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Yr 2 - Renal > Physiology of the Kidney > Flashcards

Physiology of the Kidney Flashcards

1
Q

How much blood enters each kidney every minute?

What % of total blood pumped by the heart is it?

A

1200ml

20%

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2
Q

How is accurate measurement of glomerular filtration rate (GFR) taken?

A

Requires injection of radioactive tracer

  • Technetium (Tc99)
  • Chromium-51 (51Cr-EDTA)
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3
Q

What is creatinine clearance used as?

A

Estimation of GFR

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4
Q

Where is creatinine released from?

A

Muscle at a relatively constant rate

Relative to muscle mass

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5
Q

How is creatinine then filtered?

A

Filtered by kidneys

Some secretion into the filtrate by the proximal tubule kidneys

Not that accurate for GFR (as some is secreted as well as filtered)

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6
Q

As your serum creatinine levels increase, what does this indicate?

A

Loss of kidney function

Be aware of muscly people –> will have high creatinine but good kidneys

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7
Q

What are problems with using serum creatinine for measuring kidney disease?

A
  • Not specific for site of injury

- Delay in rise following acute kidney injury

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8
Q

What tends to be used instead of creatinine clearance?

A

Estimated Glomerular Filtration Rate (eGFR)

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9
Q

How is eGFR calculated?

A
  • Age
  • Sex
  • Ethnicity
  • Serum creatinine
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10
Q

What does eGFR correlate with?

A

% of kidney function

e.g. eGFR = 50 = 50% kidney function

Useful when discussing with patients

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11
Q

When will patients need to commence dialysis?

A

eGFR < 10mls/min/1.73m2

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12
Q

What is the best treatment for kidney failure?

A

Kidney transplant

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13
Q

What is dialysis?

A

Dialysis is a procedure to remove waste products and excess fluid from the blood when the kidneys stop working properly. It often involves diverting blood to a machine to be cleaned.

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14
Q

What % of kidney function is lost by the time creatinine levels rise above 104μmol/L (male) i.e. normal levels?

A

50% of kidney function lost

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15
Q

Where do 80% of the glomeruli lie?

A

Cortex of kidney

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16
Q

What is job of proximal convoluted tubule?

A

Recovers 70% of glomerular filtrate

  • Water
  • Electrolytes (Na+, Cl+, K+)
  • Glucose
  • Amino acids
  • Phosphate

Recovery and regeneration of bicarbonate

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17
Q

What is the regeneration of bicarbonate dependent on?

A

Carbonic anhydrase (enzyme)

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18
Q

What can a failure to recover and regenerate bicarb lead to?

A

Acidaemia (disrupts acid-base balance)

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19
Q

What is taken up in the ascending limb of Henle?

A
  • Na+
  • K+
  • 2Cl-
  • H20

Sodium/Potassium/Chloride cotransporter (from lumen to inside cell)

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20
Q

What drug acts at the ascending limb of Henle?

A

Loop diuretics

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21
Q

How do loop diuretics work?

A

Block uptake of Na+/K+/2Cl+ cotransporter

So water is not reabsorbed and is lost in urine

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22
Q

When are loop diuretics used?

A
  • Cardiac failure
  • Oedema
  • Chronic kidney disease
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23
Q

What are the side effects of diuretics?

A
  • Low sodium (hyponatremia)

- Low potassium (hypokalaemia)

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24
Q

What can hyponatremia lead to?

A

Serious neurological problems (coma, death)

25
Q

What can hypokalaemia lead to?

A

Cardiac arrhythmias

26
Q

What is reabsorbed at the cortical collecting duct? What is this controlled by?

A

Na+ (with H20, Cl) in exchange for K+

  • Na+, Cl-, H20 out into blood
  • K+ into tubule

Controlled by aldosterone

27
Q

What happens at the medullary collecting duct?

A

Site of urinary concentration

Water, Na+ Cl-, HCO3- reabsorption

28
Q

Where does antidiuretic hormone (ADH) act?

