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Physiology 208 > Acid-Base Balance > Flashcards

Acid-Base Balance Flashcards

1
Q

pH

A
  • measurement of a solutions H+ concentration
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2
Q

Normal pH of the body

A
  1. 4

- slightly alkaline

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3
Q

1 pH unit = ?

A

a 10-fold change in H+ concentration

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4
Q

pH changes can _______ proteins… why?

A

denature

- intracellular proteins are sensitive to pH changes

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5
Q

Changes in [H+] results in..?

A
  • disruptions in hydrogen bonds

- alters the structure

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6
Q

Acidosis

A
  • caused by a very low pH (excess H+)

- CNS depression, confusion, coma

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7
Q

Alkalosis

A
  • caused by a high pH (low H+)
  • hyper excitability in sensory neurons and muscles
  • sustained respiratory muscle contraction
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8
Q

Acid Input

A
  • result of diet and acids produced during metabolism
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9
Q

Largest daily source of acid?

A

CO2 from aerobic metabolism

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10
Q

pH Homeostasis Mechanisms

A
  1. buffers (first lie of defence)
  2. ventilations (handles 75% of
    disturbances)
  3. renal regulation of H+ and HCO3- (slowest)
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11
Q

Buffer Systems

A
  • includes proteins, phosphate ions, HCO3-
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12
Q

Buffer Molecule

A
  • moderates, but doesn’t prevent changes in pH by combining with or releasing H+
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13
Q

No buffer

A
  • adding acid to a solution causes a sharp change in pH
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14
Q

Solution + Buffer

A
  • H+ added is bound and pH change is slightly moderated or unnoticeable
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15
Q

HCO3-

A
  • large amounts present
  • the most important extracellular buffer system
  • can buffer H+ from non-respiratory sources
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16
Q

Plasma [HCO3-]

A
  • approx. 600,000x concentrated as plasma H+ (bound to Hb)
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17
Q

Relationship Btwn CO2, HCO3-, H+ in Plasma

A

CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-

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18
Q

Law of Mass Action

A
  • any change in amount of CO2, HCO3-, H+ in solution causes reaction shift until new equilibrium is reached
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19
Q

Increase in CO2

A
  • shifts equation to right creating 1 H+ and 1 HCO3-
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20
Q

Adding H+

A
  • added through metabolic source (latic acid)
  • shifts equation to the left
  • HCO3- acts as a buffer
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21
Q

How does ventilation compensate for pH disturbances?

A
  • peripheral and central chemoreceptors sense changes in plasma PCO2 and/or H+ and signals to respiratory control centre to adjust ventilation accordingly
  • can correct disturbances or cause them
22
Q

Hypoventilation

A
  • right shift

- increase CO2 so increase in H+ and HCO3-

23
Q

Hperventilation

A
  • left shift

- decrease CO2 so decrease in H+ and HCO3-

24
Q

What kind of buffers do the kidneys use?

A

ammonia and phosphate buffers

25
Q

kidneys handle the remaining ____ of pH disturbances through two mechanisms:

A

25%

mechanisms: Directly and Indirectly

26
Q

Directly

A
  • by altering the rates of excretion of reabsorption of H+
27
Q

Indirectly

A
  • by changing the rate at which HCO3- .buffer is reabsorbed or excreted
28
Q

Ammonia Buffer

A
  • within tubule cells
29
Q

Phosphate Buffer

A
  • in the lumen of kidneys
30
Q

What happens to excess H+ during Acidosis?

A
  • excess H+ is buffered by ammonia within tubule cells or enters lumen and is buffered by phosphate ions
31
Q

H+ is not _____, enters _____ via _____ only.

A
  1. filtered
  2. tubule
  3. secretion
32
Q

Proximal Tubule

A
  • secretes H+ and reabsorbs HCO3-
33
Q

_____ amounts of HCO3- filtered

A
  • high amounts
34
Q

How is HCO3- filtered?

A
  • indirectly because no apical transporter
35
Q

Process of Proximal Tubule

A
  1. NHE secretes H+
  2. H+ in filtrate combines with filtered HCO3- to form CO2
  3. CO2 diffuses into cell
  4. CO2 combines with water to form H+ and HCO3-
  5. H+ is secreted again
  6. HCO3- is reabsorbed with Na+
  7. Glutamine is metabolized to ammonium ion and HCO3-
  8. NH4+ is secreted and excreted
36
Q

Role of the Distal Nephron

A
  • controls acid excretion
37
Q

Role of the Collecting Duct

A
  • plays a significant role in the fine regulation of acid-base balance
38
Q

Type A Intercalated Cells

A
  • acidosis
  • function to increase H+ secretion and HCO3- reabsorption
  • usually accompanied by increase K+ reabsorption (hyperkalemia)
39
Q

Type B Intercalated Cells

A
  • alkalosis
  • function to increase H+ reabsorption and HCO3- secretion
  • usually accompanied by increase K+ secretion (hypokalemia)
40
Q

Three Compensatory Mechanisms

A
  1. buffers
  2. ventilation
  3. renal excretion
    - take care of most variations in plasma pH
41
Q

Acid-Base Disturbances

A
  • classified by direction of pH change and by underlying cause
42
Q

Underlying Causes of Acid-Base Disturbances

A
  1. metabolic

2. respiratory

43
Q

Changes in Plasma pH due to Acid-Base Disturbances

A
  • body buffers are ineffective at this point

- respiratory and renal compensation alleviate the change in pH

44
Q

Respiratory induced changes in pH must be resolved via ______ mechanisms

A

RENAL

- excrete H+ and reabsorb HCO3-

45
Q

Respiratory Acidosis

A
  • occurs when alveolar hypoventilation results in CO2 retention and elevated plasma CO2
  • pulmonary fibrosis and skeletal muscle disorders (muscular dystrophy)
46
Q

Respiratory Alkalosis

A
  • less common
  • occurs as a result of hyperventilation in the absence of increased metabolic CO2 production
  • in clinic: caused by excessive artificial respiration
  • physiological: anxiety induced hyperventilation
  • compensation: renal HCO3- excretion, H+ reabsorption
47
Q

Metabolic Acidosis

A
  • occurs when dietary and metabolic input of H+ exceeds H+ excretion
  • lactic acidosis (anaerobic metabolism)
  • ketoacidosis (excessive breakdown of fats and some amino acids)
  • can also occur from excessive HCO3- loss (diarrhea)
48
Q

Metabolic Acidosis Solution

A
  • resolved by respiratory (increased ventilation) and slow renal compensation (HCO3- reabsorbed, H+ excreted)
49
Q

Metabolic Alkalosis Causes

A
  1. excessive vomiting of acidic stomach contents

2. excessive ingestion of bicarbonate-containing antacids

50
Q

Metabolic Alkalosis Solutions

A
  • usually resolved rapidly by a decrease in ventilation, but effectiveness is limited because it can because hypoxia
  • renal response: HCO3- excreted, H+ reabsorbed

Physiology 208 (11 decks)

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