chapter 6 Flashcards
2 compartments for fluid
- intracellular fluids (67% of all fluid)
- extracellular fluids
extracellular fluids broken down
- plasma (20-25% of ECF)
- interstitial fluid (75-80% of ECF) the fluid in the ECM outside blood vessels
- -waste, chemicals, nutrients all move out of cells into the ECF
Simple diffusion
- Lipid soluble molecules
- Ions through channel proteins
- Water
Carrier-mediated transport
- Facilitated Diffusion
- Active transport
Diffusion
Random movement of molecules from regions of HIGHER concentration to regions of LOWER concentrations
what determines movement of molecules (3)
- Determined largely by the concentration difference
- Distances beyond 100 µm will mean the diffusion time is too long to be effective
- – Moving O2 from lungs to blood crosses epithelial cells 1-2 micrometers thick
- Molecules are always moving
diffusion rate if affected by (4)
- concentration difference
- membrane permeability to each molecule (neural membrane at rest is more permeable to K+ than Na+)
- temperate
- surface area
semipermeable
some materials allowed through, others not
non polar molecules diffuses ______ (slowly/rapidly)
rapidly
-Lipophilic (lipid-loving) substances move through easily.
Ex: Steroid hormones, O2, CO2, fatty acids
Polar molecules and hydrophilic (water-loving) ______ (do/do not) diffuse readily through the membranes without the help of special molecules and structures.
do not
a simple arficial lipid bilayer is practically _______ to ions
impermeable ; not allowing fluid to pass through
what do ion channels do
-Integral membrane proteins form channels through which ions can freely diffuse according to their gradient.
-These small channels can be specific
and only allow the diffusion of
certain ions at certain times.
what is osmosis
the net diffusion across a membrane
- solvent=water
- solute=any molecules
what are aquaporins and why do we need them
Movement of water facilitated by channel proteins called aquaporins
-water may get stuck in hydrophobic fatty acids without these
example of aquaporins
Epithelial cells of kidneys have LOTS of aquaporins, varying slightly.
Why do Kidneys need aquaporins?
for their role in regulation of plasma
what is the net movement of water
The net movement of water is from the side with more water (diluted, low solute) to the side with less water (concentrated, high solute).
–water will move faster with a higher concentration
a difference in concentration of solutes exists on either side of the membrane (t or f)
true
–membrane must be impermeable to the solute making the water move
Molarity (1M)
Moles solute/ Liter Solution
- Glucose and NaCl each weigh different grams, each dissolved in 1 Liter water separately
- Glucose has 180 grams dissolved in 1 L water, NaCl has 58.5 grams dissolved in 1 L water. There is more water used to make the 1 molar solution of NaCl
Molality (1m)
moles solute/kilogram solvent
- Use the weight and dissolve in exactly 1 Liter water, amount of water does NOT change
- Depends on the number of particles present in the solution
what is osmolality
the total molality of a solution which combines all the molecules in a solution
- osmolality is a number of solutes in the plasma
- physiology is concerned when the ratio of solutes to water changes
osmotic pressure
- can prevent osmosis
- When pure water enters a cell, the cell expands. Pure water has a osmotic pressure of zero. As more and more water comes into the cell and it expands, it will burst
isotonic solutions
have the same concentration of nonpenetrating solutes as normal plasma.
solutions isosmotic to plasma
- 0.9g NaCl/100mL water –normal saline
2. 5% dextrose– 5g glucose/100 mL water
hypo-osmotic/hypotonic
- solutions have a lower solute concentration, Lower osmolality.
- the cell will lyse (swell)
hyper-osmotic/hypertonic
solutions have a higher concentration than the cell
-the cells will crenate (shrink)
mediated transport via trasport/carrier proteins involves
- Conformational changes in transport proteins each time a molecule crosses
- Makes the process much slower and moves fewer ions compared to simple diffusion
mediated transport; facilitated diffusion
- No energy is required, channel is specific and movements are diffusional
- High–>Low (down the gradient)
-Ex: Glucose: Polar molecule that needs a transporter
Transporters may be inserted in the membrane as needed
Mediated transport; active transport
- against the gradient
- Involves the use of energy (ATP) to “pump” a molecule against its gradient
- Molecule specific and limited by saturation and the rate of conformational change.
