Nitrogen Disposal and Balance Overview

Questions and Answers

What defines a positive nitrogen balance?

Total Daily Nitrogen Losses < Total Daily Nitrogen Intake (correct)

Total Daily Nitrogen Losses = Total Daily Nitrogen Intake

Total Daily Nitrogen Losses > Total Daily Nitrogen Intake

Total Daily Nitrogen Intake < Total Daily Nitrogen Losses

In which condition is negative nitrogen balance most likely to occur?

Adults undergoing recovery from illness

Healthy children gaining weight

Individuals experiencing starvation (correct)

Athletes in intense training

What percentage of total urinary nitrogen in a protein-rich diet is urea nitrogen?

87.9% (correct)

86.1%

69.1%

100%

What is the main form of disposal for amino groups derived from amino acids in the body?

Urea Signup and view all the answers

What percentage of nitrogen-containing components of urine is urea responsible for?

90% Signup and view all the answers

In a normal protein intake diet, what is the nitrogen contribution from creatinine?

0.61 g Signup and view all the answers

Which of the following statements about nitrogen balance is accurate?

A prolonged negative nitrogen balance can lead to protein loss. Signup and view all the answers

Which nitrogenous waste has the highest percentage representation in a protein-poor diet?

Undetermined nitrogen Signup and view all the answers

What is the total urinary nitrogen excretion (in grams) for a protein-rich diet?

42 g Signup and view all the answers

Where does the urea cycle primarily take place in the body?

Liver Signup and view all the answers

What percentage of total urinary nitrogen is contributed by ammonia nitrogen in a normal protein intake diet?

3.0% Signup and view all the answers

What is the typical daily nitrogen loss for an individual weighing 70 kg?

2 gm Signup and view all the answers

In the context of a protein-poor diet, which nitrogen compound has a lower excretion rate in grams than creatinine nitrogen?

Uric acid nitrogen Signup and view all the answers

Which of the following is a consequence of a negative nitrogen balance?

Fatigue and weakness Signup and view all the answers

How much urea nitrogen is found in a protein-poor diet (in grams)?

2.9 g Signup and view all the answers

Which nitrogen form has the lowest contribution to total urinary nitrogen across all diets presented?

Uric acid nitrogen Signup and view all the answers

What is the primary role of arginase in the urea cycle?

It facilitates the cleavage of arginine to urea and ornithine. Signup and view all the answers

Which characteristic of urea makes it suitable for excretion in urine?

Highly soluble and nontoxic. Signup and view all the answers

What is the fate of ornithine after its formation in the urea cycle?

It can enter mitochondria and continue in the urea cycle. Signup and view all the answers

What is the function of N-acetylglutamate in urea cycle regulation?

It acts as a cofactor for CPS I. Signup and view all the answers

How does the concentration of arginine influence urea synthesis post protein-rich meals?

Increases the rate of urea synthesis. Signup and view all the answers

How is N-acetylglutamate transported from the liver after its synthesis?

It diffuses into the bloodstream and travels to other organs. Signup and view all the answers

What happens to urea after it enters the blood from the liver?

It is filtered by the kidneys and then excreted in urine. Signup and view all the answers

What is the significance of the solubility of urea in biochemical processes?

It facilitates the removal of nitrogen from the body. Signup and view all the answers

What are the two sources of nitrogen that contribute to the formation of urea?

Glutamate and ammonia Signup and view all the answers

Which enzyme deficiency is associated with Type I Hyperammonemia?

Carbamoyl phosphate synthetase Signup and view all the answers

What metabolic byproduct results from the urea cycle in addition to urea?

Fumarate Signup and view all the answers

Which condition is characterized by a defect in argininosuccinate lyase?

Argininosuccinic Acidemia Signup and view all the answers

During urea synthesis, how many high-energy phosphates are consumed?

4 Signup and view all the answers

What is a potential consequence of hyperammonemia?

Increased blood ammonia levels Signup and view all the answers

Which symptom is NOT typically associated with diseases involving urea cycle defects?

Peripheral neuropathy Signup and view all the answers

How does the urea cycle help in nitrogen disposal?

