11/17/2014 Medical Physiology Transport Physiology Steven Grassl Flashcards
Define active transport.
Movement of solute across a membrane UP its concentration gradient (from low [] to high [])
______ transport is defined as movement of solute from a place of high electrochemical potential on one side of a membrane to a place of low electrochemical potential on the other.
Passive
T/F: In no instance would a passive transport mechanism mediate net transport of a charged solute in a direction across the cell membrane that opposed both the chemical and electrical driving forces acting on the ion.
True
What is the most important distinguishing feature of active transport versus passive transport?
Active transport can generate and maintain an electrochemical or chemical potential difference across a membrane.
Give an example of a non-equilibrium steady state.
Na/K ATPase
How are uncharged solute differences classified?
As chemical potentials. For example, glucose is uncharged, so there can be no voltage difference across a membrane, only a chemical difference.
Ion transporters, antiporters and symporters all mediate what kind of transport?
Active transport
Channels and uniporters generally mediate what kind of transport?
Passive
What bonds are broken to drive active transport?
Phosphate bonds of ATP
In epithelial cells such as in the kidney and intestine, different secondary active _____ mediate concentrative, intracellular accumulation of solutes such as glucose, amino acids, vitamins, mono and dicarboxylates etc.
symporters
Name the two types of secondary active transport.
- Cotransport - symporter 2. Countertransport - antiporter
Name the primary active transport method.
Pump
Solute potential equilibrium and net zero differential across the membrane occurs in:
Passive transport
In secondary active transport, what does secondary mean?
The mode of transport is indirectly dependent on the hydrolysis of ATP and a primary active transport process
Which is a faster mode of transport, channels or carrier-mediated transport?
Channels, by many orders of magnitude
How is the steady state distribution of Na and K maintained?
Active transport of ATPase, and leak channels that move Na in and K out (opposite the direction of the pump)
How many Na ions are transported into the cell via the Na/K ATPase?
NONE! The Na/K pump moves 3 Na OUT of the cell and 2 K IN to the cell
What is the shape of the slope of a graph of simple diffusion?
Straight line, linear relationship between [X] and Jx (transport rate, aka Vx)
What is the shape of the slope of a graph of carrier-mediated or facilitated diffusion?
Asymptotic, determined by [X] where higher [X] eventually levels off at Vmax (or Jmax)
In facilitated diffusion/Michelis Menton kinetics, when does [X] = Km?
At 1/2Vmax
What is Vmax?
The maximal transport rate achievable in carrier-mediated or facilitated diffusion (Michelis Menton kinetics)
T/F: The interaction of a substrate with a transporter may or may not result in the transport of of the substrate across the membrane.
True. Sometimes the transport can be inhibited.
Amiloride specifically inhibits what?
The epithelial Na channel and the epithelial Na/H exchanger
What is phloridzin?
Phloridzin is a non-transported chemical analog of glucose. It inhibits the glucose-Na cotransporter.
T/F: Phloridzin inhibits both the Na/glucose cotransporter and the Na/succinate cotransporter.
FALSE. Phloridzin only inhibits the Na/glucose cotransporter.
What is transport stoichiometry?
The number of substrate molecules transported across a membrane in one complete cycle.
What is the stoichiometric coupling or the Na/glucose cotransporter?
1:1, both Na and glucose moving the same direction across the membrane
Define electrogenicity.
A property that describes the membrane potential difference as well as the substrate concentration difference
Define acidosis at the level of the ion transporter.
Na in for H out (excess of acid in blood)
Define alkalosis at the level of the ion transporter.
HCO3- out for Cl- in (excess of base in blood)
