Cell Physiology

Question 1

ex. cell conc. of Na

ECF [Na⁺]=?

Answer 1

145 mEq/L

Question 2

ICF PH

Answer 2

7.2

EXF PH= 7.4

ICF slightly more acidic

Question 3

The expression of this identifying protein is down-regulated in virally infected cells.

• Important cell surface protein that plays a functional role in immunity.

Answer 3

MHCI- functions in identifying self vs. non-self

Question 4

ECF and ICF conc.’s of Mg²⁺ and Ca^{<strong>2+</strong>}

Answer 4

Greater ECF concentrations but still very little.

[Ca²⁺]_ICF = 10^-4

[Mg²⁺]_ECF = 1-2 mEq/L

[Ca²⁺]_{<span>ECF</span>} = 0.5

Question 5

ECF conc. Cl^-

Answer 5

110 mEq/L

Just like Na⁺, there is higher ECF conc.

Question 6

Osmolarity

Answer 6

Osmolarity= concentration of particles (Osm/L)
g =number of particles in solution (Osm/mol)

[e.g., gNaCl = 2; ~ucose = 1] C = concentration (mol/L)

Two solutions that have the same calculated osmolarity are isosmotic. If two solutions have different calculated osmolarities, the solution with the higher osmolarity is hyperos- motic and the solution with the lower osmolarity is hyposmotic.

Question 7

Osmolarity eq.

Compare osmolarity of 1M CaC1₂ and 1M KCl

isotonic, hypertonic, hypotonic solutions

Answer 7

Osmolarity=g.C.RT

Theosmoticpressureincreaseswhenthesoluteconcentrationincreases.Asolutionof1M CaC12 has a higher osmotic pressure than does a solution of 1 M KCl because, for a given volume, the number of osmotically active particles is higher.

The higher the osmotic pressure of a solution, the greater the water flow into it.

Two solutions having the same effective osmotic pressure are isotonic because no water flows across a semipermeable membrane separating them. If two solutions separated by a semipermeable membrane have different effective osmotic pressures, the solution with the higher effective osmotic pressure is hypertonic and the solution with the lower effective osmotic pressure is hypotonic. Water flows from the hypotonic to the hyper- tonic solution.

Question 8

Reflection coefficient (σ)

Answer 8

is a number between zero and one that describes the ease with which a solute permeates a membrane.

a. If the reflection coefficient is one, the solute is impermeable. Therefore, it is retained in the original solution, it creates an osmotic pressure, and it causes water flow. Serum albumin (a large solute) has a reflection coefficient of nearly one.
b. If the reflection coefficient is zero, the solute is completely permeable. Therefore, it will not exert any osmotic effect, and it will not cause water flow. Urea (a small solute) usually has a reflection coefficient of close to zero and it is, therefore, an ineffective osmol e.

Question 9

The pathophysiology of this protein (transporter) manifest in typeII diabetes

Answer 9

Insulin receptor (receptor protein)

Question 10

ICF conc. of K⁺

Answer 10

140 mEq/L

Question 11

The luminal enzyme of PCT of neophrons that interconverts carbon dioxide and water into proton and carbonate

Answer 11

luminal carbonate anhydrase- Generally requires Zn (considered metalloenzyme)

Question 12

Pathophysiology of this enzyme causes proximal renal tubular acidosis

Answer 12

Luminal carbonic anhydrase located in proximal convoluted tubules (PCT) of nephrons.

Question 13

The pathophysiology of this career protein causes diabetes mellitus

Answer 13

GLUT4- Glucose Sodium symporter

Question 14

Composition of cytosol (relative to ECF)

ICF vs ECF composition

Answer 14

Differs markedly from ECF in terms of electrolytes and PH. Consists of intracellular fluid, which contains many soluble proteins, ions, metabolites, and cytoskeletal elements.

Question 15

Nicotinic receptors on muscle cells are an example of:

• A class of protein

Answer 15

Transmembrane protein and function as Na+_gated ion channel

Question 16

ECF PH=?

Answer 16

7.4

Question 17

maximal effective osmotic pressure

Question 18

Na⁺-gated channels

Answer 18

The activation gate of the Na⁺ channel in nerve is opened by depolarization.

The inactivation gate of the Na⁺ channel in nerve is closed by depolarization.

When both the activation and inactivation gates on Na⁺ channels are open, the channels are open and permeable to Na+ (e.g., during the upstroke of the nerve action potential).

