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Block 2; Week 8 > Keef 1 > Flashcards

Keef 1 Flashcards

1
Q

What are the 3 lines of defense to buffer the blood?

A

1st line of defense: chemical buffering
2nd line of defense: CO2 by the lungs
3rd line of defense: regulation of acid & bicarb by the kidneys

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2
Q

What do the kidneys do to help buffer?

A

Conserve bicarbonate when you need it
Make new bicarbonate
Excrete excess bicarbonate (during alkalosis)
Excrete fixed acid

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3
Q

Where is bicarb absorbed in the kidney & @ what percentages when the body is in acidosis?

A

80% reabsorption in the PCT
15% in the ascending limb of the loop of Henle
5% in the late DCT & cortical & beginning medullary collecting duct

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4
Q

How is bicarb reabsorbed in the PCT?

A

H+ is secreted into the lumen thru the sodium gradient (Na+ reabsorption). It combines w/ bicarb in the lumen & forms carbonic acid. Carbonic anhydrase makes it into CO2 & H20. The CO2 diffuses into the epithelial cell. Carbonic anhydrase in there turns it back into carbonic acid. This dissociates into H+ & bicarb. The bicarb is reabsorbed thru exchange of Cl- into the cell. The H+ is secreted back into the PCT lumen.

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5
Q

What are the 2 types of cells in the DCT? Which is more prevalent?

A

principal cells & intercalated cells.

principal cells are more prevalent…

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6
Q

Which of the DCT cells is responsible for acid secretion?

A

alpha intercalated cells

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7
Q

What are the principal cells of the DCT responsible for?

A

for aldosterone-sensitive sodium reabsorption

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8
Q

T/F Thru the reabsorption of bicarb there is greater excretion of H+.

A

False. The H+ is mainly cycled thru as a way of reabsorbing bicarb…but secreted H+ doesn’t equate to excreted H+.

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9
Q

In the PCT how low can the pH become?

A

6.0

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10
Q

Which membrane in the nephron is particularly low to H+ ions?

A

The DCT membrane. If the H+ gets in the lumen–>it stays there.

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11
Q

T/F there is no carbonic anhydrase on the membrane of the DCT or inside the cells.

A

False. They are in the cells, but not on the membranes.

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12
Q

How low can the luminal pH get in the distal nephron?

A

4.4

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13
Q

When there are already so many hydrogen ions in the lumen of the distal nephron…how do you shove more in there?

A

you do it thru the hydrogen potassium pump & the hydrogen ion pump. These both put hydrogen ions in the lumen thru ATP consumption.

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14
Q

What is a pretty normal pH for your urine?

A

~pH=6

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15
Q

In an alkalotic patient…what happens to the H+ in the urine…& the bicarb? Where is the biggest difference in bicarb reabsorption?

A

H+ in the urine decreases
pH of the urine increases to like 7.5 maybe
79% of the bicarb is reabsorbed in the PCT & then you get maybe 1-2% excretion of bicarb (higher fractional excretion).

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16
Q

What are some important uses of carbonic anhydrase inhibitors, such as Diamox?

A

Antiglaucoma, diuretics, antiepileptics, mountain sickness, glaucoma, gastric & duodenal ulcers, neurological disorders, osteoporosis

17
Q

What is the story of carbonic anhydrase inhibitors with mountain sickness?

A 
Go to a high elevation
Low pO2
Higher ventilation rate
Lower PaCO2
Respiratory Alkalosis
Take Diamox
Carbonic Anhydrase blocked
Bicarb excretion
pH returned to normal
18
Q

What is the drawback of taking Diamox for mountain sickness?

A

the water will follow the bicarb that is excreted & it will also act as a diuretic…
Osmotic Diuresis
Dehydration may result. Need to take fluids.

19
Q

What are the 2 methods for eliminating fixed acids?

A
  1. titratable acids

2. formation of ammonium

20
Q

How does the whole titratable acid thing work?

A

HPO4- becomes H2PO4 when the lumen becomes acidic enough–>this allows it to be excreted.

21
Q

How does the whole ammonium thing work?

A

Glutamine is broken down in the epithelial cells of the PCT only into ammonium & bicarb. The bicarb is reabsorbed & the ammonium is secreted into the lumen (exchanged with Na+).

  • *then the ammonium is reabsorbed.
  • *the ammonia is again secreted in the Collecting Duct & it will form ammonium to be excreted.
  • *its actions are determined partially by luminal pH
22
Q

What does aldosterone do to the cells of the collecting duct?

A

Principal Cells: causes sodium reabsorption & potassium secretion
Intercalated Cells: causes H+ secretion & in proportion to this bicarb reabsorption

23
Q

How can you determine the bicarb reabsorption rate?

A

Bicarb Reabsorption Rate=Bicarb Filtered Load - Bicarb Excretion Rate
**b/c the bicarb excretion is negligible, reabsorption rate = filtered load.

24
Q

What are the 2 things that the kidneys simultaneously do? How?

A

Make new bicarbonate
Excrete Acid
**the breakdown of H2CO3

25
Q

What is the equation for H+ excretion?

A

H+ excretion = Titratable Acid + Ammonium

26
Q

What is the equation for net acid excretion?

A

Net Acid Excretion = titratable acid + ammonium + bicarb in the urine

27
Q

What is the net acid excretion equal to?

A

the amount of new bicarb generated…

28
Q

In a normal person, what are the normal amounts of titratable acid, ammonium excreted, & bicarb excreted?

A

TA: 20mmol
Ammonium: 40 mmol
bicarb: 1 mmol
**normal urine pH is 6.0

29
Q

Which is greater in amount…new bicarb produced or the bicarb reabsorbed?

A

The reabsorbed bicarb is far greater than the produced bicarb.

30
Q

What does the amount of bicarb reabsorbed equate to?

A

the amount of H+ secreted

31
Q

Which is greater: the amount of H+ secreted or excreted?

A

Secreted!!!

32
Q

Which excretion is always greater: the amount of ammonium or titratable acid?

A

Ammonium!!

33
Q

What will potassium sparing diuretics do to body pH & K+ levels? What states will this produce?

A

Volume Pressure decrease
Less K+ excretion–>hyperkalemia
Less H+ excretion–>acidosis

34
Q

What will potassium losing diuretics do to body pH & K+ levels? What states will this produce?

A

Volume pressure decrease
More K+ excretion–>hypokalemia
More H+ excretion–>alkalosis

35
Q

Explain how potassium losing diuretics have their effect.

A

Take thiazide.
More NaCl flow in the collecting duct.
More sodium reabsorption promoting more potassium secretion @ principal cells.
More potassium @ intercalated cells promotes the hydrogen potassium pump. More H+ is therefore secreted.
This is ultimately what causes increased K+ & H+ excretion.

36
Q

Explain how potassium sparing diuretics have their effect.

A

Take amiloride.
Sodium reabsorption blocked in the collecting duct. thus, no extra potassium secretion.
thus, in the intercalated cells there is not a promotion of the potassium hydrogen pump & increased H+ secretion.
Overall, there is reduced K+ & H+ excretion.

Block 2; Week 8 (6 decks)

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