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Physiology > Renal Filtration and Blood Flow > Flashcards

Renal Filtration and Blood Flow Flashcards

1
Q

What are the 3 general processes that determine the amount of a substance that appears in urine?

A

1) Glomerular filtration
2) Reabsorption of the substance from tubular fluid back into blood
3) Secretion of the substance from blood into tubule fluid.

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2
Q

What is the first step in the production of urine?

A

Ultrafiltration of the plasma by the glomerulus

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3
Q

How much of the cardiac output do the kidneys receive and why?

A

They receive 25% of the CO which far exceeds their metabolic need and this allow for flow to be adjusted with demand as in when working out.

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4
Q

What is the filtration fraction?

A

Ratio of GFR/RPF

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5
Q

What is the normal value of the filtration fraction?

A

20%

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6
Q

What is the composition of the ultra filtrate like?

A

The ultrafiltrate is devoid of cellular elements and is essentially protein free. The salt and organic compound concentrations are similar in the ultrafiltrate and
plasma.

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7
Q

How are GFR and RFP regulated?

A

Autoregulation

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8
Q

What is the filtration barrier in the renal corpuscle based upon?

A

Size and Charge

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9
Q

What size particles are freely filtered?

A

Particles less than 7000 Da and 20 Å are freely filtered

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10
Q

What size molecules are impermeable?

A

Molecules around 70000 Da and 42 Å are impermeable.

Albumin is 66K Da and it is nearly impermeable

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11
Q

What charge molecules are filtered more readily?

A

Cationic molecules are filtered more easily than anions

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12
Q

Why are proteins not filtered very easily, or at all?

A

Most proteins are negatively charged

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13
Q

Why are anions harder to filter?

A

The filtration barrier contains fixed polyanions that will repel the negatively charged proteins

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14
Q

How does glomerular capillary hydrostatic pressure affect filtration?

A

Favors

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15
Q

How does glomerular capillary oncotic pressure affect filtration?

A

Impedes

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16
Q

How does Bowman space hydrostatic pressure affect filtration?

A

Impedes

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17
Q

How does Bowman space oncotic pressure affect filtration?

A

Favors

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18
Q

What happens with higher GFR values?

A

It results in greater filtration and also greater water and salt excretion

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19
Q

What is the Bowman space oncotic pressure normally at?

A

0 as there is little protein in the BS to extrude water from the glomerulus

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20
Q

What is the equation for the net filtration pressure (NFP)?

A

NFP = (pGC - πGC) - (pBC - πBC)

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21
Q

What is the equation for the GFR?

A

GFR = kF(pGC - πGC - pBC)

kF = filtration coefficient

22
Q

What happens to the πGC along the nephron?

A

The πGC increases along the nephron towards the end as the water leaves the tubule and the solutes concentrate in it.

23
Q

What is kF?

A

It is the product of the intrinsic permeability of the glomerular capillary and the glomerular surface area available for filtration.

24
Q

How is the GFR regulated normally?

A

It is regulated by changing the pGC

25
Q

What are the ways that the pGC can be altered?

A
  1. Changes in the afferent arteriolar resistance
  2. Changes in the efferent arteriolar resistance
  3. Changes in renal arteriolar pressure
26
Q

How does an increase in the afferent arteriolar resistance affect the pGC?

A

Decreases the pGC

27
Q

How does an increase in the efferent arteriolar resistance affect the pGC?

A

Increases the pGC

28
Q

How does an increase in the blood pressure affect the pGC?

A

Increases the pGC

29
Q

What are the changes that occur in kidney stones?

A

Increase the pBS which leads to decreased GFR

30
Q

What is the ratio of vascularization of the renal cortex to the renal medulla?

A

Cortex gets 90% of the RBF

Medulla gets 10% of the RBF with 8% in the outer portion and 2% in the inner portion

31
Q

What is the ration of the cortical nephrons to the juxtamedullary nephrons?

A

7 to 1

32
Q

What capillaries are confined to the renal cortex?

A

Glomerular Capillaries

Peritubular Capillaries

33
Q

What capillaries dive into the renal medulla?

A

Vasa Recta Capillaries

34
Q

What happens to the hydrostatic (P) pressure from the renal artery to the renal vein?

A

P decreases

35
Q

Where do the largest decreases in the P occur?

A

Afferent and the efferent arterioles as they have the highest resistance

36
Q

What happens to the oncotic pressure (π) in the glomerular capillaries?

A

π increases in the GC as the concentration of the plasma proteins increases during filtration.

37
Q

What happens to the oncotic pressure π in the peritubular capillaries?

A

π decreases in the peritubular capillaries as the dilution of the capillaries occurs during reabsorption

38
Q

What happens as a result of constriction of the afferent arteriole?

A

pGC decreases
GFR decreases
RBF decreases

39
Q

What happens as a result of constriction of the efferent arteriole?

A

pGC increases
GFR increases
RBF decreases

40
Q

What happens as a result of dilation of the afferent arteriole?

A

pGC increases
GFR increases
RBF increases

41
Q

What happens as a result of dilation of the efferent arteriole?

A

pGC decreases
GFR decreases
RBF increases

42
Q

What are the two mechanisms of auto regulation in the kidney?

A

Myogenic

Tubuloglomerular

43
Q

What is the auto regulatory range and what happens outside of it?

A

100 - 180 mmHg is the auto regulation range.

180 leads to increased RBF and GFR

44
Q

What happens when the arterial pressure falls below 70 mmHg?

A

Renal shutdown occurs and GFR goes to 0 mL/min but the kidney is still perfused, just no urine is formed.

45
Q

What happens to the kidney when arterial pressure falls to 0 mmHg (or absolute minimum - mean circulatory pressure)?

A

Renal death occurs and RBF goes to 0 mL/min and the kidney is no longer perfused.

46
Q

How does myogenic auto regulation occur?

A

With increases in pressure, vasoconstriction will occur to increase resistance and decrease flow and with decreases in pressure, vasodilation will occur to decrease resistance and increase flow.

47
Q

How does tubuloglomerular auto regulation occur?

A

Increases in GFR will increase the [NaCl] in the loop of Henle which is sensed by the macula densa and turned to a signal to increase the arteriolar resistance and decrease the GFR. Low [NaCl] will cause the opposite.

48
Q

What is involved in the extrinsic regulation of GFR and RBF?

A
  • Sympathetic innervation of the afferent and efferent arterioles
  • Hormones and other substances in blood
49
Q

What happens to the GFR and RBF in hemorrhage where blood volume decreases?

A

Decreases

50
Q

What happens to the GFR and RBF with dehydration where the renin and angiotensin increases?

A

Decreases

51
Q

What happens to the GFR and RBF with severe hypoxia at high altitudes?

A

Decreases

Physiology (81 decks)

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