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Respiratory physiology > Acid base balance > Flashcards

Acid base balance Flashcards

1
Q

what is an acid?

A

a molecule capable of releasing a hydrogen ion
* an acidic solution has a H+ concentration greater than water (PH less than 7)

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2
Q

WHAT ARE VOLTAILE ACIDS?

A
  • Acids produced by the oxidative metabolism of CHO, fat & protein
  • excreted through lungs as CO2 gas
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3
Q

what are fixed acids?

A

acids that do not leave solution, ie once they are produced they remain in body fluids until eliminated by the kidneys
eg phosphoric acid

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4
Q

how are fixed acids generated?

A

through the catabolism of amino acids, phospholipids and nucleic acids

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5
Q

what is a base?

A

a molecule capable of combining a hydrogen ion
* an alkaline solution has a H+ concentration lower than water ( ie PH greater than 7)

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6
Q

Why is acid base balance important?

A
  • H+ ions affect the activity of enzymes and** interact with many electrically charged molecules**
  • most chemical reactions in the body are** highly sensitive to H+**
  • the maintenance of H+ within a normal range** is essential for normal metabolic reactions**
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7
Q

Describe the Ph scale

A
  • acidity and alkalinity are expressed on the PH scale
    * PH 0 - is strongly acidic - increase in H+
  • **PH 14 **is strongly basic or alkaline - decrease in H+
  • a PH of 7 in the middle of this scale is neutral
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8
Q

what is the equation for PH?

A

PH = -LOG [H+]

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9
Q

in order to function properly, what is the PH of the blood (approx)?

A

close to 7.4
* range PH (6.8-7.8)

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10
Q

what are the 3 mechanisms controlling blood PH?

A
  1. Buffers
  2. respiratory - ie increasing or decreasing ventilation
  3. renal contributions
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11
Q

what are PH buffer systems?

A

PH buffer systems are a combination of a weak acid and weak base that exist in balance under normal PH conditions

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12
Q

what is the most important buffer system for blood and ECF?

A
  • bicarbonate/carbonic acid buffer system
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13
Q

what is **another example **of a buffer system (other than HCO3-/H2CO3)?

A

haemoglobin buffer system

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14
Q

When body fluids become acidic, what is used to nuetralise the H+?

A
  • HCO3-
  • therefore [HC03-] is reduced
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15
Q

when body fluids become alkaline, what is used to neutralise the PH?

A
  • H+ is consumed to neutralise the PH, therefore more HCO3- is produced from dissocaition of carbonic acid
  • therefore [HCO3-] increased
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16
Q

What are the main functions of the H2CO3/HCO3- buffer system?

what does this system do when body fluids are acidic vs alkaline?

A
  • most important system for blood and ECF
  • when body fluids become acidic, the HCO3- is used to neutralise the PH - H+ conc increases
  • when body fluids become alkaline, H+ is consumed to nuetralise the PH and therefore more HCO3- is produced from H2CO3 dissociation - HCO3- conc decreases
17
Q

Describe the haemoglobin buffering system

A
  • hydrogen ions are buffered by haemoglobin molecules
  • H+ combine with reduced Hb
  • this system is the** only intracellular buffer system **with an **immediate effect on ECF PH **
  • helps prevent major changes in PH when plasma PCO2 is rising or falling
18
Q

what are other examples of buffer systems - other than H2CO3/HCO3- and haemoglobin?

A
  1. plasma proteins
  2. phosphate buffer system
19
Q

describe the phosphate buffer system

A
  • consists of the anion H2PO4- (weak acid)
  • works like the carbonic acid-bicarbonate buffer system
  • important buffering PH of ICF
20
Q

what are the limitations of the phosphate buffer system?

A
  • provide only temporary solution to acid-base imbalance
  • do not eliminate H+ ions
  • supply of buffer molecules is limited
21
Q

How does the respiratory system contribute to acid base balance?

A

by increasing or decreasing ventilation

22
Q

in response to an increase in CO2 (acid) in the blood, what is the respiratory systems response?

Describe the steps and final outcome

A
  • if there is an increase in CO2,** then the blood is more acidic** (decrease in PH)
  • this stimulates the medullary respiratory centre
  • the** brain increases the depth and rate of breathing **
  • therefore increase in CO2- increase in PH- increase in ventilation -increase in CO2 exhaled-decrease of CO2 in blood - decrease in [H+]- increase in PH
23
Q

what is the respiratory systems response to a decrease in CO2?

describe steps and the final outcome

A
  • a decrease in CO2 means an increase in PH (more basic)
  • therefore the rate and depth of breathing declines
  • reduction in the amount of CO2 eliminated from lungs
  • therefore- an increase in PH - decrease in ventilation - decrease in exhaled CO2- increase of CO2 in blood - decrease in PH (more acidic)
24
Q

How does the renal system contirbute to acid base balance?

A
  • if PH is acidic - then more H+ secretion
  • if PH is basic - then less H+ secretion

Respiratory physiology (17 decks)

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