CH 5: Membranes Flashcards
Interstitial fluid
Should have little to no proteins
Compartments in body
Are in a state of chemical disequilibrium
- ultimately what the body wants
Plasma membrane
Control of material exchanges
- mediation of cell-environment interactions
- membrane permeability/impermeability
Diffusion
The movement of a substance from an area of high substance con. to an area of low substance con. due to RANDOM THERMAL MOLECULAR MOTION
NO ENERGY, HAPPENS NATURALLY
Diffusion can occur in?
- air
- solids
- liquids
Absolute zero
Molecules no longer move
- never rlly reached
- bodies constantly are using diffusion
- randomness net of diffusion
Homeostasis is?
Chemical disequilibrium
Rate of diffusion: factor & relationship
Temp is directly proportional
Rate of diffusion: factor & relationship
Molecular weight is inversely proportional
Rate of diffusion: factor & relationship
Surface area is directly proportional
Rate of diffusion: factor & relationship
Gradient is directly proportional
Rate of diffusion: factor & relationship
Membrane permeability is directly proportional
Rate of diffusion: factor & relationship
Distance is inversely proportional
- due to diffusion using NO ENERGY
Flux
Amount of a substance that crosses a defined surface area PER UNIT TIME
Diffusion equilibrium
State in which the diffusion fluxes in opposing directions are equal, resulting in a NET FLUX OF ZERO
Methods of passage through a lipid bilayer
- Passive transport
- Active Transport
Passive transport
NO ENERGY INPUT
2 ways:
1. Diffusion directly thru the membrane
2. Diffusion thru membrane protein
Diffusion through membrane protein
- Channels
- Carrier-mediated transport
Other types of channels are gated/regulated by the cell
- Stimulus-gated
- Voltage-gated
- Mechanosensitive
*Open for milliseconds
Stimulus-gated
Respond to ligand binding
- closes channel when ligand dislodges
ex: neurotransmitters, hormones
Voltage-gated
Respond to changes in voltage (membrane potential)
ex: action potentials
Mechanosensitive
Respond to physical distortion
ex: tactile (receptors in our skin)
Channels can be very specific…
Can be:
- anion only
- cation only
- even specific for a particular ion
Active Transport
REQUIRES ENERGY
2 diff ways:
1. Primary active transport
2. Secondary active transport
3. Vesicular transport
Primary active transport
- utilizes transmembrane protein (a physical pump)
- non-covalent bonds are no longer sufficient…use covalent bonds (PO4-)
- 4 types of ion ATPase (primary active)
4 types of ion ATPase (primary active)
- Na+ – K+
- Ca++
- H+
- H+ – K+
Sodium Potassium pump
maintains membrane potential
Calcium pump
Plasma membrane & organelles
- cardiac muscle cells & smooth ER
Hydrogen pump
Mitochondria & plasma membranes
- kidney
Hydrogen Potassium pump
Plasma membranes
- stomach
Secondary active transport
Using gradients from primary active transport
Vesicular transport
Uses ATP
- looking at > 1 molecule “much more magnified”
- cytoskeleton uses ATP
- moves BIGGER substances (hormones/neurotransmitters)
2 diff types:
1. Endocytosis
2. Exocytosis
Endocytosis
- Phagocytosis “cell eating”
- Pinocytosis “cell drinking”
Exocytosis
Contents of cell are released
Osmosis
The movement of water from an area of high water (low solute) concentration to an area of low water (high solute) concentration due to random thermal molecular motion
- diffusion of water
- membrane permeability is essential
*all factors that apply to diffusion also apply to osmosis
Osmotic pressure
Measurement of potential force w/in osmosis
- amount of force needed to oppose osmosis
Osmolarity
Concentration of a solution expressed as number of solutes per liter (REGARDLESS OF SOLUTE TYPE)
- moles = 6.022 x 10^23 molecules/atoms
(Avogadro’s number)
Hypotonic
A solution that has lower concentration
Hyperosmotic
A solution that has higher concentration than another solution
- exert greater osmotic force
Isoosmotic
Solutions that have equal concentration
Tonicity
Describes the volume change of a cell placed in a solution
- very specific
- must refer to 2 things
Tonicity must refer to 2 things…
- Talk ab a cell & compare to a cell
- Must be dealing w/ NON-PENETRATING solutes
Crenate
“shrinking”
RBC normal shape
Biconcave disc
Basic principles of electricity
How things get across a membrane
Opposites attract…
Oppositely charged particles come together to perform work
- separating (+) charge from (-) charge REQUIRES ENERGY
Electricity: ECF vs ICF
- ECF is more positive
- ICF is more negative
Electrical potential (E)
Voltage difference b/t 2 points
“separation of charge”
Voltage (V)
Measure of potential (separated charge) to do work (units of potential)
“how much power you have to work with”
Membrane potential (Vm or Em)
Voltage difference b/t the inside & outside of the cell
Current (I)
Movement of an electrical charge
- can be H, Na, Etc.
