Membrane Flashcards
Permeability differences between capillaries and cell membranes
Capillaries have increased permeability and cell membranes have decreased permeabilities
Are proteins found in the interstitial fluid?
No. If proteins are found here, pathology is likely in the plasma. Albumin is found in the interstitial fluid.
Ionic composition in the plasma
Mostly Na+ and Cl-.
Small amounts of HCO3- and proteins.
Ionic compounds in the interstitial fluid
Mostly Na+ and Cl-
Small amounts of HCO3-
Albumin
Ionic compounds in the intracellular fluid
High levels of K+, Miscellaneous phosphates, and proteins Small amounts of Na+, HCO3- and Cl-
What ionic compound is found in the plasma and intracellular fluid but not the interstitial fluid?
Proteins
Why should Ca2+ be maintained at a low level in the cell but not outside the cell?
Needs to be at low levels inside the cell. If calcium is high intracellularly, it can be damaging.
Homeostasis chemical signals control and regulate
Absorption, secretion, and regulation by negative and positive feedback. The majority of reactions inside the cell are negative feedback.
Primary example of positive feedback
Head of fetus pushes against cervix, nerve impulses from the cervix are transmitted to the brain, the brain stimulates the pituitary gland to secrete oxytocin, oxytocin is carried in the bloodstream to the uterus, oxytocin stimulates uterine contraction and pushes fetus towards cervix.
Dehydration occurs when
There is a loss of water in the extracellular fluid, resulting in an increased level of NaCl. This causes water to flow out of the cell, into the extracellular fluid and decreases the volume of all cells.
Edema
Increase in rate of fluid filtration out of a capillary bed exceeds the ability of lymphatic to return to vascular system.
Symptoms of heat stroke/dehydration
Confusion/disorientation
Do elderly patients and babies dehydrate easily or not?
They both dehydrate easier. The amount of water in an elderly person (above 60) is much lower than an adult. If pt is taking a diuretic (urinates more often) they will also loose water quicker.
Babies have much smaller reservoirs of water than adults do. Therefore, it is depleted quicker.. especially when battling illnesses that deplete water rapidly.
In what direction can lipids of a phospholipid bilayer move
Lipids can move horizontally, but cannot move vertically to the other side of the phospholipid bilayer.
Terminal sugars on lipid bilayer membrane
Anacetylglucosamine or sialic acid. both have negative charge.
Factors in determining the resting membrane potential
Water, ions, phospholipid membrane, and proteins. Also, movement across the membrane also determines the potential.
Examples of molecules that the lipid bilayer is permeable to
Oxygen, CO2, steroids.
Permeable to water as it flows through aquaporins.
Gradient levels across the plasma membrane
O2, Na+, CO2 and K+
There is more O2 and Na+ outside the cell
There is more CO2 and K+ inside the cell.
(This is what creates the electrochemical gradient)
Diffusion
Random mixing of particles in a solution as a result of the particle’s kinetic energy.
Molecules move away from an area of high concentration to an area of low concentration. Temperature, concentration, size, surface are and distance all have an effect.
- Increase temp, increase diffusion
- Smaller the molecule, faster the diffusion EXCEPT large lipophilic molecule will diffuse through membranes quicker than small polar molecules
- Increase surface area/volume, increase diffusion
- Distance and diffusion are inverse. Smaller the distance, quicker the diffusion.
Osmosis is facilitated by what
Channel proteins called aquaporins. Aquaporin expression and insertion into the membrane varies among cell types. These are especially important in the kidney.
Osmolarity
The total solute concentration of a solution
1 osmol is equal to
1 mol/liter of solute particles
Ex: a liter of solution containing 1 mol of glucose has a concentration of 1 osmol per liter where a liter of solution containing 1 mol of NaCl contains 2 osmol of solute per liter.
Higher the osmolarity, ___ the water concentration
Lower
Brownian motion
Random mixing of particles in a solution as a result of the particles kinetic energy.
