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6 out of 8

GFR increases if(DNB June-2009)

A Afferent arteriole constricts

B Afferent arteriole dilates

C Efferent arteriole constricts

D Efferent arteriole dilates

Ans. C Afferent arteriole dilates, Efferent arteriole constricts

Determinants of the GFR:­

  1. GFR == Kf x Net filtration pressure
  2. Net filtration pressure = (PG - PB - G + B)

a. PG = Glomerular hydrostatic pressure (= 60 mm Hg), promotes filtration

b. PB = Hydrostatic pressure in Bowman's capsule (=18 mm Hg) which opposes filtration

c. PG = Glomerular capillary colloid osmotic pressure (=32 mm Hg), which opposes filtration

d. PB = Bowman's capsule colloid osmotic pressure which promotes filtration, normally its value is zero

e. Therefore

Net filtration pressure = (PG - PB - G + B)

= 60 -18 - 32 + 0

= +10 mm Hg

  1. Kf = Glomerular capillary filtration (ultrafiltration) co-efficient Kf is a measure of the product of the hydraulic conductivity (i.e. its permeability) and surface area of the glomerular capillaries. Its normal value for kidney is 12.5 ml/min/mm Hg of filtration pressure or 4.2 ml/min/mm Hg per 100 gm of kidney.

Factors that increase or Decrease GFR

I. Kf - "although increased Kf raises GFR, and decreased Kf reduces GFR, changes in Kf probably do not provide a primary mechanism for the normal day to day regulation of GFR Kr- if decreases →↓GFR

a. Measangial cells contraction →↓ Kf →↓GFR; Angiotensin II important regulator of the mesangial cells contraction contraction →↓area available for filtration.

b. in thickness of the Glomerulary capillary BM i.e. glom. capi. permeability →↓ Kf →↓GFR ego chr. HTN, DM Agents causing contraction or Relaxation of measangial cells i.e. , or Kf i.e. -­or GFR.





Angiotension II (M.I.)

Dopamine (in low dose)








LT-C4 and D4


II. Glomerular capillary Hydraustatic pressure (PG)

a. Changes in glomerular hydrostatic pressure (PG) serve as the primary means for physiological regulation of GFR

b. In PG raises GFR whereas in PG reduces GFR Under physiological condition, PG is determined by three variable.

i. Arterial pressure: due to autoregulation mechanism, kidneys maintain a relatively constant PG when BP fluctuates, but when the mean systemic arterial pressure drops below 90 mm Hg, there is a sharp drop in GFR Angiotension II formation increases in cases of arterial pressure or hypovolemia causes constraction of efferent arterioles →↑ PGtends to maintain GFR

ii. Afferent arteriolar resistance (RA) Constriction of afferent arterioles Renal Blood flow →↓ glomerular hydrostatic pressure (PG) -7 JGFR Dilatation of afferent arterioles Renal Blood flow →↑ PG →↑GFR

iii. Efferent arteriolar Resistance (RE)

Constriction of efferent arterioles has biphasic effects on GFR.

1) Moderate constriction: Renal Blood flow does reduces too much

2) Severe constriction: ↓↓ Renal Blood flow Due to Donnan effect increase in glomerular colloid Osmotic pressure exceeds the increase in glomerular capillary hydrostatic pressure, therefore net filtration force actually decreases causes in GFR.

Summary of factors that can Decrease the GFR :

Physical determinants

Physiological/Pathophysiological causes

  1. Kf due to

- in glomerular Capillary permeability

- filtration surface area

DM, Chr. HTN (diffuse glomerular disease)

Nephro loss in progressive RF

b. PB→↓ GFR

Urinary tract obstruction

c. Oncotic pressure G →↓ GFR

Renal blood flow, plasma proteins – eg. Hemo concentration due to severe vol depletion, myeloma or other dysproteinemias.

d. PG→↓ GFR

Dec. afferent diameter, efferent arteriole dilation

Arterial pressure as in circulatory shock

Angiotension II (e.g. ACE-inhibitors)

Sympathetic activity, Vasoconstrictor hormones (e.g NorAdr, Endothelin)