gfr factors. 17.02.13
TRANSCRIPT
Dr. Ashok Solanki
Renal handling of substances
Dr. Ashok Solanki
Dr. Ashok Solanki
Dr. Ashok Solanki
Dr. Ashok Solanki
Dr. Ashok Solanki
Dr. Ashok Solanki
Factors affecting G.F.R.
Changes in renal blood flow
Changes in glomerular capillary hydrostatic pressure
Changes in systemic blood pressure
Afferent or efferent arteriolar constriction
Changes in hydrostatic pressure in Bowman's capsule
Ureteral obstruction
Edema of kidney inside tight renal capsule
Changes in concentration of plasma proteins: dehydration, hypoproteinemia, etc (minor factors)
Changes in Kf
Changes in glomerular capillary permeability
Changes 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
Dr. Ashok Solanki
Dr. Ashok Solanki
Dr. Ashok Solanki
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
Dr. Ashok Solanki
Dr. Ashok Solanki
Dr. Ashok Solanki
Dr. Ashok Solanki
Dr. Ashok Solanki
Tubuloglomerular feedback
Dr. Ashok Solanki
Dr. Ashok Solanki
Dr. Ashok Solanki
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
Dr. Ashok Solanki
Dr. Ashok Solanki