Flashcards in Cell And General Physiology Deck (68):
Are non-polar molecules lipophilic or phobic, hydrophilic or phobic; give an example?
Nonpolar molecules are lipophilic and hydrophobic; examples are isoflurane and oxygen
Are polar molecules lipophilic or phobic, hydrophilic or phobic; give an example?
Polar molecules are lipophobic and hydrophilic; examples are glucose and water
Large water soluble (hydrophilic or hydrophobic?) molecules and __________ (like Na+, K+, Cl-) are _______ (most or least) likely to penetrate lipid bilayers.
Large water soluble (hydrophilic, lipophobic) molecules and ions (like Na+, K+, Cl-) are least likely to penetrate lipid bilayers.
They must use channels to enter and exit cells and cross the blood brain and placental barriers.
Name examples of hydrophobic molecules that readily cross the lipid bilayers.
O2, N2, benzene
Name some small uncharged polar molecules that readily cross the lipid bilayers.
H20, urea, glycerol, CO2
Name some large uncharged polar molecules the Do Not readily cross the lipid bilayers.
Name some examples of ions that Do Not readily cross the lipid bilayers.
H+, Na+, HCO3-, K+, Ca+, Cl-, Mg+
Proteins are reabsorbed from the proximal tubule of the kidney by ___________ (pinocytosis or phagocytosis).
Pinocytosis (cell drinking); but both of the processes are a form of endocytosis.
Macrophages engulf bacteria by the process of ______. (Phagocytosis, exocytosis, pinocytosis)
Neurotransmitters are released from nerve terminals by the process of _________.
Name some examples of ligands that attach to receptors and what happens in this process.
Chemicals, drugs, Neurotransmitters, and hormones are all ligands.
The specific channel typically opens and substances specific to the channel diffuse down their concentration gradients through it.
At the neuromuscular junction, acetylcholine binds to the nicotinic receptor and the channel opens to sodium ions (which diffuse in), potassium ions (which diffuse out), and calcium ions (which diffuse in). Which is the ligand in this scenario? What type of channel is this?
Acetylcholine; ligand gated channel
Explain what happens with an enzyme-linked receptor.
A ligand on the outside of the cell binds to its receptor and activates an enzyme on the cytoplasmic surface (inside the cell) of the membrane .
Explain first and second messengers involved in enzyme-linked channels.
The ligand that binds to the extra cellular wall is the first messenger and the enzyme released inside the cell acts as the second messenger.
Exception to this is the skeletal neuromuscular junction where acetylcholinesterase projects outward into the synaptic cleft so it can metabolize acetylcholine.
What are the best known proteins for relaying messages from receptors to enzymes?
G-proteins.... Either stimulatory g-proteins (Gs) or inhibitory (Gi)
When a beta agonist binds to its receptor, explain the role of cAMP.
Ligand binds to receptor and G protein, either Gs or Gi, relays a response to the enzyme (adenylate cyclase)... When the enzyme is stimulated by Gs, cAMP (the second messenger) is formed inside the cell, which then triggers an intracellular event.
Example: In cardiac muscle cAMP increase cardiac contractility and in bronchial smooth muscle it relaxes bronchial smooth muscle cells.
The adenylate cyclase enzyme (cAMP) is inhibited by Gi, which would stop the cell process. Beta adrenergic receptors operate Gs, while some muscarinic receptors operate Gi.
What are the 3 subunits of Gs and Gi?
Gamma, beta, alpha
What is the primary role of G-proteins?
To relay or shuttle messages or signals from receptors to enzymes.
Name some common second messengers.
Cyclic adenosine mono phosphate (cAMP), cyclic guanosine mono phosphate (cGMP), calcium, calmodulin, inositol triphosphate (IP3)
Second messenger action is tissue specific. What is an example of this concept as it relates to the heart and lungs?
Increased cAMP in heart increases Ca causing increased contractility.... In the lungs, increased cAMP causes decreased Ca concentration leading to smooth muscle relaxation.
B1 versus B2 stimulation... Both involve Gs and adenylate cyclase.
What cells involve the Na-K pump?
The sodium potassium pump is found in all cells
What is the function of the sodium potassium pump?
Keep intracellular K high and intracellular Na low. Uses energy derived from the breakdown of ATP to move 3 Na ions out in exchange for 2 K ions.
Why is insulin an effective agent in treating hyperkalemia?
Insulin stimulates the Na-K pump... Driving K into cells (3 Na out, 2 K in). Insulin opens glucose channels, which permits the transfer of glucose into fat and skeletal muscle cells.
What is the purpose of the glucose component of the glucose-insulin therapy for hyperkalemia?
Prevents hypoglycemia. Insulin stimulates Na-K pump but also opens glucose channels, permitting transfer of glucose into fat and skeletal muscle cells.
Why do beta-2 adrenergic receptor agonists (like ritodrine and terbutaline) promote hypokalemia?
They stimulate the Na-K pump.... Driving K into cells
Define competitive antagonism.
When an antagonist (key) plugs the target receptor (lock), but instead of activating (unlocking) it... It blocks true agonists from binding.... And in return nothing happens.
When the wrong key is in the lock, the correct key cannot be inserted.
What is the difference in extra cellular and intracellular concentrations of common ions?
Extra cellular pertains to serum concentration (our lab values); intracellular pertains to cytoplasmic (indirectly considered based on plasma levels and assumed gradients)
Normal extra cellular (meq/L) |. Intracellular
1: Na. __________. ___________
2: K+. __________. ___________
3: Ca. __________. ___________
4: Mg. __________. ___________
5: Cl. __________. ___________
6: PO4:__________. ___________
7: HCO3:_________. ___________
1: Na. 145/10
2: K. 4/140
3: Ca. 2-2.5/
In the neuron: Is the Na-K pump the only means of moving K in or out of the cell?
