Gastrin is released by G cells and stimulates Parietal cells to secrete hydrochloric acid. Why is it not acting in a paracrine fashion instead of endocrine?
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1$\begingroup$ Is this question based on the content of a course? $\endgroup$– Bryan Krause ♦Mar 9, 2020 at 19:02
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$\begingroup$ Nope, it is not. $\endgroup$– NeriusMar 10, 2020 at 0:08
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Paracrine signalling would mean not merely that gastrin is signalling the same organ, but that it is signalling nearby cells in the same organ - so that a few parietal cells close by respond, while the others perhaps would ignore the signal because maybe the paracrine signal would be degraded. While the distinction is not absolute - there are shades of gray in all these things - blood gastrin tests are commonly done and medically relevant ( https://medlineplus.gov/ency/article/003697.htm ). Because you can look at gastrin level as a whole-body characteristic, it is certainly appropriate to call it an endocrine signal.
Though their role is less emphasized, bear in mind that there are gastrin-producing G cells in the duodenum as well, and gastrin affects other digestive organs.
