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Biochemistry (MPAS) > Lecture 7: Acid-Base Imbalance on Control (I) > Flashcards

Lecture 7: Acid-Base Imbalance on Control (I) Flashcards

1
Q

Why regulate acidity?

A

Protein structure and enzymatic activities are dependent on pH

Inability to maintain pH within acceptable levels will stop enzyme reactions and lead to death

Body has developed various mechanisms (buffers) to maintain pH within a narrow range of 7.37-7.44 (Limits of pathological range – 6.8-7.8)

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2
Q

How does the body maintain the pH balance?

A

Acid-Base balance is maintained with the aid of buffers.

3 main buffer systems

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3
Q

What are the three main buffer systems of the body?

A

Bicarbonate – extracellular buffer

Phosphate – intracellular

Proteins - intracellular (acidic and basic side chains)

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4
Q

Volatile acids

A

CO2

Produced by cellular oxidation, TCA cycle

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5
Q

Non volatile acids

A

Catabolism of proteins and S-containing amino acids

Partial oxidation of fatty acids and glucose ( -OH butyrate, acetoacetate, lactate)

Ingestion of nonvolatile acid precursors (Phospholipids, Phosphoproteins, nutrients with more inorganic anions than inorganic cations)

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6
Q

How is CO2 used as a buffer system?

A

used as a buffer system to prevent rapid changes in extracellular pH

CO2 reacts with water to form carbonic acid: CO2 + H2O H 2CO3 H+ + HCO3-

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7
Q

Production of CO2 by body

A

Body produces 13000-15000 mmol of CO2 per day

If not removed, would be hazardous to health

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8
Q

What organs are involved in maintenance of acid-base balance?

A

Lungs

RBC

Kidneys

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9
Q

Henderson Hasselbach equation

A

pH = 6.1 + log(bicarbonate)/pCO2

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10
Q

How is normal pH range maintained?

A

by regulating the levels of bicarbonate ion concentration and pCO2 (concentration of carbon dioxide) in the blood.

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11
Q

What does binding of H+ to Hb do to Hb?

A

Reduces affinity for H+

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12
Q

Carbonic anhydrase

A

Converts CO2 and H2O into H2CO3 and reverse

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13
Q

CO2 transport in tissues and in lungs

A

See figure

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14
Q

Where does reabsorption of bicarbonate ions occur primarily?

A

Proximal tubule

See figure

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15
Q

Regulation of HCO3 concentration

A

Regulated by kidneys, depending on acid-base imbalance

Can only REDUCE the amount it reabsorbs

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16
Q

Where is H+ secreted predominantly?

A

Distal tubule

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17
Q

Which compensatory mechanisms are the fastest?

A

Lungs are faster than kidneys

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18
Q

When is ammonia buffer system used?

A

During extreme starvation and acidic conditions, amino acids are broken down to produce ammonia.

Ammonia can be used to buffer the H+

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19
Q

What is acidemia

A

acidic blood

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20
Q

What is alkalemia?

A

alkaline blood

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21
Q

What is acidosis?

A

Process which creates excess H+

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22
Q

What is alkalosis?

A

Process which creates a deficit in H+

23
Q

Compensation

A

Describes the change that occur to avoid pH changes

24
Q

Respiratory

A

Changes in pCO2

25
Q

Metabolic

A

Changes in HCO3-

26
Q

Metabolic acid-base disorders

A

directly cause changes in the bicarbonate ion (or H+) concentration.

The changes are corrected by respiratory effects (via lungs).

27
Q

Respiratory acid-base disorders

A

Directly change the pCO2.

Corrected by metabolic effects (kidneys)

28
Q

Metabolic acidosis

A

decreased [HCO3-] concentration in blood.

Increased H+ causes low HCO3- (used to neutralize)

29
Q

Metabolic alkalosis

A

increased [HCO3-] in blood.

30
Q

Respiratory acidosis

A

increased CO2 concentration in blood

31
Q

Respiratory alkalosis

A

decreased CO2 concentration

32
Q

Reasons for reduced bicarbonate ion leading to metabolic acidosis

A

Increased production of hydrogen ions

Diabetic ketoacidosis, consequences of lack of insulin

Lactic acidosis due to tissue hypoxia, liver disease, cardiac arrest , hemolytic anemia

Methanol poisoning- metabolized to formic acid which builds up;

Ethylene glycol poisoning – metabolized to glycolic acid

Acid ingestion – (acid poisoning)

Salicylate (Aspirin) poisoning –uncouples oxidative phosphorylation, inhibits Krebs cycle, leading to acidosis from production of multiple organic acids

Diarrhea

Pancreatic/intestinal or biliary fistulae or drainage

Decreased H+ excretion

33
Q

Compensatory response to metabolic acidosis

A

Hyperventilation (respiratory alkalosis)

H+ combines with HCO3- which is converted to carbonic acid

Carbonic acid dissociates into CO2 and H20 which are exhaled

(low pCO2)

34
Q

Clinical effects of metabolic acidosis

A

can lead to hyperkalaemia and potentially cardiac arrest.

