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* need help...
 #520940  
  futuredoctor19 - 07/23/10 18:26
 
  1) T tubules enhance which of the following processes in striated muscle cells?
(a) delivery of the action potential to the interior of the myocytes
(b) reinforcement of the cell surface for the attachment of myofibrils
(c) scavenging of a nonhydrolysed neurotransmitter to terminate the contraction stimulus
(d) storage of higher concentrations of intracellular calcium to uniformly initiate contraction?
(e) structural stabilization of the postsynaptic membrane at the neuromuscular junction

a lot of ppl think its A...what abt D??

2) A healthy 25M who has been training for a marathon during the past 6 months runs 15 miles daily. Endurance training of normal skeletal muscle leads to which of the following muscle adaptations?
(a) fiber-size reduction
(b) fiber-type conversion from type I (slow) to type II (fast)??
(c) hyperplasia of myocytes
(d) ↑ capillary to fiber ratio
(e) ↑ G6P activity

is it B or D??

3) A Healthy subject receives a 2 L OF ISOTONIC SALINE. Assuming no urine excretion, which of the following is the expected increase in volume (in L) of the extracellular fluid compartment?
a) 0.3
b) 1.0
c) 1.3
d) 1.7
e) 2.0.

IS IT E?? can someone pls explain

4) A 60 year old woman is undergoing surgical excision of a renal cell carcinoma thrombus that extends into the right renal vein. During this procedure, the vena cava is temporarily occluded above the renal veins. Increased venous pressure is most likely to be noted in which of the following veins during the period of occlusion?

a)external iliac
b)hepatic…
c)IMA
d) portal
e)splenic

i know a lot of ppl think its A....wat abt B?? why is B incorrect




 
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* Re:need help...
#2154035
  yeabiruh - 07/23/10 19:35
 
  Hi future ...thanks for posting the question ...

Here is my thinking

For 1==U said why not D-But storage of higher concentrations of intracellular calcium to uniformly initiate contraction is done BY SARCOPLASMIC RETICULUM.

For 2==the training IS ENDURANCE training NOT STRENGTH training ..here is the difference between the two...

a-Endurance is achieved by repetitive contractions of muscle fibers. Repetitive contractions require a continuous supply of energy, and muscle fibers with aerobic (oxidative) capabilities (slow oxidative, fast oxidative glycolytic) are suited to the job the repetitive contractions enhance aerobic enzymes, mitochondria, and the fuels needed for repetitive contractions

HENCE THE CORRECT ANSWER IS D

Choices b AND E will be for STRENGTH training

b-Strength comes from lifting heavy loads a few times. The effects of strength training are most noticeable in fast-twitch fibers. Training effects include increases in contractile proteins (actins and myosin) and tougher connective tissue. The increased strength comes from greater cross-sectional area, which means more contractile protein to exert force.
 
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* Re:need help...
#2154038
  yeabiruh - 07/23/10 19:40
 
  FOR 3 == the infusion IS WITH ISOTONIC fluid.....if u INFUSE isotonic fluid there is no change in the osmolarity of the ECF ---because of this there is NO NET movement of fluid betwween the ECF and ICF===hence all the fluid stays in the ECF---MAKING THE INCREASE IN ECF VOLUME 2L

For 4==If u block IVC at the renal vein pressure INCREASES DOWNSTREAM not UPSTREAM ...remember venous blood moves from downward -upward direction(unlike the arterial blood flow)....
 
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* Re:need help...
#2154069
  futuredoctor19 - 07/23/10 20:47
 
  thank you so much! i have a few more questions...

NBME 5 block 3
3 graphs showing the relationship between cardiac output and HR, EDV, and SV for healthy elderly men and healthy younger men. It shows that EDV and SV is higher in the elderly compared to the younger population. Which of the following age related anatomic changes contribute to well-maintained cardiac output in the elderly men?
a) Dilated ascending aorta
b) Left ventricular dilation
c) LVH…
Is it C....coz i saw a similar question in UW which kinda explains this question….isolated systolic hypertension in an elderly patient is caused by an age-related decrease in the compliance of the aorta and its proximal major branches. In other words, the aorta has (increased stiffness) now. So if the aorta becomes stiff then there will be an increased pressure in LV leading to LVH. am i thinking right on this?

From NBME form 7:
[44] A healthy 40F inhales to total lung capacity and then exhales forcefully. The rate of expiratory airflow is highest at total lung capacity and ↓ linearly as exhalation continues. Which of the following is the most likely cause of the observed ↓ in expiratory airflow?
(a) airway compression
(b) ↓ expiratory effort
(c) ↓ intrapleural pressure
(d) doming of the diaphragm
(e) ↑ elastic recoil

A healthy 24M is participating in a study of swallowing. The manometric pressure changes that occur while this man swallows are shown in a graph. (Anyone rmr this question, im not able to show the graphs here).

