Glomerular Filtration is High and is Regulated Precisely

Dr. Ashok Solanki

The 4 basic functions of the kidneys

• Ultrafiltration by glomerular capillaries

Dr. Ashok Solanki

Glomerular capillaries a network of high pressure capillary bed fiters fluid ata rate about 180 lit/day

Dr. Ashok Solanki

Dr. Ashok Solanki

Glomerular filtration• The glomerulus is a collection of twisted

capillaries• that receive blood from the afferent arteriole of

the renal blood supply• and exit the kidney via the efferent arteriole• Ultrafiltrate is the product of glomerular

filtration of blood following its passage through a glomerular fi ltration barrier

Dr. Ashok Solanki

Glomerular fitration Substances in the blood are

filtered through capillary fenestrae between endothelial cells (single layer).

filtrate then passes across the basement membrane and through slit pores between the foot processes

(also called pedicels) and enters the capsular space.

From here, the filtrate is transported to the lumen of the proximal convoluted tubule.

Dr. Ashok Solanki

Dr. Ashok Solanki

Junction- the JGA

Blood flows into the glomerulus throughthe afferent arterioles and leaves theglomerulus through the efferentarterioles. The proximal tubule exits Bowman’s capsule.

Dr. Ashok Solanki

Dr. Ashok Solanki 1404.02.2013

Dr. Ashok Solanki

Renal handling of substances

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Dr. Ashok Solanki

Tubuloglomerular feedback

Dr. Ashok Solanki

GFR = Kf . (PG – PB – pG + pB)

The GFR is determined by

the sum of the hydrostatic pressure

colloid osmotic forces across the glomerular membrane

Bowmens capsule hydrostatic pressure

the glomerular capillary filtration coefficient, Kf

GFR = Kf . Net filtration pressure

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Autoregulation of GFR

• Afferent arteriolar feedback mechanism for regulating GFR

• Efferent arteriolar feedback mechanism for regulating GFR

• Myogenic mechanism regulating GFR- resist stretching during increase arterial pressure – stretch of vascular wall increase calcium ions entry from ECF into the cell – contract the cells – increase vascular resistance – decrease GFR and RBF

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Factors affecting GFR1. Glomerular capillary hydrostetic pressure –

- arterial pressure

- afferent arterial resistance

- efferent arterial resistance

2. Colloidal osmotic pressure of glomerulus –

3. bowmen’s capsular hydrostetic pressure – ureteric stone, obstruction of

urinary tract

4. RBF – GFR directly related to RBF

5. Sympathetic stimulation

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Factors affecting GFR

• Decrease Kf decrease GFR• Increase Kf increase GFR• In some diss. Lower Kf by reducing the

number of functional glo. Capillaries• Increase thickness of the glo. Capillaries• Chronic uncontrolled hypertension and

diabetes mellitus

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Autoregulation of GFR

Afferent arteriolar feedback mechanism for regulating GFREfferent arteriolar feedback mechanism for regulating GFRMyogenic mechanism regulating GFR- resist stretching during increase arterial pressure – stretch of vascular wall increase calcium ions entry from ECF into the cell – contract the cells – increase vascular resistance – decrease GFR and RBF

Dr. Ashok Solanki

Glomerular capillary filtration coefficient - Kf

The Kf is a measure of the product of the hydraulic conductivity and surface

area of the glomerular capillaries

Kf = GFR / Net filtration pressure

GFR – 125 ml / min

Net filtration pressure – 10 mm of Hg

Kf – 12.5 ml / min /mm of Hg

4.2 ml/min/mm of Hg/100g of kidney wt.

Dr. Ashok Solanki

Dr. Ashok Solanki

Net filtration pressure • Forces favoring filtration (mm Hg) glomerular hydrostatic pressure - Pg 60 bowmen’s capsule colloid osmotic pressure – πb 0 • Forces opposing filtration (mm Hg ) bowmen’s capsule hdrostatic pressure - Pg 18 glomerular capillary colloid osmotic pressure – πg 32Net filtration pressure = 60 – 18 – 32 = +10 mmof Hg

Dr. Ashok Solanki

Forces promoting & opposesing filtration

• Net filtration force is +ve causing filtration

Dr. Ashok Solanki

GFR is sum of Kf x Net filtration pressure

The amount of the glomerular filtrate by all the nephrons of both the kidneys

in a one minute is called GFR

GFR = filtration fraction x RBF

In the average human adult, the GFR is about 125 ml / min. or 180 L / day

Filtration fraction – the fraction of the renal plasma which becomes the filtrate

Filtration fraction = GFR / RBF

Dr. Ashok Solanki

Glomerular Filtration is High and is Regulated Precisely

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