if humans need salt, why does seawater dehydrate us?

Question

I’ve come to understand that the reason humans shouldn’t drink seawater is that it requires more water to get rid of that salt through urine. But if salt is a necessary nutrient, why would the body need to get rid of it at all? If your body were low on salt, what it be good for you to drink seawater?

Edit: added follow-up hypothetical question

In: Biology

Answer 1

To answer the hypothetical, no. The reasoning is that water always follows salt. So the salt concentration in your body is too low vs the seawater, thus more water is sucked out than absorbed. The absorption of water in many animals is passive via this process