A

Medullary collecting duct

29
Q

Where is ADH stored?

A

Posterior pituitary

30
Q

What is effect of ADH?

A

Stimulates water reabsorption –> concentrated urine

31
Q

What happens when water needs to be preserved (e.g. dehydration)?

A

ADH levels increase
More water reabsorbed
More concentrated urine

32
Q

What is osmolality?

A

“Osmolality” refers to the concentration of dissolved particles of chemicals and minerals – such as sodium and other electrolytes – in your serum. Higher osmolality means more particles in your serum. Lower osmolality means they’re more diluted

33
Q

What is optimum plasma osmolality?

A

285 mOsm/L

34
Q

What is the normal daily urine output?

A

1.5-2 L of urine

35
Q

What is the normal urine osmolality?

A

50-1400 mOsm/L

50 –> very diluted
1400 –> very concentrated

36
Q

What is urine osmolality regulated to maintain?

A

Plasma osmolality

37
Q

What is it important to regulate urine osmolality?

A

To maintain plasma osmolality

38
Q

Why do the kidneys concentrate urine during periods of decreased fluid intake?

A

To conserve salt and water

Maintain circulating volume and blood pressure

39
Q

What is the mechanism responsible for urine concentration called?

A

Counter current mechanism

40
Q

How does the counter current mechanism work?

A

High concentration gradient in the medulla

Enables reabsorption of water from the filtrate

  • In proximal tubule
  • In collecting duct
41
Q

What is insensible loss?

A

Loss of fluid not through urine

Sweating, faeces, respiration

42
Q

During states of fluid loss, what happens?

A
  • Increased ADH

- Increased renin

43
Q

What is effect of increased renin?

A

Renin converts angiotensinogen to angiotensin I

ACE converts angiotensin I to angiotensin II (vasoconstriction)

Angiotensin II stimulates release of aldosterone which increases Na+ reabsorption

44
Q

What is glomerular filtration?

A

The movement of substances from the blood within the glomerulus into the capsular space

45
Q

What is tubular reabsorption?

A

The movement of substances from the tubular fluid back into the blood

46
Q

What is function of glomerulus?

A

Filters small solutes from blood

47
Q

What is function of Bowman’s capsulse?

A

Collects what is filtered through the glomerulus

48
Q

What is the function of the proximal convoluted tubule?

A

1) Reabsorbs 65% of filtrate volume: nutrients(glucose, amino acids)/ ions(Na/bicarb)/ water
2) Secretes toxins (ammonia, creatinine, organic acids, some drugs)
3) Adjusts filtrate pH

49
Q

What is function of descending limb of loop of Henle?

A

Water reabsorption (aquaporins) = increased osmolality

50
Q

What is function of ascending limb of loop of Henle?

A

Reabsorbs Na/Cl =r educes osmolalityUrea secreted (urea recycling)

51
Q

What is function of distal convoluted tubule?

A

Hormone controlled

Aldosterone: reabsorb Na (Cl follows), secrete K

PTH: reabsorb Ca

Reabsorb bicarb and water, synthesizes bicarb

52
Q

What is function of collecting duct?

A

Concentrates urine using osmotic gradient

ADH: reabsorb water

Reabsorb/secrete various ions (sodium, potassium, hydrogen ions, bicarb) to maintain blood pH

53
Q

What is GFR?

A

Refers to the ultrafiltrate of plasma which crosses the glomerular barrier into the urinary space

Equal to the total filtration rates of all the functioning nephrons

54
Q

What is used instead of GFR?

A

eGFR as bette predictor of risk

55
Q

What does eGFR take into account?

A

Serum creatinine, sex, age, race

56
Q

How does ethnicity affect GFR?

A

Higher average muscle mass in African patients –> higher creatinine generation rate = higher GFR at same level of sCr

57
Q

How does sex affect GFR?

A

Men have more muscle mass

58
Q

How does age affect GFR?

A

Younger people have greater muscle mass

Yr 2 - Renal (16 decks)

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