Acid-Base Balance Part 1 Flashcards
What is the Henderson-Hasselbach equation
ph = pK + log [ (HCO3/H2CO3) ]
what is the ratio of bicarbonate (salt) to carbonic acid (acid) which results in a normal pH of 7.40
20 : 1
What is the equation which describes the bicarbonate-carbonic acid system
CO2 + H20 H2CO3 H+ + HCO3-
what enzyme catalyzes the reversible reaction in the equilibrium equation?
Carbonic anhydrase
What two cell types contain carbonic anhydrase
RBC’s and renal epithelial cells only
What is the modified Henderson-hasselbach equation as used in the bicarbonate:carbonic acid buffer system
pH = pK + log [ HCO3/ (alpha) (pCO2) ]
What are the values for pK in the blood and alpha, the solubility coefficient
pK = 6.1 alpha = 0.031
Two reasons why hemoglobin is an important whole blood buffer, regulating acid-base balance both in the lungs and the tissues
- RBC’s contain carbonic anhydrase (enzyme that converts the three forms of carbon dioxide)
- Has 9 histidine residues on each of its four chains that can accept carbon dioxide molecules forming stable amide bond
Physiologic importance of the isohydric shift in red blood cells
It is important because it is a set of chemical reactions by which oxygen is released to the tissues and carbon dioxide is taken up WHILE the blood remains at a constant pH
Process of the isohydric shift in red blood cells
- CO2 is generated from metabolism
- it joins with water to become H2CO3 (by carbonic anhydrase)
- It then splits to become an H+ ion and HCO3-
- H ion attaches to hemoglobin to become reduced hemoglobin
- when that happens, oxygen is given to the tissues
Chloride shift:
- movemnt of bicarbonate and chloride
**bicarb goes out of the cell and Cl- goes into the cell
Chloride shift:
- how this shift is responsible for the hyper-or hypochloremia noted in acid-bace disturbances for which the body is compensating
*This regulates how much Cl- is getting into the cell so if its to low then its hypochloremia
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Protein and phosphate buffer system according to specific sites of action (blood,tissue, and/or organs)
Protein Buffer system: 2/3 buffering power in blood and most of the buffering power intracellularly
Phosphate Buffer system: minor component of blood but great importance in the kidneys and RBC’s
Protein and phosphate buffer system according to processes involved
Protein: it accepts hydrogen ions because of its histidine residues
Phosphate: hydrogen ions are added to filtrate in the forming urine. Dibasic phosphate picks up a hydrogen ion to become monobasic
Rank the body’s buffer systems in order of their importance
Whole blood: Hemoglobin is most important
Plasma: Bicarbonate most important, then protein, then phosphate
State the organ which regulates the respiratory component and the organ which regulates the metabolic component of acid-base balance
Respiratory: lungs
Metabolic: kidneys
Pulmonary hyperventilation:
- how does it regulate the acid-base balance according to how it alters the bicarbonate:carbonic acid ratio, thus compensating for acidosis or alkalosis
Hyperventilation increases CO2 release, decreasing the denominator in of the H-H equation
Pulmonary hypoventilation:
– how does it regulate the acid-base balance according to how it alters the bicarbonate:carbonic acid ratio, thus compensating for acidosis or alkalosis
Hypoventilation decreases CO2 release, increasing the denominator of the H-H equation
Four specific mechanisms by which the kidney regulates acid-base balance
- Reabsorption of bicarbonate
- Excreting excess H+ by exchanging Na+ for H+
- Forming titratable acids with phosphate
- Excreting excess H+ as NH4+
Reabsorption of bicarbonate
- How does it correct for acidosis or alkalosis
In filtrate:
HCO3 in filtrate + H ions from renal cells form carbonic acid (H2CO3), this breaks down into H2O and CO2 which enter the renal tubular cells
In renal cells:
H2O and CO2 come together to form H2CO3. This breaks down into H+ ion and HCO3-. Bicarb goes into the interstitial fluid
Excreting excess H+ by exchanging Na+ for H+
- How does it correct for acidosis or alkalosis
In renal cells:
H2CO3 (carbonic acid) breaks down into H+ ion and bicarbonate. H+ ions are exchanged (out) for a sodium (in)
Forming titratable acids with phosphate
- How does it correct for acidosis or alkalosis
IN filtrate:
NaHPO4 joins with the secreted H ion to form NaH2PO4 which is a titratable acid that is excreted in the urine
Excreting excess H+ as NH4+
- How does it correct for acidosis or alkalosis
H ion plus NH3 are secreted by the renal cells. They come together to form NH4+ which is excreted in the urine
How does the kidney excrete acid via sodium hydrogen ion exchange?
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How does the kidney excrete acid via sodium hydrogen ion exchange including
- How mechanism maintains the Gibbs-Donnan equilibrium
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How does the kidney excrete acid via sodium hydrogen ion exchange including
- Interrelationship of hydrogen, sodium, and potassium ions’ reabsorption and secretion
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How does the kidney excrete acid via sodium hydrogen ion exchange including
- The reabsorption of bicarbonate when sodium is reabsorbed
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