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Urinary System Physiology SA > Acid and Balance > Flashcards

Acid and Balance Flashcards

1
Q

Why is the pH of the ECF very closely monitored

A

As metabolic reactions are exquisitely sensitive to the pH of the fluid which they occur in

ie high reactivity of H+ ions can cause a change in configuration and functions of proteins - especially in enzymes

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2
Q

What is the normal pH and its range of the ECG

A

ph 7.4

Range 7.3-7.43

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3
Q

What defines the pH

A

Henderson-Hasselbalch equation defines the pH in terms of ratio acid to base

𝑝𝐻=𝑝𝐾+ log [𝐴−]/[𝐻𝐴]

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4
Q

What only contributes to the pH

A

Free H+ ions

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5
Q

What is the sources of H+ ions in the body

A

Respiratory Acid - Via respiration

Metabolic acid via metabolism

Diet

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6
Q

Why is carbonic acid (H2CO3) not a normally a contributor to increased acid

A

H2CO3 depends on the amount of CO2 dissolved in the plasma so an increase H2CO3 production causes an increase in ventilation,

(not an increase in acid production)

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7
Q

What is the purpose of buffers in the body

A

minimise changes in pH when H+ ions are added or removed

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8
Q

What kind of buffers are there in the body

A

Extracellular buffer

Intracellular buffer

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9
Q

What is the extracellular buffers in the body

A

Bicarbonate Buffer system
(most important buffer)

Plasma protein buffer

Dibasic phosphate buffer

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10
Q

What is the bicarbonate buffer the most important buffer

A

As pH is proportional to (HCO3)/PCO2

So the independent regulation of the (HCO3) and PCO2 is the basis of the compensatory mechanism to determine and maintain pH

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11
Q

What is the affect on pH and PCO2 if (HCO3-) decreased

A

The pH and the partial pressure of CO2 also decreases

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12
Q

What is the Normal value and range of PCO2

A

5.3KPa
(Range - 4.8-5.9KPa)

OR

40mmHg
(Range 36- 44mmHg)

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13
Q

What is the normal value and range of (HCO3-)

A

24mmoles

range 22-26mmoles

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14
Q

What is intracellular buffers

A

Primary intracellular buffers are proteins, organic and inorganic phosphates and in the erythrocytes haemoglobin

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15
Q

What is the occurs when ICF buffers buffer H+

A

causes changes in plasma electrolytes,

so to maintain electrochemical neutrality, movement of H+ must be accompanied by a Cl- in red cells or exchanged for a cation, K+

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16
Q

What is the clinical implications, of ICF buffer, in acidosis

A

So in acidosis (increase H+) the movement of K+ out of the cells into the plasma can cause hyperkalemeia

which can cause depolarisation of excitable tissues resulting in ventricular fibrillation and death

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17
Q

Why are buffers so important in the body

A

We receive 50-100moles H+ per day from diet, as present as free H+ in total body water causing a pH of 1.2-2.4

But due to the buffers the pH remains remarkebly constant at 7.4

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18
Q

What affect does metabolism have on respiratory acid

A

Metabolism produces CO2, which produces a respiratory acid loading

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19
Q

Why is the bicarbonate buffer, not an ordinary buffer system

A

If this was an ordinary buffer system then as increases H+ initially drives the reaction to the right, then over time an equilibrium would form

In bicarbonate buffer the reaction is pulled to the righr, greatly increasing the buffering capacity of the bicarbonate

the production of CO2 by the equilibrium shifting to the right stimulates ventilation, the ventilation then causes the elimination of the CO2, preventing the mechanism going backward

this is called acute respiratory regulation

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20
Q

What occurs to the H+ in acute respiratory regulation

A

The H+ is not being eliminated from the body, as the HCO3 has buffered the H+ and the respiratory compensation has greatly increased the buffering capacity so that free H+ ions are prevented from contributing to the pH

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21
Q

How does metabolism affect respiratory acid

A

Metabolism produces CO2 which causes respiratory acid loading

22
Q

What is the ratio of HCO3 to H2CO3 at pH 7.4

A

HCO3 : H2CO3

20:1

Basically you need 20 HCO3 for 1 H2CO3

23
Q

What occurs in respiratory regulation

A

An increase in PCO2, tiggers an increase in ventilation,

Reducing the PCO2

24
Q

What occurs in renal regulation

A

The kidney regulates the (HCO3) in an acid load

25
Q

How does the kidney regulate HCO3

A

By generating new HCO3

Reabsorbing filtred HCO3

26
Q

What does kidney regulation depend upon

A

the active H+ ion secretion from the tubule into the lumen

27
Q

What occurs in the mechanism of reabsorbing filtered HCO3, in kidney regulation

A

Active H+ secretion from tubule cells coupled to passive Na+ reabsorption

The filtered HCO3- reacts with secreted H+ to form H2CO3

H2CO3 is broke down into CO2 and H2O by carbonic anyhydrase on the luminal membrane

