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Advanced Biochemistry > Renal Function 9/11 > Flashcards

Renal Function 9/11 Flashcards

1
Q

What are the 6 major functions of the kidney?

A
  1. Urine formation
  2. Maintenance of fluid and electrolyte balance
  3. Regulation of acid-base balance
  4. Excretion
  5. Endocrine functions
  6. Plasma protein conservation
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2
Q

What 3 processes are involved in urine formation?

A
  1. Glomerular filtration of blood
  2. Tubular reabsorption of useful molecules
  3. Tubular secretion of wastes, or compounds/electrolytes in excess of the bodys needs
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3
Q

What is the glomerular filtration rate?

A

130ml/min (of blood filtered through the glomerulus/bowmans capsule)

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4
Q

What is the physiological role of the glomerulus?

A

Filtration of blood

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5
Q

What is the physiological role of proximal convoluted tubule?

A

Reabsorbs water, all glucose, salts, amino acids, and to varying extents urea, uric acid, bicarbonate, phosphate, chloride, potassium and magnesium

Secretes products of metabolism eg salts, H+ and ammonia

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6
Q

What is the physiological role of the loop of Henle?

A

Aids in reabsorption of water, Na+ and Cl-

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7
Q

What is the physiological role of distal tubule?

A

Adjusts for electrolyte and acid-base balance homeostasis through control of ADH and aldosterone

(reabsorbs/secretes K+ depending on bodys needs, aldosterone stimulates Na+ reabsorption and K+ secretion, secretes ammonia, uric acid and H+, reabsorbs HCO3-)

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8
Q

What is the physiological role of collecting duct?

A

Final site for concentrating/diluting urine - controls reabsorption of water, Na+, Cl-, and urea

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9
Q

How is urea formed?

A

Formed as part of protein metabolism - amino group removed from the amino acid (deamination) produces NH4+ which is toxic, converted to urea by the liver

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10
Q

What hormone stimulates Na+ and K+ reabsorption and secretion?

A

Aldosterone

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11
Q

How does the kidney regulate fluid balance?

A

Regulates fluid output to cope with extremes of overhydration or dehydration

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12
Q

What molecules does the kidney regulate in electrolyte balance?

A

Sodium
Chloride
Potassium
Calcium and Magnesium

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13
Q

What hormone controls calcium and magnesium balance?

A

PTH

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14
Q

How does the kidney regulate acid base balance?

A

HCO3- reabsorption and generation

H+ secretion into urine

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15
Q

What compounds does the kidney excrete?

A

Nitrogenous wastes such as urea, creatinine, and uric acid

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16
Q

Why is urea a poor indicator of renal function?

A

The kidneys have a large reserve capacity to excrete urea so plasma concentration does not rise until renal function is reduced to 50%

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17
Q

What controls the rate of urea production?

A

Protein in diet
Rate of protein synthesis in liver
Liver function (only place urea cycle exists so decreased liver function = increased urea levels)

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18
Q

How is creatinine derived?

A

Derived from the non-enzymatic conversion of creatine in muscle at a rate constant in proportion to muscle mass

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19
Q

Why is creatinine a good indicator of renal failure?

A

Because creatinine is freely filtered and excreted by the kidney, none is reabsorbed

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20
Q

How is uric acid derived?

A

Derived from oxidation of purines

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21
Q

Why is uric acid a good indicator of renal failure

A

Because it is freely filtered and secreted/reabsorbed by the kidney

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22
Q

In the 5th function of the kidney, what hormones does it produce?

A

5th function - endocrine function

Calcitriol/Vitamin D - inactive vitamin D is converted to the active form by an enzyme only present in the kidney
Renin - part of the RAAS system to secrete aldosterone
Erythropoitein - produced by kidneys to stimulate red blood cell production in bone marrow

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23
Q

How does the kidney maintain plasma protein conservation?

A

The glomerulus is only permeable to small amounts of albumin and low molecular weight proteins, will only see increased protein in urine if the glomerular membrane is damaged

24
Q

What are the 3 types of acute kidney disease?

A
  1. Pre-renal
  2. Intrinsic
  3. Post-renal
25
Q

What does pre-renal ACI cause and what is it caused by?

A

Marked decrease in renal blood flow/renal perfusion

Caused by volume depletion (eg decreased water intake/dehydration)
Haemorrhage
Myocardial infarction (heart doesn't pump properly)
26
Q

What does intrinsic ACI cause and what is it caused by?

A

Intrinsic damage to kidney structures resulting in acute tubular necrosis (death of tubular epithelial cells)

Caused by prolonged/severe underperfusion of kidneys eg low blood pressure
Nephrotoxins - toxic substances that inhibit, damage, or destory cells or tissues of the kidney

27
Q

What does postrenal ACI cause and what is it caused by?

A

Urinary tract obstruction/obstruction of urine outflow from kidneys

Caused by stones, tumor, enlarged prostate gland

28
Q

Define oliguria.

A

Urine output <400ml/24h

29
Q

Define anuria.