Increased [H+] can also act as a stimulant of the respiratory center in the brain, further stimulating rapid breathing.

35
Q

What is the anion gap?

A

biochemical measurement that is usually used for assessing acid-base imbalance relating to metabolic acidosis.

36
Q

What ions are measured in the calculation of ion gap?

A

Na+, K+, Cl- and HCO3-

37
Q

What does a large anion gap indicate?

A

Presence of a strong acid

38
Q

What is the anion gap in a healthy human?

A

6-18 mM

39
Q

What happens to anion gap when lactate, acetoacetate, or hydroxybutyrate are produced?

A

Anion gap increases

40
Q

Anion gap in metabolic acidosis

A

Reduced bicarbonate is balanced by increased chloride anions

Gap is normal

41
Q

Conditions resulting in metabolic alkalosis

A

Loss of hydrogen ions in the gastric/stomach fluid during vomiting.

As seen in infant pyloric stenosis (closing of the pylorus)

Incorrect administration of bicarbonate ion solution to correct for acidosis

Ingestion of absorbable alkali/sodium bicarbonate in large amounts

Potassium deficiency.

Usually, in the kidneys, sodium ion is absorbed, whereas potassium and hydrogen ions are excreted to maintain electrical neutrality in kidney tubular cells. However, in the absence of normal levels of potassium, more hydrogen ions are lost (i.e. more acid being lost making the blood more more alkaline/basic) than usual (to compensate for the less amount of potassium being excreted).

42
Q

Compensatory response to metabolic alkalosis

A

Hypoventilation

Respiratory acidosis

(increased CO2)

43
Q

What are respiratory acid-base disorders caused by?

A

Change in pCO2 in plasma

Can be acute or chronic

44
Q

Compensation in respiratory imbalances

A

No compensation in acute conditions relative to chronic because the metabolic compensatory effect by the kidneys takes days

45
Q

Acute respiratory acidosis - cause? concentrations?

A

Cause: air is blocked (hypoventilation)

pCO2 increases (hypercapnia)

pH decreases

46
Q

Examples of conditions that result in acute respiratory acidosis

A

Choking
Bronchopneumonia
Acute exacerbation of asthma
Anesthetics, sedatives (depression of respiratory centre)
Acute respiratory acidosis can cause coma and death if not resolved quickly

47
Q

Chronic respiratory acidosis - cause, compensation.

A

Chronic airway diseases

Maximum renal/kidney compensation: secretion of H+ and reabsorption of HCO3-

HCO3- will be high, pH will be normal

48
Q

Respiratory alkalosis

A

Low pCO2

Low H+ (high pH)

49
Q

Causes of decreased pCO2

A

Respiratory centre stimulants e.g. salicylates

Voluntary hyperventilation

Anxiety (acute condition)

Mechanical over ventilation in an intensive care patient

Cerebral disturbances e.g. trauma, raised intra cranial pressure, or hypoxia, both of which can stimulate the respiratory centre to increase gas exchange

Pulmonary disease – pulmonary edema, pulmonary embolism

50
Q

Compensatory response to respiratory alkalosis

A

Kidneys reduce reabsorption of HCO3-, resulting in metabolic acidosis

51
Q

Metabolic and respiratory acidosis

A

such as in:
Bronchitis and kidney failure/renal impairment, with a raised carbon dioxide concentration, low pH, and very low bicarbonate ion concentration because of the reduce excretion of the hydrogen ions, when compared to bronchitis alone.

52
Q

Salicylate poisoning

A

stimulates respiratory centre directly to induce hyperventilation which leads to respiratory alkalosis.

The effects of the compound on metabolic pathways leads to metabolic acidosis.

53
Q

Hyperventilation

A

causing respiratory alkalosis, followed by prolonged nasogastric suction (removing hydrogen ions) that causes metabolic alkalosis.

54
Q

What do extremely high O2 levels indicate?

A

Mechanic ventilation

Biochemistry (MPAS) (10 decks)

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