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Control and regulation of GFR and renal blood flow

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.

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Control and regulation of GFR and renal blood flow

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  1. 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.

  2. Control and regulation of GFR and renal blood flow • Hormonal and autacoid control of renal circulation. • Norepinephrine, epinephrine, and endothelinconstrict renal blood vessels and decrease GFR. • Angiotensin IIconstricts 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 NOdecreases renal vascular resistance (induces dilation) and increases GFR. • Prostaglandinsincrease renal blood flow and increase GFR.

  3. 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.

  4. Autoregulation of GFR and renal blood flow Sherwood’s Human Physiology 14-12 5th Ed. & 14-11 6th Ed.

  5. 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.

  6. Autoregulation of GFR and renal blood flow • Tubuloglomerular Feedback Mechanism. • Involves theJuxtaglomerular complex which ismade 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.

  7. 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.

  8. 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.

  9. Tubuloglomerular Feedback Mechanism. ↓ Arterial pressure • 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. ↓ Glomerular Hydrostatic pressure ↓ GFR ↓Macula densa NaCl Renin Angiotensin II afferent arteriole resistance efferent arteriole resistance Guyton’s Textbook of Medical Physiology 26-15

  10. Tubuloglomerular Feedback Mechanism. ↑ Arterial pressure • 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. ↑ Glomerular Hydrostatic pressure ↑ GFR ↑Macula densa NaCl Afferent arteriole constriction ↓ GFR hydrostatic pressure ↓ GFR to Normal Sherwood’s Human Physiology 14-13 5th Ed. & 14-12 6th Ed.

  11. Tubular Reabsorption • For a substance to be reabsorbed it must first betransported across the tubular epithelial membraneinto interstitial space and thenthrough the peritubular capillary membraneinto the blood. Sherwood’s Human Physiology 14-17 5th Ed. & 14-14 6th Ed.

  12. Tubular Reabsorption • Water and solutes are transported via: • Transcellular route • Paracellular route • Bulk flow into the bloodstream Guyton’s Textbook of Medical Physiology 27-1

  13. Tubular Reabsorption • Transcellular route • Substance needs to traverse 5 distinct barriers • Paracellular route • Substance needs to traverse 3 distinct barriers Sherwood’s Human Physiology 14-17 5th Ed. & 14-14 6th Ed.

  14. Tubular Reabsorption • Passive transport • Due to electrical and chemical gradient (Urea and Cl-) • Osmosis • Active transport • Primary active transportNa+- K+-ATPase. • Pinocytosis • Especially for reabsorption of proteins. Guyton’s Textbook of Medical Physiology 27-1 & Sherwood’s Human Physiology 14-18 5th Ed & 14-15 6th Ed

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