Editing Kidney functions
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==Kidney functions== | ==Kidney functions== | ||
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===Renin-angiotensin system=== | ===Renin-angiotensin system=== | ||
- | *The overall scheme is that | + | *The overall scheme is that angiotensin is present in the blood, renin cuts it into angiotensin 1, ACE cuts angiotensin 1 into angiotensin 2. |
- | **Note that angiotensinogen comes from the liver, renin comes from the kidney, and ACE (angiotensin converting enzyme) comes from the | + | **Note that angiotensinogen comes from the liver, renin comes from the kidney, and ACE (angiotensin converting enzyme) comes from the liver. |
- | Did Homor Smith explain why it makes sense that one enzyme should come from the | + | Did Homor Smith explain why it makes sense that one enzyme should come from the liver and the other from the lungs? |
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*Angiotensin 2 is all about increasing blood pressure and therefore has effects on the vasculature (think constriction), the adrenal cortex (think aldosterone, and the brain (think thirst). | *Angiotensin 2 is all about increasing blood pressure and therefore has effects on the vasculature (think constriction), the adrenal cortex (think aldosterone, and the brain (think thirst). | ||
**Angiotensin 2 causes vasculature to constrict, thus increasing the blood pressure. | **Angiotensin 2 causes vasculature to constrict, thus increasing the blood pressure. | ||
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*The macula densa cells can respond to both high and low NaCl concentrations: | *The macula densa cells can respond to both high and low NaCl concentrations: | ||
- | **When NaCl concentrations are | + | **When NaCl concentrations are high, filtrate flow rate is too slow. The macula densa cells signal to the granular cells to release renin. |
***Recall that renin will increase blood pressure systmeically because angiotensin 2 causes vasoconstriction, aldosterone release at the adrenal gland, and AVP release at the posterior pituitary. | ***Recall that renin will increase blood pressure systmeically because angiotensin 2 causes vasoconstriction, aldosterone release at the adrenal gland, and AVP release at the posterior pituitary. | ||
***It makes sense that low flow rate should lead to release of renin by the granular cells because increased blood pressure (at the afferent arteriole) causes an increase in filtrate formation (increased blood flow will push more fluid through the fenestrations at the glomerulus and thus generate more filtrate). | ***It makes sense that low flow rate should lead to release of renin by the granular cells because increased blood pressure (at the afferent arteriole) causes an increase in filtrate formation (increased blood flow will push more fluid through the fenestrations at the glomerulus and thus generate more filtrate). | ||
- | + | So this wouldn't cause immediate vasoconstriction, right, b/c renin would have to cut angiotensinogen up and then that would have to go to the lung and then back to the kidney as angiotensin 2, right? | |
***Note that macula densa cells signal to granular cells via PGE2, a prostaglandin produced by COX2 in the macula densa cells. | ***Note that macula densa cells signal to granular cells via PGE2, a prostaglandin produced by COX2 in the macula densa cells. | ||
***The '''granular cells have the EP4 receptor for PGE2''' from the macula densa cells. | ***The '''granular cells have the EP4 receptor for PGE2''' from the macula densa cells. | ||
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===Renal plasma clearance=== | ===Renal plasma clearance=== | ||
*There are multiple forces that cause a net movement of plasma out of the blood at the glomerulus into the filtrate: | *There are multiple forces that cause a net movement of plasma out of the blood at the glomerulus into the filtrate: | ||
- | **Pi | + | **Pi is the colloid osmotic pressure of the blood (forces into the blood) |
- | **P<sub>GC</sub> = | + | **P<sub>GC</sub> = Glomerular capillary pressure is the hydrostatic pressure from blood flow (forces into filtrate) |
- | **P<sub>BS</sub> = '''B'''owman ''' | + | **P<sub>BS</sub> = '''B'''owman '''space''' hydrostatic pressure; that is, the hydrostatic pressure of the filtrate (forces into the blood) |
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*One measure of renal function is the renal plasma clearance, defined as ml plasma / min that are cleared of a substance. | *One measure of renal function is the renal plasma clearance, defined as ml plasma / min that are cleared of a substance. | ||
*The equation is C * P = U * V where | *The equation is C * P = U * V where | ||
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*As an example: the plasma concentration is 2 mg/ml, the urine concentration is 6 mg/min. | *As an example: the plasma concentration is 2 mg/ml, the urine concentration is 6 mg/min. | ||
**C = UV/P = 6 mg/min / 2 mg/ml = 3 min/ml | **C = UV/P = 6 mg/min / 2 mg/ml = 3 min/ml | ||
- | + | What does the dot over the V mean? | |
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*One might wonder why the urinary inulin is more concentrated than the plasma inulin. | *One might wonder why the urinary inulin is more concentrated than the plasma inulin. | ||
**Its because while none of the inulin gets reabsorbed, so many of the other filtered molecules (including water) ''do get reabsorbed''. | **Its because while none of the inulin gets reabsorbed, so many of the other filtered molecules (including water) ''do get reabsorbed''. | ||
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===Endogenous creatinine clearance=== | ===Endogenous creatinine clearance=== | ||
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*A normal day has about 1440 minutes in it. | *A normal day has about 1440 minutes in it. | ||
*So a normal kidney filters 125 ml plasma / min * 1440 min = 180 L / day. | *So a normal kidney filters 125 ml plasma / min * 1440 min = 180 L / day. | ||
- | **And we have about 3.5 L of | + | **And we have about 3.5 L of plasma (filtered 50 times per day) and 14 L of extracellular fluid (filtered 13 times per day). |
===Filtration fraction=== | ===Filtration fraction=== | ||
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===PAH clearance=== | ===PAH clearance=== | ||
- | *The clearance of | + | *The clearance of p-aminohippurate (PAH) has been shown to model well the renal plasma flow (RPF). |
*Note that PAH is not normally found in blood plasma. | *Note that PAH is not normally found in blood plasma. | ||
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*An '''extraction ratio''' is the amount of a compound entering the kidney versus the amount excreted in the urine. | *An '''extraction ratio''' is the amount of a compound entering the kidney versus the amount excreted in the urine. | ||
*PAH has an extraction ratio of nearly 1, meaning that nearly all of the PAH that enters the kidney gets filtered out into the filtrate urine. | *PAH has an extraction ratio of nearly 1, meaning that nearly all of the PAH that enters the kidney gets filtered out into the filtrate urine. | ||
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===Renal blood flow versus renal plasma flow=== | ===Renal blood flow versus renal plasma flow=== | ||
- | *Renal blood flow and renal plasma flow are not the same value | + | *Renal blood flow and renal plasma flow are not the same value. |
- | * | + | *RBF = RPF / (1 - hematocrit) |
*Recall that a normal renal plasma flow (RPF) is 660 ml plasma / min. | *Recall that a normal renal plasma flow (RPF) is 660 ml plasma / min. | ||
*Recall that a normal plasma / hematocrit ratio is 0.45. | *Recall that a normal plasma / hematocrit ratio is 0.45. | ||
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*Then calculate the renal blood flow (RBF). | *Then calculate the renal blood flow (RBF). | ||
**RBF = RPF / (1 - Hct) | **RBF = RPF / (1 - Hct) | ||
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