4_HST110 Glomerular Filtration 2017

Question 1

What substances in the blood are filtered by the kidneys?

Answer 1

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

Question 2

What substances are NOT filtered by the kidneys?

Answer 2

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

Question 3

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

Answer 3

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

Question 4

What is the filtration fraction?

Answer 4

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

Filtration fraction = GFR / RPF ~20%

Question 5

What is the filtered load?

Answer 5

Amount of a substance that is filtered per unit time

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

Question 6

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

Answer 6

Size and charge

Question 7

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

Answer 7

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

Question 8

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

Answer 8

X = negatively
Y = positively

Question 9

What are the normal ranges for GFR?

Answer 9

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

Question 10

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

Answer 10

X = all nephrons
Y = kidney function

Question 11

What are the determinants of GFR?

Answer 11

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

Question 12

What is the equation for filtration rate?

Answer 12

Filtration rate = permeability x SA x NFP

Question 13

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

Answer 13

X = filtration coefficient (Kf)

Question 14

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

Answer 14

X = hydrostatic pressures
Y = oncotic pressures

Question 15

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

Answer 15

X = out
Y = in

Question 16

What is the equation for NFP?

Answer 16

NFP = (P_GC – π_GC) – (P_BS – π_BS)

or

NFP = (P_GC + π_BS) – (P_BS + π_GC)

Question 17

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

Answer 17

GFR = Kf x [P_GC – (P_BS + π_GC)]

Question 18

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

Answer 18

X = P_GC

Question 19

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

Answer 19

X = decreases

Question 20

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

Answer 20

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

Question 21

What is the equation for renal plasma flow?

Answer 21

RPF = (1 – Hct) x RBF

subtract blood cell components to get plasma

Question 22

What 3 factors regulate GFR and RBF?

Answer 22

Regulation of glomerular capillary hydrostatic pressure (PGC)

Autoregulation
Myogenic response
Tubuloglomerular feedback

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

Question 23

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

Answer 23

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

Question 24

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

Answer 24

Dilation of EITHER: Increased RBF

Constriction of EITHER: Decreased RBF

Question 25

What are the effects of dilation or constriction of afferent or efferent arterioles on P_GC and GFR?

Answer 25

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

Question 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?

Answer 26

Autoregulation

Question 27

What is the typical autoregulation range for RBF and GFR?

Answer 27

90-180 mmHg

Question 28

What are the 2 mechanisms of autoregulation?

Answer 28

Pressure sensitive -> Myogenic response

Chemo sensitive -> Tubuloglomerular feedback

Question 29

What is tubuloglomerular feedback and where does it take place?

Answer 29

“Crosstalk” between the tubular system and the glomerulus

Takes place at the juxtaglomerular apparatus

Question 30

What are the signal, sensor, and effector of the tubuloglomerular feedback mechanism?

Answer 30

Signal: NaCl delivery to the distal tubule
Sensor: macula densa
Effector: vascular smooth muscle cells within the afferent arteriole

Question 31

Follow the process of the tubuloglomerular feedback mechanism starting at increased GFR

Answer 31

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

Question 32

What is the effect of RAAS on RBF & GFR (in states of decreased renal perfusion)?

Answer 32

Angiotensin II causes constriction of BOTH afferent and efferent arterioles, but the effect is greater on the EFFERENT arteriole