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EMS > Lecture 27: Acid-base Homeostasis 1 > Flashcards

Lecture 27: Acid-base Homeostasis 1 Flashcards

1
Q

What are acids?

A

Acids are H+ donors

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2
Q

Name a strong acid?

A

HCl

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3
Q

Name a weak acid?

A

Carbonic acid

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4
Q

What are bases?

A

Bases are H+ acceptors

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5
Q

Name a base?

A

Bicarbonate

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6
Q

What is a buffer?

A

is a chemical (weak acid and its conjugate base) in solution which resists (minimizes) the change in [H+].

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7
Q

What is the chemical buffer system in blood?

A

In blood, the principle buffer system is the weak acid (H2CO3) and its conjugate base (HCO3-)

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8
Q

What is pH?

A

Negative logarithm of the hydrogen ion concentration(mol/L)
pH = -log10[H+]

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9
Q

Why do we use pH rather than [H+]?

A

pH scale was devised to cope with the wide range of H+ concentrations encountered in chemistry (taking logarithms makes it more manageable)

However Use of H+ rather than pH is becoming more prevalent in medicine, as it is a direct reflection of acid-base status

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10
Q

What is the relationship between pH and [H+] ?

A
  • Change inversely.
  • Exponential (non-linear) relationship
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11
Q

What are the reference ranges for blood?

A

pH: 7.35- 7.45
[H+]: 35 - 45 nmol/L

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12
Q

When is blood acidaemic?

A

If pH <7.35 ([H+] > 45 nmol/L), the patient is acidaemic

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13
Q

When is blood alkalaemic?

A

If pH >7.45 ([H+] < 35 nmol/L), the patient is alkalaemic

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14
Q

Why are changes in [H+] important within the body?

A
  1. Changes in [H+] can affect the surface charge and physical conformation of proteins (e.g. enzymes), changing their function
  2. The gradient of [H+] between the inner and outer mitochondrial membrane drives oxidative phosphorylation
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15
Q

When is H+ disposed from the body?

A

24hExcretion by lungs~ 20000 mmol/24h
Gluconeogenesis, Oxidation~ 1300 mmol/24h
Re-esterification,
Oxidation~ 650 mmol/24h
Oxidation~ 500 mmol/24h
Oxidation of amino acids~ 1100 mmol/24h
Excretion by the kidneys(Fixed acid) ~ 50 mmol/24hNote

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16
Q

When is H+ produced within the body?

A

Tissue respiration (CO2)~ 20000 mmol/24h
Glycolysis (Lactate)~ 1300 mmol/24h
Lipolysis (Free Fatty acids)~ 650 mmol/24h
Ketogenesis (Ketoacids)~ 500 mmol/24h
Ureagenesis (H+)~ 1100 mmol/24h
Sulphur-and Phosphate a.a.Metabolism ~ 50mmol/24h

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17
Q

What is Respiratory acid-base disturbance?

A

Abnormality affecting lung ability to excreted CO2

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18
Q

What is Non-respiratory (Metabolic) acid-base balance?

A

Abnormality anywhere else in the body except lungs

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19
Q

What is a strong acid?

A

an acid that fully dissociates its H+ ions

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20
Q

What is a weak acid?

A

an acid that partially dissociates its H+ ions

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21
Q

How does changes in pH affect proteins?

A

changes in H+ concentrations can affect the surface charge and physical conformation of proteins, changing their functions

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22
Q

How can changes in pH affect aerobic respiration?

A

the gradient of [H+] between the inner and outer mitochondrial membrane drives oxidative phosphorylation and if this balance is interrupted, so is aerobic respiration

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23
Q

How does tissue respiration affect H+ levels in the blood?

A

respiring tissues produce CO2 which can form H+ ions when transported in red blood cells

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24
Q

How is H+ produced by sulphur and phosphate metabolism controlled?

A

the H+ is excreted by the kidneys

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25
Q

How is the H+ produced by respiring tissues controlled?

A

CO2 is excreted by the lungs

26
Q

How does glycolysis affect blood pH?

A

it produces lactate, lowering pH

27
Q

What two metabolic processes remove lactate from the blood, minimising the pH changes caused by glycolysis?

A

1) gluconeogenesis

2) Oxidation

28
Q

How does lipolysis affect blood pH?

A

it produces free fatty acids, lowering pH

29
Q

What 2 metabolic processes removes free fatty acids from the blood, minimising pH changes caused by lipolysis?

A

1) re-esterification

2) oxidation

30
Q

How does ketogenesis affect blood pH?

A

it produces keto acid, lowering pH

31
Q

Which metabolic process removes keto acids from the blood, minimising the pH change causes by ketogenesis?

A

oxidation of keto acids

32
Q

What metabolic process helps minimise the pH decrease caused by ureagenesis?

A

oxidation of amino acids

33
Q

Give the general equation for anaerobic glycolysis:

A

glucose -> 2 lactate + 2H+

34
Q

How does the body respond to increasing lactate (decrease in pH) production during exercise?

