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Renal Physiology > Kidney Function 1 > Flashcards

Kidney Function 1 Flashcards

1
Q

What are the major functions of the kidney?

A
  • water and sodium homeostasis
  • acid-base balance
  • control of ECF ion concentration (K, Ca, Mg, Cl, HPO4)
  • excretion of waste products and xenobiotics
  • endocrine secretions (EPO, renin, VitD3, PGI2)
  • formation of concentrated (1200mOs/L) or dilute urine (30mOs/L)
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2
Q

What are the features of superficial cortical glomeruli (SCG)?

A
  • 85% of glomeruli
  • short LOH; penetrate short distance into medulla
  • efferent arterioles give rise to cortical capilaries surrounding PCT & DCT
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3
Q

What are the features of juxtamedullary glomeruli (JMG)?

A
  • 10-15% of glomeruli
  • at junction of medulla and cortex
  • long LOH; penetrate deeply into medulla to papilla
  • efferent arterioles become vasa recta around LOH
  • responsible for the concentration gradient of the kidney that allows formation of concentrated urine
    • 300mOs at junction
    • 1200mOs at papilla
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4
Q

Normal renal blood flow in a 70kg human is

A

1L/min (total including both kidneys) ~20% of CO

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5
Q

What percentage of cardiac output flows through the renal vasculature per minute?

A

20%

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6
Q

What is normal haematocrit (packed cell volume)?

A

(% of RBCs in blood)

40% - women

45% - men

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7
Q

What is filtered from the renal blood flow?

A

plasma

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8
Q

Renal plasma flow to the kidney is

A

~600mL/min

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9
Q

Normal glomerular filtration rate (GFR) is

A

120mL/min (both kidneys)

60mL/min (each kidney)

approximately 180L/day of plasma is filtered

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10
Q

What volume of plasma is filtered per day?

A

approximately 180L/day of plasma is filtered

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11
Q

Average urine output is

A

1-2L/day

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12
Q

What is the function of the peritubular capillaries?

A
  • come from efferent arteriole
  • surround nephron closely
  • take up 178L of 180L of plasma that is filtered per day
    • maintains ~1-2L/day urine output
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13
Q

What comprises the juxtaglomerular apparatus (JGA)?

A
  • terminal thick ascending LOH
  • afferent and efferent arterioles
  • macula densa cells in thich ascending LOH
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14
Q

What is the formula for MAP?

A

MAP = DP + 1/3(SP - DP)

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15
Q

What is the blood pressure range for which renal autoregulation can function?

A

70-180mmHg

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16
Q

Glomerular pressure is

A

constantly ~50mmHg

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17
Q

What are the functional roles of the JGA and macula densa cells?

A

function in autoregulation and tubuloglomerular feedback

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18
Q

What is tubuloglomerular feedback?

A
  • part of autoregulatory function of glomerulus
  • macula densa cells detect NaCl in thich ascending LOH/DT junction
  • feedback via paracrine mediators (eg adenosine released from MD cells) to alter tone of afferent (only) arteriole
    • adenosine causes vasoconstriction
    • other mediators eg prostaglandins cause dilation
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19
Q

What are the two components of autoregulation?

A

tubuloglomerular feedback and the myogenic reflex

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20
Q

What is the myogenic reflex (renal)?

A
  • afferent arteriole responds to stretch by contracting - it resists change by mitigating the dilating force
  • helps maintain glomerular pressure of ~50mmHg
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21
Q

What are the roles of the macula densa?

A
  • functions in tubuloglomerular feedback
  • functions in renin release from epithelial cells of the afferent arteriole
  • these are independent functions - renin release is NOT involved in tubuloglomerular feedback
22
Q

What is clearance?

A
  • amount of plasma removed per unit time
  • clearance of a specific plasma constituent eg Na is the volume of plasma which is cleared of Na over time
    • eg rate of urinary excretion of Na/plasma concentration of Na
    • renal clearance = UV/P
      • U = urinary concentration of substance
      • V = rate of urine, usually per day
      • P = plasma concentration
23
Q

What is excretion?

A

urine concentration of substance x urine volume

UV

24
Q

Why is creatinine clearance used to approximate GFR?

A
  • net reabsorbtion and secretion of creatinine are equal
  • therefore it is effectively all filtered and all cleared (no reabsorption) and the rate is equal to GFR
25
Q

What components of the glomerular structure contribute to filtration?

