Chapter 5: Membrane Dynamics Flashcards
What are the two body fluid compartments?
- cells (ICF)
* ECF - fluid that surrounds the cells
the buffer between the cells and outside environment
ECF
what makes up the ECF?
interstitial fluid
blood plasma
what state are the ICF and ECF in?
osmotic equilibrium
brought about by the free movement of water between the ICF and ECF, so the fluid concentrations are balanced on the two sides of the membrane
osmotic equilibrium
an uneven distribution of solutes between ICF and ECF
chemical disequilibrium
how is disequilibrium maintained?
Living cells use energy to maintain this state of disequilibrium
- the charge difference between the ICF and ECF
* can create electrical signals
electrical disequilibrium
osmotic, chemical, and electrical disequilibrium are considered what?
dynamic steady states
what is the goal of homeostasis?
to maintain the dynamic steady states of the body compartments
- solvent for all living cells
* can move freely in and out of cells by water-filed ion channels and special water channels
water
special water channels
aquaporins
why do women have less water/kg of body mass?
due to more adipose tissue which occupies most of the cell volume
what is the cell membrane composed of and in what amounts?
ICF - 2/3
ECF - 1/3
plasma - minimal
what is extracellular fluid made of and what amounts?
plasma -25%
interstitial fluid - 75%
the movement of water across a membrane in response to a solute concentration gradient
osmosis
in which direction does water move?
Water moves to dilute the more concentrated solution or from areas where it (water) is in higher concentrations to where it (water) is in lower concentrations
when does osmosis stop?
when there is no more net movement
- pressure that opposes the movement of water into a compartment
- Measured in atmospheres (atm) or (mmHg
osmotic pressure
how can osmosis be measured quantitatively?
- osmotic pressure
* concentrations of solutions
- concentrations are expressed as this
* number of moles of dissolved solute/L of solution
molarity
the number of osmotically active particles per liter of solution (osmol/L = OsM, or milliosmoles/L =mOsM)
osmolarity
concentration expressed as osmoles of solute per kilogram of water
osmolality
why is osmolality used clinically?
because it is easy to estimate peoples body water content by weighing them
what does 1 pure L of water weigh?
1kg
how do you compare osmolarities of two solutons?
- isosmotic
- hyperosmotic
- hypoosmotic
the same number of solute particles per unit volume
isoosmotic
contains more particles per unit volume
hyperosmotic
contains less particles per unit volume
hypoosmotic
the ability of a solution surrounding a cell to cause that cell to gain or lose water
tonicity
what does osmolarity compare?
two solutions
what does tonicity compare?
solution and a cell
will osmolarity or tonicity tell you what happens to a cell placed in a solution?
tonicity
what does tonicity depend on?
depends on osmolarity and the nature of the solutes in the solution
- can enter and stay in a cell
* examples: urea & glucose
penetrating solutions
- *cannot cross the cell membrane, and therefore osmosis of water must occur for the solutions to reach equilibrium
- *tonicity depends on these
- example: NaCl
nonpenetrating solutes
cell higher conc. of nonpenetrating to solution.
hypotonic
cell lower conc. of nonpenetrating to solution.
hypertonic
cell and solution same nonpenetrating
isotonic
what kind of solutions are always hypotonic?
hypoosmotic
what does the tonicity of a solution describe?
describes the volume change of a cell at equilibrium
how do you determine tonicity?
by comparing nonpenetrating solute concentrations in the cell and the solution
where is net water movement?
into the compartment with the higher concentration of nonpenetrating solutes
- is a general form of biological transport
* caused by a pressure gradient where fluids flow from high pressures to low pressures
bulk flow
what are specific forms of transport?
diffusion, protein-mediated transport, vesicular transport
what are transport mechanisms across the membrane classified as?
active or passive
what is included in active transport?
- vesicular transport (ATP)
- exocytosis
- endocytosis
- phagocytosis
- protein mediated
- direct or primary active(ATPases)
- indirect or secondary active transport
concentration gradient created by ATP
indirect or secondary active transport
what is included in passive transport?
- simple diffusion
- protein mediated
- facilitated diffusion
- ionn channel
- aquaporin channel
- form of passive transport (kinetic energy inherent
* Molecules move from areas of higher concentration to areas of lower concentration (down a concentration gradient
diffusion
passive only) occurs with steroids, lipids, and small lipophilic molecules
simple diffusion
*helps us describe the movement of molecules across the membrane
*Diffusion rate increases when:
surface area, concentration gradient or the membrane permeability increase
Fick’s law of diffusion
- describes the flux of a molecule across the membrane
* Diffusion rate/surface area=conc. gradient X mem. Permeability
rearranged fick’s law
what is the equation for membrane permeability
membrane permeabililty = lipid solubility/molecular size
what factors affect rate of diffusion through membrane?
- lipid solubility
- molecular size
- concentration gradient
- membrane surface area
- composition of lipid layer
what are membrane proteins classified as?
classified based on structure and function
what do structural proteins do?
- create cell junctions
- connect membrane to cytoskeleton
- connect cell to extracellular matrix
what proteins are structural?
integral proteins
peripheral proteins
which proteins are classified as functional?
membrane transport
membrane enzymes
membrane receptors
moving molecules across membranes
protein-mediated transport
what are the two categories of protein-mediated transport?
channel proteins
carrier proteins
- (no binding site for ion) = rapid movement (millions of ions/sec) limited to small size molecules.
- create a water-filled pore
channel proteins
may be specific or may allow ions of similar charge and size pass
ion channels
what are the two groups of ion channels?
open channels (leak) gated channels (chemically gated, voltage gated, mechanically gated)
- (transporters) = slower movement (1000 to 1,000,000 mol/sec) can move larger molecules
- Open to one side of the membrane or the other, but never both
carrier proteins
what are the classifications of carrier proteins?
