Lecture 2 Flashcards
1/3 of total body fluid
Extracellular fluid (ECF)
2/3 of total body fluid
Intracellular fluid (ICF)
What percentage of body weight is water?
55-65%
(T/F) Diffusion is a type of active transport
False
random movement/distribution of dissolved particles
Diffusion
Type of diffusion consisting of movement across lipid portion of membrane
Simple Diffusion
Type of diffusion consisting of movement through water filled membrane channel
Facilitated diffusion
Type of diffusion consisting of movement using carrier molecules
Facilitated diffusion
What does dn stand for in the diffusion rate equation?
number of molecules inside cell (mol)
What does dt stand for in the diffusion rate equation?
diffusion time (sec)
What does P stand for in the diffusion rate equation?
permeability constant for a particular molecule (cm/sec)
What does A stand for in the diffusion rate equation?
surface area of the cell membrane (cm2)
What does C stand for in the diffusion rate equation?
concentration of diffusing molecule (mol/cm3)
What does X stand for in the diffusion rate equation?
width of cell membrane (cm)
What does dn/dt stand for in the diffusion rate equation?
Diffusion rate
In the context of facilitated diffusion, what does Vmax mean?
The saturation constant
(when carrier proteins are at max capacity and can no longer transport additional solute)
In the context of the facilitated diffusion equation, what does K mean?
constant determining speed of saturation (mol/cm4)
Which type of diffusion reaches a plataeu in diffusion rate?
Passive or facilitated?
Facilitated
Movement of solute against its concentration gradient
Active transport (aka primary active transport)
Coupling one molecule to the transport of another. May be with or against the concentration gradient
Secondary active transport
This type of active transport is extremely important in the transport of molecules across the renal and intestinal epithelium
Secondary active transport
Net diffusion of water across a membrane
Osmosis
Movement of water driven by osmosis
Osmotic flow
Indication of force of pure water moving into a solution
with higher solute concentration
Osmotic pressure
(T/F) Clinically, Osmolarity = Osmolality
True
What is the equation for manually calculating osmolarity/osmolality?
2[Na+] + (glucose/18) + (BUN/2.8)
Calculate the osmolarity/osmolality:
Na = 140, Glucose = 90 and BUN = 12
289
This term is defined as the effect of osmotic solutions on cell volume
Tonicity
Solution that does not cause osmotic flow across membrane (normal saline, 0.9%NaCl)
Isotonic
Solution that causes osmotic flow into cell
• Patho Example: hemolysis (hemo-, blood + lysis, loosening)
Hypotonic
Causes osmotic flow out of cell
Patho example: crenation of RBCs
Hypertonic
Know how to read a Darrow-Yennet Diagram
Know it
For ions to move across a membrane, they must have 2 things available. What are they?
A gradient (driving force)
A path to move on (its almost impossible for ions to move across a lipid membrane)
In regards to ion movement, which type of gradient is more sensitive: Chemical or electrical?
Electrical
When the membrane potential is 0, or there is no electrical gradient, the configuration of ions is considered to have the highest _______
entropy
In regards to membrane potentials, what does Vm stand for?
Voltage across the membrane
The unit of measurement for a membrane potential, in other words the potential energy of an ion across the cellular membrane.
Vm (voltage)
Does a + Vm indicate a greater membrane potential than a - Vm?
No
(doesn’t matter if the charge is + or - because there is still charge which indicates polarity)
(T/F) In physiological cells, very small movements of ions induce big changes in the Vm
True
When discussing membrane potentials in physiology, the ________ compartment is always considered the reference.
intracellular
A ________ _________ arises when there is a difference in charge across the membrane
membrane potential
A(n) _________ Potential is the difference in charge (measured in millavolts (mV)) across the membrane that exactly offsets the energy in an ion’s concentration gradient
Equilibrium
(T/F) Equilibrium potentials are specific to each ion
True
Also called “Nernst Potential” or “Reversal Potential”
Equilibrium potential
What is the Nernst equation for calculating equilibrium potentials?
