Cell Signalling and Transduction
Why is it that inhaling nitric oxide reduces blood pressure only in the lung tissue and not elsewhere in the body*?

None of these
Because nitric oxide cannot cross cell membranes and enter the blood
Because other body tissues use a different signaling molecule
Because nitric oxide breaks down quickly and thus cannot travel far

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Cell Signalling and Transduction
The signaling molecules called steroid hormones

never enter the blood of humans
bind to cell surface receptors to trigger chemical cascades
are hydrophilic and so cannot penetrate the plasma membrane
are made in one location of the body but have their effects some distance away

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