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Renal System > RBF and GFR > Flashcards

RBF and GFR Flashcards

1
Q

What is each nephron composed of?

A
  1. Glomerulus
  2. Proximal tubule
  3. loop of henle
  4. Distal tubule
  5. Collecting ducts
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2
Q

List the blood flow of the kidneys starting with the renal artery

A
  1. Renal artery
  2. Lobar arteries
  3. Interlobar arteries
  4. arcuate arteries
  5. Interlobular arteries
  6. Afferent arteries
  7. Glomerulus
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3
Q

List the flow of filtrate starting with the glomerulus

A
  1. Glomerulus
  2. Prox. convoluted tubule
  3. prox. straight tubule
  4. Thin limb
  5. Thick ascending limb
  6. Macula Densa
  7. Distal convoluted tubule
  8. connecting segment
  9. connecting duct
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4
Q

Unique feature to renal vascualture?

A

Unlike other organs, they have 2 capillary beds:

  1. Glomerular
  2. Peritubular
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5
Q

Pressure profile of renal vascualture maintains high hydrostatic pressure by dropping arteriovenous pressure in 2 steps. What are the 2 steps?

A
  1. afferent arteriole
  2. Efferent arteriole
  • drops about 35 mmHg each
  • 3rd drop also in peritubular capillary
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6
Q

In addition to the 2 step drop in hydrostatic pressure, what else helps glomerular filtration?

A

The change in osmotic pressure:

- High oncotic pressure in the efferent arteriole followed by a low oncotic pressure in the peritubular capillary

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7
Q

3 processes that leads to urine formation?

A
  1. Glomerular filtration
  2. Tubular reabsorption
  3. Tubular secretion
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8
Q

Why filter large amounts of body fluids and solutes only to reabsorb them?

A
  1. High GFR allows the kidney to rapidly remove waste products from the body that depend primarily on kidney for their excretion. Most waste products are poorly reabsorbed, therefore, rapid filtration leads to rapid excretion of waste products, otherwise they would be toxic to cells.
  2. high GFR allows body fluids to be filtered and processed several times a day. This allows the kidney to precisely and rapidly control the change in body fluid volume and composition.
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9
Q

What is GFR?

A

the rate at which plasma is filtered through glomerulus

  • 130 ml/min (180L/day)
  • decreases w/ age and renal disease
  • indicator of renal function
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10
Q

What is filtration fraction?

A

The ration of GFR to renal plasma flow

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11
Q

Composition of filtrate?

A

Similar to plasma (no blood cells) but w/o large proteins

- has 4-5% more anions (4-5% less cations) due to Gibbs Donnan effect

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12
Q

Filtration barriers:

A
  1. Capillary endothelium - leaky than capillaries of other organs
  2. Basement membrane - meshwork of type 4 collagen and proteoglycan fibrils
  3. Epithelium (podocyte monolayer) - extend foot processes forming slit pores
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13
Q

Filtration selectivity of Capillary endothelium?

A

Barrier to blood cells and large proteins

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14
Q

Filtration selectivity of BM?

A

barrier to many molecules

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15
Q

Filtration selectivity of epithelium?

A

Prevents diffusion of large molecules

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16
Q

Filterability of solute is dependent on?

A
  1. Size

2. Charge

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17
Q

What is proteinuria? What barrier failure causes this?

A

Protenuria is a condition when you detect protein in the urine

  • barrier failure in the glomerulus
  • abnormal circulating proteins (Breakdown of tissues) (proteins produced by tumor cells)
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18
Q

Nephritic syndrome:

A

Proteinuria due to filtration of albumin and CELLS

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19
Q

Nephrotic syndrome:

A

Proteinuria - filtration of proteins, but NOT CELLS

- due to opening of slit pores or loss of charge selectivity

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20
Q

Determinants of GFR?

A

GFR = filtration coefficient x Net filtration pressure

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21
Q

What determines the filtration coefficient?

A
  1. Hydraulic conductivity - the ease with which the fluid flows through
    - determined by the size and shape of the pores
  2. surface area of glomerular capillary
22
Q

Fact: Any factor that reduces Kf either by reducing hydraulic conductivity or surface area would reduce GFR.

A

Fact example:
In diabetes mellitus GFR is reduced as the Kf is reduced due to increase in basement membrane thickness, so reduced hydraulic conductivity and damaged capillaries, so reduced surface area.

23
Q

What is the net filtration pressure?

A

the difference between the forces that favor filtration and forces that oppose filtration

  • glomerular hydrostatic pressure is the major force that favors filtration. The oncotic pressure in the Bowman’s space is another force that favors filtration
  • the oncotic pressure in the capillary is high due to plasma proteins, This is the major force that oppose filtration. The other opposing force is the Bowman’s space is hydrostaic pressure caused by fluid accumulation.
24
Q

Fact:
The net filtration pressure is glomerular hydrostatic pressure + Bowmans space oncotic pressure – glomerular oncotic pressure and bowman space hydrostatic pressure.

A

Fact:
The net filtration pressure is glomerular hydrostatic pressure + Bowmans space oncotic pressure – glomerular oncotic pressure and bowman space hydrostatic pressure.