Eion = 61mV/z log ([Ion]o/[Ion]i)
z = # of valence electrons specific to the ion
If a K+ ion has an Ek = -94mV (this means that intracellularly a charge of -94mV is needed to counteract the + charge created from the small extracellular concentration of K+), What would theoretically happen to Ek if the extracellular K+ is increased to 20mM (this would be altering the Nernst equation components)?
Ek will decrease
(This question is testing knowledge of how the Nernst equation works. All ions have a specific, set equilibrium potential (Eion) for the normal concentrations in a homeostatic human body. Under pathologic conditions, or when altering EC concentrations, Eion can change due to concentration gradient changes.
(T/F) The farther away Vm is from Eion, the lesser the driving force is on that ion
False
(greater the driving force)
Which ion has the greatest driving force on it?
A. K+ at Vm of -62mV (EK = -94mV)
B. Na+ at Vm of -62mV (ENa = +62mV)
C. Cl- at Vm of -62mV (ECl = -62mV)
B. Na+
(greater difference between Vm & ENa)
A measure of the ability of an ion to diffuse across the membrane (due to open ion channels)
Conductance (gion)
the inverse of resistance
conductance (gion)
The higher the conductance of an ion, the _____ Vm will be to that ion’s equilibrium potential (closer or farther?)
closer
Why is K+ conductance (gion) so much higher than the other ions?
At rest, most ion channels that are open conduct K+ (these channels are called K+ leak channels)
(T/F) At rest, most ion channels that are open conduct K+
True
What is the resting membrane potential within a homeostatic human body?
-70mV
Why is the resting membrane potential highly negative?
The inside of the cell needs to be at a highly negative charge to repel the extremely low concentration of extracellular K+ ions that can easily pass through the open ion channels. This, paired with the fact that K+ has a much higher conductance than the other ions, lead to the resting membrane potential being closer to the K+ Nuerst potential (Eion).
(Remember under normal homeostasis, the extracellular K+ concentration is 4mM & intracellular K+ concentration is 140mM)
A complex of proteins that come together to form a water-filled pore that spans the cell membrane
Ion channel
Type of ion channel that open or close when when Vm changes
Voltage-gated
Type of ion channel that open or close when ligand binds to channel complex (receptors)
Ligand-gated
Na+ channels open and close very ______
quickly
K+ channels open ______, and many
types stay open long
slower
Ca++ channels open and close ______
slowly
Vm - Eion = ?
NDF (Net driving force)
This is the current when ions move through channels. Magnitude depends on NDF.
When channel opens, ionic current direction and magnitude depends on the ____ ______ ______
net driving force
Term for the Vm required for conformational change in
ion channel protein structure (aka Vm required to open an ion channel)
Threshold
When ________ is reached, action potentials are initiated
threshold
What is the threshold for all ion gates to open?
-50mV
The current Vm is -55mV. Are all ion gates open?
No
(Vm needs to be -50mV or lower (more positive))
The n-gate is in the channel for what ion?
K+
The m-gate and h-gate are in the channel for what ion?
Na+
Which is the slowest voltage gate channel?
n-gate
(for K+ ions)
(T/F) Leak channels are open at resting membrane potential
True
(T/F) Voltage-gated channels are open at resting membrane potential
False
Different ion channels are involved in different phases of the _____ _______
action potential
What molecule binds to the nicotinic receptor to exceed the threshold of the voltage-gated ion channels, therefore inducing a current and muscle contraction d/t increased Na+ & K+ permeability?
Acetylcholine
During an action potential, does K+ enter or leave the cell?
Leaves the cell
During an action potential, does Na+ enter or leave the cell?
Enters the cell
Responsible for muscle contraction
Action potential
Action potentials will be the same magnitude every time unless _________ potentials change
equilibrium potentials
Common cause of equilibrium potential changes
Extracellular ion concentration changes (aka serum ion levels)
During a cardiac action potential, does Ca2+ enter or leave the cell?
Enter
The ‘lethal’ ingredient in lethal injection is a bolus of KCl. Why is this lethal?
The extreme extracellular concentration of K+ Prevents the cell from depolarizing because K+ does not want to leave the cell. The cells cannot re-establish resting membrane potential.
