Urine Production: Filtration Flashcards

1
Q

what metabolic waste products are made in the liver?

A

urea
creatinine
bilirubin

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2
Q

where is urea reabsorbed?

A
  • most reabsorbed in PCT (30-40%)
  • small amount in medullary collecting duct
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3
Q

what is creatinine made from?

A

muscle breakdown

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4
Q

how much creatinine is reabsorbed in the kidney?

A

none

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5
Q

what is bilirubin made from?

A

breakdown of RBC

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6
Q

name the steps of urine production

A
  1. filtration in glomerulus
  2. reabsorption in PCT
  3. counter-current concentration in loop of Henle (& collecting duct)
  4. secretion in DCT
  5. excretion in collecting duct
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7
Q

what is the first step of urine production?

A

filtration

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8
Q

where does filtration occur?

A

glomerulus

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9
Q

what is the osmolarity in the glomerulus?

A

300

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10
Q

how much blood is in the kidney at all times?

A

20%

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11
Q

glomerular filtration is based on ____

A

size

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12
Q

the glomerulus is composed of…

A

fenestrated capillaries reinforced by basement membrane, and podocytes (slit pores)

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13
Q

what is the normal glomerular filtration rate (GFR)?

A

~125 mL/min

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14
Q

how does filtrate compare to plasma?

A

same but no protein

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15
Q

what is the equation for filtered load?

A

plasma concentration x GFR

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16
Q

what osmolarity is considered hypotonic?

A

less than 300 mmol

17
Q

what osmolarity is considered hypertonic?

A

more than 300 mmol

18
Q

what osmolarity is considered isotonic?

A

300 mmol

19
Q

what effect would a 50% decrease in efferent arteriolar resistance have on GFR?

A

substantial decrease

20
Q

with a chronic decrease in GFR by 50%, what changes in plasma concentration would you find for:
- creatinine
- K+
- glucose
- Na+
- phosphate
- H+

A
  • creatinine increases until renal excretion of creatinine returns to normal
  • glucose, K, Na, H stay constant (closely regulated)
  • phosphate maintained until GFR below 20-30% of normal
21
Q

what changes would you expect in renal blood flow, GFR, and peritubular capillary hydrostatic P, from a 50% decrease in afferent arteriolar resistance and no change in arterial pressure?

A
  • increase renal blood flow
  • increase GFR
  • increase peritubular capillary hydrostatic P
22
Q

what is the net pressure driving glomerular filtration given the following:
- glomerular capillaries hydrostatic P = 50mmHg
- Bowman’s space hydrostatic P = 12mmHg
- glomerular capillaries colloid osmotic P = 30mmHg
- no protein in glomerular ultrafiltrate

A

50 - 12 - 30 = 8mmHg

23
Q

what is the concentration of urea in tubular fluid at the end of the proximal tubule compared to the plasma?

A

higher than concentration of urea in the plasma

24
Q

how does urea reabsorption in the proximal tubule compare to in the cortical collecting collecting tubule?

A

PCT > collecting tubule
(40-50% in PCT; none in collecting tubule)

25
Q

what is the equation for net glomerular filtration pressure?

A

glomerular hydrostatic P - bowman’s hydrostatic P - glomerular osmotic P