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Physiology Block 4- Renal Physiology > Renal Transport of Ions and Organic Solvents > Flashcards

Renal Transport of Ions and Organic Solvents Flashcards

1
Q

How does chronic renal failure affect the BUN, plasma phosphate, and plasma calcium?

A

Increased BUN, phosphate and decreased calcium

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2
Q

How does chronic renal failure cause decreased plasma calcium?

A

Decreased formation of Vitamin D, decreasing the absorption of calcium from the gut

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3
Q

In order for homeostasis to be maintained, what percentage of daily urea produced must be excreted daily?

A

Equal amounts- 100%

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4
Q

Where is urea produced?

A

Liver

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5
Q

What percentage of the total urine osmolality is due to urea?

A

40%

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6
Q

What are BUN levels? What is the normal range? At what value should a patient go on dialysis?

A

Blood Urea Nitrogen- mg elemental nitrogen/ dL plasma; 7-18 mg/dL; >100 mg/dL

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7
Q

What is the relationship between BUN and GFR?

A

Inversely proportional

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8
Q

What are elevated BUN levels possibly indicative of?

A

Reduced kidney function

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9
Q

What is medullary recycling of urea? What is the physiologic importance of this occurring?

A

The bidirectional transport mechanism by which urea is reabsorbed by the PT and IMCD, and it is secreted by the loops of Henle; it establishesand prevents dissipation of high [urea] in the intermedulla so kidney conserves H2O

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10
Q

With normal urine flow, what percentage of the original filtered urea load is excreted?

A

About 40%

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11
Q

What is the number one waste product that must be excreted by the kidneys?

A

Urea

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12
Q

What drives the paracellular diffusion of urea?

A

Water reabsorption increases the luminal urea concentration

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13
Q

What are the mechanisms by which urea is reabsorbed?

A

Paracellular diffusion and transcellular via urea transporters

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14
Q

What causes glucose in the urine?

A

Uncontrolled diabetes or glucosuria (glucose transporter mutation); When the plasma glucose overwhelms the nephrons ability to reabsorb it

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15
Q

Where it the most glucose reabsorbed? What percentage of filtered glucose is reabsorbed here? What are the other sites of reabsorption?

A

PCT- 98%; Proximal straight tubule

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16
Q

How is glucose reabsorbed by the proximal convoluted tubule?

A

Through SGLT2 transporter in apical membrane and then GLUT2 in BL membrane

17
Q

What are the relative capacities and affinities of the SGLT1 and SGLT2 receptors?

A

SGLT1- low capacity, high affinity; 2- high capacity, low affinity

18
Q

What is the ratio of sodium to glucose transported through SGLT1? SGLT2?

A

SGLT1- 2:1; SGLT2- 1:1

19
Q

How can the filtered load of glucose be calculated?

A

Plasma glucose x GFR

20
Q

What is Tm(g)? What is its typical value? At what plasma glucose are carriers saturated?

A

The maximal reabsorptive rate of glucose; 400 mg/dL; ~200 mg/dL

21
Q

Why is there a splay seen in the glucose titration curve?

A

Nephrons have different filtered loads of glucose and expression of SGLTs

22
Q

Which organic solutes are reabsorbed almost completely by the proximal tubule?

A

Amino acids, peptides, mono-,di- and tricarboxylates, and urate

23
Q

What is the primary way phosphate homeostasis is maintained?

A

Renal excretion

24
Q

What structure reabsorbs most of the filtered phosphate? How much?

A

PT reabsorbs 80%

25
Q

Approximately how much of filtered phosphate is excreted under normal conditions?

A

10%

26
Q

What is the mechanism by which phosphate is reabsorbed?

A

Through Na+/Pi cotransporter

27
Q

How does PTH affect renal phosphate handling?

A

INcreased serum phosphate stimulates the release of PTH, which inhibits renal phosphate reabsorption

28
Q

Typically what is the level of PTH secretion in patients with chronic renal failure? Why?

A

Increased– A decreased GFR decreases the excreted phosphate and increases plasma phosphate; decreased formation of Vitamin D decreased GI absorption of Ca2+, decreasing the plasma concentration

29
Q

What forms of calcium can be filtered? Which forms cannot be? What is the relative amount of both?

A

Calcium bound to protein (40%) cannot be; Calcium that is complexed with sulfate, citrate, or phosphate (15%) or ionized (45%) can be

30
Q

What percent of filtered Ca2+ is reabsorbed? Where is it mostly done?

A

99%; 70% in the proximal tubule

31
Q

Where are calcium-sensing receptors located? What is their function?

A

In the TAL; increased ECF calcium decreases reabsorption

32
Q

What is the mechanism by which PTH stimulates calcium reabsorption?

A

TRPV5 Ca++ channels in the DCT

33
Q

How do the kidneys contribute to the formation of Vitamin D?

A

Kidneys synthesize 1-alpha-hydroxylase

34
Q

How can chronic renal failure cause osteodystrophy?

A

Increased serum phosphate increases PTH secretion which increases bone resorption

Physiology Block 4- Renal Physiology (9 decks)

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