If either the activation or inactivation gate on the Na⁺ channel is closed, the channel is closed and impermeable to Na+.

For example, at the resting potential, the activation gates are closed and thus the Na⁺ channels are closed.

Question 19

If the intracellular [Na+] is 15 mM and the extracellular [Na+] is 150 mM, what is the equilibrium potential for Na”’?

Answer 19

ENa• = -60mV/z log (Ci)/(Co)

=-60mVIog 0.1

=+60mV

Question 20

Resting membrane potential

Answer 20

• is approximately -70 mV, cell negative.
• is the result ofthe high resting conductance to K⁺, which drives the membrane potential toward the K⁺ equilibrium potential.
• At rest, although the inactivation gates on N^a+ channels are open (having been opened by repolarization from the preceding action potential),theactivationgateson Na⁺ channels are closed and thus the Na⁺ channels are closed and Na⁺ conductance is low.

Question 21

Upstroke of action potential

Answer 21

(1) Inward current depolarizes the membrane potential to threshold.
(2) Depolarization causes rapid opening of the activation gates of the Na+ channels. Now, both activation and inactivation gates are open and the Na+ conductance of the membrane promptly increases.
(3) The Na+ conductance becomes higher thanthe K+ conductance, and the membrane potential is driven toward (but does not quite reach) the Na+ equilibrium potential of+65 mV. Thus, the rapid depolarization during the upstroke is caused by an inward Na+current
(4) Theovershootisthebriefportionatthepeakoftheactionpotentialwhenthemem- brane potential is positive.
(5) Tetrodotoxin mxt and lidocaine block these voltage-sensitive Na+ channels and abolish action potentials.

Question 22

Repolarization of action potential

Answer 22

(1) Depolarization also closes the inactivation gates ofthe Na+channels (but more slowly than it opens the activation gates). Closure of the inactivation gates results in clo- sure of the Na+ channels, and the Na+ conductance returns toward zero.
(2) Depolarization slowly opens K+ channels and increases K+conductance to even higher levels than at rest. Tetrathylammonium (TEA) blocks these votlate channels.
(3) The combined effect of closing the Na+ channels and greater opening of the K+ channels make the k conductance higher than the Na+ conductance and the membrane potential is repolarized. Thus, polarizaiton is caused by an outward K+ current

Question 23

Synthesis and storage of ACh in the presynaptic terminal

Answer 23

Choline acetyltransferase catalyzes the formation of ACh from acetyl coenzyme A (CoA) and choline in the presynaptic terminal.
ACh is stored in synaptic vesicles with ATP and proteoglycan for later release.

Question 24

Diffusion of ACh to the postsynaptic membrane (muscle end plate) and binding of ACh to

nicotinic receptors

Answer 24

The nicotinic ACh receptor is also a Na+ and r+ ion channel.
Binding of ACh to a subunits of the receptor causes a conformational change that opens the central core of the channel and increases its conductance to Na+ and K+. These are examples of ligand-gated channels.

Question 25

EPP

End plate potential in the postsynaptic membrane

Answer 25

1. Because the channels opened by ACh conduct both Na+ and K+ ions, the postsynaptic membrane potential is depolarized to a value halfway between the Na+ and K+ equilib- rium potentials (approximately 0 mV).
2. The contents of one synaptic vesicle {one quantum) produce a miniature and plata potential (MEPP), the smallest possible EPP.
3. MEPPs summate to produce a full-fledged EPP. Tha EPP is not an action potential, but simply a depolarization ofthe specialized muscle end plate.

Question 26

EPSPs

Excitatorypostsynapticpotentials

Answer 26

1. are inputs that depolarize the postsynaptic cell, bringing it closer to threshold and closer to firing an action potential.
2. are caused by opening of channels that are permeable to Na+ and 1(+, similar to the ACh channels. The membrane potential depolarizes to a value halfway between the equilibrium potentials for Na+ and K+ (approximately 0 mV).

Question 27

Excitatory neurotransmitters & Inhibitory neurotransmitters

Answer 27

Excitatory neurotransmitters include ACh, norepinephrine, epinephrine, dopa- mine, glutamate, and serotonin.

Inhibitory neurotransmitters are y-aminobutyric acid (GABA) and glycine.

Question 28

Inhibitory postsynaptic potentials

Answer 28

are inputs that hyperpolarize the post synaptic cell, moving it away from threshold and farther from firing an action potential
are caused by opening Cl- channels. The membrane potential is hyperpolarized toward the cl- equilibrium potential (-90 mV).