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NBME 24 Answers

nbme24/Block 1/Question#32

A 24-year-old man receives an injection of ...

Increased lymph flow

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 +4  upvote downvote
submitted by nor16(37),

Histamine increases microvascular permeability, i.e. Fluid + Proteins, this increases pressure in the interstitium > lymph flow increases

 +3  upvote downvote
submitted by famylife(49),

There is "a direct action of histamine on the lymphatic smooth muscle via stimulation of H1 (and in some vessels H2) receptors. H1 receptors enhance and H2 receptors slow down lymphatic pumping, the dominant effect being an increased contractile activity."


 +2  upvote downvote
submitted by fahmed14(18),

Histamine plays a major role in the cardinal signs of inflammation. It helps mediate vasodilation and vascular permeability (via endothelial cell contraction). These two functions are already contrary to A, B, C, and D. By increasing fluid in the interstitial space, you can reason that there will be increased lymph flow.

youssefa  If more transudates are leaking into the interstitium wont this dilute the interstitial proteins and cause a decrease in oncotic pressure and increase in interstitial hydrostatic pressure? +4  
titanesxvi  @youssefa I think because it is an exudate from increased permeability of venules, the oncotic pressure in the interstitium is not going to decrease +2  
thotcandy  @youssefa transudate is like pulmonary edema due to CHF, no proteins, just fluid congestion and leaking out. That would decrease interstitial oncotic pressure because it has very little protein. Exudate due to inflammation/histamine has a high amount of protein (due to inc permeability) so the IOP doesn't change. +