Acid-Base Balance

Question 1

Why is pH important in human physiology?

Answer 1

Controls speed of biochemical reactions by controlling speed or enzymes activity and electrical reactions

Question 2

What does pH stand for?

Answer 2

Potential of hydrogen

Question 3

What is an acid?

Answer 3

Can donate a hydrogen ion

Question 4

What is a base?

Answer 4

Can accept a hydrogen ion

Question 5

What happens when an acid (HA) is added to water?

Answer 5

Dissociates reversibly:
HA -> H⁺ + A
Yields a free H⁺ and its conjugate base (A¯)

Question 6

What is an example of an acid in the body?

Answer 6

Gastric acid

Question 7

What solutions in the body are close to being neutral?

Answer 7

Urine
Saliva
Blood
Tears

Question 8

What pH is normal blood?

Answer 8

7. 35 (venous)

7. 45 (arterial)

Question 9

What is the name for when blood pH is below 7.35?

Answer 9

Acidosis (acidaemia)

Question 10

What is the name for when blood pH is above 7.45?

Answer 10

Alkalosis (alkalaemia)

Question 11

Within what blood pH range would a person die?

Answer 11

Below 6.8 and above 8.0

Question 12

Why is abnormal blood pH dangerous?

Answer 12

Disrupts many enzyme systems and electron transport chain in mitochondria

Question 13

Where do most hydrogen ions in the body originate from?

Answer 13

Cellular metabolism

Question 14

What acids are produced in cellular metabolism?

Answer 14

Carbonic, sulphuric, phosphoric and others

Question 15

What pH is the human diet?

Answer 15

Almost neutral

Question 16

Which food group produces the most acid?

Answer 16

Protein

Question 17

Which 3 ways can acid be produced in the body?

Answer 17

Breakdown of food 
Metabolic activity (e.g. lactic acid in exercise)
Metabolically-produced CO2 forming carbonic acid with water

Question 18

Which disease state involves excess acid production?

Answer 18

Diabetic keto acidosis (DKA)

Question 19

How is carbonic acid produced in the body?

Answer 19

Aerobic respiration of glucose

Question 20

How is lactic acid produced in the body?

Answer 20

Anaerobic respiration of glucose

Question 21

How is sulfuric acid produced in the body?

Answer 21

Oxidation of sulfur-containing amino acids

Question 22

How are acidic ketone bodies produced in the body?

Answer 22

Incomplete oxidation of fatty acids

Question 23

How is phosphoric acid produced in the body?

Answer 23

Hydrolysis of phosphoproteins and nucleic acids

Question 24

What concentration is the metabolic production of CO2 in order to lead to production of carbonic acid?

Answer 24

15 mol/d

Question 25

What concentration is the metabolic production of lactic acid?

Answer 25

1.5 mol/d

Question 26

What concentration is the metabolic production of acids produced by diet and metabolism (e.g. ketoacids)?

Answer 26

60 mmol/d

Question 27

What condition can cause formation of formic acid?

Answer 27

Methanol poisoning

Question 28

What condition can cause formation of glycolic, glyoxylic and oxalic acids?

Answer 28

Ethylene glycol poisoning

Question 29

What 4 conditions can cause formation of lactic acid?

Answer 29

Drugs/toxins, CO poisoning, hypothension/hypoxia and liver disease

Question 30

What conditions cause formation of acetoacetate?

Answer 30

Uncontrolled diabetes and starvation

Question 31

What 3 mechanisms limit changes in pH? How long does each one take to act?

Answer 31

Chemical buffer systems in blood and ICF – immediate action The respiratory centre in the brain stem – acts within 1-3 minutes Renal mechanisms – requires hours to days to affect pH changes

Question 32

What is a buffer?

