Step I NBME 6 question

[determined1.]

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Pulmonary calculation q

Q - The following pulmonary pressures (in mm of hg) were measured in a animal who was breathing spontaneously
hydrostatic capillay pressure 12
oncotic cap pr 20
hydrostatic interstitial pr -5
oncotic inst pr 15
filtration coefficient of pul microvasculature is 1ml/min/100g tissue/mm hg pressure,and reflection coefficient of protein is 1.which of the following best represents the magnitude and direction of fluid
flux in this animal?
magnitude in ml/min direction

a) 2 cap to inst space
b) 2 inst space to cap
c) 12 cap to inst space
d) 12 inst space to cap
e) 22 cap to inst space
f) 22 inst space to cap

------------------------------------------
I was able to get 12, but I didn't know which direction it would go. Can anyone please explain?

Thank you

=(Hc-Hi)-(Oc-Oi)

12-(-5)=17---- hydrostatic presuure
20-15=5------oncotic pressure
17-5=12

 

[dfib slim]

Pulmonary calculation q

Q - The following pulmonary pressures (in mm of hg) were measured in a animal who was breathing spontaneously
hydrostatic capillay pressure 12
oncotic cap pr 20
hydrostatic interstitial pr -5
oncotic inst pr 15
filtration coefficient of pul microvasculature is 1ml/min/100g tissue/mm hg pressure,and reflection coefficient of protein is 1.which of the following best represents the magnitude and direction of fluid
flux in this animal?
magnitude in ml/min direction

a) 2 cap to inst space
b) 2 inst space to cap
c) 12 cap to inst space
d) 12 inst space to cap
e) 22 cap to inst space
f) 22 inst space to cap

------------------------------------------
I was able to get 12, but I didn't know which direction it would go. Can anyone please explain?

Thank you

=(Hc-Hi)-(Oc-Oi)

12-(-5)=17---- hydrostatic presuure
20-15=5------oncotic pressure
17-5=12

It's easier to add them in terms of direction.
Cap hydro + int onc = 27 pushing fluid out.
Int hydro + cap onc = 15 pushing fluid in.
Net is 12 fluid out. Choice C.

 

[determined1.]

So, if it's positive then Fluid out of capillary and if it's negative then fluid into capillary?

 

[dfib slim]

Depends on the order you subtract. Your statement is true if you subtract fluid pressure in from pressure out.

 

[determined1.]

I always subtract Hydrostatic first then Oncotic and then subtract both, (Hc-Hi)-(Oc-Oi) so I can't always say if it's positive then Fluid out of capillary and if it's negative then fluid into capillary?

Then what? what's the general rule?

 

[dfib slim]

If you use that form of the starling equation then positive is outward pressure and negative is inward pressure.

 

[determined1.]

If you use that form of the starling equation then positive is outward pressure and negative is inward pressure.

Ok thanks ...

 

[determined1.]

Another q I need clarification on:

1. An 8-year-old boy has had generalized edema for 2 months. Laboratory studies of serum show:

Glucose =89 mg/dL
Creatinine =0.9 mg/dL
Urea nitrogen (BUN) = 11 mg/dL
Albumin = 2.8 g/dL
Urinalysis shows 4+ protein and oval fat bodies. The most likely cause is a disorder involving which of the following structures?

A ) Afferent arterioles only
B ) Afferent and efferent arterioles
C ) Glomerular capillary loops
D ) Glomerular mesangial region
E ) Tubulo-interstitial region

Ans= C

My question is since in minimal change dz we have effacement of podocyte wouldn't that make the problem area to be Tubulo-Interstitial region?

 

[dfib slim]

Another q I need clarification on:

1. An 8-year-old boy has had generalized edema for 2 months. Laboratory studies of serum show:

Glucose =89 mg/dL
Creatinine =0.9 mg/dL
Urea nitrogen (BUN) = 11 mg/dL
Albumin = 2.8 g/dL
Urinalysis shows 4+ protein and oval fat bodies. The most likely cause is a disorder involving which of the following structures?

A ) Afferent arterioles only
B ) Afferent and efferent arterioles
C ) Glomerular capillary loops
D ) Glomerular mesangial region
E ) Tubulo-interstitial region

Ans= C

My question is since in minimal change dz we have effacement of podocyte wouldn't that make the problem area to be Tubulo-Interstitial region?

Tubulo-interstitial region refers to the tubules and interstitium, not the glomerulus.

 

[determined1.]

Tubulo-interstitial region refers to the tubules and interstitium, not the glomerulus.

Ah, I think I know where I was wrong.

 

[determined1.]

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