No. Continuously open (leak) K channels located in the lipid bilayer of the surface membrane of the neuron permit outward diffusion of K+. K diffuses out of the cell down a concentration gradient. Negatively charged particles (namely proteins) are left behind.... So the outside of the cell becomes lined with K ions and the outside of the cell becomes lined with proteins (negative charges). ALL other ions are impermeable... Because Na and Ca channels are closed in the resting neuron.
What ion is the greatest determinant of resting membrane potential in excitable tissues (neurons, skeletal muscle cells, smooth muscle cells, and cardiac muscle cells)?
What is the change in resting membrane potential associated with acute hyperkalemia?
The diffusion gradient for K is reduced because the rate of diffusion out of the cell is decreased, so the resting potential is diminished and the cell depolarizes.
What is the change in resting membrane potential associated with acute hypokalemia?
Diffusion gradient for K is enhanced because the rate of diffusion out of the cell is increased, the resting potential is increased and thus the cell hyperpolarizes
What is the normal resting potential for the neuron?
In hyperkalemia it shifts towards -60... With hypokalemia it shifts towards -80
In the neuron, where are voltage gated sodium channels primarily found?
in the axon
What happens (in regards to channels) when a nerve axon depolarizes?
fast voltage gated Na channels open causing abrupt depolarization (outside cell is temporarily negative and inside positive); FVG Na channels close quickly... called the inactivated state; voltage gated K channels open... diffusion of K out of cell cause repolarization and restoration of membrane potential; Na-K pump extrudes Na that has entered the cell and recaptures K that was lost
Can another action potential be fired during the inactivated state of a fast voltage gated Na channel?
NO!! no matter how intense
How does the "inactivated state" apply to cardioplegia, succinylcholine, and local anesthetics?
cardioplegia: high K concentration of solution cause membrane depolarization, locking Na channels in inactive state; Succinylcholine: depolarization of the skeletal muscle motor end plate causes Na channels to become inactivated; Local anesthetics: interrupt nerve conduction by locking Na channels in the inactivated state
When is the inactivated state of fast voltage gated Na channels complete?
when the K channels close and the membrane repolarizes
What is most responsible for resting membrane potential?
K efflux (through leak channels)
What ion is responsible for depolarization?
What ion is responsible for repolarization?
What is the absolute refractory period?
when Na channel is in inactivated state, another action potential cannot be fired
All of the following are true of the lipid bilayer EXCEPT:
1) it has cholesterol as one of its components
2)it contains only saturated fatty acids
3)it is comprised mostly of phospholipids
4)provides an environment in which proteins can function
FALSE is 2; does not contain only saturated fatty acids
The Na-K pump is stimulated by:
Channels, receptors, and enzymes are all considered to be __________.
Proteins are usually embedded in two layers of ______ called the ____________ ___________.
lipid, phospholipid bilayer
What is the cell membrane (cell wall) made up of?
50% lipids (phospholipids, glycolipids, cholesterol) & 50% proteins (channels, receptors, enzymes)
Name synonyms of nonpolar.
Non-polar molecules have what properties in relation to lipids and water?
rapidly dissolve in lipids but not water
oxygen and isoflurane are examples of ______ molecules?
What is the difference in charge with non-polar and polar molecules?
non-polar have positive and negative charges with NO POLE.... so even distribution of charges; polar have positive and negative charges clustered into different regions
Name synonyms of polar.
Polar molecules have what properties in relation to lipids and water?
dissolve readily in water but not fat (lipids)
What are some examples of polar molecules?
glucose and water
What charge do ions possess?
they have a net charge... either positive (cations) or negative (anions)
What are some examples of ions?
Name the 2 primary functions of the lipid bilayer.
1) barrier to substances NOT small or NOT lipid soluble
2) provides environment for membrane proteins to function
Name some common large/uncharged polar molecules and also some ions that do not cross the lipid bilayer.
large, uncharged, polar: H2O, urea, glycerol, CO2
ions: H+, Na+, HCO3-, K+, Ca2+, Cl-, Mg2+---> ALL IONS
**Remember that sugars are large and polar
What are the 2 mechanisms that enable a cell to "know" what to bring into the cell?
1) receptors-- provide the specificity
2) clathrin-- a protein coat, provides the mechanism to convert a planar membrane into a spherical structure (vesicle)
What is the main difference between metabotropic and ionotropic receptor?
metabotropic controls an enzyme, while ionotropic operates a channel
What is responsible for relaying messages from receptors to enzymes?
In cardiac muscle, ligand--> receptor--> Gs--> cAMP= _________
increased calcium concentration--> increased contractility
In the bronchi, ligand--> receptor--> Gs--> cAMP= ________
decreased calcium concentration--> bronchodilation
Name some common second messengers:
cAMP (cyclic adenosine monophosphate), cGMP (cyclic guanosine monophosphate), calcium, calmodulin, inositol triphosphate (IP3)
***second messengers are TISSUE SPECIFIC
What are the primary functions of the Na-K pump?
1) keep intracellular K+ high and intracellular Na+ low
2) uses energy derived from ATP--> 3 Na+ IN, 2 K+ OUT
What function does insulin have on the Na-K Pump?
1) stimulates the pump--> driving K+ into cells
2) opens glucose channels--> permitting transfer of glucose into fat and skeletal muscle cells (hypoglycemia if not treated with glucose during the treatment of hyperkalemia)
What effect does beta 2 adrenergic agonists have on the Na-K pump?
1) stimulates the pump--> promoting hypokalemia
**examples= albuterol, ritodrine, and terbutaline