Physiology Lecture 2 Flashcards
Cell Membrane
Phospholipid Bilayer - Hydrophilic outside and hydrophobic inside; barrier for water and water-soluble molecules
Proteins - Allows for movement of substances through membrane
Proteins within Membrane
Ion channels
Carrier proteins (picks up a substance at one side of a protein and drops it at the other)
Pumps (uses energy because against concentration gradient)
Receptors (allow for communication between cells)
Enzymes
Types of transport through a membrane
Diffusion (no energy required) and active transport (energy required)
Diffusion
Random movement in all directions
2 types - simple diffusion and facilitated diffusion
Simple diffusion
Movement through membrane, channel protein, or pore
Lipid-soluble molecules move readily through the membrane (rate depends on lipid solubility) - oxygen, carbon dioxide, alcohol, and steroid hormones
Water can pass freely through any channel or pore
Water-soluble ions cross via SPECIFIC water-filled channels or pores
Selectivity of channels
Selective permeability due to different composition
Gated channels
Ungated vs Gated Channels
Ungated channels - always open (specific ion is always diffusing through pore); leak channels (important for electrical signals)
Gated channels - Open and close in response to a stimulus
1) Voltage-gated channels - sensitive and dependent; dependent on differences in electrical potentials across the membrane (gate is opened to restore potential difference)
2) Chemical (Ligand)-gated channel - open and close when stimulated by chemical binding (ex. - Acetylcholine)
Facilitated Diffusion
Required interaction of transported molecule with a carrier protein which aids passage
Rate of Diffusion
Simple diffusion = exponential rate
Facilitated Diffusion = logarithmic increase (dependent on the rate at which carrier protein can change conformation due to stimulus; Vmax cannot be greater than the rate of this change in conformation)
Net Diffusion
Average direction of diffusion
Net rate diffusion is affected by..
Concentration gradient (down concentration gradient)
Membrane electrical potential - electrical potential across membrane is equal in magnitude but opposite in direction to the concentration force (Nernst Potential - EMF (mV) = +/- 61 log (Co/Ci) )
Osmosis
Net diffusion of water
Osmostic Pressure
Amount of pressure required to counter osmosis (i.e. higher osmolarity = higher osmotic pressure)
Osmotic pressure caused by the number of particles present in a solution REGARDLESS of the molarity of the particle
Measured in HHmg
Osmolarity
Number of osmotic particle / volume
Since osmotic pressure and therefore osmolarity is dependent on the number of particle NOT molarity, it is important to remember whether or not a compound dissociates in H20. If dissociation occurs, then there will be an increase in the number of particles and in result an increase in osmolarity and osmotic pressure
