Nitrogen Excretion

Question 1

what are major end products of amino acid catabolism?

Answer 1

• CO2
• H2O
• Urea

Question 2

the urea cycle is important in removal of what? where does the urea cycle occur?

Answer 2

NH3, in the liver

Question 3

what is the only site for complete urea cycle?

Answer 3

the liver (N incorporated into urea)

Question 4

what are the main sources of NH3??

Answer 4

• portal blood (30%)
• catabolism of amino acids (ex: lysine)
• transamination (20%)
• deamination of glutamine (10%)

Question 5

what regulates the urea cycle?

Answer 5

• rate of amino acid catabolism (short term)
• dietary protein level (long term)
• glucocorticoids & glucagon increase ureagenesis

Question 6

the starvation state ______ ureagenesis

Answer 6

INCREASES

Question 7

what happens in the urea cycle?

Answer 7

1. glutamine and glutamate make ammonia (NH3) which combines with CO2 to form carbamoyl-PO4
2. carbamoyl- PO4 enters the urea cycle and combines with Ornithine to yield Citruline
3. Citruline and aspartate combine to give arginino-succinate
4. arginino-succinate becomes arginine and fumarate (fumarate leaves the cycle)
5. arginine is broken down to urea and ornithine

Question 8

low dietary protein ________ ureagenesis

Answer 8

DECREASES

Question 9

Glucocorticoids & glucagon _______ ureagenesis

Answer 9

INCREASE

Question 10

Purines are degraded to what?

Answer 10

Uric acid and NH3

Question 11

what is the glomerular filtration rate do? what does it use?

Answer 11

used to evaluate the kidney functions –> Creatinine excretion

Question 12

Oxaloacetate is _______ to ________ which combines with citruline in the urea cycle

Answer 12

Oxaloacetate is transaminated to aspartate.