Lecture 2

Question 1

What is creatinine used for and what are its recommended levels?

Answer 1

Produced at a constant rate by creatine and creatine phosphate breakdown. It’s excretion in urine over 24 hours is proportional to muscle mass and so provides an estimate of muscle mass can be used to compare to levels of other hormones etc in urine. Also used as an indicator of renal function as it raised upon nephron damage.

Men 14-26 mg/kg

Women 11-20 mg/kg

Referees to excretion in urine per day

Question 2

When is a positive nitrogen balance normal?

Answer 2

In pregnancy or in adult suffering from malnutrition

Negative balance is never normal

Question 3

How much nitrogen in body and how much excreted daily?

Answer 3

2kg with 16g excreted daily with 14g in urine and faeces and loss of 2g in hair skin and nails etc

Question 4

What happens to amino acids in liver?

Answer 4

Split into amino group and carbon skeleton. Amino group excreted as urea and carbon skeleton broken into ketogenic and glucogenic amino acids.

Question 5

Glucogenic vs ketogenic

Answer 5

Glucogenic carbon skeleton goes to glucose or glygoegen (gluconeogenesis)

Ketogenic skeleton goes to ketone bodies or fatty acids

Question 6

Example of a ketogenic, glucogenic and amino acid that is both?

Answer 6

Ketogenic= lysine

Glucogenic- alanine

Both= tyrosine

Question 7

Effect of glucocorticoids such as cortisol n protein reserves?

Answer 7

Causes them to be mobilised

Question 8

What is Cushing’s syndrome?

Answer 8

Excess cortisol causes excessive protein breakdown. Get striae due to weakened skin. Often seen on stomach as cortisol contributes to obesity also.

Question 9

Give an example of a conditionally essential amino acid?

Answer 9

Tyrosine

Question 10

Why does the amino group need to be removed?

Answer 10

Allows carbon skeleton to be utilised in oxidative metabolism

Question 11

What are the two main pathways of nitrogen removal?

Answer 11

Transamination and deamination

Question 12

What is the difference between transamination and deamination?

Answer 12

Transamination transfers the amino group to a keto acid to form wither glutamate or aspartate.

Deamination liberates a free amino group as ammonia which is then converted to urea and excreted or ammonia itself is excreted directly.

Question 13

What important enzymes carry out transamination?

Answer 13

AST (alanine aminotransferase) and ALT (aspartate aminotransferase).

Plasma ALT and AST levels measured when checking liver function. Liver is damaged if these are elevated in blood. Death cap mushroom also elevates these

Question 14

Some useful characteristics of urea?

Answer 14

Non toxic

Chemically inert

Very water soluble

Question 15

What is interesting about the urea cycle?

Answer 15

Occurs in liver and uses 5 enzymes.

Cycle is inducible so a low protein diet or starvation will lower enzymes levels.

In this state consuming too much protein will result in re-feeding syndrome as enzymes will be saturated and ammonia toxicity (hyperammonaemia).

Risk factors include a BMI of under 16, more than 15% weight loss unintentionally in the past 3-6 months and 10 or more days with little or no nutrition.

Re feed at 5-10 kcal/kg/day and gradually raise to full after a week

Question 16

What do urea cycle defects lead to?

Answer 16

Hyperammonaemia and accumulation of urea cycle intermediates

Question 17

Urea cycle defects symptoms?

Answer 17

Vomiting 
Lethargy 
Irritability
Seizures 
Coma 
Mental retardation

Question 18

How to treat urea cycle defects?

Answer 18

Low protein diet and replace amino acids wit keto acids in diet

Question 19

Hyperammonaemia effects?

Answer 19

Blood level should be 25-40 micro moles per litre.

Disruption of cerebral blood flow

Alteration of blood brain barrier

PH effects (alkaline)

Question 20

How is nitrogen transported from amino acids to the liver for disposal?

Answer 20

Made into alanine or glutamine

Question 21

What is the heel prick test?

Answer 21

A test done on every newborn to look for various genetic abnormalities such as sickle cell disease and PKU and homocystinurea.

Question 22

What is phenylketonuria (PKU)?

Answer 22

Deficiency in phenylalanine hydroxylase. Phenylketones accumulate in tissue and give urine a musty smell (like a hamsters). Phenylalanine also is used to make tyrosine for dopamine and adrenaline etc so leads to tyrosine deficiency.

Can cause mental retardation if untreated in newborns due to lack of adrenaline etc signalling molecules. Also leads to seizures and developmental delay.

Treat by having a low phenylalanine diet enriched with tyrosine

Question 23

What is homocystinuria?

Answer 23

Problem with methionine breakdown. Have a low methionine diet. Affects connective tissue, CNS and muscles. Elevated homocysteine levels also associated with cardiovascular disease