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I understand the basics of digestion. I know that nutrients get absorbed by the microvilli, enter the bloodstream and travel to the liver but after all that, what is the biological mechanism that guides these nutrients to the proper receiving location?

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Broadly speaking, nutrients that enter the blood from the gut, and those that are released into the blood by the liver, are available to any cells that require them. So there is no "guiding to the correct location" in the sense that you suggest.

Lipids for example are present in the various lipoproteins and can be acquired from these by all cells. Iron is bound to transferrin, and any cell with transferrin receptors can internalise the transferrin and take the iron. Glucose is available in solution in the plasma, and free fatty acids are bound to serum albumin in the blood. During starvation the liver produces ketones ("ketone bodies") which are taken up by many different tissues/cell types.

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  • $\begingroup$ Are you saying that myriad nutrients just float along through the blood stream just bumping into myriad receptors at random and when there is a connection, the nutrient will be absorbed? $\endgroup$
    – max
    Apr 8, 2014 at 9:49
  • $\begingroup$ @max Basically, yes. $\endgroup$
    – Alan Boyd
    Apr 8, 2014 at 14:57
  • $\begingroup$ Pharmacokinetics must be a fun field! How different a concentration of iron, e.g., do different organs see? Clearly depends on rate of flow vs binding rate... $\endgroup$
    – AJK
    Dec 20, 2017 at 6:34

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