24. Nitrogen Excretion Flashcards
What is nitrogen excretion dependent on?
Protein intake
Protein synthesis
Protein breakdown
Renal function
What are the stages of amino acid catabolism?
Transamination
Oxidative deamination
Urea cycle
What are the products of transamination?
Alpha-keto acid
Glutamate
What are the products of oxidative deamination of glutamate?
Ammonia
Alpha-ketoglutarate
What is transamination?
Amino portion of one amino acid is transferred to a keto acid
What enzyme carries out oxidative deamination?
Glutamate dehydrogenase
What is the purpose of the urea cycle?
NH3 is converted to safe form for excretion
Where does the urea cycle take place?
Cytosol and mitochondria of liver
What are the steps in the urea cycle?
- NH3 + CO2 + 2ATP= Carbamoyl phosphate + 2ATP + P
(carbamoyl phosphate synthetase 1) - Carbamoyl group transferred from carbamoyl phosphate to ornithine to create citrulline
(Ornithine transcarbamoylase)
Citrulline released into the cytosol - Citrulline + ATP + aspartate= argininosuccinate + AMP + PPi
(Argininosuccinate synthetase) - Argininosuccinate cleaved to form fumarate and arginine
(Argininosuccinate lipase) - Arginine is hydrolysed to urea and ornithine
(Arginase)
What drives urea transport in the nephron?
Passive diffusion
What does the amount of urea present in the urine depend on?
ADH
-promotes expression of UT-A urea transporters in the collecting duct
What are the nitrogenous components of urine?
Urea
Creatinine
Uric Acid
Ammonia
What is the main role of creatinine in the body?
Facilitates ATP production in energy dependent tissues
Where and from what is creatine made?
Liver
Arginine
Where is creatine phosphorylated?
Muscle
Brain
What is creatinine formed from?
Created spontaneously from phosphocreatine
What does plasma levels of creatinine depend on?
Muscle bulk
What is uric acid?
End product of purine metabolism
What causes hyperuricaemia?
High purine intake
Poor renal handling
What does hyperuricaemia lead to?
Gout
Kidney stones
Where and by what is ammonia produced intrarenally?
Glutamate metabolism
PCT
What can increase levels of ammonia?
Liver disease
Diet
UTIs
What does urine volume depend on?
Fluid intake Fluid loss Hormones Osmotically active substances in tubular fluid Drugs Pathological conditions
What can cause urine to have an unusual colour?
Dehydration
Medication
Disease
Diet