Which of the following traces best represents muscle activity in the upper esophageal sphincter?
A B C D E


This is the last question from block 4 of nbme form 7. i would love to get an understanding of this concept coz it has shown up on people's exams many times as i heard. Two chemical reactions are shown schematically, each with its ΔG. C represents the same compound in each reaction.

A==>B+C (ΔG= -11.1 kcal/mol)
C+D==>E (ΔG= +6.4 kcal/mol)

For the reaction shown, which of the following sets of values is most likely correct for ΔG and direction?
(a) ΔG 17.5, direction 1
(b) ΔG 17.5, direction 2
(c) ΔG -4.7, direction 1
(d) ΔG -4.7, direction 2
(e) ΔG -17.5, direction 1
(f) ΔG -17.5, direction 2




 
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* Re:need help...
#2154071
  martin99 - 07/23/10 20:50
 
  Yeabiru
Good explaination.
 
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* Re:need help...
#2154082
  yeabiruh - 07/23/10 21:06
 
  For the last question here is my understanding....The question is about bordwell thermodynamic cycle (same as HESS law)....

This law can be applied to find out the answer for NBME 7 Block 4 question 50 ...

Here is the explanation

--Bordwell thermodynamic cycles deal with the summation of Gibbs free energy (ΔG) values

--it is an extension of Hess's law which states For any chemical reaction, the change in enthalpy in going from reactants to products is constant, regardless of the set of reaction steps used to bring the overall reaction about.

--To calculate the overall enthalpy change for a chemical reaction, the enthalpy changes for each individual reaction during the process are added together

--Hence in the question they give us
For the first reaction Change in G =-11.1

For the second reaction Change in G=+6.4

Calculating the Change in G for the third reaction (using the above principle)=-4.7

Interpreting the change in G -4.7 =the reaction is spontaneous and the direction of the reaction is from left to right (from reactants to products).....

Any other input appreciated....

 
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* Re:need help...
#2154095
  yeabiruh - 07/23/10 21:32
 
  More on Gibbs Free Energy

--it is a thermodynamic function

--it is the single most useful criterion for predicting the direction of a chemical reaction and the composition of the system at equilibrium

--the direction of the chemical reaction can be from the reactant to the product or viceversa

or at equilibrum depending on the SIGN of the GIBBS FREE ENERGY

--ΔG = ΔH – T ΔS...S stands for ENTROPY --*this equation is to calculate the Gibbs free

energy of INDIVIDUAL COMPONENTS (products and substrates) OF THE REACTION

--*Make Note The Standard Gibbs energy of the reaction (taking into consideration the

products and substrates)=


ΔG° = Σ ΔGf°(products)– Σ ΔGf°(reactants)--we have to know this

--ΔG determines the direction and extent of chemical change

so let us write a chemical reaction

A + B ====> C

A and B are reactants (substrates)
C is product

---if the free energy of the reactants is greater than that of the products, the entropy of the world will increase when the reaction takes place as written, and so the reaction will tend to take place spontaneously.(Exorgonic)

-- Conversely, if the free energy of the products exceeds that of the reactants, then the reaction will not take place in the direction written, but it will tend to proceed in the reverse direction.

In summary====>

ΔG° = Σ ΔGf°(products)– Σ ΔGf°(reactants)

ΔG° < 0 reaction can spontaneously proceed to the right: A +B → C
ΔG° > 0 reaction can spontaneously proceed to the left: A +B← C
ΔG° = 0 the reaction is at equilibrium; the quantities of A +B and C will not change



Some examples---

Problem Example 1
Find the standard Gibbs energy change for the reaction

CaCO3(s) → CaO(s) + CO2(g)

The ΔGf° values for the three components of this reaction system are CaCO3(s): –1128 kJ

mol–1, CaO(s): –603.5 kJ mol–1, CO2(g): –137.2 kJ mol–1.

Solution: Substituting into ΔG° = Σ ΔGf°(products)– Σ ΔGf°(reactants), we have

ΔG° = (–603.5 –137.2) – (–1128) kJ mol–1 = +130.9 kJ mol–1 indicating that the process is

not spontaneous under standard conditions (i.e., solid calcium carbone will not form solid

calcium oxide and CO2 at 1 atm partial pressure at 25° C
 
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* Re:need help...
#2154121
  yeabiruh - 07/23/10 22:22
 
  For A healthy 24M is participating in a study of swallowing...manometric pressure readings ...

Exactly the same picture is in KAPLAN PHYSIO GI SECTION ......i dont remeber the pages as i dont have it
 
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