Editing Renal blood flow, glomerular filtration
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==Renal blood flow and glomerular filtration== | ==Renal blood flow and glomerular filtration== | ||
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*The blood flow rate can be described by the number of ml of blood that flow in a certain time (min) to a certain mass of tissue (g). | *The blood flow rate can be described by the number of ml of blood that flow in a certain time (min) to a certain mass of tissue (g). | ||
**ml / min / g | **ml / min / g | ||
- | *The flow rate within the kidney is | + | *The flow rate within the kidney is highest in the cortex (good for inducing filtration) and lowest in the medulla (good for preventing "washout" of solutes in the interstitium). |
- | + | What is washout? | |
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===Autoregulation of renal blood flow and GFR=== | ===Autoregulation of renal blood flow and GFR=== | ||
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*Myogenic GFR regulation | *Myogenic GFR regulation | ||
- | **This mechanism is not unique to the kidney | + | **This mechanism is not unique to the kidney, many vascular beds use it, including the brain. |
**Recall that the point is to keep GFR at some constant levels and that an increased arterial blood pressure would increase GFR. | **Recall that the point is to keep GFR at some constant levels and that an increased arterial blood pressure would increase GFR. | ||
**So as arterial blood pressure increases, we want to myogenically decrease the blood pressure to maintain the same GFR. | **So as arterial blood pressure increases, we want to myogenically decrease the blood pressure to maintain the same GFR. | ||
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*Sympathetic nervous control of the renal blood flow works by '''rapidly, temporarily constricting the afferent arterioles'''. | *Sympathetic nervous control of the renal blood flow works by '''rapidly, temporarily constricting the afferent arterioles'''. | ||
**This is a prioritization of water retention and continued blood flow to other organs over the proper function of the kidneys. | **This is a prioritization of water retention and continued blood flow to other organs over the proper function of the kidneys. | ||
- | *Sympathetic nervous control is achieved through | + | *Sympathetic nervous control is achieved through renin and catecholamines (epinephrine and norepinephrine). |
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**Renin starts the angiotensin pathway which leads to angiotensin 2 and thus vasoconstriction, aldosterone release, and AVP release (all of which elevate blood pressure). | **Renin starts the angiotensin pathway which leads to angiotensin 2 and thus vasoconstriction, aldosterone release, and AVP release (all of which elevate blood pressure). | ||
**'''Epinpehrine and norepi bind the a1-adrenoreceptors''' to directly cause vasoconstriction of the vascular smooth muscle. | **'''Epinpehrine and norepi bind the a1-adrenoreceptors''' to directly cause vasoconstriction of the vascular smooth muscle. | ||
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***Angiotensin 2 makes sense because it generally serves to conserve and reabsorb water, and decreasing RBF will slow filtrate flow and thus allow the tubule cells to reabsorb more of the H20. | ***Angiotensin 2 makes sense because it generally serves to conserve and reabsorb water, and decreasing RBF will slow filtrate flow and thus allow the tubule cells to reabsorb more of the H20. | ||
- | === | + | ===Dampening effect of prostaglandins on renal vasoconstriction=== |
*We have seen that sympathetic nerves cause vasoconstriction at the kidney (renin + epi / norepi -> vasoconstriction of the afferent arteriole). | *We have seen that sympathetic nerves cause vasoconstriction at the kidney (renin + epi / norepi -> vasoconstriction of the afferent arteriole). | ||
*We have also seen that prostaglandins cause vasodilation at the kidney (vasodilation of the afferent arteriole). | *We have also seen that prostaglandins cause vasodilation at the kidney (vasodilation of the afferent arteriole). | ||
*Finally, we know that '''NSAIDs decrease prostaglandin synthesis systemically'''. | *Finally, we know that '''NSAIDs decrease prostaglandin synthesis systemically'''. | ||
