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9 Cards in this Set
- Front
- Back
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Autoregulation: Relative constancy of GFR and RBF is possible despite marked changes in arterial blood pressure between 75 and 160 due to two mechanisms...
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o Myogenic mechanism
o Tubuloglomerular feedback |
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Sympathetic stimulation (can override autoregulation in times of emergency)
Why is this significant and when does it occur? Does this mechanism INCREASE OR DECREASE renal blood flow? |
Significant in reducing GFR in severe acute disturbances in arterial blood pressure (brain ischemia, severe hemorrhage, severe hypotension)
o In response to acute reactions especially hypotension/hypovolemia that is severe and persistent and cant correct itself will have sympathetic control that can override autoregulation and can clamp down and reduce renal blood flow in order to preserve blood flow to brain, heart, and rest of the body Decreases flow. |
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Myogenic Mechanism
Individual blood vessels resist stretching (contract) during increased arterial pressure... What effect does this have? |
This contraction:
1. Prevents over-distention of the afferent arteriole 2. Raises the vascular resistance of the afferent arteriole 3. Vasocontricts the afferent arteriole 4. Prevents excessive increased in RBF and GFR (keeps them relatively constant) |
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Increased arterial pressure stretches the actual walls of the arterioles so that by the Law of Laplace (tension = pressure x radius) as you pressurize, the wall tension goes up and they respond by contracting back down...
Explain how this works... |
1. This mechanism prevents over distention of afferent arterioles and increases vascular resistance leading to vasoconstriction and prevents excess increase in GFR and RBF
2. If increase in pressure and increase in resistance→ it will keep flow constant 3. Decrease in the radius of these vessels mean that there is an increasing resistance 4. F = P/R will be kept constant so when pressure comes hammering down on kidneys, they respond with a myogenic response |
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Tubuloglomerular feedback: is in control of RBF and GFR in response to changes in Na+ concentration in the distal tubule.
Explain how this works.... |
1. This regulates size of (constriction) afferent arteriole so that regulates GFR
2. If tubule gets overloaded with fluid it can decrease GFR for that nephron only (each individual nephron talks to its own afferent arteriole) 3. It is a way of monitoring whether the nephron is overloaded with flow 4. If Na composition goes up these cells can trigger constriction of the afferent arteriole 5. If Na levels drop, the nephron will dilate the afferent arteriole |
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Macula densa - Structure / Function
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Specialized epithelial cells of the distal tubules that:
• Sense change of Na+ concentration in tubular fluid • Trigger afferent arteriolar vasodilation or constriction • Increases or decrease RBF and GFR in a negative feedback mechanism |
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Explain the negative feedback mechanism in the macula densa...
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If increase arteriole pressure that simultaneously increases GBF and glomerular capillary pressure at each individual nephron, will have an increase in GFR, so the proximal tubule and the Loop of Henle is chugging along reabsorbing as much Na as its used to absorbing but if GFR increases, there will be more Na and Cl left at the distal tubule so will show as an increased delivery of NaCl to macula densa
Macula densa will increase afferent arteriolar constriction and that will feedback to decrease GBF |
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Glomerular Filtration Rate Depends on Glomerular Capillary Permeability AND Surface Area
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Glomerular capillary filtration coefficient = hydraulic conductivity X surface are of glomerular capillaries
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Explain how glomerular surface area affects GFR
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• By modulating the surface area of glomerular capillaries, the number of functioning nephrons is on determinant of the GFR
o In chronic renal disease as the number of functional nephrons decrease, GFR DECREASES • How much liquid moves out depends on all the pressures but also has to do with how leaky they are and the surface area • If don’t have as much surface area then won’t have as much filtration even if the starling forces stay the same • The surface area is what can change in some diseases- as nephrons die off, every time you lose a nephron you lose the surface area of the capillary |
