Cell Physiology Flashcards
How do we calculate the flux in the simple diffusion?
Which are the factors that increase permeability?
Metabolic energy needed?
J=-PA(c1-c2)
#radius of the molecule #oil /water partion coefficient(^) #memebrane thickness
Passive/zero E/downhill
Do CO2 and O2 cross the cell membrane.?
Yes ,just as steroid hormones because they are lipid soluble substances.
Na+,Cl-,glucose and H2O do NOT dissolve in the lipid of the membrane->carriers needed
What are the characteristics of carried mediated transport?
#stereospecificity #saturation(Tm,Vm) #competition
What is the difference between glucose D and L transportation?
Which one is the natural isomer?
Glucose D,the natural isomer, is transported by facilitated diffusion
,while glucose L via Na cotransport (?)
How much energy does the facilitated diffusion consumes?
Zero.it occurs downhill and it’s passive BUT it is much more rapid than simple diffusion.
Plus:exhibits saturation/competition/stereospecificity
Glucose facilitated diffusion can be inhibited by one molecule.which one?
Galactose
Give three examples of primary active transport…
Na+,K+,ATP
Ca2+,ATP. [SERCA]
H+,K+,ATP
UPHILL,active
Na+,Ca2+ is an example of ……..transport
Secondary active countertransport
Na+,K+,2Cl is an example of…… Transport.
Secondary active cotransport
Na+,H+ is an example of…..transport.
Secondary active counter transport
How is osmolarity measured?what does it stand for?
What is the equation?
By freezing point depression.it is the concentration of osmotically active particles in a solution
Osm=g*C
Water flow FROM HYPOsmotic TO HYPERosmotic
[πχ σε CaCl2 g=1+2]
What is the equation for osmotic pressure?
How is the water flow determined?
π=gcRT. [van Hoff]
High π means hypertonic solution
Low π means hypotonic solution
Water flows FROM the HYPOtonic TO the HYPERtonic
What is the reflection coefficient for albumin?σ
One.
the solute is impermeable to albumin > high osm.pressure> causes water flow
What is the reflection coefficient for urea?
Zero.
The solute is completely permeable> no osmotic effect>no water flow> ineffective osmole
What are the selective characteristics of ion channels?
#size
#distribution of charges(negative charge>permeable to kations)
(Positive charge>permeable to anions)What’s the Nernst equation(equilibrium potential)?
What does it stand for?
E=-2,3RT/zF *log [Ci/Ce]
Z= charge of the ion(Na+=+1)
It says what potential would exactly balance the tendency for diffusion down the concentration gradient;at what potential would the ion be at electrochemical equilibrium
Equilibrium potentials for Na, K,and resting membrane….?
Ena=+65mV
Ek=-85mV
Resting membr.potential =-70mV :at rest,far more permeable to K+ than Na+
Inward flow=less negative=depolarizing
Outward flow=more negative =hyperpolarizing
Tetrodotoxin(TTX) and lidocaine abolish action potentials.where do they act?
They block the voltage-sensitive Na+ channels ,so that they do not open in case of depolarization of the membrane> no action potential occurs
What is the act of tetraethylammonium (TEA)..??
It blocks the voltage gated K+ channels> no outward K+ current> inhibition of repolarization of the membrane potential
What is the threshold?
Threshold is the membrane potential at which the action potential is inevitable>net inward becomes larger than net outward current>self sustained deporarization
What is the site of generation the action potentials?which factors can increase it?
They generate only at the nodes of Ranvier
Factors that increase conduction velocity are:
#fiber size:^diameter of a nerve fiber=decreased resistance=^velocity
#myelination:saltatory conduction
Digitalis and ouabain inhibit….?
Na+,K+,ATPase !
After the deporarization of the presynaptic cell,an ion enters the cell..which one?
Ca2+ causing release of the neurotransmitter .
Explain the process of Ach synthesis in the pre synaptic cell
Choline+acetyl-co-A= Ach. [by choline acetyl transferase ]
Stored in synaptic vesicles along with ATP and proteoglycans.
