Chapter 5: Membrane Transport

extracellular fluid

interstitial fluid

blood plasma

osmolarity/osmolality

hyperosmotic/hyposmotic/isosmotic

osmosis

penetrating/nonpenetrating solute

passive transport (diffusion)

active transport

concentration gradient

channel (protein)

carrier (protein)

cotransporter

ATPase (“pump”)

saturation (of a transporter)

endocytosis/exocytosis

electrochemical gradient

equilibrium potential

depolarize/hyperpolarize

Describe and relate the three body fluid compartments (Fig 5.1)

Recognize that plasma, interstitial fluid, and intracellular fluid are in equilibrium with respect to total osmolality; and that extracellular fluid and intracellular fluid differ in ionic composition (remember all those Na+ and K+ pumps!)

Recognize that adult humans are 45-60% water depending on age and sex

Identify or give the osmolarity of human body fluids (300mOsM is only a slight
lie)

Recognize that water will move (osmosis will occur) to the area of higher osmolarity, regardless of the concentration of any specific solute

Describe some molecules that can easily cross cell membranes (without a specific transporter) by simple diffusion and some molecules that cannot; recognize that size and hydrophobicity/lipid solubility are the two most important factors in this

Differentiate between a) simple and facilitated diffusion, b) facilitated diffusion and active transport, c) a channel and a carrier, and d) primary and secondary active transport, giving examples of each

Recognize that most ion channels are gated (can be either open or closed), and that changing ion channels from open to closed or vice versa underlies much of physiology

Explain the difference in a) purpose/function and b) direction and speed of ion movement between ion pumps and ion channels

Recognize or identify that glucose needs a carrier to cross a cell membrane (facilitated diffusion), and that it is typically phosphorylated inside cells to keep the concentration gradient “pulling” glucose in (Fig 5.13

Given the size and hydrophobicity of a molecule, and concentrations on both sides of a membrane, predict through what mechanism and in what direction it will cross the cell membrane

Understand epithelial transport well enough to draw the physical relationship between the lumen of an organ, its epithelial cells and the interstitial fluid on the basolateral side (near the blood supply) and predict the movement of molecules across these cells given concentration gradients and other relevant information

Identify K+ as being the major intracellular ion and Na+ and Cl- as being the major extracellular ions—and know how they get to be there!

Recognize that the membrane potential = the voltage across the membrane, and that all animal cells maintain internally-negative membrane potentials

Explain why the sodium equilibrium potential (ENa) and the potassium equilibrium potential (EK) are different; know approximate real-life values for both ENa and EK

Predict qualitatively how changes in permeability to an ion or to ion
concentration gradients would change the equilibrium potential for that ion

Calculate the equilibrium potential for an ion using the simplified Nernst equation

Explain or identify what causes the resting membrane potential