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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
What does pre-renal ACI cause and what is it caused by?
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
What does intrinsic ACI cause and what is it caused by?
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
What does postrenal ACI cause and what is it caused by?
Urinary tract obstruction/obstruction of urine outflow from kidneys Caused by stones, tumor, enlarged prostate gland
28
Define oliguria.
Urine output <400ml/24h
29
Define anuria.
Urine output <100ml/24h (suggests obstruction or catastrophic injury to both kidneys)
30
What clinical/biochemical manifestations would you see in acute kidney injury.
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
What increases someones risk of CKD?
``` Diabetes Smoking High blood pressure Family history Obesity 60 years or older Aboriginal or Torres Strait Islander ```
32
How does CKD develop?
Fewer nephrons are functioning so the remaining nephrons must filter more to compensate - can't continue doing this so the nephrons die
33
What is compensatory hyperfusion?
Increased perfusion of blood through an organ
34
What is compensatory hypertrophy?
Increased cell size
35
Define kidney damage.
Pathological abnormalities or markers of damage, including abnormalities in blood or urine tests or imaging studies.
36
What are the 5 stages of CKD.
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
What are the causes of CKD?
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
Describe the loss of excretory and glomerular function in CKD.
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
Describe the disbalance of water and electrolytes in CKD.
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
Describe metabolic acidosis in CKD
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
Describe loss of endocrine function in CKD
Develops from decreased renal synthesis of erythropoitein (hormone responsible for bone marrow stimulation for RBC production) causing anaemia
42
Describe hypocalcemia/bone disease in CKD.
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
What are the 3 things you would look at when investigating renal disease?
1. Excretory function 2. GFR 3. Protein conservation
44
Describe what you are looking for when testing the excretory function of the kidney.
Urea and creatinine levels
45
What are the non renal causes of increased urea?
High protein diet Haemorrhage Gross tissue damage Acute starvation
46
What are the renal factors of increased urea?
Low GFR due to decreased renal perfusion or intrinsic renal disease
47
What are creatinine levels in the body dependant upon?
Muscle mass
48
What are urea levels in the body dependant upon?
Liver function, diet, and protein metabolism
49
What are the disadvantages of creatinine measurement in CKD compared to urea
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
Define glomerular filtration rate (GFR)
The flow rate of filtered fluid through the body
51
How is GFR measured?
Creatinine is used as a marker | clearance = urine creatinine x urine volume/serum creatinine x 24hr
52
Why is creatinine used as a marker of GFR?
Because it is only filtered and not reabsorbed
53
What are the advantages of creatinine as a marker of GFR?
Endogenous (dont need to introduce substance into the body) Creatinine is produced at a constant rate per day Freely filtered and not reabsorbed
54
What are the disadvantages of creatinine as a marker of GFR?
It is only an estimate of GFR | About 10% is secreted (not filtered) by the renal tubules - this increases as kidney function declines
55
What 2 things are looked at when looking at protein conservation of the kidney?
Glomerular proteinuira | Tubular proteinuria
56
What is glomerular proteinuria?
When large amounts of high MW proteins enter the glomerular filtrate and enter the urine
57
What is tubular proteinuria?
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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