25
Q

How can the net filtration pressure (and therefor the GFR) be regulated?

A
  1. changing the glomerular hydrostatic pressure.
    - This can be changed by changing the resistance of afferent and efferent arterioles.
    - Clinical corrections are hypertension, arterial stenosis
  2. Changing Bowman’s Space hydrostatic pressure
    - Lower urinary tract obstruction – stones, hypertrophic prostate
  3. Changing cap. oncotic pressure
26
Q

Increase Aff. resistance

A
  • GFR: dec

- RPF: dec

27
Q

Decrease Aff. resistance

A
  • GFR: inc

- RPF: inc

28
Q

Increase Eff. Resistance

A
  • GFR: Inc

- RPF: dec

29
Q

Decrease Eff. Resistance

A
  • GFR: dec

- RPF: inc

30
Q

Increase Eff. and Aff resistance

A
  • GFR: dec

- RPF: dec

31
Q

Decrease Eff. and Aff. resistance

A
  • GFR: inc

- RPF: inc

32
Q

Fact:
ΔTTG = caused by change in protein concentration in glomerular capillary blood

*low capillary flow -> inc FF -> inc TTG -> dec net filtration pressure -> dec GFR

A

Fact:
ΔTTG = caused by change in protein concentration in glomerular capillary blood

*low capillary flow -> inc FF -> inc TTG -> dec net filtration pressure -> dec GFR

33
Q

Where is the net filtration pressure the highest?

A

The afferent end

  • because the capillary oncotic pressure gradually rises from the afferent end t the efferent end
34
Q

What is auto-regulation of GFR?

A

Maintenance of constant GFR in the face of changes in mean arterial pressure, venous pressure, obstructions

  • when the physiologic regulatory mechanisms are overridden to change GFR we call it a pathophysiologic condition
35
Q

T or F: The auto-regulation of GFR is independent of systemic influences,

A

T

  • so systemic neurohormonal regulation is not involved in the mechanism of auto regulation of GFR.
36
Q

What occurs during auto-regulation that prevents the an increase in RPF and therefore prevents increase in GFR above 70mm Hg?

A

Increase in renal vascular resistance (arteriolar resistance)

  • The renal vascular resistance is not altered by renal arterial pressure up to 60-80 mm Hg
37
Q

Normal GFR?

A

Normal GFR is 180 L/day,

- fluid reabsorption in nephron is 178.5 L/day and therefore urine excretion is 1.5 L/day.

38
Q

Possible mechanisms of autoregulation that change arteriolar resistance

A
  1. Myogenic mech - direct stimulation of arteriolar smooth muscle. . When the arterial blood pressure increases it directly stimulates smooth muscle cells in arteriole resulting in contraction and control the blood flow
  2. Tubuloglomerular feedback mechanism - chloride concentration in the tubular fluid regulates the resistance of afferent arteriole by a feedback machanism
39
Q

Where does the Tubuloglomerular feedback mech occur?

A

juxtaglomerular apparatus
- the area where the Macula Densa of the thick ascending limb of LOH comes in contact with the afferent arteriole of the glomerulus of the same nephron

40
Q

Higher NaCl in MD =>

A

Increase afferent arteriolar resistance

=> decreased GFR

41
Q

Lower NaCl in MD =>

A

Decreased afferent arteriolar resistance

=> Increased GFR

42
Q

Mechanism by which Chloride in the MD affects the arteriolar resistance?

A

It is believed that macula densa senses the NaCl concentration and sends signal to juxtaglomerular cells and arteriolar smooth muscle cells.

43
Q

What are the nuerohormonal regulatory mechanisms of GFR?

A
  1. RAAS
  2. Sympathetic Nervous system
  3. Hormones
    - endothelin
    - NO
    - prostaglandins
44
Q

Mechanism for the secretion of renin by the macula densa

A

Low ECFV or Arterial blood pressure results in low RBF and therefore low GFR:
=> low chloride (NaCl) NaCl and flow in tubular fluid stimulates cells in the macula densa via a DECREASE in intracellular Ca2+

45
Q

Affect of renin secretion:

A

Renin release => conversion of alpha2globulin into Angiotensin I (in circulation)

=> Angiotensin I -> Angiotensin II (in lung and kidney)

Angiotensin II is a renal (afferent) arteriolar constrictor => decrease GFR

46
Q

Regulation of GFR via sympathetic nervous system.

A
  1. Stimulates vasoconstriction (afferent arterioles)
  2. Stims renin secretion and Na+ reabsorption
  3. decrease Kf by stimulating mesangial cells.
47
Q

Result of sympathetic stim on renal system under normal conditions

A

Not important under normal conditions

- autoregulation mechanism dominates!

48
Q

Result of sympathetic stim on renal system under severe condition of ECFV loss

A

Sympathetic stim overrides autoregulation

49
Q

Hormones that promote vasoconstriction of renal arterioles?

A
  1. Adrenaline (Afferent > efferent)

2. Endothelin I ( Aff. = Eff. )

50
Q

Hormones that promote vasodilation of renal arterioles?

A
  1. Nitric oxide

2. Prostaglandins

Renal System (19 decks)

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