Ohm’s law
I = E/R (electrical potential/resistance)
Resistance
Is membrane permeability
What happens to a cell in a hypertonic solution?
Cell shrinks
Crenates
What happens to a cell in a hypotonic solution?
Cell swells
What happens to a cell in an isotonic solution?
Cell doesn’t change size
Normal intracellular concentration
300 mOsm
- NON-penetrating solutes
Membranes are not necessarily permeable…
But facilitated through CHANNELS & carriers
g = conductance
= 1/R
then,
I = gE
Equilibrium potential (Ex)
The voltage that would exist across a membrane if it were exclusively permeable to one ion in which a voltage force is equal & opposite to concentration force
- if membrane potential is at equilibrium potential, then there is no driving force for that ion
- as membrane potential deviates from Ex, then an increased driving force is created
Net flux (driving force) is present if not at?
Equilibrium potential
- one gradient is larger than the other
Separation of charge
Aka gradient
- more gradient, more current (flow of ions)
Normal physiological concentration: Na+
ECF: 150 mOsm
ICF: 15 mOsm
Ratio: 10:1
E: +60 mV
- body will never reach +60…there will always be a gradient
Normal physiological concentration: K+
ECF: 5 mOsm
ICF: 150 mOsm
Ratio: 1:30
E: -90 mV
- skeletal muscles will reach -90
Normal physiological concentration: Cl-
ECF: 110 mOsm
ICF: 7 mOsm
Ratio: 15:1
E: -70 mV
Homeostasis fluctuates around?
Normal physiological values of equilibirum potential
Nernst Equation
Ex = RT/zF * log [X]o/[X]i
- o = outside cell
- i = inside cell
R
Universal gas constant
(8314.9 J/KgmolK)
T
Absolute temperature (K)
F
Farday’s number
(96,485 C/mol of charge)
z
Charge of ion
(+1/-1)
For sodium at normal body temp…
RT/zF simplifies to the constant 61
By convention, outside of the cell equals?
zero
Inside of the cell is stated as?
Excess charge relative to the outside of the cell
*whatever # we are using is referring to INSIDE the cell
At rest, all cells have _______ membrane potential
Negative
Resting membrane potential
Voltage difference between the inside & outside of the cell when the cell is not active
(-70 mV in neurons)
- “at rest”
- will vary for different cell/tissue
Separation of charge
Electrical gradient
- the greater the separation of charge, the larger the electrical gradient
- less separation of charge, the smaller the electrical gradient
Vm = 0mV
No separation of charge
Changes happening in electrical gradients are significantly relative to changes in?
Concentration gradient
“Relative distribution of ions”: 2 questions
- Is the membrane PERMEABLE?
- Is there a GRADIENT?
—-opposites attract
Membrane potential (Vm) is influenced by?
- Permeability of membrane to an ion
- Ion gradient
Proportionate ion flux maintains what?
Steady-state
Ion flux and membrane potential play an important role in?
Cellular & organismal function
- Changes in Vm cause cellular responses in excitable & non-excitable tissues
The beta cells of pancreas produce & secrete what?
Insulin
Insulin is required by most cells to absorb what?
Glucose from the plasma (and interstitial fluid)
How can beta cells monitor blood glucose concentrations?
Through changes in membrane potential
Glucose range (normal)
70-100
