chemical disequilibrium
solutes are concentrated in either one compartment or the other
electrical disequilibrium
cations and anions are not distributed equally between the body compartments
osmotic equilibrium
water moves freely between the cells and extracellular fluid
osmosis
movement of water across a membrane in response to a concentration gradient
osmolarity
to compare solution concentrations, we express the concentration in terms of the number of particles (ions or intact molecules) per liter of solution, expressed as milliosmoles per liter
(mOsM)
tonicity
describes the cell volume change that occurs at equilibrium if the cell is placed in that solution
hypotonic
cells swell
hypertonic
cells shrink
isotonic
cell does not change size at equilibrium
nonpenetrating solutes
the relative concentrations of ? in the cell and in the solution determine tonicity
penetrating solutes
contribute to the osmolarity of a solution but not to its tonicity
bulk flow
pressure gradient moves a fluid along with its dissolved and suspended materials.
passive transport
transport that does not require the input of energy
diffusion
passive movement of molecules down a chemical (concentration) gradient from an area of higher concentration to
an area of lower concentration
equilibrium
net movement stops when the system
reaches ?, although molecular movement continues
structural proteins
membrane proteins that maintain cell shape and form cell junctions
membrane-associated enzymes
membrane proteins that catalyze chemical reactions and help transfer signals across
the membrane
receptor proteins
membrane proteins that are part of the body's signaling system
transport proteins
membrane proteins that move many molecules into or out of the cell
channel proteins
form water-filled channels that link the intracellular and extracellular compartments
gated channels
regulate movement of substances through them by opening and closing, may be regulated by ligands, by the electrical
state of the cell, or by physical changes such as pressure
carrier proteins
never form a continuous connection between the intracellular and extracellular fluid. They bind to substrates, then
change conformation.
facilitated diffusion
protein-mediated diffusion, it has the
same properties as simple diffusion
active transport
moves molecules against their concentration gradient and requires an outside source of energy
primary active transport
transport where energy comes directly from ATP
secondary active transport
transport that uses the potential energy stored in a concentration gradient and is indirectly driven by energy from ATP
glucose transporter (GLUT)
example of a transporter that uses facilitated diffusion; moves glucose into and out of the cell depending on concentration gradient
Na+ K- ATPase
most important primary active transporter
sodium glucose transporter (SGLT)
example of a secondary active transporter
specificity
ability of a transporter to move only one molecule or a group of closely related molecules
competition
related molecules may compete for a single transporter
saturation
occurs when a group of membrane transporters are working at their maximum rate
phagocytosis and endocytosis
two processes by which large macromolecules and particles are brought into cells
exocytosis
process by which material leaves cells; vesicle membrane fuses with the cell membrane before releasing its contents into the extracellular space; requires ATP
membrane recycling
vesicles that come into the cytoplasm by endocytosis are returned to the cell membrane
receptor-mediated endocytosis
ligands bind to membrane receptors
that concentrate in coated pits or caveolae
clathrin or caveolae
in receptor-mediated endocytosis, ligands bind to membrane receptors that concentrate in
apical and basolateral surfaces
where different membrane proteins are found on transporting epithelia; this polarization allows one-way movement of molecules across the epithelium
paracellular
molecules cross epithelia by moving between the cells
transcellular
molecules cross epithelia by moving through the cells
transcytosis
process by which large molecules cross epithelia; includes vesicular transport
electrical gradient
although the total body is electrically neutral, this is created when diffusion and active transport of ions across the cell membrane, with the inside of cells negative relative to the extracellular
fluid
resting membrane potential difference
electrical gradient between the extracellular fluid and the intracellular
fluid
electrochemical gradient
movement of an ion across the cell membrane is influenced by
equilibrium potential
membrane potential that exactly opposes the concentration gradient of an ion