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SF3- EXAM 3 (Camelita) > Renal Hemodynamics, Blood Flow > Flashcards

Renal Hemodynamics, Blood Flow Flashcards

1
Q

Glomerular filtration rate

A

An index of renal function

NOTE: Kidneys can control GFR and renal blood flow through neurohumoral and local instrinsic mechanisms

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2
Q

How is renal blood flow calculated?

A

RBF= ΔP/R

ΔP= difference between renal artery pressure and renal vein pressure

R= total renal vascular resistance

NOTE: The total renal vascular resistance is the sum of all resistances in kidney vasculature

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3
Q

What is the typical renal blood flow?

A

Approximately 1100 mL/min

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4
Q

Kidneys receive between ______ and ______% of cardiac output.

A

20-22%

NOTE: Oxygen and nutrients delivered to kidneys normally greatly exceeds their metabolic needs.

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5
Q

A large fraction of renal oxygen consumption is related to ___________.

A

Renal tubular sodium reabsorption

NOTE: If we are able to dictate movement of Na, we are able to move large amounts of water and of course other electrolytes

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6
Q

How is the net filtration pressure calculated?

A

(Glomerular hydrostatic pressure)- (Bowman’s capsule pressure)- (Glomerular oncotic pressure)

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7
Q

What is the normal glomerular capillary hydrostatic pressure?

A

60 mmHg

*This is force that favors filtration

NOTE: The glomerular hydrostatic pressure does not really change much. This is important for maintaining proper filtration

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8
Q

Which forces oppose filtration? What are the normal values for each?

A
  • Glomerular colloid osmotic pressure- 32 mmHg
  • Bowman’s capsule pressure- 18 mmHg
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9
Q

What would cause an increase in the glomerular colloid osmotic pressure?

A

An increase in protein concentration within the capillary, as filtered substance leaves the gloemrular capillary

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10
Q

What happens to glomerular capillary hydrostatic pressure, if resistance is increased in the efferent arterioles?

A
  • It would initially cause a transient increase in glomerular capillary hydrostatic pressure
  • This transient increase is however short-lived because resistance in either the afferent or efferent, decreases renal blood flow.
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11
Q

What affect would the blockage of prostagladin synthesis have on GFR?

A

Decrease

NOTE: This is usually i,portant only when there are other disturbances that are already tending to lower GFR

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12
Q

Endothelin is a potent _________ (vasoconstrictor/vasodilator).

A

Vasoconstrictor

*Release of endothelian will result in a decrease in GFR

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13
Q

What affect does angiotensin II have on the renal flow and GFR?

A

Decreases renal flow and maintains GFR

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14
Q

Myogenic Mechanism to Autoregulation

A
  1. INcrease in volume at afferent arterioles
  2. Stretch sensed by vascular smooth muscle of afferent arteriole
  3. Activation of L-type Ca++ channels
  4. Vasoconstriction
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15
Q

Flow of renal plasm

A

Afferent arteriole-> Efferent arteriole-> Peritubular capillaries-> Renal vein

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16
Q

Normal GFR

A

125 ml/min

NOTE: The glomerular filtrate composition is about the same as plasma, except for large proteins

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17
Q

Filtration fraction

A

GFR/ renal plasma flow

NOTE: The normal filtration fraction is 0.2

18
Q

Which factors would place a patient at risk for renal disease?

A

Hypertension

Diabetes

Pregnancy

19
Q

What does a standard urinary dipstick test for?

A

Proteins in urine

20
Q

Microalbuminuria

A

Urine excretion of >30 but <150 mg of albumin per day

21
Q

What are some causes of microalbuminuria?

A

Early diabetes

Hypertension

Glomerular hyperfiltration

NOTE: Diabetic patients with microalbuminuria are 10-20 fold more likely to develop persistent proteinuria

22
Q

Normal Kf

A

12.5 mL/min per mmHg

23
Q

Kf

A

Hydraulic conductivity x surface area

*Kf is not normally highly variable

24
Q

Which diseases can reduce Kf and GFR?

A
  • Chronic hypertension
  • Obesity/ diabetes mellitus
  • Glomerulonephritis
25
Q

True or false. Bowman’s capsule hydrostatic pressure normally changes as a function of GFR, not a physiological regulator of GFR.

A

True

26
Q

What conditions increase bowman’s capsule hydrostatic pressure?

A
  • Tubular obstruction
  • Kidney stones
  • Tubular necrosis
  • Urinary tract obstruction
  • Prostate hypertrophy/cancer
27
Q

How is the filtration fraction related to the glomerular oncotic pressure?

A

Directly related.

28
Q

Net filration pressure _________ (decreases/increases) along the glomerulus because of increasing glomerular colloid osmotic pressure.

A

Decreases

29
Q

What factors influence glomerular hydrostatic pressure?

A
  • Arterial pressure (effect is buffered by autoregulation)
  • Afferent arteriolar resistance
  • Efferent arteriorlar resistance
30
Q

True or false. Autoregulation is regards to renal blood flow and GFR but not urine flow.

A

True

NOTE: With an increase in mean arterial pressure, urine flow increases. However, with an increase in mean arterial pressure renal blood flow and glomerular filtration rate will remain the same, if autoregulation comes into play.

31
Q

Summary of determinants of GFR

A
32
Q

When is angiotensin II released to maintain GFR?

A

Low sodium diet

Volume depletion

*The main point of angiotensin is to prevent a decrease in GFR

33
Q

What affect do prostaglandins have on GFR?

A

Prostaglandins decrease resistance and therefore increase GFR and RBF

NOTE: Blockage of prostaglandin synthesis will lead to a decrease in GFR but this is only important when there are other disturbances that are already tending to lower GFR. So nonsteroidal antiinflammatory drugs should be given to volume depleted patients or patients with heart failure, cirrhosis.

34
Q

What affect does endothelial-derived nitric oxide have on GFR?

A

Endothelial- derived nitric oxide causes a decrease in resistance, so an increase in GFR.

NOTE: This substance protects against excessive vasoconstriction. Patients with endothelial dysfunction, such as atherosclerosis, may have greater risk for excessive decrease in GFR in response to stimuli such as volume depletion.

35
Q

What affect does endothelin have on GFR?

A

Endothelin cause an increase in resistance and henceforth causes a decrease in GFR.

36
Q

In what conditions will endothelin antagonists be useful?

A
  • Hepatorenal syndrome
  • Acute renal failure
  • Hypertensive patients with chronic renal failure
37
Q

Summary of neurohumoral control of GFR and renal blood flow

A
38
Q

What factors are important in maintaining urine volume?

A

Good autoregulation

Adaptive increase in tubular reabsorption

39
Q

Myogenic mechanism

A
  1. Increase in arterial pressure
  2. Increase in stretch of blood vessel
  3. Increase in cell Ca++ entry
  4. Increase in intracellular Ca++
  5. Increase vascular resistance
  6. Decrease in blood flow and GFR
40
Q

How do the afferent and efferent arterioles respond to prerenal AKI respectively?

A

Afferent arterioles

  • Response to decrease in renal blood flow by increase in vasodilating prostaglandins
    • Blunted by NSAIDS that inhibit prostaglandin prostaglandin production

​​Efferent arterioles

  • Response to decrease in renal blood flow by preferential constriction of efferent arteriole by Angiotensin II
    • Blunted by ACE inhibitors/ ARBs that inhibit Angiotensin II production

SF3- EXAM 3 (Camelita) (23 decks)

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