4_HST110 Glomerular Filtration 2017 Flashcards

1
Q

What substances in the blood are filtered by the kidneys?

A
  1. Ions (e.g. Na+, K+)
  2. Organic molecules (e.g. glucose, amino acids)
  3. Small peptides (e.g. insulin, antidiuretic hormone)
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2
Q

What substances are NOT filtered by the kidneys?

A

Cellular elements (e.g. red blood cells, white blood cells) and most proteins

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3
Q

What is the criteria for a substance to be freely filtered? (e.g. most low molecular weight substances)

A

Concentration in the filtrate is the same as its concentration in the blood plasma

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4
Q

What is the filtration fraction?

A

The proportion of the renal plasma flow that is filtered by the glomerulus

Filtration fraction = GFR / RPF ~20%

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5
Q

What is the filtered load?

A

Amount of a substance that is filtered per unit time

Filtered load of substance X = GFR * [X]plasma

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6
Q

Substances are filtered based on what two criteria in the glomerular filtration barrier?

A

Size and charge

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7
Q

What are the molecular weight cutoff values for easily filtered, less readily filtered, and not filtered substances?

A

Easily: 7 kDa
Less Readily: 7-70 kDa
Not Likely Filtered: > 70 kDa

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8
Q

For large macromolecules: For any given molecular radius, (X) charged molecules are less readily filtered and (Y) charged molecules are more readily filtered

A
X = negatively
Y = positively
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9
Q

What are the normal ranges for GFR?

A

Males: 90-140 mL/min
Females: 80-125 mL/min
Avg: 125 mL/min (180 L/day)

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10
Q

GFR represents the sum of filtration rates of (X) in the kidney and can be used as an index of (Y)

A
X = all nephrons
Y = kidney function
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11
Q

What are the determinants of GFR?

A
  1. permeability of the capillaries
  2. capillary surface area
  3. net filtration pressure (NFP) acting across the capillaries
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12
Q

What is the equation for filtration rate?

A

Filtration rate = permeability x SA x NFP

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13
Q

Capillary surface area is difficult to estimate, so we define a parameter called the (X) as the product of the hydraulic permeability and surface area

A

X = filtration coefficient (Kf)

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14
Q

NFP is the algebraic sum of (X) and (Y)

A
X = hydrostatic pressures
Y = oncotic pressures
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15
Q

Hydrostatic pressure tends to promote movement of fluid (X) of vessels. Osmotic pressure opposes this, promoting movement of fluid (Y)

A
X = out
Y = in
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16
Q

What is the equation for NFP?

A

NFP = (P_GC – π_GC) – (P_BS – π_BS)

or

NFP = (P_GC + π_BS) – (P_BS + π_GC)

17
Q

What is the equation for GFR? Given oncotic pressure in Bowman’s space is essentially 0

A

GFR = Kf x [P_GC – (P_BS + π_GC)]

18
Q

In normal individuals, GFR is generally regulated by changes in (X)

19
Q

Net filtration pressure (X) from the beginning of the glomerular capillaries to the end due to the increase in oncotic pressure in the Glomerular Capillary as water leaves

A

X = decreases

20
Q

What is the equation for Renal Bloow Flow? (RBF)

A

RBF = 0.20 to 0.25 * Cardiac Output = 1.1 L/min

21
Q

What is the equation for renal plasma flow?

A

RPF = (1 – Hct) x RBF

subtract blood cell components to get plasma

22
Q

What 3 factors regulate GFR and RBF?

A

Regulation of glomerular capillary hydrostatic pressure (PGC)

Autoregulation
Myogenic response
Tubuloglomerular feedback

Renin-Angiotensin-Aldosterone system (in states of decreased renal perfusion)

23
Q

Regulation of Glomerular Hydrostatic Pressure (PGC) depends on what 3 things?

A

Systemic arterial blood pressure (i.e. overall renal perfusion)
Afferent arteriolar resistance
Efferent arteriolar resistance

24
Q

What are the effects of dilation or constriction of afferent or efferent arterioles on RBF?

A

Dilation of EITHER: Increased RBF

Constriction of EITHER: Decreased RBF

25
What are the effects of dilation or constriction of afferent or efferent arterioles on P_GC and GFR?
However, because the afferent arteriole controls glomerular inflow and the efferent arteriole controls glomerular outflow, changes in the arterioles have opposite effects on glomerular pressure: Afferent arteriole: inflow Dilation - increased PGC & GFR Constriction - decreased PGC & GFR Efferent arteriole: outflow Dilation - decreased PGC & GFR Constriction - increased PGC & GFR
26
Like most organs, the kidneys can regulate their blood flow by adjusting vascular resistance to changes in arterial blood pressure. What is this called?
Autoregulation
27
What is the typical autoregulation range for RBF and GFR?
90-180 mmHg
28
What are the 2 mechanisms of autoregulation?
Pressure sensitive -> Myogenic response | Chemo sensitive -> Tubuloglomerular feedback
29
What is tubuloglomerular feedback and where does it take place?
“Crosstalk” between the tubular system and the glomerulus Takes place at the juxtaglomerular apparatus
30
What are the signal, sensor, and effector of the tubuloglomerular feedback mechanism?
Signal: NaCl delivery to the distal tubule Sensor: macula densa Effector: vascular smooth muscle cells within the afferent arteriole
31
Follow the process of the tubuloglomerular feedback mechanism starting at increased GFR
Increased GFR - Increased tubular fluid flow rate - increased NaCl delivery to Macula Densa - increased vasoconstrictor signals from macula densa (adenosine) - increased afferent arteriolar constriction = decreased RBF and GFR
32
What is the effect of RAAS on RBF & GFR (in states of decreased renal perfusion)?
Angiotensin II causes constriction of BOTH afferent and efferent arterioles, but the effect is greater on the EFFERENT arteriole