- uniport
- cotransporters
- symport
- antiport
transport one kind of molecule
uniport
transport more than one molecule at a time
cotransporters
transport more than one molecule at the same time in the same direction
symport
- transport more than one molecule at the same time in opposite directions
- exchangers
antiport
always down concentration gradient.
facilitated diffusion
- against concentration gradient (creates a state of disequilibrium
- requires energy, ATP
active transport
- uses ATP or some other energy source directly to transport substances( ATPases or pumps).
- example: sodium-potassium pump
primary active transport
- powered by a concentration gradient or electrochemical gradient created by primary active transport
- most driven by sodium
- energetically efficient way to bring molecules into a cell
secondary active transport
Na+, K+, ATPase, sodium potassium pump
antiport transport
Ca^2+, ATPase
uniport transport
H+, ATPase or proton pump
uniport
H+, K+, ATPase
antiport
what do carrier mediated transport (active & passive) demonstrate?
- specificity
- competition
- saturation
What are the components of specificity?
- GLUT1 (most cells)
- GLUT2 (liver& kidney)
- GLUT3 (neurons)
(each GLUT transporter has a higher binding affinity for different hexoses sugars)
competition
(cell can adjust the # of carrier proteins up or down to increase or decrease transport capacity)
saturation
brings glucose across cell membrane
GLUT transporter
a competitive
inhibitor that binds to the GLUT transporter but is
not itself carried across the membrane
maltose
transport can reach a maximum
rate when all the carrier binding sites are filled with substrate
saturation
is the movement of large macromolecules into and out of the cell
vesicular transport
what moves materials into and out of the cell in vesicular transport?
- into the cell
- phagocytosis
- endocytosis
- out of the cell
- exocytosis
engulfs bacterium and other large particles by pushing out membrane surface
phagocytosis
occurs more frequently, membrane surface indents, and vesicles formed are much smaller than phagocytosis
endocytosis
nonselective endocytosis
pinocytosis
highly selective endocytosis
receptor-mediated endocytosis
- a process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane
- energetically expensive
exocytosis
- absorb (lumen to ECF) or secrete (ECF to lumen) materials must transport substances inward across the membrane on one side of the cell and outward across the membrane on the opposite side
- each side must possess different transport systems
epithelial cells
what is the structure of epithelial cells?
- polarized
- apical membrane (muscosal)
- basolateral membrane (serosal)
how does movement across epithelium occur?
- paracellular transport
* transcellular transport
can change tightness, ex. claudins
paracellular transport
can alter their permeability by inserting or withdrawing membrane proteins
transcellular transport
what are the steps of transepithelial absorption of glucose?
- Na+ glucose symporter brings glucose into cell against its gradient using energy stored
- GLUT transporter transfers glucose to ECF by facilitated diffusion
- Na+, K+, ATPase pumpes Na+ out of the cell, keeping ICF Na+ concentration low
uses vesicular transport to move large molecules across the membrane
transcytosis
what is an example of transcytosis?
infants absorb maternal antibodies from breast milk, infant intestinal epithelium to ECF)
How does transcytosis occur across the capillary endothelium?
- Plasma proteins are concentrated in caveolae, which undergo endocytosis and form vesicles
- vesicles cross the cell with help from the cytoskeleton
- vesicle contents are released into interstitial fluid by exocytosis
arise due to membrane potential
electrical driving forces
the difference in electrical potential (form of potential energy) or voltage that exists across the membranes cells
membrane potential
how is a membrane potential built?
The concentration gradient creates an electrical gradient, so in combination the electrical and concentration gradients create the electrochemical gradient
what is the cell membrane potential like at the start?
When we begin, the cell has no membrane potential:
The ECF (composed of Na+ and Cl– ions) and the ICF
(K+ and large anions, A-) are electrically neutral
How is the membrane potential started?
- insert a leak channel for K+
- K+ starts to move out of the cell down its concentration gradient
- The A- can’t follow K+ out of the cell cause the cell is not permeable to A-
- additional K+ leaves the cell
- the negative charge inside the cell begins to attract ECF K+ back into the cell: an electrical gradient in the opposite direction from the concentration gradient
For any ion, the membrane potential that exactly opposes a given concentration gradient is…
equilibrium potential
how do you calculate equilibrium potential?
Nernst equation
Eion=61/zlog([ion]out/[ion]in) where z is the charge of the ion
when is the nernst equation used?
used for a cell that is freely permeable
to only one ion at a time
electrical gradient seen in all living cells
resting
a form of stored energy
potential
determined by the combined contributions of the concentration gradient and the membrane permeability for each ion (Goldman equations)
resting membrane potential
what are important ions in resting membrane potential?
potassium
sodium
sodium-potassium pump
more permeable to the cell than sodium. (30 ICF to 1 ECF)
potassium
less permeable to the cell. (1 ICF to 15 ECF)
sodium
(3 sodium out, 2 potassium in) maintains resting membrane potential
sodium-potassium pump
what happens if the membrane potential becomes less negative that the resting potential?
the cell depolarizes
what happens if the membrane potential becomes more negative than the resting potential?
the cell hyperpolarizes
when the cell becomes less negative.
depolarization
when the cell becomes more negative.
hyperpolarization
what happens when a beta cell is at rest?
. The KATP channel is open, and
the cell is at its resting membrane potential
what happens when a beta cell secretes insulin?
Closure of KATP channel
depolarizes cell, triggering exocytosis of insulin
resting cell membranes are most permeable to what?
K+
what happens to the membrane potential of a cell that suddenly becomes more permeable to Na+?
it becomes more positive