A
  • size restriction (up to ~1000 daltons):
    • fenestrations of the capillary inside the glomerulus
    • basal lamina
  • charge restriction (negatively charged, repel negative charges eg albumin)
    • basal lamina
    • foot processes of podocytes
26
Q

Microalbuminuria indicates

A
  • elevated (but small) amounts of albumin in the urine of diabetics (not easily detected in normal urine)
  • suggests damage to the basal lamina in the glomerulus
    • first stage in advanced/long-standing diabetes is loss of negative charges to repel plasma proteins from being filtered
27
Q

The filtration fraction of renal plasma flow is

A

0.2 (~20%)

28
Q

Hydrostatic pressure in the glomerular capillary is

A

50mmHg

29
Q

Hydrostatic pressure in Bowman’s capsule is

A

10mmHg

30
Q

Oncotic pressure in the glomerular capillary is

A

25mmHg

31
Q

Oncotic pressure in Bowman’s capsule is

A

~0mmHg (99% of proteins are not filtered)

32
Q

The driving force of filtation is

A

15mmHg

33
Q

Oncotic pressure in the efferent arteriole is

A

40mmHg

(from proteins remaining while water and solutes are filtered)

34
Q

What happens to GFR when the afferent arteriole constricts?

A

GFR decreases because glomerular capillary pressure decreases

35
Q

What happens to GFR when the efferen arteriole constricts?

A

GFR increases due to increased glomerular capillary pressure

36
Q

Angiotensin II acts on which arteriole, to produce what?

A
  • vasoconstriction of the efferent arteriole via Ang II receptors (more pronounced on efferent arteriole)
  • increases the filtration fraction
  • ACE inhibitors reduce [AngII] tf decrease filtration fraction
37
Q

Autoregulation occurs at

A

the afferent arteriole

38
Q

Renal blood flow =

A

delta pressure (pressure drop from afferent to efferent)

resistance to flow

39
Q

Adenosine acts preferentially on

A

afferent arteriole (vasoconstriction)

40
Q

Thromboxane acts preferentially on

A

afferent arteriole (vasoconstriction)

41
Q

Where is renin released from?

A
  • granular cells that line the afferent arteriole only at junction with entrance to the glomerulus
  • these cells replace the normal arteriolar endothelium
42
Q

What is the role of renin?

A

increase BP and salt retention

43
Q

Renin is released in response to

A
  • volume depletion and blood pressure decrease (passive contraction of the afferent arteriole)
  • decreased Na sensed by MD cells over a period of time
    • mechanism is unknown but is different to TGF (seconds to minutes)
  • activation of sympathetic nerves to the kidney
    • epi or NE stimualte b1-aRs in JG cells
44
Q

How much creatinine is normally produced per day?

A

~10mmol

45
Q

What is the average plasma concentration of creatinine?

A

50µmol/L

46
Q

Creatinine clearance is measured by

A

24-hour urine collection (~2L)

47
Q

Normal urine concentration of creatinine is

A

4.5mmol/L

48
Q

How much creatinine is excreted per day? Cleared per day?

A

50µmol/L x 180 L/day = 9000µmol/day = 9mmol/day

(10mmol/day is produced; remaining 1mmol increases plasma concentration until excretion matches production - tf over 180L plasma per day are filtered of creatinine)

49
Q

How is inulin used to calculate GFR?

A
  • not made by body, must be infused at a constant rate
  • completely filtered by glomerulus but neither secreted nor reabsorbed by the tubules
  • tf equal to GFR
50
Q

What is normal glucose clearance?

A

0; ~900mmol is freely filtered per day but 100% is reabsorbed by secondary active transport

51
Q

When does glucose appear in the urine?

A
  • glucose beyond normal range of 4-6mmol
  • excess overcomes secondary active transport mechanism of reabsorption
  • tf not all glucose is reabsorbed and appears in the blood
52
Q

What is the clearance of penicillin?

A
  • 150mL/min (greater than GFR, 120mL/min)
  • penicillin is freely filtered at glomerulus
  • not recognized by any transporters in renal tubule tf not reabsorbed
  • presence in tubule stimulates secreting systems to secrete penicillin left in the peritubular capillaries into the lumen
  • very rapidly excreted
    • used to be rx with probenecid to suppress secretion

Renal Physiology (4 decks)

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