Transport Flashcards
What is diffusion?
- molecules “go down the concentration gradient”
- no energy required, cheap for cell
Why does diffusion occur?
- molecules have kinetic energy, are in constant motion
- mol’s move randomly and collide
- leads to even distribution
What factors increase the rate of diffusion?
1) increase concentration gradient, opposing electrical gradient
2) increase in temp.
3) increase membrane surface area
4) decrease diffusion distance
5) small molecular weight
What is simple diffusion?
-no E required
-molecules move down the concentration gradient
through air eg. smell of coffee
through water eg. milk in coffee
through gel eg. antibiotics diffuse through agar media
How does simple diffusion happen across the cell membrane?
- between phospholipid molecules
- lipid soluble materials eg. alcohol, steroid hormones, drugs
- small uncharged molecules eg. O2, CO2 between cells of lungs and tissues
What are the characteristics of channel mediated diffusion?
- no E required
- molecules move down concentration gradient
- molecules move across membranes through channel proteins which they couldn’t get through without
What are the characteristics of channel proteins?
- -transmembrane proteins
- nonspecific, molecule transported does not bind specifically to channel protein
- limits molecule by size, charge eg. water, ion
- some channels open randomly eg. leak channels (always opened not controlled)
- some channels are controlled eg. voltage gated channels, ligand-gated channels (another molecule binds to it), or mechanically gated channels (stays closed unless something pulls/pushes open)
eg. Na+ entry into muscle cells to stimulate contractions
What are the characteristics of carrier-mediated or facilitated diffusion?
- no E required
- mol’s move down conc. gradient
- mol’s move across a membrane through a carrier protein
What are the characteristics of carrier proteins?
- transmembrane protein
- specific, molecules to be transported must bind specifically to site on carrier protein
- binding triggers protein to change shape
- protein only open to one side of membrane at a time
eg. glucose or amino acid transporter
What is osmosis?
- net diffusion of water through a selectively permeable membrane
- no E required
- water molecules move down a concentration gradient
- water molecules moves through channels called aquaporins
What is water concentration gradient determined by?
-solute concentration gradient
What happens when solute concentration increases?
-water concentration decreases
What way does water move?
- from an area on low solute to an area of higher solute (solute draws water)
- from high water concentration to low water concentration
What happens in the intravenous infusion of normal saline and Dextran?
- water exits cell, cell crenates
- cell is hypotonic to the solution
- water enters interstitial fluid and back to the blood
- expands - increased blood volume
- this is good for patients with low BP so the blood can continue to be pumped to the brain and the rest of the body
Why is normal saline (NaCl) used instead of water for intravenous delivery of drugs and RBCs?
-if pure water was added, the cell would swell and lyse. By adding saline (isotonic to cell) it will not make the cell lyse or crenate so the delivery of drugs and RBCs will be hopefully successful
