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HLSC 128 - Human Physiology II > Chapter 15 - Acid/Base Balance > Flashcards

Chapter 15 - Acid/Base Balance Flashcards

1
Q

What does acid-base balance refer to?

A

the regulation of free H+ concentration in body fluids

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2
Q

Acids ______ hydrogen ions

A

liberate (separate)

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3
Q

Bases ____ hydrogen ions

A

accept (combine with free H+)

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4
Q

What do acids do in solution?

A

dissociate to release free H+ and anions

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5
Q

What do bases do in solution?

A

combine with H+ and remove it from the solution

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6
Q

Why are other substances that contain H+ not considered acids? (ie. carbohydrates)

A

the hydrogen is tightly bound within their structure and never liberated as free H+

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7
Q

A ______ acid has a greater tendency to dissociate than a ____ acid

A

strong; weak

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8
Q

What is an example of a strong acid?

A

HCl

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9
Q

What is an example of a weak acid?

A

Carbonic acid H2CO3

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10
Q

Dissociation Constant

A

-K
-extent of dissociating in a given acid is constant

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11
Q

The _____ the base, the more readily it can bind to free H+ in a solution.

A

stronger

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12
Q

Dissociation Constant Equation

A

[H+][HCO3]/[H2CO3]=K

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13
Q

What is pH used to express?

A

the concentration of H+

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14
Q

What is a pH of 7?

A

neutral

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15
Q

What is a pH less than 7?

A

acidic

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16
Q

What is a pH greater than 7?

A

basic

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17
Q

pH equation

A

-log[H+]=pH

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18
Q

A high pH corresponds to a _____ H+ concentration

A

low

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19
Q

What is the arterial pH range that is compatible with life?

A

between 6.8 and 8.0

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20
Q

Acidosis

A

when general body pH falls below 7.35

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21
Q

Alkalosis

A

when general body pH is above 7.45

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22
Q

Why is venous blood slightly more acidic than arterial blood?

A

it contains more CO2 which reacts with H2O to generate more carbonic acid

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23
Q

Acidaemia

A

when plasma pH falls below 7.35

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24
Q

Alkalaemia

A

when plasma pH rises above 7.45

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25
Q

What are the 3 main consequences of pH fluctuations in the body?

A
  1. changes in excitability of nerve and muscle cells
  2. influence enzyme activity
  3. influence on K+ levels
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26
Q

A state of acidosis leads to an overall ______ of the CNS

A

depression

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27
Q

A state of alkalosis leads to an overall ______ of the nervous system

A

hyper-excitability; sensory division of PNS usually affected first, then motor division, then CNS

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28
Q

How do changes in pH affect enzyme activity?

A

-may go outside the optimal range and denature the enzyme

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29
Q

How are K+ levels influenced by pH changes?

A

-H+ and K+ secretion in renal tubule is is an indirect relationship
-ie. if more H+ is eliminated then less K+ is excreted
-may affect cardiac function

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30
Q

What are the 3 lines of defence against pH changes?

A
  1. Buffer systems
  2. Respiratory mechanisms
  3. Kidneys
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31
Q

What is a chemical buffer system?

A

a mixture of two chemical compounds in a solution that minimize pH changes when either an acid or base is added or removed

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32
Q

Chemical buffer system is the ____ line of defence.

A

first

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33
Q

In a buffer system, one substance must ____ with free H+ if the [H+] falls, and the other must ____ with H+ if the [H+] rises

A

yield; bind

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34
Q

The body has ___ types of buffer systems.

A

4

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35
Q

Carbonic Acid:Bicarbonate Buffer System Role…

A

primary ECF buffer against non-carbonic acid changes

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36
Q

Protein Buffer System Role…

A

Primary ICF buffer; also buffers ECF

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37
Q

Hemoglobin Buffer System

A

Primary buffer against carbonic acid changes

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38
Q

Phosphate Buffer System

A

Important urinary buffer; also buffers ICF

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39
Q

Why is the H₂CO₃:HCO₃⁻ buffer system so effective in the ECF?