By converting ammonia to urea for excretion Signup and view all the answers

What immediate precursor of glutamate is involved in oxidative deamination?

Aspartate Signup and view all the answers

What is the result of the irreversible nature of urea synthesis?

It requires more energy for ATP regeneration. Signup and view all the answers

What condition is primarily associated with the shift in the equilibrium of the glutamate dehydrogenase reaction toward glutamate formation?

Liver disease Signup and view all the answers

What is the main consequence of decreased a-ketoglutarate levels due to high concentrations of ammonia?

Reduced cellular oxidation Signup and view all the answers

High levels of ammonia can lead to coma and death primarily due to disruptions in what metabolic cycle?

TCA cycle Signup and view all the answers

Which of the following conditions is NOT a direct cause of acquired hyperammonemia?

High protein diet Signup and view all the answers

The formation of collateral circulation around the liver is primarily associated with which condition?

Liver cirrhosis Signup and view all the answers

What is a key factor that makes the brain particularly vulnerable to the effects of hyperammonemia?

High energy production rate by the TCA cycle Signup and view all the answers

Which of the following is a consequence of portal blood shunting into systemic circulation due to liver disease?

Reduced access to detoxify ammonia Signup and view all the answers

What biochemical process is primarily altered due to elevated ammonia levels during liver disease?

Glutamate synthesis Signup and view all the answers

Study Notes

Nitrogen Disposal Overview

Total urinary nitrogen varies by protein intake: normal (13.2 g), protein-poor (23.28 g), protein-rich (42 g).
Urea nitrogen represents a significant portion of urinary nitrogen (86.1% in normal diet).
Other nitrogenous compounds in urine include ammonia (3%), creatinine (4.6%), uric acid (1.6%), and undetermined nitrogen (4.7%).

Positive and Negative Nitrogen Balance

Positive Nitrogen Balance: Daily nitrogen losses are less than intake, commonly found in growing children and recovering adults.
Negative Nitrogen Balance: Daily nitrogen losses exceed intake, seen in conditions like tissue wasting and starvation; can lead to dangerous protein loss.

Urea Cycle

Urea cycle occurs exclusively in the liver and is essential for nitrogen disposal.
Urea serves as the main form to excrete nitrogen derived from amino acids (90% of nitrogen in urine).
Arginase is pivotal for urea synthesis, primarily acting within the liver.

Urea Composition and Synthesis

Urea synthesis involves combining ammonia, aspartate, bicarbonate, and ATP to produce urea and fumarate.
Nitrogen in urea is sourced from free ammonia and aspartate; glutamate contributes indirectly via oxidative deamination and transamination.

Urea Cycle Regulation

N-Acetylglutamate (NAG) is essential for activating carbamoyl phosphate synthetase I (CPS I), which initiates the urea cycle.
NAG increases the affinity of CPS I for ATP, optimizing urea synthesis.

Genetic Defects and Disorders

Genetic defects in urea cycle enzymes can lead to severe conditions:
- Type I Hyperammonemia: Carbamoyl phosphate synthetase defect.
- Type II Hyperammonemia: Ornithine transcarbamoylase defect.
- Citrullinuria: Argininosuccinate synthase defect.
- Argininosuccinic Acidemia: Argininosuccinate lyase defect.
- Hyperargininemia: Arginase defect.
Symptoms of these defects include hyperammonemia, which can cause toxic ammonia accumulation leading to brain damage and episodic encephalopathies (e.g., convulsions, ataxia).

Mechanism of Ammonia Toxicity

High ammonia levels can cause coma and death, severely affecting cellular metabolism.
Acquired hyperammonemia is linked to liver disease (viral hepatitis, ischemia).
TCA cycle intermediates (like α-ketoglutarate) become depleted with elevated ammonia, hampering ATP production, especially in the brain, which has high energy demands.

These notes encapsulate the critical components of nitrogen disposal relating to amino acids and associated metabolic pathways.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz explores the critical processes of nitrogen disposal, including urinary nitrogen variations with protein intake and the implications of positive and negative nitrogen balance. It also delves into the urea cycle's role in nitrogen excretion, focusing on liver functions and key enzymes involved. Test your knowledge on these essential biochemical concepts!