EX1; Excitable Cells; Ions/Transport Flashcards
What three types of cells are considered excitable cells
neurons
sensory cells
most muscle cells
What categorizes an excitable cell
their physiologic functions rely critically on electrical events in their plasma membrane
What three things categorize a mechanism of cell-to-cell (intercellular) communication
very rapid
allow precise timing of signals between cells
allow complex patterns of communication between cells
This is a mechanism for sensing environmental changes (light, sound, temp, etc.)
stimuli from environment; electrical events in receptor cells
This is a mechanism for triggering intracellular events
electrical events in cells; intracellular changes that are either rapid or can accumulate over time
This is the activation to initiate an event
excitation
What are the three major components of excitation
extracellular fluid
intracellular fluid
membrane
What is the composition of extracellular fluid
primarily ions, proteins, and other molecules
high NaCl concentration
What is the composition of intracellular fluid
ions, much higher concentrations of proteins, other molecules
high KCl concentration
This allows cells to communicate with one another
the differences between the inside (KCl) and outside (NaCl) of cells
What is the composition of the membrane
phospholipid bilayer and proteins (equal amount), small (~5%) carbohydrates
This characteristic of cell membranes is essential to excitation
permeability
What is the permeability of a membrane to an ion an index of
the ability of the ion to cross the membrane; if the ions can readily cross the membrane, then the membrane has a high ion permeability
Changes in the permeability that are these two things are essential to excitation in cells
ion-specific
exquisitely timed
This is random diffusion down an electrical or concentration gradient; organic molecules or ions
simple diffusion
These type of molecules diffuse rapidly through the membrane which is 50% lipid; solubility in lipid is high
non-polar organic molecules; O2, CO2, fatty acids, steroids
Does the diffusion of non-polar organic molecules require energy?
No; no energy is required
These type of molecules cross membranes via channels which are proteins, often several subunits and generally specific for that molecule
ions
This is the amount of a substance crossing a surface per unit of time
flux
Diffusion between two compartments is always what
bi-directional; 1 to 2 and 2 to 1
This is the difference between the two unidirectional fluxes
net-flux
When net-flux is zero, the system is referred to be in a state of what
diffusion equilibrium
What are the two types of mediated transport
facilitated diffusion
active transport
This type of mediated transport has no energy requirement; a membrane protein serves as a carrier to translocate a molecule across a membrane
facilitated diffusion
This type of mediated transport requires energy; a molecule is bound to a transporter (pump) and it moves up the concentration and/or electrical gradient
active transport
What two things does energy effect involving active transport
the affinity of the transporter for the ligand on one side of the membrane more than the other
rate of transporter conformational change
What is the energy source of the primary active-transport model
hydrolysis of ATP
What is the primary-active transport model
hydrolysis of ATP
transporter becomes phosphorylated
changes affinity for solute (ligand)
increases transport rate
What is the secondary-active transport model
uses energy in ion concentration gradient across membrane
transporter has 2 binding sites
What three factors determine the rate of flux
number of transporters in the membrane
extent of transporter saturation
rate of transporter conformational change
What are three types of channels
ligand-sensitive (chemically regulated) voltage sensitive (voltage regulated) mechanosensitive
What are the three basic steps in mediated transport
ligand binds to transporter
transporter undergoes conformational change
ligand is released on other side of membrane
This is the bulk flow of water across a membrane; shrinking or swelling
osmosis
Water is polar and therefore diffused down its concentration gradient through these channels
aquaporins
This is the total solute concentration in a solutaion
osmolarity
1. 0 osmol = 1.0 mol solute
1. 0 mol NaCl = 2.0 osmols
What is the osmolarity of extracellular fluid
300 mOsm
300 mOsm of non-penetrating solutes; no change in cell volume is what type of solution
isotonic
< 300mOsm of non-penetrating solutes; cell swells, is what type of solution
hypotonic
> 300 mOsm of non-penetrating solutes; cell shrinks, is what type of solution
hypertonic
300 mOsm of non penetrating solutes plus penetrating solutes is what type of solution
isoosmotic
< 300 mOsm of non penetrating solutes plus penetrating solutes is what type of solution
hypoosmotic
> 300 mOsm of non penetrating solutes plus penetrating solutes is what type of solution
hyperosmotic
True or False
A solution can be hyper osmotic and isotonic at the same time
True
This is engulfment of fluid and particles from the extracellular space
endocytosis
This is engulfment of small particles with or without small volume of ECF; performed by all cell types
pinocytosis
This is engulfment of large particles or cellular debris; performed by specialized cells
phagocytosis
This is the export of material from a cell
exocytosis
What is the purpose of exocytosis
replaces membrane patches internalized through endocytosis
What is the mechanism of release of molecules synthesized within cells
secretion