Released by exocytosis when intracellular Ca2+ is increased
Explain the act of Ach in the neuromuscular junction
Binding to nicotinic receptors > increasing conductance to Na and K>
MEPP(miniature end plate potential ) >EPP
❗️EPP NOT an action potential!just depolarizing muscle end plate.
Degradation of Ach is through…
Achetylocholinesterase (AchE)> 1/2 of choline is taken back via Na cotransport
Action of botulinum toxin…
Blocks the release of Ach from presynaptic terminals>total block out
Action of neostigmine…
Inhibits AchE >prolongs and enhances actions of Ach (treatment for myasthenia Gravis)
Curare action…
Competes with Ach for receptors>decreased EPP >paralysis
Hemicholinium action…
Blocks reuptake of choline into presynaptic cells>depletes Ach stores
What’s the cause of skeletal muscle weakness and fatigability of myasthenia Gravis?
It is due to antibodies to the Ach receptor resulting in a reduced NUMBER of Ach receptors on the muscle end plate
What is the impact of hyperkalemia in muscle contraction?
High extracel.comc Lowers the driving force of K>Ek is lower>thus the resting membrane potential is less negative>membrane in a depolarizing mode>προφυλακτικα kleinoun oi inactivation gates on Na channels>less Na inward >that makes action potential more difficult to be made>muscle contraction is more difficult to be made>muscle weakness
HYPERKALEMIA
remember that hyperkalemia causes a depolarization in the resting membrane potential
this depolarization increases the likelihood that the cardiac muscle cell membrane will generate inappropriate action potentials (causing arrhythmias)
even more seriously, larger depolarizations prevent cardiac action potentials from occurring, and therefore heart contractions will stop completely (cardiac arrest)
How is depolarizing potential created? EPSP
Opening of Na,K, chanels>depolarizing to a value halfway[approximately 0]
How is hyper polarizing potential created IPSP?
By opening Cl - channels(equilibrium potential:-90)
GABA,Glycine
Which enzyme converts NE to E?
Which are their metabolites?
N methylotransferase(adrenal medulla) They turn into VMA,NMN via COMT and MAO
Dopamine receptors
D1:activating cAMP
D2:inhibiting cAMP
Which is the pathophysiology of Parkinson disease?
It involves degeneration of dopaminergic neurons that use D2
Which is the pathophysiology of Schizophrenia?
It involves increased levels of D2 receptors
Which is the most prevalent excitatory neurotransmitter in the brain?
Where does it act?
Glutamate. There are 4subtypes of receptors. #three ionotropic ligand-gated ion channels (px NMDA) #one metabotropic G pr receptor
Which are the GABA receptors?
GABAa:^Cl- conductance
GABAb:^k+ conductance
How do benzodiazepines and barbiturates act?
At the GABA a receptors
What is the site of T tubules?
At the junction of A and I bands and makes intimate contact with the terminal cisternae of SR
They carry the depolarization from the sarcolemmal
What are the dihydropyridine receptors?
Voltage sensitive proteins in the T tubules
The L-channels that increase inward Ca2+ at the plateau phase of myocardial action potential>they produce the Ca-induced-Ca release that causes contraction
To what molecular is Ca2+ bound to in the SR?
To calsequestrin
After the depolarization of the T tubule and conformation of the dihydropyridine ,there is release of Ca2+ from the SR .by which channel?
By the ryanodine receptor
How is it possible for a muscle to be in rigor?
At the first step of muscle contraction no ATP is bound to myosin >myosin is tightly attached to actin>in the absence of ATP this state is permanent >rigor
When will the tension in a stretched muscle be maximum?
When there is maximum overlap of thick and thin filaments
What’s the relationship between force and velocity?
The velocity of shortening decreases as the after load increases
Compare the contraction between skeletal and smooth muscle..
Skeletal. Smooth
Upstroke: Inward Na Inward Ca
Mechanism: Act.potential>T tubules. Act.potential>opens voltage
Ca from SR>connect to. Ca channels or through IP3
Troponine C. >connect to calmodulin>
Kinase>phosporylates myosin
Give two characteristics of unitary smooth muscle that differ from skeletal muscle…
#spontaneous depolarization #gap junctions
Solution of 300 mM mannitol is …. Tonic
Isotonic
Solution of 150mM NaCl is …tonic
Isotonic
