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Renal > Acid base > Flashcards

Acid base Flashcards

1
Q

What is .3pH range of the ECF?

A

7.35-7.45

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2
Q

What are the three systems that control the pH of the body?

How do the systems control the pH and how fast do they work?

A

Buffer- immediate uses acids and bases to prevent pH changes

Resp- removes CO(Volatile acid) regulates plasma HCO3

Kidneys- more powerful takes longer. excretes acids and bases as necessary

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3
Q

What is the buffering system for extracellular fluids?

What catalyzes this reaction?

A

Carbonic Acid - Bicarbonate
Buffer System
H2O + CO2 ->//

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4
Q

What is the relationship of pH and HCO3 and CO2?

A

pH= HCO3/.03pCO2

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5
Q

What is the normal ratio of HCO3/.03PCO2 fa pH of 7.4?

What is the log(20/1)?

A

[HCO3-] / .03PCO2 = 20:1*

its the ratio not the amount

Log of 20/1= 1.3
adding that to 6.1 = 7.4

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6
Q

What regulates HCO3?

What is the normal value of HCO3?

A

HCO3 regulated by kidneys

HCO3- =24mM

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7
Q

What regulates PCO2?

What is the normal value of PCO2?

A

PCO2 regulated by the lungs

arterial PCO2= 40 mmHg

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8
Q

What must be maintained in order to maintained the body pH at 7.4?

A

intake must equal excretion

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9
Q

What are sources of acid and alkali for intake and metabolic? What is the net production acids or alkali?

A

Intake:
Acids: meats, grains, dairy
Alkali: fruits, vegetables

Metabolic production:
Acids: CO2 (volatile)
“fixed” acids*
Alkali: Metabolism of basic a.a., organic anions

A “typical” American diet results
in net endogenous acid production

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10
Q

What are the the ways we excrete acids and alkali out of the body?

A

Excretion:

Acids: “blow off” CO2
Loss of H+ in urine, vomit
Use of H+ in metabolism

Alkali:
Loss of HCO3- in urine,
diarrhea

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11
Q

What are most acid base disturbances due to?

A

Most the acid/base disturbances that you’ll deal with in renal are due to changes in “fixed” (= non-volatile) acids.

fixed acids include: lactic acid, ketoacids, sulphuric acid (from sulfur containing amino acids), others

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12
Q

What is the daily acid load?

A

Voltatile acids= CO2 15,000 mmol per day (blown off by the kidneys)

Fixed acids=70 mmol/day for a “standard” 70 kg* man)

40 mmol/day from net metabolic non-volatile acid production Sulfuric, phosphoric and lactic acids, other organic acids

30 mmol/day dietary acid absorption and net GI alkali secretion

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13
Q

How is new acid created in the body? how is it eliminated?

A

H+ is buffered by HCO3 it makes CO2 that is blown off by the lungs so HCO3 is lost from the body.

new HCO3 has to be generated. That creates a H+ as well
That H+ is excreted bound to another buffer

Fixed acids create a H+ bound Titrated by NH3-> NH4 and is also excreted
This is the 70mm/day excreted

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14
Q

How much H+ must the kidneys excrete?

A

Equal the amount to reabsorb the HCO3 filtered in GFR
Plus
enough to reabsorb the HCO3 newly generated

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15
Q

How is H+ buffered after it is secreted into the nephron (ie what are the buffering systems)?

A

1) filtered HCO3-
The majority of the H+ secreted into the lumen reacts with HCO3-

2) filtered fixed urinary buffers, including phosphate, urate, creatinine (all are filtered in their anionic base form).
3) ammonia (NH3) to NH4 that was produced and secreted into the tubular fluid by the proximal tubule epithelium.

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16
Q

What are the three steps of

H+ Secretion and HCO3- Reabsorption/Production?

A

Intracellular production of H+ and HCO3- using CA (inside renal epithelial cells)

Transport of H+ from the cell into the lumen

Transport of HCO3- from the cell into the ECF

17
Q

What are the steps of H+ secretion into the Lumen?

A

H+ are secreted into the lumen by NHE

The secreted proton (H+) reacts with filtered bicarbonate (HCO3-) to form carbonic acid (H2CO3), which then dissociates into CO2 + H2O

CO2 diffuses back into cells of the nephron

CO2 reacts with water to form H2CO3-> HCO3 and H+

HCO3 is transported into ECF

H+ is secreted back across the apical membrane continuing the cycle

18
Q

How does the body handle nonvolatile acids?

