֍Metabolism of Ammonia֍
֍Sources of ammonia:
1) From Glutamine: Most of the ammonia is excreted
into urine as NH4+ (acid-base balance).
2) From bacterial action in the intestine (normal flora):
ammonia is formed from urea by bacterial urease in the
intestinal lumen. This ammonia can be absorbed from the
intestine by the portal vein and is converted again to urea
by the liver.
3) From amines: amines in diet, and monoamines that
acts as hormones and neurotransmitters give rise to
ammonia by amine oxidase.
4) From purines and pyrimidines: in the catabolism of
purines and pyrimidines, amino group attached to the
rings are released as NH3.
֍ Transport of ammonia to the liver
The ammonia that was formed from oxidation deamination in different tissues, is
going to be converted to urea to become less toxic. This takes place only in
hepatocytes, so ammonia must be transported from peripheral tissues to the
hepatocytes(liver).
Ammonia is a hydrophilic molecule(polar), so it can move easily
but there is a problem in that.
The problem is that Ammonia is a very toxic molecule, so while it
is moving in the blood to reach the liver , it causes toxicity to the
blood.
So, what is the solution for a such situation?
-Transferring ammonia in a hidden form (AA) so it won't cause
toxicity to the blood.
֍Sources of ammonia:
1) From Glutamine: Most of the ammonia is excreted
into urine as NH4+ (acid-base balance).
2) From bacterial action in the intestine (normal flora):
ammonia is formed from urea by bacterial urease in the
intestinal lumen. This ammonia can be absorbed from the
intestine by the portal vein and is converted again to urea
by the liver.
3) From amines: amines in diet, and monoamines that
acts as hormones and neurotransmitters give rise to
ammonia by amine oxidase.
4) From purines and pyrimidines: in the catabolism of
purines and pyrimidines, amino group attached to the
rings are released as NH3.
֍ Transport of ammonia to the liver
The ammonia that was formed from oxidation deamination in different tissues, is
going to be converted to urea to become less toxic. This takes place only in
hepatocytes, so ammonia must be transported from peripheral tissues to the
hepatocytes(liver).
Ammonia is a hydrophilic molecule(polar), so it can move easily
but there is a problem in that.
The problem is that Ammonia is a very toxic molecule, so while it
is moving in the blood to reach the liver , it causes toxicity to the
blood.
So, what is the solution for a such situation?
-Transferring ammonia in a hidden form (AA) so it won't cause
toxicity to the blood.
