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REB > 24. Nitrogen Excretion > Flashcards

24. Nitrogen Excretion Flashcards

1
Q

What is nitrogen excretion dependent on?

A

Protein intake
Protein synthesis
Protein breakdown
Renal function

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2
Q

What are the stages of amino acid catabolism?

A

Transamination
Oxidative deamination
Urea cycle

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3
Q

What are the products of transamination?

A

Alpha-keto acid

Glutamate

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4
Q

What are the products of oxidative deamination of glutamate?

A

Ammonia

Alpha-ketoglutarate

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5
Q

What is transamination?

A

Amino portion of one amino acid is transferred to a keto acid

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6
Q

What enzyme carries out oxidative deamination?

A

Glutamate dehydrogenase

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7
Q

What is the purpose of the urea cycle?

A

NH3 is converted to safe form for excretion

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8
Q

Where does the urea cycle take place?

A

Cytosol and mitochondria of liver

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9
Q

What are the steps in the urea cycle?

A
  1. NH3 + CO2 + 2ATP= Carbamoyl phosphate + 2ATP + P
    (carbamoyl phosphate synthetase 1)
  2. Carbamoyl group transferred from carbamoyl phosphate to ornithine to create citrulline
    (Ornithine transcarbamoylase)
    Citrulline released into the cytosol
  3. Citrulline + ATP + aspartate= argininosuccinate + AMP + PPi
    (Argininosuccinate synthetase)
  4. Argininosuccinate cleaved to form fumarate and arginine
    (Argininosuccinate lipase)
  5. Arginine is hydrolysed to urea and ornithine
    (Arginase)
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10
Q

What drives urea transport in the nephron?

A

Passive diffusion

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11
Q

What does the amount of urea present in the urine depend on?

A

ADH

-promotes expression of UT-A urea transporters in the collecting duct

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12
Q

What are the nitrogenous components of urine?

A

Urea
Creatinine
Uric Acid
Ammonia

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13
Q

What is the main role of creatinine in the body?

A

Facilitates ATP production in energy dependent tissues

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14
Q

Where and from what is creatine made?

A

Liver

Arginine

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15
Q

Where is creatine phosphorylated?

A

Muscle

Brain

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16
Q

What is creatinine formed from?

A

Created spontaneously from phosphocreatine

17
Q

What does plasma levels of creatinine depend on?

A

Muscle bulk

18
Q

What is uric acid?

A

End product of purine metabolism

19
Q

What causes hyperuricaemia?

A

High purine intake

Poor renal handling

20
Q

What does hyperuricaemia lead to?

A

Gout

Kidney stones

21
Q

Where and by what is ammonia produced intrarenally?

A

Glutamate metabolism

PCT

22
Q

What can increase levels of ammonia?

A

Liver disease
Diet
UTIs

23
Q

What does urine volume depend on?

A 
Fluid intake
Fluid loss
Hormones
Osmotically active substances in tubular fluid
Drugs
Pathological conditions
24
Q

What can cause urine to have an unusual colour?

A

Dehydration
Medication
Disease
Diet

25
Q

What can cause urine to be cloudy?

A

Mucous, sperm, prostatic fluid

Blood cells, bacteria

26
Q

What is urine sediment?

A

Urine that has been centrifuged to concentrate the substances

27
Q

What are Hyaline casts?

A

Cylindrical particles made of coagulated protein released by tubule cells (Tamm-Horsfall mucoprotein)
Substances can become trapped in cast in disease

28
Q

What could cause the formation of crystals in urine?

A

pH change

Concentrations increase

29
Q

How is proteinuria diagnosed?

A

Foamy urine

Dipstick test

30
Q

What are the 3 main mechanisms that cause proteinuria?

A

Glomerular
Overload/prerenal
Tubular

31
Q

What is glomerular proteinuria?

A

Caused by disease in the glomerulus
eg. diabetic nephropathy
Excess proteins filtered into urine

32
Q

What is Overload/ Prerenal proteinuria?

A

Presence of excess amounts of filterable, low Mr proteins

Eg. Amylase in acute pancreatitis

33
Q

What is tubular proteinuria?

A

Low reabsorption of filtered proteins in the PCT

Eg. Fanconi syndrome

REB (29 decks)

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