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Cardiovascular And Respiratory System > Acid-base Balance > Flashcards

Acid-base Balance Flashcards

1
Q

What is an acid ?

A

A substance that can release or donate hydrogen ions

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2
Q

What is a base ?

A

A substance that can combine with or accept hydrogen ions

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3
Q

What is the pH of blood ?

A

Blood is maintained at approximately pH 7.35 to 7.45 under normal conditions in the arterial blood

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4
Q

What is the pH of the plasma/ECF ?

A

7.4

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5
Q

What is the the narrow physiological pH range ?

A

7.35 - 7.45

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6
Q

What is the narrow vital pH range ?

A

6.8 - 7.7

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7
Q

What does it mean when acids and bases are weak or strong ?

A

Strength of acids and bases depends on how completely they dissociate in solution
- strong = complete dissociation
- weak = partial dissociation

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8
Q

What is the equation to calculate pH ?

A

pH = -log [H+]

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9
Q

What is the relationship between H+ concentration and pH ?

A
  • concentrations of acids and bases is proportional to [H+]
  • as solutions get more acidic pH decreases
  • a pH change of 1 reflects a 10 fold change in [H+]
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10
Q

What is meant by a neutral solution ?

A

The concentration of hydrogen ions and hydroxyl ions is equal

H2O > OH- + H+

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11
Q

Why do small pH changes cause big problems ?

A
  • most enzymes only function within narrow pH ranges
  • acid base balance can also affect electrolytes (Na+, K+, Cl-)
  • proteins can be denatured
  • nerve and cardiac function altered
  • can also affect hormones
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12
Q

Why does the body produce more acids than bases ?

A
  • acids are taken in with foods e.g. in meat
  • acids are produced by the metabolism of lipids and proteins
  • cellular metabolism produces carbon dioxide

CO2 + H2O <> H2CO3 <> H+ + HCO3-

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13
Q

What are volatile acids ?

A

All acids produced in the body are non-volatile except for carbonic acid

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14
Q

What are non volatile acids ?

A

An acid produced from sources other than carbon dioxide
- produced from the incomplete metabolism of carbohydrates, lipids and proteins
- examples include lactic acid, phosphoric acid, beta-hydroxybutyrate and acetoacetic acid

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15
Q

What are the sources of hydrogen ion loss ?

A
  • loss of H+ in vomit
  • loss of H+ in urine
    (cause an increase in pH)
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16
Q

What are the sources of hydrogen ion gain ?

A
  • generation from carbon dioxide
  • from metabolic products : phosphoric acid, lactic acid and ketones
  • loss of bicarbonate ions in diarrhoea
  • loss of bicarbonate ions in urine
    (cause a decrease in pH)
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17
Q

What type of food is ideal to keep an acid base balance ?

A

60% alkaline foods and 40% acidic foods ideal

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18
Q

What is the normal value of HCO3 ?

A

22 - 26 mEq/L

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19
Q

What controls the partial pressure of carbon dioxide in alveolar gas ?

A
  • the rate of carbon dioxide production by the body
  • the rate of alveolar ventilation
20
Q

What causes arterial partial pressure of carbon dioxide to increase in healthy individuals ?

A
  • increase in carbon dioxide production
  • insufficient alveolar ventilation
21
Q

What is hypercapnia ?

A
  • a decrease in ventilation without a similar decrease in oxygen consumption or carbon dioxide production
  • ventilation does not meet the metabolic needs of the body
22
Q

What causes hypercapnia ?

A

Can occur :
- in disease states which increase physiological dead space
- when respiratory muscles are paralysed or the chest wall is damaged
- when tidal volume is reduced by CNS depression

23
Q

What are the consequences of hypercapnia ?

A
  • excess carbon dioxide in arterial blood
  • primarily affects acid base balance
  • elevated production of carbon dioxide generated H+
24
Q

What is respiratory acidosis ?

A

An acidic environment as a result of excess carbon dioxide

25
Q

What is hypocapnia ?

A

When ventilation is in excess of metabolic needs or carbon dioxide is exhaled at a greater rate than production

26
Q

What causes hypocapnia ?

A

Can occur :
- during acute asthma attacks
- under conditions of stress
- at altitude

27
Q

What are the consequences of hypocapnia ?

A
  • primarily affects acid base balance
  • decreased production of carbon dioxide generated H+
28
Q

What is respiratory alkalosis ?

