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10/29/2010
1
ObjectivesObjectives
� To discuss factors that control GFR.
� To address how B.P. can affect GFR & introduce topic of renal suppression.
� To outline the different control mechanisms that influence filtration rates.
� To introduce the renin-angiotensinmechanism to regulate GFR.
Factors affecting GFRFactors affecting GFR
o Total surface area
o Filtration membrane permeability
o NFP changes
Kidney diseases (increase NFP)
Hemorrhage (decrease NFP)
o Blood Pressure changes (direct correlation)
o Dehydration – inhibits filtrate formation.
Blood Pressure FactorsBlood Pressure Factors
Hypotension – If extreme then glomerular filtration will stop:
If GBHP = CHP no filtration
Termed renal suppression.
Hypertension – not as significant because the body has stretch receptors that constrictsafferent arterioles. Maintains GFR
Control of GFRControl of GFR
Intrinsic Controls – Adjusting resistance to blood flow.
Maintains a nearly constant GFR when MAP is in
the range of 80–180 mm Hg
A. Myogenic mechanism – stretching muscles of afferent arterioles
B. Tubuloglomerular feedback mechanism –
Controls vasodilation or vasoconstriction of the afferent arterioles, located in walls of distal tubules – respond to osmotic signals; senses changes in the juxtaglomerular apparatus
Control of GFRControl of GFR
Extrinsic Controls – Maintains systemic BPA. Sympathetic nervous system controls – Release of
norepinephrine constrict afferent arterioles and thus decrease filtration formation.
B. Renin-angiotensin mechanism -Juxtaglomerular cells (JG) cells that sense blood
pressure changes in the afferent arteriole release renin.* See Fig 25.12
* Renin ultimately raises BP (See pg 16-18 in SG)
Figure 25.12
Stretch of smoothmuscle in walls of afferent arterioles
Blood pressure inafferent arterioles; GFR
Vasodilation ofafferent arterioles
GFR
Myogenic mechanismof autoregulation
Release of vasoactivechemical inhibited
Intrinsic mechanisms directly regulate GFR despite
moderate changes in blood pressure (between 80 and 180 mm Hg mean arterial pressure).
Extrinsic mechanisms indirectly regulate GFR
by maintaining systemic blood pressure, whichdrives filtration in the kidneys.
Tubuloglomerularmechanism ofautoregulation
Hormonal (renin-angiotensin)mechanism
Neural controls
SYSTEMIC BLOOD PRESSURE
GFR
Macula densa cellsof JG apparatus of kidney
Filtrate flow andNaCl in ascendinglimb of Henle’s loop
Targets
Granular cells ofjuxtaglomerularapparatus of kidney
Angiotensinogen Angiotensin II
Adrenal cortex Systemic arterioles
(+) Renin
Release
Catalyzes cascaderesulting in conversion
(+)
(+)
(+)
Kidney tubules
Aldosterone
Releases
Targets
Vasoconstriction;peripheral resistance
Blood volume
Na+ reabsorption;water follows
Systemic
blood pressure
(+)
(+)
(–)
Increase
Decrease
Stimulates
Inhibits
Baroreceptors inblood vessels ofsystemic circulation
Sympatheticnervous system
(+)
(–)
Vasodilation ofafferent arterioles
10/29/2010
2
Effects of Angiotensin IIEffects of Angiotensin II
1. Constricts arteriolar smooth muscle, causing MAP to rise
2. Stimulates the reabsorption of Na+
◦ Acts directly on the renal tubules
◦ Triggers adrenal cortex to release aldosterone
3. Stimulates the hypothalamus to release ADH and activates the thirst center
Effects of Angiotensin IIEffects of Angiotensin II
4. Constricts efferent arterioles, decreasing peritubular capillary hydrostatic pressure and increasing fluid re-absorption
5. Causes glomerular mesangial cells to contract, decreasing the surface area available for filtration
Glomerulus
Glomerular capsule
Afferent arteriole
Efferent arteriole
Red blood cell
Podocyte cell body (visceral layer)
Foot processesof podocytesParietal layer
of glomerularcapsule
Proximaltubule cell
Lumens of glomerularcapillaries
Endothelial cellof glomerularcapillary
Efferent arteriole
• Macula densa cellsof the ascending limbof loop of Henle
• Granular cells
• Extraglomerularmesangial cells
Afferent arteriole
Capsularspace
Renal corpuscleJuxtaglomerular
apparatus
Mesangial cellsbetween capillaries
Juxtaglomerularapparatus