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Unit 7: Physiology > filtration & clearance (6) > Flashcards

filtration & clearance (6) Flashcards

1
Q

define “glomerular filtration”

A

“the process by which plasma is filtered across the glomerular capillaries to form a protein free ultrafiltrate in bowman’s space”

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2
Q

what is the first step in urine formation?

A

separation of an ultrafiltrate at the glomerulus

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3
Q

what drives the net efflux of plasma ultrafiltrate

A

Differences in oncotic & hydrostatic pressure (starling forces) across the glomerular capillaries

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4
Q

what is the approx GFR in a human in ml/min?

what is the GFR in L/day?

A

125 mL/min

180 L/day

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5
Q

how often can the entire ECF be recycled through the kidneys?

A

every 2 hours

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6
Q

what is greater: the filtration coefficient in the glomerular capillaries or the systemic capillaries

A

the glomerular filtration coefficient is 200x greater than the coefficient in the systemic capillaries

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7
Q

what is something unique tot he glomerular capillaries that is not seen in the systemic capillaries

A

This small decrease in pressure occurs from the beginning of the capillary to the end despite a decrease in plasma volume and is due to post capillary efferent arteriole constriction

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8
Q

what are the 2 reasons that oncotic pressure increases along the length of the glomerular capillary?

A

due to plasma filtration

and due to plasma protein concentration

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9
Q

what would cause the oncotic pressure of bowman’s capsule to increase?

A

nephritic syndrome

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10
Q

what are the 3 barriers that the ultrafiltrated has to cross to get into bowman’s space?

A
  1. the endothelial cells of the glomerular capillaries
  2. capillary basement membrane
  3. the podocytes on the visceral epithelial layer
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11
Q

what two barriers will block anion filtration?

A

the capillary basement membrane and the capillary podocytes

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12
Q

what are 4 examples of “freely filterable solutes”

A

water, NaCl, glucose and inulin

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13
Q

how much of person’s blood goes to the kidenys?

A

20%

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14
Q

how much of renal blood flow is renal plasma flow?

A

about 55%

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15
Q

how can filtration rate be determined?

A

GFR/RPF

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16
Q

what range should urine output be in?

A

1 ml/min to 10 ml/min

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17
Q

at what level of plasma flow does GFR reach its maximum?

A

at 600 ml/min

18
Q

tell me about what results from an increase in plasma flow through the glomeruli

A
  • increase in surface area of the glomerular capillaries
  • filtration of the plasma increases until all the glomerular surface area is filtering plasma and a maximal rate of glomerular filtration is achieved
19
Q

if the renal blood flow is decreased to zero, how much is the kidney able to filter

A

NONE. come on ppl- gotta know this

20
Q

what is the result of afferent arteriolar constriction?

A

decrease in RPF

decrease in glomerular capillary hydrostatic pressure

21
Q

when is the surface area of glomerular capillary mediating filtration depend on flow?

A

at low renal plasma filtration levels

22
Q

what is the result of efferent arteriolar constrictin?

A

decrease in RPF

increase in glomerular capillary hydrostatic pressure

23
Q

what value can provide an index of the number of functioning nephrons in the kidneys?

A

GFR

24
Q

at what GFR does renal failure begin at?

A

20 ml/ min

loss of 85% of the nephrons

25
Q

what is the “renal clearance” of a substance?

A

virtual volume of plasma from which a solute is completely removed from the plasma by the kidney per unit time

26
Q

renal clearance of a solute can be used to measure the GFR if what 4 properties are present

A
  1. Freely filtered at the glomerulus
  2. Not reabsorbed in any segment of the nephrons
  3. Not secreted in any segment of the nephrons
  4. Not synthesized by the kidney (not metabolized by the kidney)
27
Q

what is the exogenous solute used to measure GFR?

A

inulin

28
Q

what is the endogenous solute used to measure GFR?

A

creatinine

29
Q

what is inulin?

A
  • inulin is a fructose polymer

- given via IV infusion to maintain constant plasma (inulin) and measured very accurately in plasma & urine

30
Q

what is a normal creatinine plasma level?

A

1 mg/ 100 mL

31
Q

what does it mean if the creatine level is higher than normal?

A

that the creatinine clearance is going down and could indicate renal failure

32
Q

what does it mean if a solute has a clearance ratio to inulin that is less than 1?

A

means that the concentration of that solute in the urine is less than that in the plasma
means that the solute is being reabsorbed

33
Q

what does it mean if a solute has a clearance ratio to inulin that is greater than 1?

A

means that the solute is being secreted in addition to being filtered in the kidneys

34
Q

define the fractional excretion of water

A

The fraction of the glomerular filtrate NOT absorbed from the tubular fluid along the nephrons and therefore appearing as urine

35
Q

how can fractional excretion of water be estimated?

A

from plasma to urine inulin concentration ratio

36
Q

what % of filtered water is excreted in the urine if there is a 100x more concentration level of inulin in the urine over plasma

A

1%

37
Q

what is the fractional excretion of water in a time of dehydration?

A

less than 1 %

38
Q

in L/min, what is renal blood flow

A

1.2 L/min

39
Q

describe the importance of autonomic innervations in kidney auto-regulation

A

tricked ya! autonomic innervations are not important and kidney auto-regulation can still occur in their absence.
auto-regulation is considered “intrinsic” to the kidneys

40
Q

what cells provide tubuloglomerular feedback? what are they sensing?

A

macula densa cells sensing an increase or decrease in GFR to cause an increase/decrease in resistance (constriction) of an afferent arteriole to return GFR levels to normal

Unit 7: Physiology (19 decks)

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