A

Alkaline environment due to a decrease in H+ because of a decrease in carbon dioxide

29
Q

What is acidemia ?

A
  • pH less than 7.35
  • increased H+ concentration
  • happens due to an increase in non volatile acid > metabolic acidosis
  • happens due to failure to remove carbon dioxide from the blood > respiratory acidosis
30
Q

What is alkalaemia ?

A
  • pH greater than 7.45
  • decreased H+ concentration
  • can happen due to an increase in base > metabolic alkalosis
  • can happen due to decreased carbon dioxide > respiratory alkalosis
31
Q

Summarise respiratory acidosis

A
  • increased partial pressure of carbon dioxide of plasma
  • inadequate ventilation or significant carbon dioxide in the air
  • increased formation of carbonic acid which dissociates
32
Q

Summarise respiratory alkalosis

A
  • decreased partial pressure of carbon dioxide of plasma
  • increased alveolar ventilation
  • decreased formation of carbonic acid
33
Q

Summarise metabolic acidosis

A
  • fall in plasma pH accompanied by a fall in plasma bicarbonate
  • increase in metabolically derived acids (ketoacidosis)
  • loss of base
  • failure of renal tubes to excrete H+
34
Q

Summarise metabolic alkalosis

A
  • excess of non volatile base in the plasma
  • vomiting > loss of HCl
  • partial pressure of carbon dioxide is unchanged
  • increase in plasma bicarbonate
35
Q

How is blood pH kept closely regulated at 7.35 - 7.45 ?

A

There are 3 lines of defence :
- blood buffers
- respiration
- renal acid excretion

36
Q

At what time scale do the 3 lines of defence operate ?

A

• buffers - seconds
• respiration - minutes
• renal acid excretion - hours/days

37
Q

What is a buffer ?

A

A mixture of substances in solution that can resist changes in [H+] when strong acids or bases are added

38
Q

Summarise the function of buffers in resisting pH changes

A
  • buffering is the first stage in maintaining acid base balance
  • buffer systems are located in ICF and ECF compartments
  • the most important plasma buffer systems are the bicarbonate-carbonic acid system and haemoglobin
  • phosphate and plasma proteins are the most important intracellular buffers
39
Q

Describe the bicarbonate - carbonic acid buffer

A
  • in the lung and kidney
  • renal mechanisms don’t act as quickly as in the lungs
  • when it absorbs H+, bicarbonate converts to carbonic acid which dissociates to form carbon dioxide and water
  • excess carbon dioxide will stimulate central chemoreceptors
  • alveolar ventilation will increase and excess carbon dioxide is excreted via the lungs
40
Q

Describe how haemoglobin acts as a buffer

A
  • bicarbonate ions are exported out of the cell in exchange for chloride ions so haemoglobin buffers the resulting hydrogen ions
  • bicarbonate ions are used as a buffer throughout the body

Hb + H+ > HHb

41
Q

Describe how plasma proteins act as buffers

A
  • in extracellular fluid, a small amount of buffering is made possible by plasma proteins
  • this works in tandem with the bicarbonate buffering system
  • buffering occurs at specific amino acids
  • amphoteric molecules will release or bind hydrogen ions
42
Q

Describe the role of phosphate in acting as a buffer

A
  • plays a minor role in the ECF due to low concentrations
  • plays a larger role in intracellular buffering
  • phosphate buffering plays a major role in the kidney where it is responsible for buffering H+ fluctuations in the urine
43
Q

Summarise respiration as a compensation mechanism

A
  • the respiratory system compensates for metabolic acidosis and alkalosis by excreting or preserving carbon dioxide
  • body pH can be adjusted by changing the rate and depth of breathing
  • only works with volatile acids
44
Q

Describe renal compensation as a line of defence

A
  • the renal system compensates for respiratory acidosis and alkalosis by excreting or preserving H+
  • can eliminate large amounts of acid
  • can also excrete base
  • can conserve and produce bicarbonate ions
  • most effective regulator of pH
  • if kidneys fail pH balance fails
45
Q

What are the chemical buffer systems ?

A
  • bicarbonate buffer system
  • phosphate buffer system
  • protein buffer system
46
Q

What are the physiological buffers ?

A
  • respiratory mechanism
  • renal mechanism

Cardiovascular And Respiratory System (11 decks)

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