Urea Cyle

Question 1

Aminotransferase enzymes are responsible for transamination reactions of a.as. The two that are measured clinically are?

Answer 1

Aspartate aminotransferase
Alanine aminotransferase

Higher levels indicate more leakage from damaged hepatocytes

Question 2

What happens to excess a.as that are not used protein synthesis?

Answer 2

Excess amino acids are metabolised (not stored for use as potential energy because this can be done more efficiently using other energy sources). The carbon skeleton, as an α-keto acid, is fed into the citric acid cycle to be incorporated into glucose production whilst the ammonia is largely excreted, although some is used in the biosynthesis of amine containing substances.

Question 3

The glucose - alanine cycle: proper !!

Answer 3

In muscle, alanine is the principal ammonia scavenger and transporter. Glutamate collects the ammonia, the enzyme alanine aminotransferase (ALT) transaminates the amino group from glutamate, forming α ketoglutarate, and the amino group gets attached to pyruvate, formed from glycolysis, making alanine. This gets transported in the blood, taken up by the liver where the reverse reaction occurs and the ammonia gets converted to urea. Pyruvate is re- cycled into glucose.

Question 4

Affects of a defect in the urea cycle:

Answer 4

The common thread to them all is the elevation of ammonia levels in the blood.

Neurotoxicity associated with Ammonia.
Elevated blood ammonia is seen in severe liver disease, whether it be as a result of liver failure due to infection, toxicity or substantial surgical resection. This is something that is seen in the clinical practice (not uncommonly) and since ammonia is neurotoxic, is one of those things that staff are conscious of when a patient with liver disease becomes confused or comatose . As the urea can travel t the brain and cause a stop of the TCA cycle.

Question 5

Albumin:

What is it?

Function?

Answer 5

A highly soluble, single polypeptide protein

9-12g produced per day

1. Binding and transportation - 4 binding sites - utilised by drugs such as warfarin and NSAIDS
2. Maintenance of oncotic pressure
3. Anticoagulant effect

Question 6

What causes albumin to decrease?

Consequences?

Answer 6

Decreased synthesis - e.liver disease

Increased loss - haemorrhage, burns, some syndromes

Consequences — colloid oncotic pressure decreased leading to oedema

Decreased transportation

Question 7

How does albumin travel?

Answer 7

Albumin leaves the circulation via the interstitium to the lymph system and back to the circulation via the thoracic duct.

Rate known as transcapillary escape rate