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20 Cards in this Set
- Front
- Back
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The tubular cells are connected by tight junctions at their luminal edges, but there is space between the cells along the rest of their lateral borders. TRUE/FALSE
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TRUE. Infact, much of the Na+ is actively transported into these extensions of the interstitial space, the lateral intercellular spaces.
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List several ways that sodium is filtered in the proximal tubule?
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Normally about 60% of the filtered Na+ is reabsorbed in the proximal tubule, primarily by the Na+-H+ exchange.
Another 30% is absorbed via the Na+-2Cl-K+ cotransporter in the thick ascending limb. App. 7% is absorbed by Na+-Cl- cotransport in the distal convoluted tubule. |
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How is glucose removed from the urine?
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by secondary active transport. It is filtered at a rate of app. 100mg/min(80mg/dL of plasma x 125mL/min). essentially all of the glucose is removed.
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The amount of glucose reabsorbed is proportionate to what?
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It is proportionate to the amount filtered and hence to the plasma glucose level(Pg) times the GFR up to the transport maximum(Tmg).
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What is the Tmg in men and women?
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In men it is about 375mg/min, and in women about 300mg/min.
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What is the renal threshold for glucose?
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It is the plasma level at which the glucose first appears in the urine in more than the normal minute amounts.
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However, the actual renal threshold is about 200mg/dL. TRUE/FALSE
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TRUE. This appears to be the case of arterial plasma, which corresponds to a venous level of about 180mg/dL. It has been shown that the actual renal threshold is less than the predicted. In an ideal situation, if the Tmg in all of the tubules was identical and if all the glucose were removed from each tubule when the amount filtered is below the Tmg. This is not really the case, and in humans, the actual curve is rounded and deviates considerably from the ideal curve. This is called "splay".
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Regarding transport mechanism, glucose and Na+ bind to the common carrier SGLT 2 in the luminal membrane, and glucose is carried into the cell as Na+ moves down its electrical and chemical gradient. TRUE/FALSE
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TRUE.
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What is the difference between the d- isomer and L- isomer of glucose?
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The common carrier specifically binds the d- isomer of glucose, and the rate of transport of d- glucose is many times greater than that of l- glucose.
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What is phlorhizin?
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Glucose transport in the kidney is inhibited, as in the intestine by the plant glucoside, phlorhizin, which competes with d- glucose for binding to the carrier.
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Regarding secondary active transport, Na+ is pumped out of the cells by Na+-K+ ATPase and the amino acids leave by passive or facilitated diffusion to the interstitial fluid. TRUE/FALSE
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TRUE.
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What is Dent's disease?
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Some chloride is reabsorbed with na+ and K+ in the thick ascending limb. In addition, two members of the family of Cl channels have been identified in the kidney. Mutations in the gene for one of the renal channels is associated with Ca+ containing kidney stones and hypercalciuria(dent's disease).
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What is Dent's disease?
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Some chloride is reabsorbed with na+ and K+ in the thick ascending limb. In addition, two members of the family of Cl channels have been identified in the kidney. Mutations in the gene for one of the renal channels is associated with Ca+ containing kidney stones and hypercalciuria(dent's disease).
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List some other substances secreted by the tubules?
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Derivatives of hippuric acid in addition to PAH.
Phenol red and other sulfonphthalein dyes Penicillin iodinated dyes. All of these are secreted into tubular fluid. |
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Substances that are normally produced in the body and secreted by the tubules include...
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Ethereal sulfates
Steroids and other glucuronides 5-hydroxyindoloacetic acid(principle metabolite od serotonin). |
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What is tubuloglomerular feedback?
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As the rate of flow through the ascending limb of the loop of henle and first part of the distal tubule increases, glomerular filtration in the same nephron decreases and conversely a decrease in flow increases the GFR.
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What is the sensor for tubuloglomerular feedback?
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The sensor for this is the macula densa. the amount of fluid entering the distal tubule at the end of the thick ascending limb depends on the amount of Na+ and Cl- in it.
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How does Na+ and Cl- enter the macula densa?
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They enter via the Na+-K+-2Cl cotransporter in their apical membanes.
The increased Na+ causes increased ATP hydrolysis causes more adenosine to be formed. Adenosine is secreted from the basal membrane of the cells and acts via Adenosine A1 receptors on the macula densa cells to increase their release of Ca+ to the vascular smooth muscle in the afferent arterioles. This will cause afferent vasoconstriction and a decrease in GFR. |
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What is glomerulotubular balance?
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An increase in GFR causes an increase in the reabsorption of solutes, and of water in the proximal tubule, so that in general the percentage of the solue reabsorbed is held constant.
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Normally, a 180L of fluid is filtered through the glomeruli each day, while the average daily urine volume is about 1 L. TRUE/FALSE
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TRUE.
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