*So, it makes sense that giving NSAIDs to a pt who is volume depleted (or otherwise has poor kidney function) is bad because it will reduce prostaglandin synthesis, therefore reduce the amount of vasodilation force on the afferent arteriole, and result in lower RBF, lower GFR, and less filtration. | *So, it makes sense that giving NSAIDs to a pt who is volume depleted (or otherwise has poor kidney function) is bad because it will reduce prostaglandin synthesis, therefore reduce the amount of vasodilation force on the afferent arteriole, and result in lower RBF, lower GFR, and less filtration. | ||
- | + | Where do the prostaglandins come from? Is there a local, renal source? | |
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===Hallmark of glomerular disease=== | ===Hallmark of glomerular disease=== | ||
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===Glomerular filtration occurs over 3 layers=== | ===Glomerular filtration occurs over 3 layers=== | ||
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*There are three major layers in the glomerulus through which a molecule must pass to get from the blood to the filtrate. | *There are three major layers in the glomerulus through which a molecule must pass to get from the blood to the filtrate. | ||
*The first layer is the capillary's endothelium. | *The first layer is the capillary's endothelium. | ||
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**The endothelial cells of the arteriole sit on the basement membrane. | **The endothelial cells of the arteriole sit on the basement membrane. | ||
*The last specialization are the podocytes. | *The last specialization are the podocytes. | ||
- | **Podocytes sit on the | + | **Podocytes sit on the outside of the basement membrane and send out feet from their cell body. |
**The feet of neighboring podocytes rest very near to one another to form small slits through which only small molecules can pass. | **The feet of neighboring podocytes rest very near to one another to form small slits through which only small molecules can pass. | ||
**The slits formed by the podocytes are called '''filtration slits''' or '''slit pores'''. | **The slits formed by the podocytes are called '''filtration slits''' or '''slit pores'''. | ||
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**Blood colloid pressure (Pi<sub>GC</sub>) wants to keep stuff in the blood. | **Blood colloid pressure (Pi<sub>GC</sub>) wants to keep stuff in the blood. | ||
***Note that the blood colloid pressure (P<sub>GC</sub>) increases proximal to distal in the capillary as water is filtered out. | ***Note that the blood colloid pressure (P<sub>GC</sub>) increases proximal to distal in the capillary as water is filtered out. | ||
- | **Filtrate colloid pressure (P<sub>FC</sub>) wants to keep stuff in the interstitial fluid | + | **Filtrate colloid pressure (P<sub>FC</sub>) wants to keep stuff in the interstitial fluid. |
**Capillary hydrostatic pressure (P<sub>GC</sub>) wants to force stuff out of the capillary. | **Capillary hydrostatic pressure (P<sub>GC</sub>) wants to force stuff out of the capillary. | ||
- | **Filtrate hydrostatic pressure (P<sub>BS</sub> | + | **Filtrate hydrostatic pressure (P<sub>BS</sub>wants to force fluid into the blood. |
***P<sub>BS</sub> is negligible. | ***P<sub>BS</sub> is negligible. | ||
*There is a constant called the '''glomerular ultrafiltration coefficient (K<sub>f</sub>) that accounts for the normal surface area and capillary permeability. | *There is a constant called the '''glomerular ultrafiltration coefficient (K<sub>f</sub>) that accounts for the normal surface area and capillary permeability. | ||
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**If there is vascular damage, the glomerular ultrafiltration coefficient may decrease. | **If there is vascular damage, the glomerular ultrafiltration coefficient may decrease. | ||
- | *'''GFR = K<sub>f</sub> * (P<sub>GC</sub> - P<sub>BS</sub> - Pi<sub>GC</sub>) | + | *'''GFR = K<sub>f</sub> * (P<sub>GC</sub> - P<sub>BS</sub> - Pi<sub>GC</sub>) |
**That is GFR = ultrafiltration coefficient * (capillary hydrostatic pressure - filtrate hydrostatic pressure - blood colloid pressure). | **That is GFR = ultrafiltration coefficient * (capillary hydrostatic pressure - filtrate hydrostatic pressure - blood colloid pressure). | ||
- | ===Force differences along systemic capillaries and renal capillaries | + | ===Force differences along systemic capillaries and renal capillaries=== |
- | *There is a distinct difference between | + | *There is a distinct difference between.... |
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