A
  1. both are readily available in the ECF
  2. both these components are closely regulated by respiratory system and kidneys
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40
Q

H₂CO₃ is regulated by the ______ system

A

respiratory system via CO2

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41
Q

HCO₃⁻ is regulated by the ______ system

A

renal

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42
Q

H₂CO₃:HCO₃⁻ Buffer System Reaction

A

CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻

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43
Q

H₂CO₃:HCO₃⁻ Buffer System: What occurs when H+ is added to the plasma (not via CO2)

A

-ie. exercise; lactic acid release
-rxn. is driven to the left side
-extra H+ binds with HCO₃⁻

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44
Q

H₂CO₃:HCO₃⁻ Buffer System: What occurs when there is a decrease in H+ (not via CO2)

A

-ie. loss of HCl during vomiting
-rxn. is driven toward the right side
-dissolved CO2 and H2O form H2CO3 to generate additional H+

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45
Q

What does the Henderson-Hasselbalch Equation explain?

A

the relationship between H+ and the members of a buffer pair

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46
Q

What is the Henderson-Hasselbalch Equation for the H₂CO₃:HCO₃⁻ Buffer System?

A

pH = pK + log[HCO₃⁻]/[H₂CO₃]

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47
Q

What is the enzyme needed for CO2 and H2O to make H2CO3 (carbonic acid)?

A

carbonic anhydrase

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48
Q

What is the pK constant for H2CO3?

A

6.1

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49
Q

What is the H₂CO₃:HCO₃⁻ in ECF?

A

20:1

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50
Q

What is the pH of plasma?

A

7.4 (6.1 + log[20]/[1] = 7.4)

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51
Q

What buffering system in the most important in plasma (ECF)?

A

H₂CO₃:HCO₃⁻ Buffer System

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52
Q

What happens when the [H₂CO₃] increases (ie. 40:1)?

A

-alkalosis state
-pH 7.7

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53
Q

What happens when the [H₂CO₃] decreases (ie. 10:1)?

A

-acidosis state
-pH 7.1

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54
Q

How does the hemoglobin buffer system work?

A

-buffers H+ that is produced by CO2 between tissues and lungs
-free H+ binds to Hb

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55
Q

What is the second line of defence against pH changes?

A

the respiratory system

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56
Q

How does the respiratory system regulate pH?

A

by controlling the rate of CO2 removal

57
Q

Changes in _____ pH can change ventilation patterns

A

arterial

58
Q

Peripheral H+ detection

A

-chapter 13
-carotid and aortic bodies are chemoreceptors

59
Q

When is peripheral H+ detection important?

A

when H+ comes from non-CO2 sources

60
Q

**??What source of H+ can the respiratory system help correct?

A

metabolic; not respiratory, ironically

61
Q

What do central chemoreceptors respond to?

A

a rise in CO2

62
Q

Ventilation/CO2 removal _______ during metabolic acidosis?

A

increases

63
Q

Ventilation/CO2 removal _______ during metabolic alkalosis?

A

decreases

64
Q

H2CO3/H+ generation ______ during metabolic acidosis?

A

decreases

65
Q

H2CO3/H+ generation ______ during metabolic alkalosis?

A

increases

66
Q

If pH changes due to _____ ______, respiratory system cannot contribute.

A

respiratory failures

67
Q

What is the third line of defence against changes in pH?

A

the kidneys (H+ secretion)

68
Q

How long do the kidneys take to compensate for pH changes?

A

hours to days

69
Q

How do kidneys control pH?

A
  1. H+ excretion
  2. HCO₃⁻ reabsorption/excretion
  3. ammonia secretion
70
Q

Lungs can only remove ____ generated H+; whereas the kidneys can remove H+ generated from other acids.

A

CO2

71
Q

There is very little H+ in the initial _____, most is secreted into tubular fluid via __, __, and ___.

A

filtrate; PT, DT, CD

72
Q

What is the usual pH of urine?

A

6, acidic

73
Q

What does HCO₃⁻ reabsorption depend on?

A

tubular secretion of H+ that combines with filtered HCO₃⁻ in the lumen

74
Q

H+ secretion is linked to ____ handling

A

HCO₃⁻

75
Q

HCO₃⁻ excretion in urine _____ H+ in plasma

A

increases

76
Q

HCO₃⁻ addition to plasma ____ H+ in plasma

A

decreases

77
Q

_____ HCO₃⁻ is generated in a H+ excess

A

new; generated to buffer the excess H+

78
Q

What decreases H+ secretion?

