Round 2: Tossup 18

Expulsion of this ion is coupled to intake of another by antiporters in the PCT that are triggered by angiotensin (-5[1])II. Enterochromaffin-like cells produce histamine that triggers the release of this cation by binding to H2 receptors. An ATPase that couples expulsion (-5[1])of this ion to K+ (-5[1])intake is blocked by omeprazole. (-5[2])This (15[1])ion's secretion (15[2])alongside intrinsic factor by (*) parietal cells is blocked by PPIs. High concentration of this ion turns pepsinogen into its active form, pepsin. Because chyme is rich (-5[1])in this ion, bicarbonate is released to neutralize it upon entry into the small intestine. For 10 points, stomach acid is rich in what cation? ■END■ (10[2]0[2])

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