2 types of active transport based on source of energy
- primary=uses ATP; pumps is an enzyme
2. Secondary=uses electrochemical gradient across membrane
Primary active transport
- Na/K-ATPase pump
- moves 3 Na out and 2 K in
- both against the concentration gradient
- maintains distribution of high intracellular K and low Na
- found in every cell
- shape and affinity of transport changes
why the pump in primary active transport? (3 )
- Na+ gradients (Na+ is used in secondary transport)
- Prevents constant osmosis
- Maintain membrane potential - Counter K + leaks
Secondary active transport
- The movement of a molecule (Na+) with its electrochemical gradient is coupled with the movement of a second molecule (ex. glucose)
- Requires that proteins have 2 binding sites (one for each molecule)
- Transported molecules can be moved in the same or opposite directions
- Primary AT will move Na+ back out of the cell maintaining the gradient
- Na is moving down its gradient but glucose is moving up its gradient
- countertrasport??
Membrane Potential (Em)
An unequal distribution of charges exists across the membrane, leaving the inside cell negatively charged compared to the outside
- why?
1. permeability (higher K+)
2. Na+/k+ pump
3. Negative molecules in cell (anions that cannot penetrate the membrane)
Membrane potential: K+
- K+ accumulates at high concentrations in the cell because—
- The Na+/K+ pumps actively bring in K+
- The membrane is very permeable to K+
- Negative anions inside the cell attract cations outside the cell.
membrane potential can be measured in ______
volts
membrane potential: K+
-The concentration of K + in a normal cell is150mM K+ inside and 5mM K+ outside.
-The resulting potential difference measured in voltage would be the equilibrium potential (EK) of -90mV.
This means the inside has a voltage 90mV lower than the outside.
membrane potential Na+
- Sodium is important for establishing membrane potential.
- The concentration of sodium in a normal cell is 12mM inside and 145mM outside.
- To keep so much sodium out, the inside would have to be positive to repel the sodium ions.
- The equilibrium potential is +66mV
- The membrane is less permeable to Na+, so the actual membrane potential is closer to that of the more permeable K+.
Resting Membrane potential ;; in most cells the resting potential is between _____ and _____
- membrane is most permeable to K+, therefore a change in K+ will have the greatest effect
- K: -90 mV
- Na: +66 mV
-in most cells the resting potential is between -65mV and -85mV (neurons are usually as -70mV)
nernst equation is used to calculate _________ based on ________
equilibrium potentials ; concentration ratios
nearst equation
(61/1)log(concentration outside the cell/concentration inside the cell)
2 ways a cell moves away from resting potential
permeability, concentration
how does a cell move away from resting potential; permeability
A change in the permeability of the membrane for any ion will change the resting potential.
–Ex. When a neuron sends an impulse, it changes the permeability of Na+, driving the membrane potential closer to the equilibrium potential for Na+.
how does a cell move away from resting potential; concentration
A change in the concentration of any ion inside or outside the cell will change the resting potential.
–K+, Na+, Ca2+ and Cl− contribute to the resting potential. K+ the most!
paracrine
cell signaling
-cell to cell
synaptic
cell signaling
-neurons have a synapse communication must cross
endocrine
cell signaling
-hormones regulate via the bloodstream (hormones look for their specific active site on a protein)
receptor proteins
targets that are specific to a signal, targets may be on the cell membrane or inside the cell
secondary messengers
Regulatory molecules may bind to receptors on the cell membrane but then require a second action to carry out the function of the binding
secondary messenger example
Ex. cAMP: cyclic adenosine monophosphate
- Norepinephrine binds at receptor in membrane
- G-proteins activate adenylate cyclase Enzyme in membrane to produce cAMP
- cAMP activates protein kinase.
- Protein kinase activated carries out the action intended, opening ion channels
G proteins
G-proteins are made up of 3 subunits – alpha, beta, and gamma
- Regulatory molecule binds, alpha dissociates from beta and gamma
- One of the subunits travels through membrane to bind to effector (enzyme or protein channel)
- Alpha splits GTP to GDP and P and the subunits reaggregate around the receptor again
