Forces acting across membranes 2 Flashcards
What are the 4 mechanisms of movement?
Osmosis, Active transport, Diffusion, Filtration
Which mechanisms are passive?
Osmosis, Diffusion
How do macromolecules diffuse across a cell?
Through transporters
What are carrier-mediated transport proteins?
Another word for transporter proteins. Act as a valve for larger molecules, too big for carrier proteins. Change shape when a molecule passes through.
Passive diffusion vs Facilitated diffusion
Passive involves gas. Lipophillic gasses (o2, n2,) pass faster than lipophobic ones (co2)
What causes protein channels to open?
Chemical or electrical charge change
How do voltage-gated channels work?
Open/close due to a change in the electrical gradient across a membrane
Where are voltage-gated channels mostly found?
Muscle and nerve cells
What is a ligand-gated channel?
These cause a conformational change in the channel protein when a chemical/hormone binds to a receptor on the membrane, opening or closing its gate accordingly.
What factors drive ions to cross a membrane?
Electrical gradient and concentration gradient
What is the electrochemical gradient?
The gradient for which ions will flow.
What is electrochemical equilibrium?
When both electrical and chemical gradients are in balance. This ‘rarely’ happens
What is active transport?
Uses ATP to drive movement of ions/molecules against a concentration gradient
How does Na+K+ ATPase work
Pumps 3 Na+ out of the cell and 2 K+ in the cell. 40% of body’s resting energy is used for this process.
What is an electrogenic pump
One which generates current by pushing ions across a membrane, leading to translocation of net charge
How is osmotic equilibrium achieved?
Body has no barriers to water so conc. all over is equal, despite different volumed.
How are osmosis and diffusion co-dependent?
Where we have diffusion, we always have osmosis (solute and water move in opposite directions). Where we have osmosis, we may or may not have diffusion (depending on permeability of membrane)
Define Osmolarity
The conc. of a solution based on no. of solute particles per litre, in osmoles
What is the osmolarity of normal human plasma?
285mOsmol/L (300 to remember)
What does the volume of a cell depend on?
The number of non-penetrating particles on either side of a membrane
Define Hypo-osmotic, Isosmotic and Hyperosmotic
Hypo - a cell containing fewer solute particles per litre of solution, relative to another cell. Iso - same no. of solute particles per litre between 2 cells. Hyper - opposite to hypo
What is Tonicity?
The ability of an extra-cellular solution to move water into or out of a cell by osmosis. Takes into account relative solute conc. of solution and cell, and the cells permeability.
What do the terms Hypertonic, Isotonic and Hypotonic refer to?
The state of a solution depending on how it affects the volume of a cell when places in said solution.
Isosmotic vs Isotonic?
Isotonic solution - different osmotic pressure in and out a cell. Isotonic - 2 solutions have the same osmotic pressure.
Isotonic involves only non-pen particles, isosmotic involves pen and non-pen.
Isotonic tells us volume of solution, while Isosmotic tells only conc.
What happens when you transfuse a patient with pure water?
Solutions in the body become hypotonic and cells increase in volume, eventually bursting. Can cause death
What solution should we use to transfuse most patients?
0.9g 150mOsmol/L saline (NaCl). Contains 300 particles which is the same as our plasma’s normal mOsmol/L. It is isotonic.
