Why does the body convert NH₄⁺ to urea for excretion?

Question

Accepted Answer

Hi, everybody. Let's focus on our next question. Which of the following statements about the urea cycle is or are true. We've got four statements numbered one through four and then four answer choices. A through D listing different possible correct answers. We have at least one answer choice that involves two correct statements. So make sure we don't uh get careless, make sure we look at all of our statements. So statement one says ammonia is directly excreted by the liver into the bloodstream for removal from the body. Well, this one's pretty easy. This is not a true statement as we recall the whole purpose they recycle is that urea is, excuse me, the ammonia is toxic. You don't want that building up in the body for any length of time at all. So instead ammonia will be converted to urea through the urea cycle in the liver. Ammonia is too toxic. You don't want that building up in any way. So, ammonia is converted to urea by the urea cycle in the liver. So instead of being directly excreted, it's converted to urea, it's then transported to the kidneys for removal from the body. So we know that student one is incorrect. Let's move on to statement two. Now, a quick note here, if you were on a test on a test in a hurry note that none of our answer choices. So the answer choices are A two only B three only C four only or D two and four. Number one isn't even an option. So if we were on a test in a hurry, I would have looked at those things and not even considered option one. So now we look at number two, ammonia produced from amino acid metabolism is detoxified in the liver via the re the urea cycle where it is converted into urea or safe excretion. And I just realized I wanted to do that underlining with blue. So I switched it out, but this is a true statement. So statement number two is true. So we want to look back at our answer choices and see if that helps us eliminate anything. Well, choice B says three only. So that would be out. Choice C says four only. So uh we're going to be going between choice A which is two only and choice D which is two and four. Now notice again right now we're down to choice between two and four because two is in both of those places, but four is only in choice D. So when just in interest of time on a test, I would go straight to statement four, skip statement three. So four says NH four plus. So, an ammonium ion is primarily, yep, started to underline and read again, converted into urea by the liver and excreted through the urea cycle. Well, this one might be a little tricky but um the ammonium ion is not as toxic as toxic as ammonia. So it doesn't need to be converted into anything. So this statement is untrue, we'll cross out, converted into your Yeah, and excreted through the urea cycle. Instead, ammonium ions are directly excreted by the kidneys. So since statement four is incorrect, we know that choice D two and four is incorrect and just by elimination, then we have our answer of choice. A statement two only, just to be thorough, we will look at statement three which says urea is synthesized in the kidneys. It's part of the urea cycle and then excreted in the urine. Well, this is incorrect. It is not synthesized in the kidneys. It's synthesized in the liver that is part of the urea cycle. But in the liver, not the kidneys, then it's excreted in the urine. So choice three or statement three, excuse me, incorrect. So we have our correct statement and correct answer. So to the question, which of the following statements about the urea cycle is or are true. The answer is choice. A statement two only statement two saying that ammonia produced from amino acid metabolism is detoxified in the liver via the urea cycle where it is converted into Urea for safe excretion. See you in the next video.

Why does the body convert NH₄⁺ to urea for excretion?

Key Concepts

Ammonia Toxicity

Urea Cycle

Nitrogen Excretion

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