The greater the difference in concentration the ___ the rate of diffusion
Greater
An increase in surface area ___ the rate of diffusion
Increases
Equilibrium has been reached when
The molecules are evenly distributed
Diffusion rate increase in proportion to the
Square of the distance over which the molecules diffuses
The major factor limiting diffusion across a membrane is
The hydrophobic interior of its lipid bilayer. Molecules are a thousand to a million times slower than the diffusion rates of the same molecules through a water layer of equal thickness.
Ions such as ____ all use specific protein channels to diffuse into and out of cells
Na+, K+, Cl-, and Ca2+
Channels are a type of ___ membrane proteins that span the lipid bilayer
Integral. Channels can be single proteins, but are often aggregations of multiple proteins
Specificity of a protein channel is determined by
Pore size, charge of the channel, and binding sites.
Two types of ion channels
- Leakage (non-gated) channels are always open. Ex: nerve cells have more K+ leakage channels than Na+ leakage channels. As a result, membrane permeability to K+ is higher, which is why the resting membrane potential of -70mV is in the nerve tissue.
- Gated channels open and close in response to a stimulus, which results in neuron excitability.
Ex: voltage, ligand and mechanically gated channels
How do gated channels open
Voltage gated channels open in response to a change in voltage.
Ligand-gated channels open and close in response to particular chemical stimuli (hormone, neurotransmitter, ion) and a confirmation change.
Mechanically gated channels open with mechanical stimulation
Ligand and mechanically gated channels are very specific.
Tetrodetoxin (TTX)
Irreversible channel blocker produced by some pufferfish. Prevents the opening of voltage gated na+ channels, not allowing nerve impulses to pass.
Some anesthetics use a reversible channel blocker such as novocaine or lidocaine.
How many families of K+
6 different families, with several members in each family.
What is the nernst equation used for
Used to determine the equilibrium potential for an ion.
Nernst equation formula
E ion= 61 milli volts/ valence x log(ion in/ion out)
What is valence in the nernst equation
Valance is usually 1, but Ca2+ and Mg2+ have 2.
Cl- has -1
3 forms of passive transport
Diffusion straight through the lipid bilayer. Moves substances down their concentration gradient with only their kinetic energy.
Diffusion transport uses a channel
Facilitated diffusion- moves materials with the help of a transporter protein. Ex: moving glucose.
Mediated-transport system
Carriers bring molecules into and out of cells by conformation changes. Transporters can be saturated, meaning that there is a maximum flux of molecules that can be reached.
Two forms of active transport
- Primary active transport. The direct use of ATP to move molecules against their concentration gradient.
- Secondary active transport: The use of an electrochemical gradient across a membrane to drive the process in a secondary active transport. One molecule piggy backs with the other. (can be symporters or counter transporters)
what primary active transporter is found one very cell?
The Na+/K+ ATPase primary active transport. helps establish and maintain the membrane potential of the cell.
Another major primary active transport protein found in most cells are
Ca2+ase and _____
How many Na+ and K+ molecules are pumped in/out of the cell per ATPase turn
For every 3 Na+ transported into the cell, 2K+ molecules are pumped out of the cell.
This is pumping against the concentration gradient
What are the five types of Ca2+ channels?
L T N P Q
L is the most important clinically
How does secondary active transport occur?
Distinguished from primary active transport by its use of an electrochemical gradient across a plasma membrane as its energy source.
Transporters that mediate this have two binding sites, one for an ion (ex: Na+)and another for the co-transported molecule (ex: glucose)
Two forms of secondary active transport
Symporters: move molecules in the same direction
Countertransporters: move molecules in opposite directions
non penetrating solute
Solutes that cannot caress the membrane unassisted
Isotonic, hypotonic and hypertonic
Iso- same concentration of non penetrating solutes
hypo- have a lower concentration of non penetrating solutes
Hyper- have a higher concentration of non penetrating solutes
Normally, the osmotic pressure of the inside of the cell is ____ to the fluid outside the cell
equal
Paracellular transport
Diffusion through the paracellular pathway. Limited by the presence of tight junctions between adjacent cells. The tight junctions form a seal around the apical end of the epithelial cells. The amount of diffusion is limited by the tightness of the junctional seal.
