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*?

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

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Cell Signalling and Transduction
The signaling molecules called steroid hormones

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

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Cell Signalling and Transduction
The binding of ligands to many G-proteins linked receptors leads to shortlived

decrease in the concentration of certain intracellular signaling molecules called second messenger
decrease in the concentration of certain extracellular signaling molecules called first messenger
increase in the concentration of certain intracellular signaling molecules called second messenger
increase in the concentration of certain extracellular signaling molecules called first messenger

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