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What is the osmolarity of ECF and ICF?

300 milliOsmoles


What happens to a cell with the osmolarity of the ECF is too low?

H20 will rush into the cell and the cell will lyse


What happens to a cell with the osmolarity of the ECF is higher than that of the cell?

H20 will rush out of the cell and the cell will shrink


Two types of active transport

primary and secondary


Describe the difference between primary and secondary active transport

Primary active transport is pumped against a concentration gradient with a direct use of energy; secondary transport is an indirect use of energy, and transport is driven by the concentration gradient of another molecule (Na+).
Co-and countertransport


Na+/K+ ATPase Pump:

Active transport;

ATP is used to pump 2 K+ ions into the cell for every 3 Na+ ions that are pumped out of the cell (occurs simultaneously).

Maintains a high intracellular K+ concentration and a low intracellular Na+ concentration


Two types of secondary active transport:

Co-transport and counter-transport


Difference between co-transport and counter-transport is:

In co-transport, the extra molecule (glucose) is transported across the membrane WITH the molecule that is driving the transportation (Na+). In counter-transport, the extra molecule (i.e. calcium) is transported in the opposite direction of the driver ion.


What is a membrane potential?

charge difference across the membrane

caused by diffusion



Every cell has a

resting membrane potential


Excitable cells...

are capable of sending electrochemical impulses at the membrane


What is the resting membrane potential of a large nerve cell?

-90 mV


What is mM concentration of the K+ and Na+ ions inside and outside the cell?

K+: 140 mM inside and 4 mM outside

Na+: 142 mM outside and 14 mM inside


If a membrane were permeable only to K+, then...

K+ would diffuse down its concentration gradient until the electrical potential across the membrane countered diffusion.


After diffusion across the membrane, the Nernst equation for potassium demonstrates the resting membrane potential would be

-94 mV


If the osmolarity of the interstitial fluid and plasma is the same (equal in and out of the vessel), what happens?

Diffusion is equal
No net movement of H20


Examples of primary transport

Na+/K+ ATPase Pump (2K+ into cell with every Na+ out of the cell)

Calcium Pump - pumping calcium out of cell membrane; present in sarcoplasmic reticulum and mitochondria

Hydrogen Ion Pumps - in the gastric glands of the stomach (parietal cells secrete H+); in late distal tubule and collecting duct of the kidneys




uses some type of energy