Sometimes, bacteria or concussions can open these tight junctions.
Digitalis (heart medication)
Strengthens the force of contraction in heart by slowing the Na+/Ca2+ anti porters down so more there is less Na+ concentration across the membrane and more ca2+ remains inside the cell.
2 types of endocytosis
- Phagocytosis (cell eating by macrophages and WBCs) This is receptor mediated and pseudopods extend to form phagosome.
- Pinocytosis cell drinking (no receptor proteins, just engulfs whatever is around)
Resting membrane potential
-70mV. This means the cell is “polarized”
When is the cell “polarized”?
At resting potential, -70mv.
Why does resting membrane potential of -70mv exist?
Concentrations of ions are different on the inside vs out.
The outside is rich with Na+ and Cl-.
The inside is full of K+ and organic phosphates and amino acids (which are highly negative)
Membrane permeability difference for Na+ and K+
50-100x greater for K+. Inward flow of Na+ cannot keep up with the outward flow of K+.
Graded potentials
Small deviations from resting potential of -70mv, as opposed to being “all or none.” They arise due to mechanical (pressure, stretch) or chemical (neurotransmitter, hormone) stimulation and the amount of amplitude varies with strength. The flow of current is local and dies out after only a short distance.
Does not elicit an action potential.
Catch clamp technology
Small micro suction that sucks up small portion of a membrane and can record what the channels are doing. Allows you to record single channels.
Rapid freeze/freeze substitution
Allows you to see channels open after being stimulated.
Absolute refractory period
Cell is hyperpolarized and no action potential can occur no matter the stimulation. This occurs because the Na+ channels are inactivated and must return to the resting state before they can be reopened.
Relative refractory period
Cell is still hyperpolarized, but making its way back up to the resting potential. Action potential can occur if the stimulus is strong enough.
At this time, Na+ channels are closed and ready to go, but K+ channels are still open.
Threshold value to cause action potential
-55mv
phases of an action potential
- Chemical or mechanical stimulus causes a graded potential to reach at least -55mv
- Voltage gated Na+ channels open and Na+ rushes into the cell. This causes the depolarization phase and the cell reaches +30mv.
- Shortly after, the K+ channels will open (bc they are slower to open than Na+ channels) and the cell will repolarize/hyperpolarize down to -70mv.
- The cell reaches resting potential again due to the K+ and Na+ pump.
An example of positive feedback in action potentials
Na+ channels opening during depolarization
nerve impulse
traveling action potential
Origin of graded potentials and action potentials
Graded potentials arise on dendrites and cell bodies.
Action potentials arise only at the trigger zone of the axon hillock.
Types of channels involved with graded potentials and action potentials
Graded potentials are produced by ligand or mechanically gated channels.
Action potentials are produced by voltage gated ion channels.
Difference between graded potentials and action potential propogation
Graded potentials are localized (not propagated)
Action potentials conduct over the surface of the axon
Compare amplitude, duration, and refractory period of graded potentials and action potentials
Graded potentials- The amplitude varies depending on the stimulus, the duration is as long as the stimulus lasts and there is no refractory period.
Action potentials- The amplitude is always constant (all or none). The duration is very short but depends on if the fiber is myelinated and the size of it. There is a relative refractory period and refractory period
Continuous conduction vs saltatory conduction
Continuous- unmyelinated fibers. Step by step depolarization of each portion of the length of the axon.
Saltatory- myelinated fibers so depolarization only occurs at the nodes of ranvier where there is a high density of voltage gated ion channels. The current is carried by ions flowing through extracellular fluid from node to node.
Is the propagation of a nerve impulse related to stimulus strength?
No
Does a nerve impulse travel quicker down a larger or smaller nerve?
Ap travels quicker down a larger nerve.
- Large fibers used for-
- Medium fibers used for-
- Small fibers used for-
- Somatic sensory and motor to skeletal muscles
- Myelinated visceral sensory and autonomic preganglionic
- Unmyelinated sensory and autonomic motor