A

more lactate is oxidised

(lactate + H+ + 3O2 -> 3CO2 + 3H2O)

35
Q

How does the body remove lactate in a diseased state (e.g hypovolaemia)?

A

bicarbonate production

36
Q

Give the equation of bicarbonate removing lactate from the blood in a diseased state:

A

2 lactate + 2H+ + 2HCO3- -> 2CO2 + 2H2O

37
Q

How does the body respond to diabetic ketoacidosis?

A

increased bicarbonate regeneration to remove the H+

38
Q

What is ketoacidosis?

A

excessive ketogenesis

39
Q

Give the full 3 part bicarbonate buffering system equation:

A

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

40
Q

What acid does CO2 form when dissolved in plasma or water?

A

H2CO3 (carbonic acid)

41
Q

Give the Henderson equation:

A

[H+] (proportional to) pCO2/ [HCO3-]

42
Q

Give the Henderson- Hasselbalch Equation:

A

pH (proportional to) [HCO3-]/ pCO2

43
Q

Describe how haemoglobin acts as a buffer in red blood cells:

A

respiring tissues release CO2 into blood cells, forming carbonic acid which partially disociates an H+ ion which is buffered by haemoglobin

44
Q

What happens to the HCO3- in red blood cells following carbonic acid dissociation?

A

it passively diffuses out the cell and a Cl- ion enters to maintain electroneutrality (chloride shift)

45
Q

Why is it that many proteins can act as buffers?

A

they contain weak acidic and basic groups due to their amino acid composition

46
Q

Describe how albumin (plasma protein) acts as a buffer:

A

it has net negative charge so can mop up H+ ions

47
Q

What protein plays a key role in buffering during chronic acidosis?

A

Bone protein

48
Q

What two ions make up the phosphate buffer:

A

HPO42- (monohydrogen phosphate) and H2PO4 (dihydrogen phosphate)

49
Q

Give the equation for the phosphate buffer:

A

HPO42- + H+ <=> H2PO4-

50
Q

Give the equation for the ammonia buffer system:

A

NH3 + H+ <=> NH4+

51
Q

Why is the significance of the ammonia buffer system debated?

A

the vast majority of ammonia in the body is already in the NH4+ form

52
Q

Describe the role of the lungs in acid-base homeostasis:

A

they remove CO2 from the blood into expired gas and respond to stimulation from CO2 sensitive respiratory control mechanisms

53
Q

Give the three crucial physiological pathways the kidney facilitates in acid-base homeostasis:

A

1) reabsorption of bicarbonate in the proximal tubule

2) excretion of H+ in the distal tubule

3) regeneration of bicarbonate in the distal tubule

54
Q

Why can HCO3- not be directly reabsorbed in the kidney?

A

the luminal membranes are impermeable to HCO3-

55
Q

Describe the process of reabsorption of bicarbonate in the proximal tubule: (4)

A

1) H2CO3 is generated is tubular cells from CO2 and H2O aided by carbonic anhydrase

2) this dissociates into H+ and HCO3- with the HCO3- being pumped into the plasma with Na+ for charge balance and the H+ secreted into the glomerular filtrate in exchange for Na+ also

3) the secreted H+ ion combines with HCO3- ions in the filtrate to from H2CO3 and then CO2 and H2O by breakdown

4) the CO2 diffuses into the tubular cells, providing a substrate for continued formation of H2CO3

56
Q

Where in the kidney does reabsorption of bicarbonate take place?

A

Proximal tubule

57
Q

Where in the kidney does excretion of H+ and regeneration of HCO3- take place?

A

distal tubule

58
Q

Describe the process of excretion of H+ and regeneration of HCO3- in the distal tubule:

A

1) H2CO3 is generated from CO2 and H2O under the action of carbonic anhydrase in the tubular cell

2) this dissociates into H+ and HCO3- with the H+ being actively secreted into the glomerular filtrate in exchange for Na+

3) this H+ ion is buffered by HPO42- and excreted as dihydrogen phosphate H2PO4-

4) meanwhile, HCO3- is pumped into the plasma in exchange for Na+

59
Q

How does the action of aldosterone affect H+ excretion and bicarbonate reabsorption?

A

it leads to increased potassium and hydrogen ion secretion and sodium reabsorption (Na+ is involved in H+ excretion and bicarbonate reabsorption)

60
Q

Give 4 ways in which the liver contributes to acid-base homeostasis:

A

1) it produces buffers such as plasma proteins

2) it produces CO2 from the complete oxidation of carbohydrates and fats

3) it consumes H+ during the metabolism of lactate, ketones and amino acids

4) it produces H+ during the metabolism of NH4+ to urea via the urea cycle

61
Q

How does liver failure and subsequent ammonia build up manifest?

A

the respiratory is stimulated, causing the patient to hyperventilate and blow of CO2, leading to increased pH and respiratory alkalosis

EMS (54 decks)

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