Fate of Ammonia Unit -0 By Dr. Abdulrahman Al-Ajlan
Fate of Ammonia Ammonia, which is very toxic in the body, is converted to urea which is non toxic, very soluble and readily excreted by the kidneys. Particularly affects the central nervous system. The level of ammonia in the blood must be kept low because even slightly elevated concentrations are toxic.
Sources of body ammonia Ammonia is produced from the metabolism of a variety of compounds. 1.From amino acids. Many tissues, but particularly the liver, from ammonia from amino acids by the aminitrans ferase and glutamate dehydrogluase reactions.
Continue… 2.From glutamine The kidneys from ammonia from glutamine by the action of renal glutamine. Most of this ammonia is excreted into the urine as NH 4, which is an important acid–base balance.
Continue… 3.From bacterial action in the intestine ammonia is formed by the bacterial degradation of urea in the lumen of the intestine. Urea Bacterial NH3 Urease Urea + H 2 O Urease Co 2 + 2NH 3
Continue… 4.From amines : Amins obtained from the diet and monoamines that serve as hormones or neuro transmitters give rise to ammonia by the action of amine oxidare 5.From purines and pyrimidines
Urea Cycle One nitrogen of urea molecule is supplied by free NH 3 and the other nitrogen by aspartate The carbon and oxygen of urea are derived from CO 2 Urea is produced by the liver and then is transported in the blood to the kidneys for excretion in the urine.
Urea formation Most of NH 4 formed be deamination of amino acid in the liver is converted to urea, and the urea is excreted in the urine. Except for the brain, the liver is probably the only site of urea formation, and in severe hepatic disease, the blood urea nitrogen level falls and the blood NH 3 level rises. The synthesis of urea via the urea cycle involves the following cycle.