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Flashcards in Nitrogen Excretion Deck (22)
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1
Q

what is positive nitrogen balance? What is negative nitrogen balance?

A
2
Q

under what circumstances do we have positive nitrogen balance?

A

during pregnancy/growth - when the body protein is increasing

3
Q

Under what circumstances do we have negative nitrogen balance?

A

in a ‘catabolic state’ when we’re using our body protein for energy (malnutrition, burns, cancer)

4
Q

nitrogen excretion is dependent on what factors?

A
  • protein intake
  • protein catabolism ( inadequate caloric intake, injury, cancer)
  • renal function (85% of N excreted as urea, 5% as NH4+ and 10% as uric acid and creatine ) - nitrogen also lost in feces and skin exudates
5
Q

what are the 3 key stages of amino aicd catabolism?

A
  1. transamination - transfer of amino group to alpha ketoglutarate - generates alpha-ketoacid and glutamate
  2. oxidative deamination of glutamate - generates ammonia and alphaketoglutarate
  3. urea cycle - converts toxic NH3 to urea
6
Q

describe the process of transamination

A

transamination is the process by which the amino portion of the amino acid is transfered to a keto acid - thus generating a different amino acid

in most cases, the recieving keto acid is alpha ketoglutarate and the amino acid thus formed is glutamate

7
Q

describe the process of oxidative deamination

A

oxidative deamination of glutamate by glutamate dehydrogenase releases an alpha-ketoglutare to be recycled and generates free amonia

  • most amino aicd nitrogen can be released as ammonia in this pathway
8
Q

briefly describe the urea cycle

A

converst toxic NH3 to a safe form (urea) for excretion from the body

takes place in the liver using 5 enzymes

forms one molecule of free ammonia and one molecule of aspartate donate the two nitrogens which are combined with CO2 to form the urea molecule

9
Q

what makes up most of the solid component of urine?

A

Urea (50% of the solid component)

10
Q

urea transport in the nephron is driven by?

A

by passive diffusion - becoming progressively concentrated along the length of the tubule

11
Q

which part of the nephron is highly permeable to urea due to the presence of specific transporters?

A

the collecting duct is highly permeable = urea is reabsorbed into interstitial space

12
Q

amount of urea excreted in urine depends on what?

A

the presence/absense of ADH - upregulates urea transporters

13
Q

what percent of the osmolarity of the renal medullary interstitium is contributed by urea?

A

40-50%

14
Q

what are the nitrogenous components of urine?

A

Urea

creatinine

uric acid

ammonia

15
Q

what is creatine? what is its role?

A

creatine - main role is to faciliate ATP production in energy dependent tissues (muscle and brain)

16
Q

what is creatinine? What is its role?

A

Creatinine is formed spontaneoulsy from phosphocreatine - at a constant rate 2% of creatine levels/day

plasma level depends on muscle bulk - removed from the blood by glomerular filtration and tubular secretion

*if renal filtration is deficient, plasma creatinine increases*

measurement of creatinine in urine is used to measure kidney function

17
Q
A
18
Q

what is uric acid? What is its role in the body?

A

it is the end product of purine metabolism - freely filtered in the glomerulus with 90% being reabsorbed in the PCT

hyperuricaemia can occur due to high purine intake (meat or seafood) or due to poor renal function - leads to deposition in the joints (gout) or kidneys (kidney stones)

19
Q

what is ammonia? What is its role in the body?

A

NH3+

the majority of renal ammonia excretion derives from intrarenal production not from glomerular filtration

produced by glutamate meatbolism in acid base balance - levels are normally low - but can increase due to diet, liver disease, or UTIs

20
Q

what is the normal pH of urine?

A

5-6

21
Q

how do the different nephron components adjust urine composition?

A
  • proximal convoluted tuuble - active reabsorption of filtered ‘solutes’ this increases the interstitium osmolarity - enhancing absorption of water
  • loop of henle- the thin descending limb has low permeability to ions and urea- while being highly permeable to water - concentrates filtrate
  • loope of henle- the ascending limb is impermeable to water but is permeable to ions, contribues to the countercurrent multiplier system
  • the distal convoluted tubule - renal acidification (H+ ions pumped in) and reabsorption of Na+ and water
  • collecting duct - fine tuning of volume and urine concentration - regulated by ADH
22
Q

what is proteinuria?

A

increased levels of protein in the urine - often ‘foamy’ in appearance

3 main mechanisms that cause proteinuria =

  • glomerular proteinuria - due to disease of glomerulus
  • overload of prerenal proteinuria - persistent proteinuria without glomerular disease
  • tubular proteinuria- due to low reaborption of filtered proteins in the PCT - can be inherited or due to ingestion of drugs or toxins