Quantitative Acid-Base Balance Flashcards
What is acid-base balance in the body?
It is the regulation of [H+] in body fluids which is difficult due to continued production of H+ and CO2
What is the normal arterial pH?
7.4
What are volatile acids and non-volatile acids?
Volatile - H2CO3
Non-Volatile - Produce H+
Where is the regulation of H+ most crucial?
Intracellularly
Where is the H+ that the kidneys and the lungs act on?
Extracellular
Does the regulation of the extracellular H+ affect the intracellular H+?
Yes. H+ transfer from the intracellular space to the interstitial space is slow but from the interstitial space into the plasma is fast
How is the regulation of the extracellular H+ related to the intracellular space regulation of bicarbonate and CO2?
Bicarbonate - reabsorption from the tubular space to plasma space is low
CO2 - proton transfer as CO2 from the plasma space tot eh alveolar air is fast
What is the flow of H+ in the body?
H+ goes from the
- intracellular space to the interstitial space (slow)
- then to to the plasma (fast)
- then is removed via the lungs or kidneys
What has more capacity to reduce acidity, the lungs or the kidneys?
Lungs.
For example, the lungs exhale CO2 (13,000 mmol/day) and the kidneys excrete H+ (50 mmol/day) and reabsorb HCO3– (5,500 mmol/day).
Thus the lungs have 150 times the capacity of the kidneys to remove acidity: 150 = (13,000 mmol – 5,500 mmol) / 50 mmol.
What induces strong K+ shifts?
Mineral acids like HCl where H+ is exchanged for K+
What induces weak K+ shifts?
Organic acids like lactic acid and carbonic acid
What acid is involved with metabolic acidosis?
Lactic Acid
What acid is involved with respiratory acidosis or alkalosis?
Carbonic Acid
How is chemical buffering involved with maintaining arterial plasma [H+]?
- Pi buffering
- HCO3- buffering
- Protein buffering (Hb)
How is the renal system involved with maintaining arterial plasma [H+]?
Kidneys secrete acidic urine (H+/NH4+/H2PO4-)
and absorb HCO3-
How is the respiratory system involved with maintaining arterial plasma [H+]?
The lungs ventilate off large amounts of CO2 which could potentially become carbonic acid
What does it mean if an acid has a low dissociation constant? (Kd)
Weak acid. If it has a large Kd then it is a strong acid.
When H+ is added to an acid at a pH equal to its Kd, why does the pH not decrease as much as it should?
It will be buffered by its corresponding anion
What is the buffering power?
Resistance to changes in H+. This is the greatest when the the operating pH matches the pKd.
What is the buffering range?
It is the buffering ability that persists within one pH unit on either side of pKd
What is buffering capacity?
Strength of the buffer is related to the concentration of buffer components.
What form is favored when pH<pKa?
HA
What form is favored when pH>pKa?
A-
What is seen when pH = pKa?
HA will equal A-
What is the most important protein buffer in the blood?
Hb - imidazole group is important
What is the relevance of the protein buffering system in the body?
It is a strong buffering system and a large fraction of all chemical buffering is related to proteins.
What is the relevance of the phosphate buffering system?
It is a weak buffering system since the buffering capacity is low in the plasma but it is stronger in the kidneys.
What is the equation for the bicarbonate buffer system?
pH = 6.1 + log(kidney/lung)
Kidney - HCO3-
Lung - CO2
How is the bicarbonate buffer system an open system?
CO2 is linked to environment via lungs for ventilation
H+ is linked to environment via kidneys for excretion and urination
What compensates for the low pKd of the bicarbonate system?
The open nature of the buffer system. The bicarbonate buffer system has a very low dissociation / association constant ratio (pK = 6.1), but this buffer systems still functions efficiently because its components are continually be removed from the body.
Where do free H+ ions in the urine come from?
Strong acids such as H2SO4
