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Phys II Unit 1 > L9 Acid/Base Physiology > Flashcards

L9 Acid/Base Physiology Flashcards

1
Q

Acid/base physiology describes the regulation of …

A

H+ concentrations in the ECF

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2
Q

The three main components of the homeostatic regulation of [H+] in the body

A

Buffered (fast): bicarbonate, proteins, phosphates, etc

Respiratory compensation: alters CO2 levels

Renal compensation (slow): alters HCO3- levels

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3
Q

____ is a short-hand method of expressing [H+]

A

pH

pH = -log[H+]

Plasma [H+] = 0.00000004 moles/L = 0.00004 mEq/L

So pH = -log[0.00000004] = 7.4

A 10-fold increase in [H+] = 1 unit change in pH

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4
Q

Normal blood pH = ?

A

7.4 (pH = -log[H+] = -log[0.00000004])

Normal range is 7.37-7.42 so [H+] can vary by +7 and -5 % around it’s mean of 40 nEq/L

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5
Q

pH and [H+] are related ________

A

Logarithmically

Increasing pH from 7.4 to 7.6 will decrease [H+] by 15 nEq/L

Decreasing pH from 7.4 to 7.2 will increase [H+] by 23 nEq/L

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6
Q

Normal [H+] ranges in different parts of the body

A

Gastric HCl [H+] = 0.15mol/L —> pH = 0.8

Max urine acidity [H+] = 3x10^-5 —> pH = 4.5

Normal plasma [H+] = 4x10^-8 —> pH = 7.4
Extreme acidosis pH = 7
Extreme alkalosis pH = 7.7

Pancreatic juice [H+] = 1 x 10^-8 —> pH = 8.0

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7
Q

13,000 to 20,000 mEq/day of H+ is produced from …

A

Respiratory CO2

Almost entirely handled by lungs
Known as volatile acid

Also, significant amounts of non-volatile, or fixed, acid arise from normal and abnormal processes:
• Degradation of certain amino acids
• Additional acid loads from exercise (lactate), diabetic kenos is (ß-hydroxy butyric & acetoacetic acides), and ingestion of acids

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8
Q

We produce ____ mEq/day of fixed (non-volatile) acid

A

50 mEq/day

From gluconeogenic utilization of AAs in the liver

Sulfuric acid from methionine and cysteine catabolism (75%); phosphoric acid from phospholipid degradation (25%)

Represent major acid load that kidney must eliminate

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9
Q

Acids are H+ ________ and bases are H+ ______

A

Acid = donor, base = acceptor

HA H+ + A- (A- = conjugate base)

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10
Q

The constant K can be defined as

A

The product of [H+] and [A-] divided by [HA]

K = [A-][H+]/[HA]

Rearranged:

[H+] = K[HA]/[A-]

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11
Q

What is the Henderson-Hasselbach equation?

A

Log[H+] = log K + log [HA]/[A-]

Since pH = -log[H+], we can rearrange:

pH = pK + log[A-]/[HA]

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12
Q

________ have lower affinities for hydrogen ions which dissociate easily from the conjugate base

A

Strong acids

They also have lower pK.

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13
Q

________ have higher affinities for hydrogen ions which do not dissociate as easily from the conjugate base

A

Weak acids

Have high pKs than strong acids

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14
Q

The first line of defense against pH changes?

A

Buffers

Located in the ECF, ICF, and bone

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15
Q

The effectiveness of a buffer is proportional to:

A

Its concentration and its pK

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16
Q

The most important buffer system in ECF?

A

Bicarbonate, due to its high concentration (22-26 mEq/L).

Both CO2 and HCO3- are tightly regulated by the following equation:

CO2 +H2O H2CO3 H+ + HCO3-

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17
Q

________ consist of acid and conjugate base pairs (ie HA/A-)

A

Buffers

At low pH’s, [HA] > [A-]; at high pH’s, [A-] > [HA]

Under base load, HA can contribute H+; under acid load, A- can absorb H+. pH changes little

18
Q

Because titration curves for acids are not linear, most effective buffering is …

A

+/- one pH unit from pK

19
Q

What are the acid/conjugate base pairs for the bicarbonate and phosphate buffers systems?

