Glomerular Filtration I Flashcards Preview

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Flashcards in Glomerular Filtration I Deck (67):
1

What happens if the body does not filter enough plasma

Edema (fluid overload) and azotemic (too much urea), also electrolyte and acid-base disturbances

2

Glomerular filtration is governed by

Starling Forces

3

Glomerular Capillary Pressure (Pc)

largely determines the glomerular filtration rate (GFR)

4

Glomerular Capillary Pressure (Pc) is largely determined by

arterial BP and afferent and efferent arteriolar resistances

5

What regulates the afferent and efferent arteriolar resistances?

Hormones and SNS

6

Increased afferent arteriolar resistances will have what effect on Pc and GFR?

Vasoconstriction of the afferent arteriole causes decreased glomerular capillary pressure and decreased GFR

7

Increased efferent arteriolar resistances will have what effect on Pc and GFR?

Vasoconstriction of the efferent arteriole causes increased glomerular capillary pressure and increased GFR

8

Intrinsic permeability (Kf) of the glomerular capillary wall effects GFR, increased Kf causes

increased GFR

9

The thick ascending limb is _________ to water

impermeable

10

In the late distal tubule and the collecting duct water permeability depends on

presence of ADH

11

In the proximal tubule and descending limb of hence, water permeability is dependent on

waters concentration gradient

12

Na reabsorption drives the reabsorption of

H2O, HCO3, glucose, aa

13

Na reabsorption drives the secretion of

H+

14

Na/K ATPase drives the reabsorption of other solutes by

establishing a concentration gradient of Na, which will drive the reabsorption of Na into the cell which drives the transport of other solutes

15

If too little ATP is available for the Na/K pump

the pump will slow, the concentration gradient will decline and the reabsorption of solutes slows

16

If the plasma osmolality moves away from its set point then

the hypothalamus signals the release of ADH form the posterior pituitary, and ADH changes the permeability of the collecting duct to H2O

17

Dilution of the urine is dependent on 2 factors

ability of the thick ascending limb to transport Na w/o H2O and a low level of ADH

18

Concentration of the urine is dependent on 2 factors

ability of the thick ascending limb to set up a concentration gradient and a high level of ADH

19

What determines the osmolality of the ECF

Na, Cl, and HCO3

20

Eating salty food (increased Na intake)

results in reabsorption of H2O to correct the high osmolality (high BP)

21

ECF osmolality is corrected for at the expense of

ECF volume

22

How does the body correct for a low ECF? (low Na diet, diuretics)

Reabsorb Na, but the kidney's cannot produce H2O or Na they must be consumed

23

What signals determine the kidneys Na and water reabsorption

BP, neural mechanisms, and hormonal mechanisms

24

Pressure-Naturiesis

Arterial pressure has a DIRECT effect on Na excretion; increased BP = increased excretion of Na via INTRARENAL MECHANISM

25

How does chronic BP effect pressure-naturiesis

Shifts the relationship to the right or has a depressed slope; higher BP at same steady-state Na intake

26

Na content regulated

ECF volume

27

Body water content regulates

plasma osmolarity

28

SNGFR

single nephron glomerular filtration rate

29

GFR

sum of all the SNGFR for the 2 kidneys

30

GFR =

Kf x [(Pgc-Pbs) - (Πgc - Πbs)]

31

Oncotic pressure of Bowman's Space Πbs =

0, since there is virtually no proteins in Bowman's Space

32

Permeability of the glomerular capillaries is

~100X greater than systemic and is the reason for a high filtration rate

33

Renal Clearance

amount of solute excreted/ concentration of solute in plasma

34

Input must equal output

substance IN = excretion (out1) + return to circulation (out2) *as long as it is not being metabolized

35

How to measure excretion of solute

urine concentration of solute x urine flow rate

36

Clearance of a solute (Cx) =

(Ux x V) / Px (urine concentration of solute X x urine flow rate) / plasma concentration of solute X

37

Definition of clearance

the mL of blood plasma completely cleared of a given substance in 1 minute

38

Clearance of a substance is typically ______ than renal plasma flow

LESS; because most solutes are reabsorbed

39

Clearance can estimate

GFR and renal plasma flow (RPF)

40

Clearance determines

net reabsorption or net or secretion of a filtered substance

41

GRF can be determined by clearance IF

the substance is not metabolized, neither secreted or reabsorbed, and freely filtered

42

Filtered load =

GFR x plasma concentration of solute

43

Excretion =

Urine conc of solute x urine flow rate

44

What substances can be used then to estimate GFR?

Inulin, I-iothalamate, creatinine, Iohexol, Iothalamate

45

Inulin for GFR estimation

inulin (fructose polymer) infused via IV, gold standard

46

I-iothalamate for GFR estimation

can predict GFR via plasma clearance alone

47

Creatinine for GFR estimation

ESTIMATES GFR (some is secreted)

48

Plasma clearance used for GFR measurement

Give IV bolus of known amount and take plasma samples over time to measure the clearance which = GFR (iohexol, iothalamate)

49

For chronic kidney disease, creatinine clearance _______ GFR

OVERESTIMATES; more is SECRETED due to higher serum levels

50

Stage 1 Chronic Kidney Disease, GFR =

>90ml/min/1.73 elevated GFR

51

Stage 2 Chronic Kidney Disease, GFR =

60-89 mild decrease in GFR

52

Stage 3 Chronic Kidney Disease, GFR =

30-59 moderate decrease in GFR

53

Stage 4 Chronic Kidney Disease, GFR =

15-29 severe decrease in GFR

54

Stage 5 Chronic Kidney Disease, GFR =

Failure <15

55

With increasing age, GFR

decreases

56

Inverse relationship between plasma creatinine concentration and

GFR; if GFR decreases then plasma [creatinine] must increase * assuming production is constant 1.8

57

if Pcreatinine increases from 1-2mg then GFR

must have decreased

58

In mild to moderate renal insufficiency, creatinine

is a poor predictor of GFR because as plasma [creatinine] increases section of creatinine increases

59

plasma creatinine predicts GFR when?

when kidney's are functioning or when there is severe renal insufficiency (saturated creatinine tubular transporters); for the mild and moderate insufficiency secretion of creatinine overestimates GFR

60

What substance is cleared by the kidneys in one pass through?

PAH; kidney has HUGE ability to SECRETE PAH without saturation

61

How can PAH be used to measure RPF

Since PAH is cleared in one pass through, a bolus of PAH will all be excretion (secretion) = entry of RPF

62

Filtration Fraction

GFR/RPF -- the portion of plasma that is filtered

63

Higher filtration fraction =

greater fraction of plasma that is filtrated

64

If a solute has a clearance > GFR than

that substance is also secreted

65

If a solute has a GFR > clearance than

that substance must also be reabsorbed

66

A substance CANNOT have a clearance > than

RPF

67

How does protein-binding effect the filtration of a substance?

DECREASES FILTRATION; If a drug or hormone is protein bound than that substance CANNOT be filtered. If it is partially bound, than the fraction of bound to unbound will determine its filtration rate