Answer 32

``` Solution that can resist pH change upon addition of acid or base Able to neutralise small amounts of added acid or base, thus maintaining pH of solution relatively stable Acts quickly (although temporarily to bind or release H⁺) Consist of a weak acid and the salt of that acid functioning as a weak base ```

Question 33

What are the 3 major chemical buffer systems in the body?

Answer 33

Bicarbonate (HCO₃¯) Proteins (haemoglobin and albumin) Phosphate (PO₄³¯)

Question 34

What is the anion gap?

Answer 34

Contribution of unmeasured anions to acidosis (phosphate, ketones, cations, acetate) = [Na+]-([Cl-]+[HCO3-]) = 8-12 mEq/L

Question 35

What one substance does the respiratory centre/lungs deal with?

Answer 35

Volatile acids CO2

Question 36

How do the lungs regulate acid-base balance?

Answer 36

Eliminating or retaining CO2 by altering rate or depth of respirations

Question 37

What is normal CO2 levels in the blood?

Answer 37

35-45 mm Hg | 4.7-6.0 kPa

Question 38

What can only the kidneys rid the body of?

Answer 38

Metabolic acids - e.g. phosphoric acid, uric acid, lactic acid and ketones

Question 39

What can the kidneys prevent?

Answer 39

Metabolic acidosis

Question 40

What two tasks must the kidneys accomplish in order to maintain acid-base balance?

Answer 40

1. Reabsorption of all filtered bicarbonate | 2. Excrete the acid daily load

Question 41

What three processes do the kidneys use to accomplish their tasks effectively?

Answer 41

1. Bicarbonate reabsorption (involving sodium transport) 2. Hydrogen secretion 3. Excretion of hydrogen ions with urinary buffers – titratable acids (e.g. H⁺ + HPO₄²¯ -> H₂PO₄¯) and ammonium (NH₄⁺)

Question 42

How much bicarbonate does the proximal tubule reclaim each day?

Answer 42

4500 mEq

Question 43

What is actively excreted in various parts of the distal kidney?

Answer 43

H+ ions

Question 44

How do the lungs eliminate acid?

Answer 44

Expiration of CO2

Question 45

How does the proximal tube eliminate acid?

Answer 45

Reabsorbs bicarbonate ions

Question 46

What two ways do the distal tubule/collecting duct eliminate acid?

Answer 46

Excretion of H+ as a titratable acid | Excretion of NH4+

Question 47

How do the lungs and kidneys compensate for acidosis?

Answer 47

Lungs increase respiratory rate | Kidneys increase bicarbonate reserve

Question 48

How do the lungs and kidneys compensate for alkalosis?

Answer 48

Lungs decrease respiratory rate | Kidneys decrease bicarbonate reserve

Question 49

What is the Henderson-Hasselbach equation?

Answer 49

pH = pKₐ + log([conjugate base]/[acid]) Where: pH = -log[ H⁺] pKₐ = -log(Equilibrium constant)

Question 50

What can the Henderson-Hasselbach equation be used for?

Answer 50

To find the pH of a buffer solution | To find the ratio of conjugate base to acid of the system

Question 51

What 4 things can go wrong to affect pH?

Answer 51

Bicarbonate increase Bicarbonate decrease CO₂ increase CO₂ decrease

Question 52

What are the two types of acid-base disorders and what do they involve?

Answer 52

1. Respiratory acid-base disorders Result when abnormal respiratory function causes rise or fall in CO₂ in ECF 2. Metabolic acid-base disorders Generation of organic or fixed acids Anything affecting concentration of bicarbonate ions in ECF

Question 53

In what 3 ways can acid-base disturbances be diagnosed?

Answer 53

Clinical history Physical examination Arterial blood gas analysis

Question 54

What are the normal values of arterial blood gases?

Answer 54

``` pH = 7.35-7.45 Partial pressure of oxygen (PAO2) = >11kPa or 80-100mmHg PaCO2 = 4.7-6.0kPa or 35-45mmHg Bicarbonate = 22-26mmol/L Base Excess +/- 2mEq/L ```

Question 55

What is the respiratory indicator of acid-base imbalances?

Answer 55

PaCO2 value

Question 56

What is the metabolic indicator of acid-base imbalances?

Answer 56

HCO3 value

Question 57

What are the 4 forms of acid-base disturbance?

Answer 57

Respiratory acidosis Respiratory alkalosis Metabolic acidosis Metabolic alkalosis

Question 58

What causes respiratory acidosis and how is it compensated for?

Answer 58

``` CO2 retention from hypoventilation (e.g. COPD) Renal compensation (H⁺ excretion, HCO₃¯ gain) ```

Question 59

What causes respiratory alkalosis and how is it compensated for?

Answer 59

``` CO₂ loss from hyperventilation (anxiety or altitude) Renal compensation (H⁺ retention, HCO₃¯ loss) ```

Question 60

What causes metabolic acidosis and how is it compensated for?

Answer 60

``` Gain of acid, loss of base from diarrhoea, keto-acidosis, lactic acidosis Respiratory compensation (pCO₂<35mmHg [HCO₃¯]<22mM) ```

Question 61

What causes metabolic alkalosis and how is it compensated for?

Answer 61

``` Loss of acid, gain of base from vomiting, hypokalemia, ingestion of HCO₃¯ Respiratory compensation (pCO₂>45mmHg [HCO₃¯]>28mM) ```