A

-when filtered load of HCO₃⁻ is increased
-less H+ is available to combine with

79
Q

HCO₃⁻ cannot be reabsorbed without ___ secretion

A

H+; thus more HCO₃⁻ is excreted in urine making it more basic

80
Q

What do the kidneys do to H+ when plasma pH falls below normal (acidosis)?

A

-increased H+ secretion and excretion
-decreased plasma [H+]

81
Q

What do the kidneys do to HCO₃⁻ when plasma pH falls below normal (acidosis)?

A

-reabsorption of all the filtered HCO₃⁻ and addition of NEW HCO₃⁻ to the plasma
-results in increased plasma [HCO₃⁻]

82
Q

What do the kidneys do to H+ when plasma pH rises above normal (alkalosis)?

A

-decreased H+ secretion and excretion
-conserves H+
-increases plasma [H+]

83
Q

What do the kidneys do to HCO₃⁻ when plasma pH rises above normal (alkalosis)?

A

-incomplete reabsorption of HCO₃⁻
-increased excretion of HCO₃⁻
-results in decreased plasma [HCO₃⁻]

84
Q

What is normal HCO₃⁻ excretion and when does it occur?

A

-zero is excreted, all is reabsorbed
-occurs when plasma is in acidosis and thus urine is acidic

85
Q

In states of acidosis kidneys ______ urine and _____ plasma to bring pH back to normal.

A

acidify; alkalinize

86
Q

In states of alkalosis kidneys ______ urine and _____ plasma to bring pH back to normal.

A

alkalinize; acidify

87
Q

How do kidneys acidify urine?

A

-H+ secretion

88
Q

How do kidneys alkalinize plasma?

A

-HCO₃⁻ conservation

89
Q

How do kidneys alkalinize urine?

A

-HCO₃⁻ elimination

90
Q

How do kidneys acidify plasma?

A

-H+ conservation

91
Q

What stops the tubular cells from excreting H+ against the concentration gradient?

A

-when tubular fluid becomes 800x as acidic as plasma
~pH 4.5

92
Q

What pH do the kidneys cease to secrete H+ into tubular fluid?

A

4.5

93
Q

What is used to prevent the concentration gradient from becoming too high?

A

buffering to reduce free H+; filtered phosphate buffers and secreted ammonia

94
Q

Why can’t HCO₃⁻ buffer urinary H+ like it can in the ECF?

A

it is not secreted simultaneously with H+ (only the excess substance is excreted ie. H+ over HCO₃⁻)

95
Q

What is secreted H+ first buffered by?

A

phosphate buffer system

96
Q

Why is phosphate present in tubular fluid?

A

dietary excess

97
Q

How does the phosphate buffer system work?

A

by absorbing H+ ions by binding with them

98
Q

Why is the additional ammonia buffer system needed?

A

-high H+ secretion the phosphate capacity is reached
-acidity rises as more H+ is secreted
-phosphate system would be overpowered on its own

99
Q

What is metabolized to produce ammonia (NH₃)?

A

glutamine; in the proximal tubular cells

100
Q

How does the ammonia buffer system act?

A

-ammonia is secreted once phosphate buffers are saturated
-NH3 combines with H+ to form ammonium (NH4)

101
Q

What does ammonia enable the kidneys to do?

A

continue secreting H+ to reduce acidosis

102
Q

Ammonium Equation

A

NH₃ + H⁺ → NH₄⁺

103
Q

How is NH₄⁺ removed from the tubules?

A

-lost in urine; tubular membranes not permeable to NH₄⁺

104
Q

Do the kidneys deal with pH changes from respiratory dysfunction or metabolic disturbances?

A

both

105
Q

A change in pH that has an underlying respiratory cause is associated with a change in [___].

A

[CO₂]

106
Q

A change in pH that has an underlying metabolic cause is associated with a change in [___].

