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PHGY 210 > Renal III > Flashcards

Renal III Flashcards

1
Q

What is the typical breakdown in inputs and outputs of water to the body?

A

Inputs: liquids, in food, metabolically produced
Output: insensible less (skin and lungs), sweat, feces, urine

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2
Q

Which forms of water loss can be regulated?

A

The urine only, by the kidneys

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3
Q

What is the typical balance of inputs and outputs of sodium to the body?

A

Intake: food
Output: feces, sweat, urine (by far the most)

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4
Q

What is the typical range of water and sodium outputs per day? What determines these outputs?

A

Water intake = water output
Sodium intake = sodium output

Water output can vary from 0.4 L/day to 25 L/day. Sodium chloride output can vary from 0.05 g/day to 25 g/day

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5
Q

What is the balance of reabsorption of secretion of sodium and water?

A

Both are almost completely reabsorbed, and there is no secretion whatsoever for either.

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6
Q

Where does the majority of sodium and water reabsorption take place?

A

In the proximal tubule

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7
Q

Where does major hormonal control of sodium and water take place?

A

In the distal convoluted tubule and in the collecting ducts.

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8
Q

Is sodium reabsorption a passive or active process? Where can it take place?

A

Sodium reabsorption is an active process that occurs in all tubular segments except the descending thin limb of Henle’s loop.

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9
Q

Is water reabsorption a passive or active process? Where can it take place?

A

Water reabsorption is passive (occurs by diffusion) and is dependent upon sodium reabsorption.

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10
Q

Describe how sodium reabsorption takes place in the cortical collecting duct.

A
  1. Na+/K+-ATPase on basolateral membrane pumps K+ into the tubular cell and Na+ into the interstitium.
  2. Na+ flows in passively through channels on the apical membrane.
  3. K+ flows out passively through channels on the apical membrane.
    At the end, the tubule has lost 1 sodium and gained 1 potassium. The blood has gained 1 sodium and lost 1 potassium.
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11
Q

Compared to how it works in the cortical collecting duct, how does the process of sodium reabsorption differ in other parts of the tubule?

A

It is nearly the same. The only difference is that different transporters mediate the transportation of Na+ into the cell depending on where along the tubule they are situated.

In the CCD, diffusion occurs via Na+ channels on the apical membrane.

In the proximal tubule, Na+ enters via an Na+-H+ antiporter or an Na+-glucose cotransporter.

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12
Q

How does sodium intake affect sodium excretion?

A

If intake increases, excretion increases and vice versa.

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13
Q

How do the kidneys sense total body sodium?

A

Since sodium is the major extracellular solute, changes in total body sodium change changes in extracellular fluid. So, total body sodium is sensed via changes in extracellular volume by baroreceptors in the cardiovascular system.

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14
Q

True or false? The plasma concentration of sodium can be used as a marker for total body sodium.

A

FALSE

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15
Q

What is the formula for renal regulation of sodium?

A

Sodium excreted = sodium filtered - sodium reabsorbed (sodium is NOT secreted in the tubules)

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16
Q

Sodium excretion is regulated by what two processes? Which is more important?

A
  1. GFR (minor role)
  2. Sodium reabsorption (most important)
17
Q

Describe the mechanism by which renal regulation of sodium by GFR occurs.

A
  • Na+ and H2O loss
  • Decreased plasma volume
  • Decreased venous pressure
    • Causes increased activity of renal sympathetic nerves
  • Decreased venous pressure
  • Decreased venous pressure
    • Causes increased activity of renal sympathetic nerves
  • Decreased ventricular end-diastolic volume
  • Decreased stroke volume
  • Decreased cardiac output
  • Decreased arterial blood pressure
    • Causes increased activity of renal sympathetic nerves

The increased activity of renal sympathetic nerves causes:
- Increased constriction of afferent arteriole
- Decrease in net GF pressure
- Decreased GFR
- Decreased Na+ and H2O excreted

18
Q

The key hormone responsible for renal regulation of sodium is […], secreted by the […]

A

Aldosterone, adrenal cortex

19
Q

What is the function of aldosterone in the renal regulation of sodium? Where does it act?

A

Aldosterone stimulates sodium reabsorption in the distal convoluted tubule and cortical collecting duct.

20
Q

ow does the amount of sodium excreted by the renal system change between having no aldesterone and having high aldosterone?

A

No aldosterone: 2% of filtered load is excreted
High aldosterone: 0% of filtered load is excreted

21
Q

What are the relative contributions of the proximal tubule, the descending limb of Henle’s loop, the ascending limb of Henle’s loop, the distal tubule, the cortical collecting duct, and the IMCD to sodium reabsorption?

A

PT: 67%
DL: None
AL: 25%
DT: 4%
CCD: 3%
IMCD: 1%

22
Q

How does aldosterone affect the process of sodium reabsorption in the cortical collecting duct cells? What effect will this have on the blood?

A

It can stimulate all the transport proteins (Na+/K+ ATPase on basolateral membrane, Na+ and K+ channels on luminal membrane). All are upregulated by aldosterone. Because of that, Na+ gets vigorously reabsorbed.

K+ secretion will also increase if you have a lot of aldosterone, which will cause low concentrations of K+ (and also H+) in the blood.

23
Q

Aldosterone secretion is mainly regulated by the […]

A

renin angiotensin system

24
Q

What is the function of juxtaglomerular cells? Where are they located?

A

They are part of the juxtaglomerular apparatus and are wrapped around the afferent arteriole. They are responsible for renin secretion when stimulated.

25
Q

What are macula densa cells and what is their function?

A

he macula densa cells are taller tubular cells that face the glomerulus. They can signal to the renin secretion cells, which stimulates the production of aldosterone.

26
Q

Describe the process by which renal regulation of sodium by reabsorption occurs.

A
  • Decreased plasma volume
    • Increased activity of renal sympathetic nerve
    • Decreased arterial pressure
    • Decreased GFR, which causes decreased flow to macula densa and decreased NaCl delivery to macula densa
  • All cause increase in renin secretion by renal juxtaglomerular cells
  • Increased plasma renin
  • Increased angiotensin 2
  • Increased aldosterone secretion by adrenal cortex
  • Increased sodium and H2O reabsorption by CCD
  • Decreased sodium and H2O excretion
    Note: The direct action of aldosterone is only on the sodium in the CCD and the DCT (less). The reabsorption of water is secondary.
27
Q

What is ANP? Where is it secreted?

A
  • ANP is a peptide hormone secreted by cells in the cardiac atria
  • Acts on the tubules to inhibit sodium reabsorption (opposite actions of aldosterone) and increases GFR
28
Q

What triggers the release of ANP?

A

Increased total body sodium (thus increased extracellular fluid/plasma volume)

29
Q

What is pressure natriuresis?

A

Pressure natriuresis is pathologic - when the BP is extremely high, it will really increase Na+ secretion in the urine (through ANP). The mechanism is poorly understood. Happens in the range of 230+ mm Hg

30
Q

Describe the process by which ANP acts in response to increased plasma volume.

A
  • Increased plasma volume
  • Cardiac atria sense distension and increase ANP secretion
  • Increased plasma ANP
    • Decreased plasma aldosterone
  • Both cause afferent arteriole dilation and efferent arteriole constriction in kidney, increasing GFR
  • Both also cause decreased Na+ reabsorption in tubules
  • Increased sodium excretion
31
Q

What does the plasma concentration of sodium indicate?

A

It indicates the relative relationship between fluid and sodium in the body (NOT total body sodium).

PHGY 210 (36 decks)

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