Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_...
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Transcript of Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_...
![Page 1: Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_ GFR. –Strong activation of renal sympathetic nerves.](https://reader034.fdocuments.net/reader034/viewer/2022051401/5697bf741a28abf838c7fe54/html5/thumbnails/1.jpg)
Control and regulation of GFR and renal blood flow
• Sympathetic nervous system activation _decreases_ GFR.– Strong activation of renal sympathetic nerves
can constrict the renal arterioles and decrease renal blood flow and GFR.
• Only strong activation due to brain ischemia or hemorrhage.
– Mild activation has insignificant effect.
![Page 2: Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_ GFR. –Strong activation of renal sympathetic nerves.](https://reader034.fdocuments.net/reader034/viewer/2022051401/5697bf741a28abf838c7fe54/html5/thumbnails/2.jpg)
Control and regulation of GFR and renal blood flow
• Hormonal and autacoid control of renal circulation.• Norepinephrine, epinephrine, and endothelin constrict renal
blood vessels and decrease GFR.• Angiotensin II constricts efferent arterioles which helps to
prevent a decrease in glomerular hydrostatic pressure and GFR.– Decreased arterial pressure or low blood volume induce
angiotensin II production.» These effects normally decrease GFR
• Endothelial-derived NO decreases renal vascular resistance (induces dilation) and increases GFR.
• Prostaglandins increase renal blood flow and increase GFR.
![Page 3: Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_ GFR. –Strong activation of renal sympathetic nerves.](https://reader034.fdocuments.net/reader034/viewer/2022051401/5697bf741a28abf838c7fe54/html5/thumbnails/3.jpg)
Autoregulation of GFR and renal blood flow
• Mechanisms which maintains renal blood flow and GFR relatively constant despite changes in arterial blood pressure.
• Myogenic Mechanism
• Tubuloglomerular Feedback Mechanism.
Sherwood’s Human Physiology 14-12 5th Ed. & 14-11 6th Ed.
![Page 4: Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_ GFR. –Strong activation of renal sympathetic nerves.](https://reader034.fdocuments.net/reader034/viewer/2022051401/5697bf741a28abf838c7fe54/html5/thumbnails/4.jpg)
Autoregulation of GFR and renal blood flow
Sherwood’s Human Physiology 14-12 5th Ed. & 14-11 6th Ed.
![Page 5: Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_ GFR. –Strong activation of renal sympathetic nerves.](https://reader034.fdocuments.net/reader034/viewer/2022051401/5697bf741a28abf838c7fe54/html5/thumbnails/5.jpg)
Autoregulation of GFR and renal blood flow
• Myogenic Mechanism of GFR– Smooth muscle cells in the afferent arteriole
respond to changes in vascular pressure
– Increase in arterial pressure leads to _constriction
– Decrease in arterial pressure leads to _relaxation_
Sherwood’s Human Physiology 14-12 5th Ed. & 14-11 6th Ed.
![Page 6: Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_ GFR. –Strong activation of renal sympathetic nerves.](https://reader034.fdocuments.net/reader034/viewer/2022051401/5697bf741a28abf838c7fe54/html5/thumbnails/6.jpg)
Autoregulation of GFR and renal blood flow
• Tubuloglomerular Feedback Mechanism.
– Involves the Juxtaglomerular complex which is made up of juxta- glomerular cells from the afferent & efferent arterioles and specialized epithelial cells in the distal tubule called the macula densa .
Sherwood’s Human Physiology 14-12 5th Ed. & 14-11 6th Ed.
![Page 7: Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_ GFR. –Strong activation of renal sympathetic nerves.](https://reader034.fdocuments.net/reader034/viewer/2022051401/5697bf741a28abf838c7fe54/html5/thumbnails/7.jpg)
Autoregulation of GFR and renal blood flow
• Tubuloglomerular Feedback Mechanism.
– Juxtaglomerular cells (JG cells)• Mechanoreceptors• Modified smooth muscle cells that secrete
renin• Leads to efferent arteriole constriction
Sherwood’s Human Physiology 14-12 5th Ed. & 14-11 6th Ed.