A

[HCO₃⁻]

107
Q

Respiratory Acidosis has a ratio of ____ than 20:1 due to an _____ in [CO2]

A

less; elevation

108
Q

Respiratory Alkalosis has a ratio of _____ than 20:1 due to a ________ in [CO2]

A

greater; decrease

109
Q

Metabolic Acidosis has a ratio of _____ than 20:1 due to a ______ in [HCO₃⁻]

A

less; decrease

110
Q

Metabolic Alkalosis has a ratio of _____ than 20:1 due to an ______ in [HCO₃⁻]

A

greater; increase

111
Q

Respiratory acidosis occurs when CO2 builds up in the blood as a result of ________

A

hypoventilation ie. COPD (emphysema and chronic bronchitis), asthma, severe pneumonia

112
Q

What does respiratory acidosis lead to?

A

increased H2CO3 production and therefore increased free H+

113
Q

Uncompensated respiratory acidosis: [CO2] is _____ and [HCO₃⁻] is ______

A

elevated; normal

114
Q

Why can’t respiratory measures compensate for respiratory acidosis?

A

-they don’t respond to respiratory abnormalities

115
Q

How does the body compensate respiratory acidosis?

A

-increasing plasma HCO₃⁻ by kidney conservation and NEW HCO₃⁻

116
Q

Metabolic acidosis encompasses all types of acidosis except for those caused by excess ___ in body fluids.

A

CO2

117
Q

Uncompensated metabolic acidosis: [CO2] is _____ and [HCO₃⁻] is ______

A

normal; reduced

118
Q

Possible causes of metabolic acidosis?

A

-severe diarrhea where HCO3- is lost from the body before it can be reabsorbed
-exercise

119
Q

How is metabolic acidosis compensated for?

A

-lungs blow off H+ (generating CO2)
-chemical buffers taking up extra H+
-kidneys excreting more H+ and conserving HCO3-

120
Q

Uraemic Acidosis

A

-serious and severe kidney failure
-kidneys cant get rid of excess H+ and it accumulates
-kidneys can’t restore pH

121
Q

Respiratory alkalosis results from ______ and is when CO2 amounts in the blood are ______

A

hyperventilation; decreased

122
Q

What are some causes of respiratory alkalosis?

A

-fever
-anxiety
-severe infection
-pregnancy
-high altitude

123
Q

Uncompensated respiratory alkalosis: [CO2] is _____ and [HCO₃⁻] is ______

A

reduced; normal

124
Q

What are the compensatory measures for respiratory alkalosis?

A

-kidneys: conserve H+ and excrete more HCO₃⁻
-chemical buffer systems liberate H+

125
Q

What is metabolic alkalosis?

A

-a reduction in plasma H+ cause by a deficiency of non-carbonic acids

126
Q

Uncompensated metabolic alkalosis: [CO2] is _____ and [HCO₃⁻] is ______

A

normal/unchanged; increased

127
Q

What are some causes of metabolic alkalosis?

A

-vomiting (H+ lost in gastric juice elimination)
-ingestion of alkaline drugs

128
Q

How is metabolic alkalosis compensated for?

A

-reduced ventilation to retain more CO2 and generate more H+
-excess HCO3- excretion by the kidneys to conserve H+

129
Q

Uncompensated alkalosis ratio

A

40:1 (pH ~ 7.7)

130
Q

Uncompensated acidosis ratio

A

10:1 (pH ~ 7.1)

131
Q

Respiratory Acidosis Causes

A

-lung disease
-respiratory center depression
-nerve or muscle disorders that reduce respiratory activity
-holding breath

132
Q

Metabolic Acidosis Causes

A

-diarrhea
-diabetes mellitus
-strenuous exercise
-uremic acidosis

133
Q

Respiratory Alkalosis Causes

A

-fever
-anxiety
-asprin poisioning
-high altitude

134
Q

What is the physiological response to acidosis?

A

-H+ secreted to reabsorb filtered HCO3-
-new HCO3- produced, H+ is excreted bound to urinary buffers (HPO4 and NH4)

135
Q

Result of the physiological response to acidosis:

A

-more new HCO3- added to blood
-plasma bicarbonate increased compensating for acidosis
-urine is highly acidic

136
Q

What is the physiological response to alkalosis?

A

-HCO3- is excreted in the urine
-little or no H+ excretion
-glutamite and ammonium excretion decreased so no new HCO3- contributed to plasma from this source

137
Q

Result of the physiological response to alkalosis:

A

-plasma bicarbonate concentration is decreased
-urine is alkaline

138
Q

Bicarbonate

A

HCO3-

HLSC 128 - Human Physiology II (11 decks)

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