Q.94 In mammals, the two important organs associated with the production and elimination of urea are
(A) gastrointestinal tract and lungs (B) gastrointestinal tract and liver
(C) kidneys and lungs (D) liver and kidneys
Urea Production and Elimination: Key Organs in Mammals
In mammals, urea is synthesized in the liver and primarily excreted by the kidneys, making liver and kidneys the two crucial organs. The correct answer is (D) liver and kidneys.
Correct Answer
The liver produces urea via the urea cycle, detoxifying ammonia from amino acid metabolism into urea, which enters the bloodstream. Kidneys filter and excrete about 50% of filtered urea in urine, regulating nitrogen balance.
Option Breakdown
| Option | Organs | Role in Urea Handling | Why Correct/Incorrect? |
|---|---|---|---|
| (A) | Gastrointestinal tract and lungs | GI tract minor urea excretion (e.g., saliva in ruminants); lungs eliminate CO₂, not urea. | Incorrect: Neither primarily produces or eliminates urea; lungs handle gases. |
| (B) | Gastrointestinal tract and liver | Liver synthesizes urea; GI minor role (e.g., colon in horses). | Incorrect: GI not major elimination site in mammals; kidneys primary. |
| (C) | Kidneys and lungs | Kidneys excrete urea; lungs irrelevant for urea. | Incorrect: Lungs don’t process urea; misses production organ (liver). |
| (D) | Liver and kidneys | Liver: urea synthesis from ammonia; Kidneys: filtration, partial reabsorption, urinary excretion. | Correct: Essential duo for ureotelic mammals maintaining nitrogen homeostasis. |
Urea Cycle Overview
Ammonia from protein catabolism is converted to urea in liver hepatocytes via ornithine cycle enzymes. Urea diffuses into blood, filtered at glomerulus; 40-60% reabsorbed based on flow, rest excreted to prevent toxicity. This question highlights ureotelism in mammals vs. uricotelism in birds.