A

HCO3-/H2CO3 (CO2)

HPO4^2-/H2PO4-

20
Q

Since the pH of blood is 7.4, which would you THINK would be the better buffer, phosphate (pK = 6.8) or bicarb (pK = 6.1)?

A

You would think phosphate because its pK (6.8) is within 1 pH unit of the homeostatic pH.

Bicarb is still more important in the blood though…

21
Q

Well then what ARE the important buffers of the blood?

A

1) Bicarbonate (53% of total buffering capacity) - pK is low (6.1) but it’s effective due to its concentration and because both the acid (H2CO3) and base (HCO3-) are regulated

2) Hemoglobin (35%): Hb- + H+ HHb
Imidazole groups on histidine and alpha amino groups are the primary buffer sites on all proteins

3) Proteins (7%): Prot- + H+ HProt
Have good pKs (6.4-7.9) but concentrations are too low

4) Phosphate (5%)
Unimportant in blood due to low concentration
VERY important in urine where concentrations are higher

22
Q

The primary INTRACELLULAR buffers are …

A

Proteins: high [IC], pK’s close to 7.4
Phosphate has the same advantages as proteins

Bicarb is a secondary intracellular buffer because concentration is low

23
Q

Why are bones a special case in the world of buffering?

A

They take up [H+] in exchange for Na+ and K+

Bone minerals may account for a significant amount of body buffering capacity during acute acid loads.

24
Q

The __________ buffer system is the most important blood buffer for pH regulation

A

Bicarbonate

25
Q

The pH of blood, as determined by the Henderson-Hasselbach equation

A

pH = pK + log [HCO3-]/(0.03 x Pco2)

pK of bicarb = 6.1
HCO3- = 24 mEq/L
Pco2 = 40 mmHg

pH = 6.1 + log(24/(0.03x40)) = 7.4

26
Q

Decreasing bicarbonate concentration OR increasing Pco2 is called…

A

Acidosis

27
Q

Increasing bicarbonate concentration OR decreased Pco2 is called…

A

Alkalosis

28
Q

Regulation of pH is called …

A

Compensation

Buffers respond quickly to acid/base disturbances, but they can’t return pH to normal (only minimize pH change)

Compensation occurs as lungs and kidneys regulate CO2 and HCO3- respectively, such that the ration of [HCO2-] to dissolved CO2 remains near 20

29
Q

Changes in [HCO3-] are termed ________ disturbances

A

Metabolic disturbances

Loss or gain of HCO3- is compensated for by both the kidneys and the lungs

After initial buffering, changes take minutes to days

30
Q

In metabolic disturbances, the _________ is quick to respond and the ________ are slow.

A

Respiratory system is quick, kidneys are slow

31
Q

Kidneys sometimes CAUSE the metabolic defect, in which case, the __________ can compensate

A

Respiratory system

32
Q

Changes in CO2 levels are termed ___________ disturbances and must be compensated for by __________.

A

Respiratory disturbances, compensated for by the kidneys

After initial buffering, compensation takes days

33
Q

Examples of metabolic acidosis

A

Plasma HCO3- decreases, caused by ingestion of acid, formation of metabolic acids (ie lactic acid) etc

34
Q

How does the body respond in cases of metabolic acidosis?

A

Respiratory system: By increasing ventilation to expel CO2

Kidneys: Synthesize new HCO3-

35
Q

Examples of metabolic alkalosis

A

Plasma HCO3- increases, due to ingestion of excessive antacids or vomiting (loss of gastric acid)

36
Q

How does the body respond to metabolic alkalosis?

A

Respiratory system: Reduces ventilation to retain CO2

Kidneys: excrete excess HCO3-

37
Q

Examples of Respiratory Acidosis

A

Plasma Pco2 increases, due to decreased ventilation (drug overdose, airway obstruction etc)

38
Q

How does the body respond to respiratory acidosis?

A

If condition persists, the kidneys will synthesize new HCO3- and excrete H+ in the urine to raise blood pH

39
Q

Examples of respiratory alkalosis

A

Plasma Pco2 decreases due to hyperventilation (stress, high altitude, etc)

40
Q

How does the body respond to respiratory alkalosis?

A

Kidneys will excrete HCO3-, causing the urine to become alkaline; blood HCO3- and pH will decrease

Phys II Unit 1 (10 decks)

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