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 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.

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 th Ed. & th Ed.

4. Autoregulation of GFR and renal blood flow
Sherwood’s Human Physiology th Ed. & th 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 th Ed. & th Ed.

6. 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 th Ed. & th 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 th Ed. & th 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 th Ed. & th 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

11. Tubuloglomerular Feedback Mechanism.
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
Sherwood’s Human Physiology th Ed. & th Ed.

13. Tubular Reabsorption
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.
Sherwood’s Human Physiology th Ed. & th Ed.

14. 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

15. Tubular Reabsorption Transcellular route Paracellular route
Substance needs to traverse 5 distinct barriers
Paracellular route
Substance needs to traverse 3 distinct barriers
Sherwood’s Human Physiology th Ed. & th Ed.

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