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MELS301 > Renal Function > Flashcards

Renal Function Flashcards

1
Q

How does the glomerulus filter incoming blood?

A

A steep pressure gradient
Negatively charged basement membrane
Semi-permeable basement membrane

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2
Q

How does the negatively charged basement membrane in the glomerulus act as a filter?

A

It repels negatively charged molecules such as proteins.

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3
Q

How does the semi-permeable basement membrane of the glomerulus act as a filter?

A

There is a molecular cut off of about 66kDa so cells, large proteins and protein bound substances are stopped this allows water, glucose, electrolytes and amino acids to pass through.

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4
Q

What is the glomerular filtrate?

A

Protein free, cell-free fluid which continues through the proximal convoluted tubule.

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5
Q

What is a typical GFR?

A

90-120mL/min

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6
Q

What is the glomerular filtration rate?

A

The volume of glomerular filtrate formed per unit of time in all nephrons of both kidneys.

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7
Q

How is the GFR measured?

A

It cannot be accurately measured so is estimated using creatinine clearance however this is a non-linear relationship and tends to overestimate, less accurate with lower GFR so older people.

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8
Q

What is the formula for GFR?

A

GFR = (urine creatinine x volume of urine per minute)/ plasma creatinine.

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9
Q

What is urea?

A

A major nitrogen containing metabolic product of protein catabolism. More than 90% is excreted by the kidney depending on the GFR, plasma renal flow and hydration.

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10
Q

How does urea relate to kidney disease?

A

You have increased plasma levels with kidney disease however this can also be affected by renal perfusion, dietary protein, and protein catabolism.

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11
Q

What is creatinine?

A

The final decomposition product of phosphocreatine, it is filtered by the glomerulus so reflects the GFR. It is formed at a constant rate, not normally reabsorbed or affected by dehydration, diet or protein metabolism, more reliable than urea but still not great.

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12
Q

Why is creatinine not ideal?

A

There is impaired excretion in renal disease which increases plasma concentration. It varies with age, gender, muscle mass if you have more muscle mass you have more creatinine. At high plasma concentrations small amounts are secreted by the tubules. Measured using the unreliable Jaffe reaction.

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13
Q

How does the Jaffe reaction work?

A

Creatinine + picric acid forms an orange complex product which can be measured spectrophotometrically.

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14
Q

What are the cons of the Jaffe reaction?

A

It has poor specificity, positive and negative interferences. Also reacts with ascorbic acid (vitamin C), glucose, ketones, protein and pyruvate. Negative interferences from bilirubin.

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15
Q

What is the reference method for measuring creatinine and why is it not used in diagnostic labs?

A

The isotope dilution mass spec. Because it is expensive and impractical.

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16
Q

What are the major cations?

A

Na, K

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17
Q

What are the major anions?

A

Cl and HCO3.

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18
Q

What is the function of electrolytes?

A

pH maintenance, muscle function, redox reactions and enzyme cofactors. Maintenance of osmotic pressure and water distribution in various fluid compartments.

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19
Q

What are the 4 main methods for measuring electrolytes?

A

Ion-selective electrodes
Spectrophotometry
Atomic absorption spectroscopy
Flame ionisation spectroscopy

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20
Q

What is potentiometry?

A

You measure the change in electromotive force between an ion selective electrode and a reference electrode in a circuit.

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21
Q

What is direct ISE?

A

Where a sample is presented directly to the electrode chamber with no dilution this is used for whole blood such as ABG analysers and POCT.

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22
Q

What is indirect ISE?

A

The sample is diluted with LISS and this is used on larger analysers.

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23
Q

What is the problem with ISE?

A

Sometimes not so specific between certain ions, electrodes are really small and if there is lots of proteins or lipids you can get protein coating which covers the permeable gaps in the membrane, contamination and salt bridges form and electrolyte exclusion effect.

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24
Q

What is the electrolyte exclusion effect?

A

A problem with indirect ISE, normally plasma is 93% water and the rest solute. Patients that have a high volume of lipid or protein occupy that volume and the water is decreased where the electrolytes are contained. This falsely decreases levels when measured by indirect ISE as it is diluted.

25
Q

What is the function of sodium?

A

It maintains normal water distribution and osmotic pressure.

26
Q

What are the symptoms of hyponatraemia (low sodium)?

A

Nausea, weakness, confusion and coma.