![Page 8: Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_ GFR. –Strong activation of renal sympathetic nerves.](https://reader034.fdocuments.net/reader034/viewer/2022051401/5697bf741a28abf838c7fe54/html5/thumbnails/8.jpg)
Autoregulation of GFR and renal blood flow
• Tubuloglomerular Feedback Mechanism.– The macula densa senses changes in the Na+ &
Cl- content in the distal tubule which can be related to the flow rate through the tubule.
• Chemoreceptors
– A decreased flow rate results in less Na+ & Cl- in the proximal tubules and therefore less would be present in the distal tubule.
Sherwood’s Human Physiology 14-12 5th Ed. & 14-11 6th Ed.
![Page 9: Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_ GFR. –Strong activation of renal sympathetic nerves.](https://reader034.fdocuments.net/reader034/viewer/2022051401/5697bf741a28abf838c7fe54/html5/thumbnails/9.jpg)
Tubuloglomerular Feedback Mechanism.
Guyton’s Textbook of Medical Physiology 26-15
• Decreased Arterial Pressure or Decreased concentration of NaCl at the macula densa results in dilation of the afferent arterioles and increased renin release to increase the GFR back to normal.
↓ Arterial pressure
↓ Glomerular Hydrostatic pressure
↓ GFR
↓ Macula densa NaCl
Renin
Angiotensin II
efferentarteriole resistance
afferentarteriole resistance
![Page 10: Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_ GFR. –Strong activation of renal sympathetic nerves.](https://reader034.fdocuments.net/reader034/viewer/2022051401/5697bf741a28abf838c7fe54/html5/thumbnails/10.jpg)
![Page 11: Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_ GFR. –Strong activation of renal sympathetic nerves.](https://reader034.fdocuments.net/reader034/viewer/2022051401/5697bf741a28abf838c7fe54/html5/thumbnails/11.jpg)
Tubuloglomerular Feedback Mechanism.
Sherwood’s Human Physiology 14-13 5th Ed. & 14-12 6th Ed.
• Increased Arterial Pressure or Increased concentration of NaCl at the macula densa results in constriction of the afferent arterioles decrease the GFR back to normal.
↑ Arterial pressure
↑ Glomerular Hydrostatic pressure
↑ GFR
↑ Macula densa NaCl
Afferent arteriole constriction
↓ GFR hydrostatic pressure
↓ GFR to Normal
![Page 12: Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_ GFR. –Strong activation of renal sympathetic nerves.](https://reader034.fdocuments.net/reader034/viewer/2022051401/5697bf741a28abf838c7fe54/html5/thumbnails/12.jpg)
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Tubular Reabsorption
Sherwood’s Human Physiology 14-17 5th Ed. & 14-14 6th Ed.
• For a substance to be reabsorbed it must first be transported across the tubular epithelial membrane into interstitial space and then through the peritubular capillary membrane into the blood.
![Page 14: Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_ GFR. –Strong activation of renal sympathetic nerves.](https://reader034.fdocuments.net/reader034/viewer/2022051401/5697bf741a28abf838c7fe54/html5/thumbnails/14.jpg)
Guyton’s Textbook of Medical Physiology 27-1
Tubular Reabsorption
• Water and solutes are transported via:– Transcellular route
– Paracellular route
– Bulk flow into the bloodstream
![Page 15: Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_ GFR. –Strong activation of renal sympathetic nerves.](https://reader034.fdocuments.net/reader034/viewer/2022051401/5697bf741a28abf838c7fe54/html5/thumbnails/15.jpg)
Sherwood’s Human Physiology 14-17 5th Ed. & 14-14 6th Ed.
Tubular Reabsorption
– Transcellular route• Substance needs to traverse 5 distinct barriers
– Paracellular route• Substance needs to traverse 3 distinct barriers
![Page 16: Control and regulation of GFR and renal blood flow Sympathetic nervous system activation _decreases_ GFR. –Strong activation of renal sympathetic nerves.](https://reader034.fdocuments.net/reader034/viewer/2022051401/5697bf741a28abf838c7fe54/html5/thumbnails/16.jpg)
Guyton’s Textbook of Medical Physiology 27-1 & Sherwood’s Human Physiology 14-18 5th Ed & 14-15 6th Ed
Tubular Reabsorption
• Passive transport – Due to electrical and chemical gradient (Urea
and Cl-)
• Osmosis• Active transport
– Primary active transport Na+- K+-ATPase.
• Pinocytosis – Especially for reabsorption of proteins.