesicles and vacuoles
What are osmoles?
Measure of solutions ability to create osmotic pressure, thus affect movement of water
What are osmoles proportional to?
Number of osmotic particles formed in solution
1 mole of nonionisable substance = 1 osmole
What is osmolality?
When concentration of water is expressed in osmoles/kg of water
Osmolar concentration of solution is osmolality
You measure osmolality not osmolarity
What is osmosis?
Diffusion of water from high hypotonic solution to hypertonic solution across a semi-permeable membrane
Diffuses until osmotic force of both sides is equal
What are aquaporins?
Integral membrane proteins
Channel for transfer of water
What is the structure of aquaporins?
At centre of channel are positively charged residues that prevent movement of charged ions (H+) and therefore don’t disrupt H+ ion gradients in ATP production
