Determinants of GFR

Dr. Sumera Gul

Associate Professor

Department of Physiology

Renal Physiology 3

Learning Objectives

• At the end of the session, the students should be able to:

• Discuss the factors causing filtration by the glomerular capillaries

• Explain the effects of increase or decrease in the factors causing filtration by the glomerular capillaries

Review

Filtration, secretion, reabsorption and excretion

Composition of glomerular filtrate

GFR

Glomerular capillary membrane

Filterability of solutes and proteins

Filtration Fraction

Determine the Filtration Fraction

• If renal blood flow is 1100ml/min

• Hematocrit is 40% (0.4)

• GFR is 125ml/min

Filtration Fraction

• = GFR/ RPF

• RPF= RBF x (1-Hematocrit)

RPF= 1100 x (1-0.4) = 660 ml/ min

FF= 125/ 660 = 0.189 or 18.9 % of RPF

GFR

• Determined by:

• NFP x Kf

• Kf = Permiability x surface area

Net Filtration Pressure

• P (g)

• P (b)

• Π (g)

• Π (b)

• NFP= ( Sum of all these forces)

Net Filtration Pressure

• P (g) = 60 mmHg

• P (b) = 18 mmHg

• Π (g) = 32 mmHg

• Π (b) = ̴ 0 mmHg

• NFP= ( Sum of all these forces)

Net Filtration Pressure

• P (g) = 60 mmHg = Favors Filtration

• P (b) = 18 mmHg = Opposes filtration

• Π (g) = 32 mmHg = Opposes filtration

• Π (b) = ̴ 0 mmHg

• NFP= ( Sum of all these forces)

• NFP= [ P(g) – P (b) - Π (g) ]

Kf

• GFR / NFP

• Kf for Glomerular capillaries = 12.5ml/min/mmHg

• Kf in other capillary systems = 0.01ml/min/mmHg

Increasing the Forced across the Membrane

• Bowman’s Capsule Hydrostatic Pressure

• Glomerular Capillary Colloid Osmotic Pressure

Arterial plasma colloid osmotic pressure

Filtration fraction

• Glomerular Capillary Hydrostatic Pressure

Urinary system

Factors Affecting GFRIncreasing Decreasing

Increase in glomerular capillary hydrostatic pressure

Decreased glomerular capillary hydrostatic pressure

Increased arterial pressure Increased glomerular colloid osmotic pressure

Increased resistance of efferent arteriole Increased resistance of efferent arteriole

Dilation of afferent arteriole Increased resistance of afferent arteriole

Increased rate of Renal Blood flow Increased bowman’s capsule hydrostatic pressure

Stones in urinary tractHydronephrosis

Decrease in filtration coefficient

SEQ

• Discuss the factors affecting the rate of glomerular filtration.

• Enlist and explain the determinant of GFR.