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Physiology Block 4- Renal Physiology > Transport of Sodium and Chloride by the Nephron > Flashcards

Transport of Sodium and Chloride by the Nephron Flashcards

1
Q

What is renal failure?

A

Kidney with function less than 10% of normal

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2
Q

How does renal failure affect blood pressure? Why?

A

BP is elevated because the kidney is failing to excrete Na+ and H2O in the urine, leading to a higher volume of fluid retained in the body

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3
Q

What is natriuresis? What is the opposite?

A

Higher than normal sodium excretion by kidneys; Antinatriuresis

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4
Q

What is the major extracellular solute?

A

Na+

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5
Q

Where does Na+ reabsorption take place within the nephron? What enzyme is required for reabsorption? Is it an active or passive process?

A

Active process takes place in all parts except the descending loop and medullary collecting ducts; requires Na+/K+-ATPase

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6
Q

By what process does water reabsorption occur? Through what protein? Where in the nephron? On what process is water reabsorption dependent?

A

By diffusion through aquaporins, which are expressed variably throughout the nephron, but are highly expressed in the proximal tubule and absent in the CD (except unless ADH is present); Dependent on Na+ reabsorption

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7
Q

How much of daily Na+ intake must be excreted to maintain homeostasis?

A

All of it

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8
Q

Where in the nephron is sodium secreted?

A

It isn’t

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9
Q

How can the amount of sodium filtered be calculated?

A

Plasma sodium concentration x GFR

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10
Q

What parameters are manipulated to regulate excretion of sodium from the body?

A

GFR and tubule transport

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11
Q

What is the primary active sodium transporter? What are some secondary active sodium transporters?

A

Na+/K+-ATPase; Na+/amino acid cotransporter, Na+/H+ exchanger, Na+/Ca++ exchanger, and Na+/Cl- exchanger

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12
Q

What renal ion channel allows for Na+ transport through the apical membrane?

A

Voltage-gated Epithelial Na+ channels

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13
Q

What generates the energy for sodium transport?

A

Na+/K+-ATPase

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14
Q

Is Na+ transport through the apical membrane of tubular epithelial cells active or passive? Across the basolateral membrane?

A

Passive across apical and active across BL

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15
Q

How are the reabsorption of sodium and water coupled?

A

Na+ moves down its conc. gradient out of tubular luman, decreasing tubular fluid osmolarity and increases ISF osmolarity, which creates an osmotic gradient causing the net diffusion of water from the tubular lumen into the ISF

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16
Q

How are Na+ and H2O moved into postglomerlar capillaries?

A

Increased oncotic pressure in the postglomerular capillaries drives bulk flow of H2O and Na+ into the capillary

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17
Q

What is the function of the proximal tubule brush border?

A

Increases surface area over which Na+ can be reabsorbed

18
Q

What is the major site of Na+ reabsorption? What percentage is absorbed here?

A

Proximal tubule- 67%

19
Q

What Na+ Cotransporters are found in the Early Proximal Tubule?

A

SGLT (Na+,glucose cotransporter); Na+-H+ antiporter, and Na+/K+-ATPase

20
Q

What is the action of acetazolamide?

A

A mild diuretic that inhibits Na+ reabsorption by inhibiting the production of H+ by carbonic anhydrase- causing Na+/H+ antiporter to be non-functional

21
Q

What drives the paracellular diffusion of NaCl in the late proximal tubule?

A

High [Cl-] in the lumen

22
Q

Where is the Na+/K+/2Cl- cotransporter located? How does it function?

A

Located in the thick ascending limb- Na+ and Cl- move down their concentration gradient, allowing K+ to be transported against its gradient

23
Q

What drives Na+ paracellular passive transport in the thick ascending loop?

A

There is a more positive charge in the tubular lumen relative to the BL membrane

24
Q

What is the action of loop diuretics?

A

Inhibit NKCC2- powerful diuretic

25
Q

Where is the Na+/Cl- cotransporter expressed?

A

Unique to DCT

26
Q

What is the action of NCC-thiazide diuretics?

A

Block the action of NCC

27
Q

What is the primary mode of Na+ reabsorption from the lumen of the collecting ducts?

A

ENaCs

28
Q

ENaCs are conditionally implanted into the apical membrane of the principal cell in response to what?

A

Aldosterone

29
Q

What is the water permeability of the collecting duct dependent on?

A

Aquaporin 2 expression stimulated by ADH

30
Q

What is the action of amiloride?

A

Diuretic that blocks ENaC

31
Q

Which of the following happen to chloride: filtration, reabsorption, secretion?

A

Only filtration and reabsorption

32
Q

If a solute has a Tubular Fluid/ Plasma ratio that increases over the course of the nephron, what does that mean?

A

It means the solute is not reabsorbed at the same rate as H2O or that it is being secreted

33
Q

Does chloride have a high or low TF/P ratio?

A

High

34
Q

What are the ways that Na+ and Cl- transport is regulated?

A

Glomerulotubular balance, antinatriuretic hormonal control, and natriuretic hormonal control

35
Q

How does glomerulotubular balance regulate Na+ and Cl- transport?

A

Spontaneous changes in GFR will be matched by a change in the filtered load of Na+ (e.g., an increase GFR will be met with an increase filtered load of Na+) such that there is no change in Na+ excretion;

36
Q

How does G-T balance affect reabsorption of Na+ by the proximal tubule?

A

G-T balance ensures that there is a constant fraction of filtered Na+ that is reabsorbed

37
Q

How do physical and luminal forces contribute to G-T balance?

A

Physical- an increased GFR means that more water is filtered, which concentrates plasma proteins and increases the oncotic pressure in the peritubular capillaries, which favors reabsorption
Luminal- Increased GFR means there is an increased filtered load of glucose and amino acids, which increases Na+ and water reabsorption because of cotransporters in the apical membranes

38
Q

What is the net effect/ role of G-T balance?

A

Decreased impact of increased filtered load on delivery to distal nephron

39
Q

What is the overall effect of aldosterone on Na+ transport?

A

Promotes Na+ reabsorption in the late nephron via the apical ENaC

40
Q

What are the individual effects of aldosterone in Na+ transport?

A

Increased trafficking of ENac to apical membrane, Increased serum glucocorticoid-stimiulated kinase (inserts ENaC into membrane), Increased prostasin (increases activity of ENaC); Increases the number and opening probability of channels, increased transcription of Na+/K+-ATPase

41
Q

What are the tubular actions of angiotensin II relevant to Na+ transport?

A

Increases Na+ reabsorption by enhancing Na+-H+ exchanger and the NCC

42
Q

Which patients would benefit from drugs that block Na+ transporters?

A

Patients with hypertension, heart failure, edema, kidney disorders, or cirrhosis of liver

Physiology Block 4- Renal Physiology (9 decks)

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