Factors Affecting G.F.R.

Dr. Ashok Solanki

Renal handling of substances

Dr. Ashok Solanki

Dr. Ashok Solanki

Factors affecting G.F.R.

Changes in renal blood flowChanges in glomerular capillary hydrostatic pressureChanges in systemic blood pressureAfferent or efferent arteriolar constrictionChanges in hydrostatic pressure in Bowman's capsuleUreteral obstructionEdema of kidney inside tight renal capsuleChanges in concentration of plasma proteins: dehydration, hypoproteinemia, etc (minor factors)Changes in Kf

Changes in glomerular capillary permeabilityChanges in effective filtration surface area

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

Dr. Ashok Solanki

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

Dr. Ashok Solanki

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

Dr. Ashok Solanki

The 4 basic functions of the kidneys

• Ultrafiltration by glomerular capillaries

Dr. Ashok Solanki

glomerular filtration and tubular function.

• bulk flow of fluid from glomerular capillary to Bowman’s space

• volume = 20% of RPF (filtration fraction), ≈ 125 ml/min• barriers to filtration• endothelial fenestrae• basement membrane• Podocytes• GFR = Kf · NFP (filtration coefficient x net filtration pressure)

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

Tubuloglomerular feedback

o Alterations in GFR due to changes in glomerular perfusion pressure will lead to an alteration in the composition of the fluid delivered to the macula densa region of the nephron tubule

o The macula densa senses these changes and acts to alter afferent arteriole tone to vary glomerular perfusion pressure to return the GFR to normalo

Dr. Ashok Solanki

Dr. Ashok Solanki

The structure of the filter1. The glomerular capillary endothelium:• A highly specialised capillary endothelium with fenestrations (windows)

to minimise the filter thickness;• This layer prevents cellular components of blood coming into contact with

the basement membrane.

2. The glomerular basement membrane:• Made of connective tissue, it is negatively charged;• This is the layer that actually acts as the filter.

3. Bowman’s epithelial cells (podocytes):• Epithelial cells with multiple projections (foot processes) which interlink

with each other• whilst still keeping a small gap between them creating a large surface

area;• Act to maintain the basement membrane, and has phagocytic functions.

Dr. Ashok Solanki

Dr. Ashok Solanki

Tubuloglomerular feedback

Dr. Ashok Solanki

Dr. Ashok Solanki

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

Dr. Ashok Solanki

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

Dr. Ashok Solanki

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

Factors Affecting G.F.R.

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