27
Q

What are the causes of hyponatraemia (low sodium)?

A

Dilution or depletion, osmotic diuresis, adrenal insufficiency, nephropathy.

28
Q

What are the symptoms of hypernatraemia? (high sodium)?

A

Thirst, tremors, irritability, confusion and coma.

29
Q

What are the causes of hypernatraemia?

A

Dehydration or gain, diarrhoea, burns, hypothalamic disorder, HHS, nephropathy.

30
Q

What is the main function of potassium?

A

Na-K ATPase pumps which maintain high intracellular concentrations.

31
Q

What are the symptoms of hypokalaemia (low potassium)?

A

Muscle weakness, irritability, paralysis, tachycardia, arrest.

32
Q

What are the symptoms of hyperkalaemia (high potassium)?

A

Mental confusion, weakness, paralysis, vascular collapse, arrest.

33
Q

Where is aldosterone produced?

A

In the adrenal cortex, it is stimulated by renin & ACE activation of angiotensinogen II. Renin secretion is triggered by low Cl-, arteriolar pressure and beta-adrenergic activity.

34
Q

What is the result of aldosterone being produced?

A

Na, Cl, and H2O absorbed.

35
Q

Where is anti-diuretic hormone produced?

A

By the posterior pituitary, stimulates by baroreceptor and hypothalamic chemoreceptor activation.

36
Q

What does anti-diuretic hormone do?

A

Increases tubular reabsorption of H2O to restore blood volume.

37
Q

What is the osmolality?

A

Osmotically active solutes per Kg of solvent. (mOsmol/kg)

38
Q

What is the equation for calculated osmolality?

A

2(Na + K) + glucose + urea

39
Q

How does freezing point depression osmometry work?

A

It is used to measure osmolality of plasma or urine. Osmotically active substances (osmolytes) decrease the freezing point of solutions. It is independent of ambient pressure and temperature changes.

40
Q

What is the osmolar gap?

A

Measured osmolality - calculated osmolality

41
Q

What is the osmolar gap useful for?

A

Detecting the presence of exogenous osmotic substances, this can be used to rule out pseudohyponataemia due to the electrolyte exclusion effect.

42
Q

What are the osmolytes that may be present with a high osmolar gap?

A 
Methanol
Ethanol
Diuretics
Isopropyl alcohol
Ethylene glycol.
43
Q

What are the symptoms of alkalosis?

A

Tetany, headaches, convulsions.

44
Q

What are the symptoms of acidosis?

A

Deep respiration, drowsiness, coma.

45
Q

What are the rapid whole body buffering methods?

A

Dilution in total body water
Buffering in blood
Buffering in extravascular ECF

46
Q

What are the slower whole body buffering methods?

A

Buffering in cells
Carbonate in bone
Ion exchange in bone.

47
Q

What is the Henderson-Hasslebalch equation?

A

pH = 6.1 x log10 (HCO3-/0.03 x pCO2)

48
Q

What does fully compensated mean?

A

pH achieves a normal range

49
Q

What does partially compensated mean?

A

pH approaches normal range

50
Q

How do the lungs compensate?

A

They respond immediately in seconds by changing pCO2 by ventilation. This is a short term response and often is incomplete.

51
Q

How do kidneys compensate?

A

They respond slowly over 2-4 days by changing HCO3- this is a long term response and often complete.

52
Q

How does acidosis imbalance potassium?

A

H+ diffuses into cells and forces out K+ causing hyperkalaemia

53
Q

How does alkalosis imbalance potassium?

A

H+ diffuses out of cells and K+ diffuses in to replace it causing hypokalaemia.

54
Q

What is the equation for anion gap?

A

(Na+ + K+) - (Cl- + HCO3)

55
Q

Why is the anion gap used?

A

It is useful for determining the cause of metabolic acidosis

56
Q

What would a negative anion gap be caused by?

A

Metabolic acidosis due to loss of HCO3. You get Cl- retention at the kidney to compensate.

57
Q

What does a positive anion gap mean?

A

Metabolic acidosis is due to a gain of acids e.g. lactate acidosis, DKA. HCO3 and other anions are consumed by buffering.

58
Q

What could be causing a positive anion gap?

A 
Methanol
Uremia
DKA
Propylene glycol
Isoniazid
Lactate
Ethylene glycol
Salicylates

MELS301 (10 decks)

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