Term
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Definition
Is filtered, secreted, and reabsorbed.
End product of amino acid metabolism.
Mainly paracellular, water dependent.
50% absorbed in proximal tubule.
60% secreted in loop of Henle (mainly ascending portion).
70% then reabsorbed in the medullary collecting duct. |
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Term
| Urea handling in the proximal tubule |
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Definition
Mainly paracellular diffusion. Some facilitated by solvent drag.
Urea transport is highly dependent on water reabsorption, which travels from the tubule to the interstitum has sodium reabsorption occurs.
Water leaving the tubule increases urea concentration, which creates a driving force for urea paracellular diffusion. |
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Term
| Urea handling in the thin descending limb |
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Definition
| As the thin descending limb travels downward, the medullary osmotic gradient increases, which provides the driving force for transcellular urea transport to the lumen through UT2 transporters. |
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Term
| Urea handling in the medullary collecting duct |
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Definition
| Urea travels through UT1 transporters in the apical side then through UT4 transporters in the basolateral side. |
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Term
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Definition
| Urea excretion is proportional to flow rate. When flow increases, urea not reabsorbed as efficiently. |
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Term
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Definition
[Glu] regulated mainly by insulin, not urinary excretion
Freely filtered in glomerulus
Completely reabsorbed
98% reabsorbed in the proximal tubule
In early proximal tubule: SGLT 2 cotransports 1 Na with Glucose. Can't extablish as high of a concentration gradient as SGLT 1. Basolateral transporter is GLUT 2.
In late proximal tubule, SGLT 1 cotransports 2 Na with one glucose. SGLT2 can establish as high concentration gradient, acts as a scavenger of glucose. Basolaterally transported by GLUT 1. |
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Term
| Glucose as marker for GFR |
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Definition
| Filtered load of glucose can overwhelm kidney reabsorptive capabilities (when over 300 mg.min). When this happens glucose is excreted and parallels the GFR and glucose clearance begins to approach inulin clearance. |
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Term
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Definition
Freely filtered.
99% reabsorbed in proximal tubule.
Have families of transporters that transport similar classes of amino acids (cystine transport, neutral amino acid transport). |
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Term
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Definition
| Defect in cystine transport, leads to amino acid excretion in urine. High concentrations of amino acids in the urine can cause crystallization into kidney stones. |
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Term
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Definition
| Defect in neutral amino acid transporter. |
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Term
| Transport of oligopeptides and proteins |
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Definition
Small peptides are filterable. Endocytosis can be transported through endocytosis or transcytosis.
Can be hydrolyzed into amino acids.
99% reabsorbed in the proximal tubule. |
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Term
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Definition
Not freely filtered, have organic and inorganic phosphate. Intracellular levels higher than extracellular mostly in bone, used for mineralization.
80% reabsorbed in proximal tubule, 10% reabsorption in distal tubule.
Reabsorbed into proximal tubule using Na, P cotransporters, electrogenic, creates - charge into lumen. |
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Term
| Phosphate transport hormones |
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Definition
1. PTH reduces PO4 transport
2. Vitamin D stimulates phosphate reabsorption, deficiency results in Ricketts.
3. ANP, Glucocorticoids, and acidosis increase excretion. |
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Term
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Definition
Mostly in intracellular fluid. Pattern of handling mimics Na.
2/3 reabsorbed in proximal tubule, 25% in thick ascending limb, 8% in DCT. |
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Term
| Calcium transport in proximal tubule |
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Definition
Reabsorption mainly done through paracellular diffusion, as water is reabsorbed, Ca concentration increases and provides the driving force for Ca diffusion. Also have transcellular Ca transporters.
Basolaterally, have Na, Ca and Ca, H antiporters. |
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Term
| Calcium transport in proximal tubule |
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Definition
Reabsorption mainly done through paracellular diffusion, as water is reabsorbed, Ca concentration increases and provides the driving force for Ca diffusion. Also have transcellular Ca transporters.
Basolaterally, have Na, Ca and Ca, H antiporters. |
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Term
| Calcium transport in distal tubule |
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Definition
Have transcellular Ca transporters.
Basolaterally, have Na, Ca and Ca, H antiporters. |
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Term
| Calcium transport in the thick ascending limb |
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Definition
Na, K, Cl transporter creates enough K concentration to generate K backleak through K channels. Creates a positive charge in lumen that fluctuates based on the rate of Na reabsorption.
Positive charge of the lumen creates impetus for paracellular Ca diffusion.
Also have transcellular transport through Ca channels.
Basolateral:
Have Ca, Na, and Ca, H antiporters. |
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Term
| Calcium transport regulation |
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Definition
Follows trends in Na transport.
PTH increases Ca reabsorption
Vitamin D increases reabsorption
Loop diuretics decrease Ca reabsorption. |
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