Physiology HW help

Question

1. Is the signaling between the adrenal medulla and cardiac muscle cells endocrine or paracrine? Why?

Answer 1

Determining if a signal is endocrine or paracrine rests on the distance the signal has to travel. In paracrine signaling, the signaling cell is beside (the Greek, "para", means "beside") the target cell. In contrast, endocrine signaling has to travel in the blood stream to reach its target. Therefore, given that the adrenal medulla will require the blood stream to act on the cardiac muscle cells, the signaling between the adrenal medulla and cardiac muscle cells is endocrine.