A

Urine output <100ml/24h (suggests obstruction or catastrophic injury to both kidneys)

30
Q

What clinical/biochemical manifestations would you see in acute kidney injury.

A

Oliguria or anuria
Hyperkalemia
Rapid or slow rise in creatinine levels
Uremia - increased levels of urea (toxic)
Diminished ability to excrete water/electrolytes = increases ECF volume = hypertension, edema, congestive heart failure

31
Q

What increases someones risk of CKD?

A 
Diabetes
Smoking
High blood pressure
Family history
Obesity
60 years or older
Aboriginal or Torres Strait Islander
32
Q

How does CKD develop?

A

Fewer nephrons are functioning so the remaining nephrons must filter more to compensate - can’t continue doing this so the nephrons die

33
Q

What is compensatory hyperfusion?

A

Increased perfusion of blood through an organ

34
Q

What is compensatory hypertrophy?

A

Increased cell size

35
Q

Define kidney damage.

A

Pathological abnormalities or markers of damage, including abnormalities in blood or urine tests or imaging studies.

36
Q

What are the 5 stages of CKD.

A
  1. Kidney damage with normal GFR
  2. Kidney damage with mild decrease in GFR
  3. Moderate decrease in GFR
  4. Severe decrease in GFR
  5. Kindey failure (dialysis)
37
Q

What are the causes of CKD?

A
  1. Loss of excretory and glomerular function
  2. Water/electrolyte disbalance
  3. Metabolic acidosis
  4. Loss of endocrine function - anaemia
  5. Hypocalcemia/bone disease
38
Q

Describe the loss of excretory and glomerular function in CKD.

A

Progressive disease in CKD
Causes increase in urea causing chronic urea (azotemia) - life threatening
Increase in plasma creatinine
Retention of phosphates, sulfates and urates

39
Q

Describe the disbalance of water and electrolytes in CKD.

A

Failure of sodium and free water excretion causes ECF volume expansion and total body volume overload - edema and hypertension
Sodium instability - overload and deficiency
Hyperkalemia - kidneys have decreased ability to excrete potassium = life threatening

40
Q

Describe metabolic acidosis in CKD

A

In CKD kidneys are unable to produce enough ammonia to excrete acids in the urine which causes an accumulation of phosphates, sulfates and other organic anions = increase in anion gap

Metabolic acidosis is associated with muscle wasting due to increased protein degredation (loss of lean body mass and muscle weakness)

41
Q

Describe loss of endocrine function in CKD

A

Develops from decreased renal synthesis of erythropoitein (hormone responsible for bone marrow stimulation for RBC production) causing anaemia

42
Q

Describe hypocalcemia/bone disease in CKD.

A

Failure to convert vitamin D into active form = causes abnormaility of bone turnover and mineralization
Secondary hyperthyroidism develops to restore plasma Ca levels leading to bone resorption

43
Q

What are the 3 things you would look at when investigating renal disease?

A
  1. Excretory function
  2. GFR
  3. Protein conservation
44
Q

Describe what you are looking for when testing the excretory function of the kidney.

A

Urea and creatinine levels

45
Q

What are the non renal causes of increased urea?

A

High protein diet
Haemorrhage
Gross tissue damage
Acute starvation

46
Q

What are the renal factors of increased urea?

A

Low GFR due to decreased renal perfusion or intrinsic renal disease

47
Q

What are creatinine levels in the body dependant upon?

A

Muscle mass

48
Q

What are urea levels in the body dependant upon?

A

Liver function, diet, and protein metabolism

49
Q

What are the disadvantages of creatinine measurement in CKD compared to urea

A

More difficult to measure
Dependant on muscle mass - significant factors in obese/malnourished, amputees, weight lifters, acutely ill patients, cancer patients)
Eating cooked meat can increase serum creatinine

50
Q

Define glomerular filtration rate (GFR)

A

The flow rate of filtered fluid through the body

51
Q

How is GFR measured?

A

Creatinine is used as a marker

clearance = urine creatinine x urine volume/serum creatinine x 24hr

52
Q

Why is creatinine used as a marker of GFR?

A

Because it is only filtered and not reabsorbed

53
Q

What are the advantages of creatinine as a marker of GFR?

A

Endogenous (dont need to introduce substance into the body)
Creatinine is produced at a constant rate per day
Freely filtered and not reabsorbed

54
Q

What are the disadvantages of creatinine as a marker of GFR?

A

It is only an estimate of GFR

About 10% is secreted (not filtered) by the renal tubules - this increases as kidney function declines

55
Q

What 2 things are looked at when looking at protein conservation of the kidney?

A

Glomerular proteinuira

Tubular proteinuria

56
Q

What is glomerular proteinuria?

A

When large amounts of high MW proteins enter the glomerular filtrate and enter the urine

57
Q

What is tubular proteinuria?

A

When the amount of protein filtered by the glomerulus is not increased but low MW proteins appear in urine because of incomplete tubular reabsorption

Advanced Biochemistry (18 decks)

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