Diffusion and Transport Flashcards
What are the main body fluid compartments?
- Intracellular
- Extracellular
- Transcellular
Transcellular fluid includes fluid in transit in the lumens of the intestinal tract, lungs, kidneys, and bladder.
What is the predominant cation in the extracellular fluid compartment?
Na+
In contrast, K+ is the predominant cation in the intracellular compartment.
What does Fick’s law for simple diffusion state?
The net flux (J) is equal to the permeability coefficient (P) times the concentration gradient (ΔC).
J = PΔC
What is the equation for the rate of flux of a substance across a barrier?
J = PA(CA – CB)
Where J is the net rate of diffusion, P is permeability, A is surface area for diffusion, CA is concentration in solution A, and CB is concentration in solution B.
What type of molecules require carrier-mediated transport to cross cell membranes?
Larger, polarized (hydrophilic) molecules
Examples include glucose and amino acids.
What is the role of insulin in facilitated diffusion?
Insulin enhances facilitated diffusion of glucose by adding more transporters (GLUT4).
Basal transporters are GLUT1.
What is primary active transport?
Transport of ions across a cell membrane against their concentration gradients using energy from ATP.
Example: Na+-K+-ATPase pump.
What is the function of the Na+-K+-ATPase pump?
Transports 3 Na+ out of the cell and 2 K+ into the cell against their concentration gradients.
This pump is present in nearly all cells.
What is the Nernst Equation used for?
To calculate the equilibrium potential (E) for an ion based on its concentration gradient.
E = (60/z)mV log (Co/Ci), where Co and Ci are the concentrations outside and inside the cell, respectively.
True or False: The movement of an ion across the cell membrane is influenced by both electrical and chemical gradients.
True
What are the two types of secondary active transport?
- Symporter (cotransporter)
- Antiporter (exchanger)
Symporters carry both Na+ and substrate in the same direction, while antiporters move Na+ in one direction and substrate in the opposite direction.
How do ion-selective channels function?
They allow specific ions to diffuse across cell membranes, often regulated by various factors such as membrane potential and ligand binding.
Example: K+-selective channels.
Fill in the blank: The driving force for ion movement across a cell membrane is influenced by the _______.
membrane potential (Vm)
What is the effect of membrane potential on Na+ and Cl- ions?
Positive ions (Na+) are attracted into the cell, while negative ions (Cl-) are repelled from entering the cell.
What happens to the transport rate in carrier-mediated transport as substrate concentration increases?
It saturates to a maximal rate (Jmax).
What is the concentration of Na+ in the extracellular fluid compared to intracellular fluid as mentioned?
Extracellular fluid: 145 mM, Intracellular fluid: 10 mM.
What is the role of Ca2+-ATPase pump?
Pumps Ca2+ out of all cells against a concentration gradient to maintain low cytoplasmic Ca2+ levels.
What are the two primary types of transport across cell membranes?
Simple diffusion and carrier-mediated transport
What drives simple diffusion across a membrane?
Concentration gradient
What is Fick’s Law related to?
It describes the rate of diffusion, stating that it is proportional to the concentration gradient
What types of molecules typically pass through membranes via simple diffusion?
Small, uncharged molecules like oxygen and nitric oxide
How do glucose and amino acids typically enter cells?
Through carrier-mediated transport due to their size and polarity
What is facilitated diffusion?
Passive transport of molecules across a membrane through transmembrane proteins
What limits facilitated diffusion?
Saturation of carrier proteins in the membrane