A

Body deals with non-volatile acid load in three steps:

Immediate neutralization of the acid load as it is produced, using ECF chemical buffers
Both HCO3- and non-bicarbonate (B-) buffers
HCO3- primary ECF buffer CO2 production

For acids buffered by HCO3-, excrete the resulting CO2 into the lungs
this HCO3- is lost from the body and needs to be replaced

Regeneration of buffer by the kidneys
Create “new” HCO3- to replace that lost as CO2
Excrete H+ to recycle non-HCO3- buffer (HB H+ + B-)

19
Q

When the kidneys secrete H+ what must happen?

A

HCO3 must be created in the same amount

20
Q

What must Net urinary acid excretion equal to, in order to maintain acid base homestasis?

A

Net urinary acid excretion = H+ excreted as TA (UTA x V) + Urinary ammonia nitrogen (UNH4+ x V) + Excretion of filtered HCO3-
(UHCO3- x V)

21
Q

What are the non HCO3 titratable buffers?

What does a secreted H+ form?

A

phosphate (most important)
urate
creatinine.

Production of the secreted
H+ created “new” HCO3-
in the cytoplasm. to replace Lost by respiratory CO2

22
Q

Why is phosphate the most important non HCO3 buffer?

A

because it is more basic than the others at pKa of 6.8

and it is the most abundant

23
Q

Where is NH3+created?

Why is it important?

A

created by the PCT and secreted it is titrated with H+ to form NH4+ and excreted.

Production of the secreted
H+ created “new” HCO3-
in the cytoplasm

24
Q

How much of the HCO3 is reabsorbed at the PCT?

How much new HCO3 is produced from TA?

A

80% filtered HCO3-
reabsorbed

55 mmol (~80%)
new HCO3-
produced
15 mmol H+ buffered
by TA
40 mmol H+ buffered
by NH3
25
Q

What is H+ secretion titrated by?

A

Proximal:
80% filtered HCO3-
78% NH3 (mostly) and TA

TALH:
10% filtered HCO3-
(NH3 reabsorbed)

Distal - OMCD:
10% filtered HCO3-
7% as TA

IMCD:
15% as TA

26
Q

What are the transporters on the apical and basolateral membranes that secretes H+?

A

Apical membrane transporters:
NHE3 (Na+/H+ exchange)

Basolateral membrane transporters:
NBCe1* (Na+, HCO3- cotransport)

27
Q

Where and from what is NH3+ synthesized and secreted?

A

It is synthesized in PCT and secreted into Lumen and form NH4+.de of cytoplasm of cells

Glutamine and glucogenesis is used to form NH4+ inside cytoplasm of cells

Glutamine transporters are found on the basolateral and apical membrtanes. Glutamine is converted to NH4+ inside cell.
NH3 and H+ dissaciates and are transported to nephron lumen to reform NH4+

28
Q

What is H+ sectretion titrated by in TALH?

A

TALH:
10% filtered HCO3-
(NH4+ reabsorbed)

The TALH continues to secrete H+ (via NHE)
NH4+ reabsorption is a physical, non-regulated process that the kidneys just have to deal with.

29
Q

What transporter secretes H+ on the apical membrane of the TALH? which transporter reabsorbs HCO3 on the basolateral mebrane of the TALH?

A

Apical membrane transporters:
NHE3 (Na+/H+ exchange

Basolateral membrane transporters:
AE2 (HCO3-/Cl-)

30
Q

How is ammonium handled in the TALH?

A

The NH4+ reabsorbed across the apical membrane of the TALH is a physical process and is not under the control of the body.

In the TALH, NH4+ may substitute for K+ on the NKCC cotransporter and through an apical K+ channel, thus it reabsorbed in this nephron segment. **

NH4 dissocites into NH3 + H+.
H+ is secreted
NH3 goes into the MCD and is secreted into TF and combines with NH3 to reform NH4

31
Q

What is secreted H+ in the OMCD titrated by?

A

Distal - OMCD:
10% filtered HCO3-
7% as TA

32
Q

What is secreted H+ titrated by in the IMCD?

A

IMCD:

15% as TA

33
Q

What does alpha and beta intercalated cells secrete? what is the importance?

A

alpha intercalated cells secrete acid;
beta intercalated cells secrete base/bicarbonate

Alpha intercalated cells secrete acid, thus are involved in reabsorption/production of HCO3-

Beta intercalated cells are fewer in number and are important if there is a net base load (ie, alkalosis); they secrete (excess) base to help bring the pH down if it gets too high

34
Q

Where is NH4+/NH3 secreted?

A

Secretion of ammonia/ammonium in the MCD is due to physical chemical gradients and is not regulated. This is because NH4+ can compete with K+ in the Na/K ATPase and be transported into the cell.

Renal (15 decks)

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