CO2 is freely permeable and enters the tubule cell, then

CO2 —> H2CO3 in the presence of carbonic anyhyrase

H2CO3 then dissociates to from H+ and HCO3-

The HCO3- passes into the peritubular capillaries with Na+

28
Q

What occurs to the H+ ion formed in the tubule cell

A

Is the source of secreted H+ ion into the lumen

No H+ ions are excreted

29
Q

Where does the bulk of HCO3 reabsorption occur

A

90% at the proximal tubule

30
Q

Why is HCO3 converted to CO2 in the reabsorbtion of HCO3 mechanisms

A

HCO3- is a large charged molecule by converting it to Co2 its much easier to save this valuable buffer

31
Q

What is the importance of renal regulation allows the reabsorption of HCO3

A

as need to buffer H+ from diet, metabolic acid and respiratory acid, so must be reabsorbed as failure to do so cases H+ adding to the ECF

32
Q

What are the two methods in kidney regulation of generating new HCO3

A

By titratable Acidity

Ammonia excretion

33
Q

What is the purpose of titratable acidity

A

used for acid loads

Measures the amount of NaOH needed to titrate urine pH back to 7.4

34
Q

What is the overall affect and importance of Titratable acid

A

Generates new HCO3- and excretes H+

35
Q

What is the importance of titrating and buffering urine

A

As in human the minimum urine pH = 4.5-5 and maximum is 8

But with a net production of 50-100mmoles H+ per day, if present as free H+ ions in urine of volume 1litre then pH =1 (which would be stingy)

36
Q

What is the mechanism of titratable acid to cause the excretion of H+

A

from the Na + HPO42- (mono basic phosphate) in the lumen, only Na+ is reabsorbed in exchange for secreted H+

The HPO42- combines with H+ and forms H2PO4- (dibasic phosphate)

37
Q

What is the purpose of how the H+ is excreted in tithable acidity

A

Phosphate takes our the H+ and gets rid of it, this prevents the H+ lowering the pH of the urine

38
Q

What is the mechanism of generating new HCO3 in triturable acidity

A

CO2 enters from the tubule from the blood, and combined with H2O to form H2CO3

This then dissociates to yield H+ and a new HCO3

The HCO3 then passes with Na+ into the peritubular capillaries

39
Q

What links the two processes in titratable acidity

A

The H+ produced in the distal cells, by the diffusion of CO2, is used as the Secretion into the lumen to form Dibasic phosphate to excrete the H+

40
Q

Where does tithable acidity occur, and why there

A

Occurs in the distal tubule

because un-reabsorbed dibasic phosphate becomes highly concentrated by the removal of volume of filtrate

41
Q

What is the purpose of ammonia excretion in kidney regulation

A

Used for acid loads

as the increased NH4+ is the main adaptive response to the kidney for acid loads

42
Q

What is the overall affect of ammonia excretion in kidney regulation

A

Generate new HCO3- and excrete H+

43
Q

Why is titratable acid initially used in acid loads rather than ammonia excretion

A

NH3 production takes 4-5 days Because renal glutaminase takes 4-5 days to reach maximum level,

then NH3 has considerable capacity to raise (HCO3)

(also takes time to switch off the ability to make NH4+ when there is excess alkali )

44
Q

What is the mechanism for ammonia excretion

A

NH3 is produced by the deamination of glutamate by renal glutaminase in the tubule cells

NH3 then moves out into the tubule lumen, where it combines with secreted H+ ions to form NH4+ and then Cl- (from NaCl) to from NH4Cl which is excreted

AT THE SAME TIME

CO2, moves from the blood and combines with water in the tubule to from H2CO3 which then dissociates
to form

H+ - which is the secreted H+
and HCO3-

The new HCO3- passes with Na+ into the peritubular capillaries

45
Q

What is the Process of ammonia excretion dependant on

A

PCO2 of the blood

46
Q

What is the activity of renal glutaminase dependant on

A

pH dependant

When intracellualr pH falls it increase renal glutaminase activity and therefore more NH4+ produced and excreted

47
Q

Where does ammonia excretion occur

A

Distal tubule and proximal tubule

48
Q

What is the difference between distal tubule and proximal tubule ammonia excretion

A

In the proximal tubules there is an NH4+/Na+ exchnager so NH4+ ions formed within the cell pass out the lumen

Where in the distal tubule, NH3 has to moves across the tubule into the lumen then become NH4

49
Q

What is the basic principle of ammonia excretion

A

basically requires you to waste amino acids to buffer pH and decrease acidosis

50
Q

What is another name for tithable acidity buffer

A

Dibasic phosphate, mono basic phosphate extracellular buffer

51
Q

What is the anion Gap

A

= Difference between the sum of principle cations (Na+ and K+) and the principal anions in the plasma (Cl- and HCO3-

Normally 14-18mmoles/L

Urinary System Physiology SA (10 decks)

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