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15 Cards in this Set
- Front
- Back
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What is a Crytalloid?
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a substance which, in solution, may pass through a semi-permeable membrane (cf. colloid)
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Define tonicity.
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refers to the effective osmotic pressure of solutions in relation to that of plasma.
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Define pH.
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pH: is the negative logarithm (to the base of 10) of the concentration of hydrogen ions
pH= pKa + log base/acid |
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Define a buffer.
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is a solution consisting of a weak acid and its conjugate base, which resists a change in pH when a stronger acid or base is added thereby minimising changes in pH
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List the determinants of the effectiveness of a buffer system.
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1- The amount of buffer present
2-its pKa 3-the pH of the carrying solution (80% of the buffering capacity happens within +/- 1 pH unit of the pKa of that buffer) 4-whether the system is an open(physiological) or closed (completely chemical) system. |
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List the major buffer systems in the body.
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1- bicarbonate
2-Hemoglobin 3-Protein 4-Phosphate |
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Write down the 'Henderson' equation.
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[H+]=K [HA]/[A-]
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What is the pKa of the bicarbonate buffer system?
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6.1
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What is the normal 'intra-cellular' pH?
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7.2 (more acidic than the plasma)
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What is Haldane effect?
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It is the increased capacity of deoxygenated blood for CO2 transport. Due to
1.↑buffering capacity ↑ CO2 is transported as bicarb 2.↑ binding of reduced Hb to CO2 forming carbaminoHb (70%) |
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What is pKa?
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pKa: is the negative logarithm (to base of 10) of the dissociation constant for a chemical reaction:
•For a reaction HA H+ + A-, dissociation constant is Ka = [H=][A-]/[HA] •Then, solve the equation for [H=], and then take the – log •You end up with: pH = pKa + log [A-]/[HA] •pKa represents the pH value at which the solute is 50% dissociated, i.e. [A-]=[HA] |
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What is the difference between a 'strong' acid and a 'weak' acid?
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a strong acid has the tendency to dissociates (HA--> H+ + A-) in an aqueous solution, so that there is a small number of HA's and very large number of the highly reactive H+ (e.g. hydrochloric acid)
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What about a weak acid?
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It largely remains as HA in the solution, with only a small number of free H+ liberated in the solution (thus preserving the pH of the solution)
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So what do buffers actually do?
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They take the liberated H+ from the strong acid and incorborate into the more (undissociated) molecule of the weak acid
-->thus we will have a larger number of weak acid HA's, however they are not really contributing to the pH of the solution |
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What is the 'weak' acid of the body?
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The most important is the carbonic acid (weak acid, found in soft drinks!)
Also, phosphoric acid is a weak acid in the body |
