Determinants of GFR

Question 1

What affects the GFR?

Answer 1

-net filtration pressure
-surface area
-permeability of membranes
**SA and membrane permeability usually stays constant and is expressed at Kf

Question 2

Coefficient of filtration (Kf)

Answer 2

-number to express the surface area and permeability of the membranes
-usually stay constant
-cannot be measured directly
-can be 400x more than filtration coefficient of other capillary networks

Question 3

What are the 4 types of forces in the glomerular capillaries and Bowman’s capsule that affect net filtration pressure?

Answer 3

1.Glomerular hydrostatic pressure (PG, promotes filtration)
2.Bowman’s capsule hydrostatic pressure (PB, opposes filtration)
3.Colloid osmotic pressure of glomerular capillaries (piG, opposes filtration)
>because larger molecules within the glomerular capillaries
4.Colloid osmotic pressure of Bowman’s capsule (piB, promotes filtration)

Question 4

GFR equation

Answer 4

GFR= Kf x (PG-PB-piG +piB)

Question 5

Net filtration rate under normal conditions

Answer 5

~10

Question 6

Changes in Kf?

Answer 6

-does not change under normal conditions
-pathological conditions such as hypertension and diabetes increase the thickness of basement membrane and reduce Kf

Question 7

Changes in Bowman’s capsule hydrostatic pressure

Answer 7

-not a primary means of regulating GFR
-can be due to pathological conditions such as blockages of ureter

Question 8

Changes in Colloid osmotic pressure of glomerular capillaries

Answer 8

-28 mm Hg in afferent arterioles; 36 mm Hg in efferent arterioles

-changes in the concentration of proteins in glomerular capillaries under abnormal conditions will result in:
1.increased colloid osmotic pressure of arterial plasma
2.changes in filtration fraction (if more plasma is filtered, the protein concentration in the glomerular capillaries increases)

Question 9

Changes in glomerulus hydrostatic pressure

Answer 9

-primary factor for physiological regulation of GFR

Question 10

What changes the hydrostatic pressure of the glomerular capillaries?

Answer 10

1.Arterial pressure
2.Afferent arteriolar resistance (more resistance=less bloodflow to glomerulus=less pressure in glomerulus; less resistance = more blood flow to glomerulus=more pressure in glomerulus)
3. Efferent arteriolar resistance (more resistance=more pressure) = biphasic effect on GFR