Lecture 3 Flashcards
What is the osmolarity of ECF?
300 milliOsmoles
What happens to a cell with the osmolarity of the ECF is too low?
cell will lyse
What happens to a cell with the osmolarity of the ECF is higher than that of the cell?
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+).
Na+/K+ 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).
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
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
