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| | =====Acidosis===== | | =====Acidosis===== |
| | In a situation of increased H<sup>+</sup> levels the body is said to be in a state of acidosis and the kidneys stop excreting HCO<sub>3</sub><sup>-</sup> and the tubular cells produce more bicarbonate. This results in more H<sup>+</sup> being buffered and the pH increases back to normal | | In a situation of increased H<sup>+</sup> levels the body is said to be in a state of acidosis and the kidneys stop excreting HCO<sub>3</sub><sup>-</sup> and the tubular cells produce more bicarbonate. This results in more H<sup>+</sup> being buffered and the pH increases back to normal |
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| − | ===Buffers of H<sup>+</sup> in Urine===
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| − | * Weak acids are filtered and act as buffers
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| − | * Ability depends upon pKa<sup>+</sup> and concentration
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| − | * Once all the bicarbonate has been reabsorbed the secreted H<sup>+</sup> combine with these instead.
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| − | * The H<sup>+</sup> ion is then excreted
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| − | =====The Role of Ammonium in the Proximal Tubule=====
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| − | * The body is able to excrete H<sup>+</sup> as ammonium NH<sub>4</sub><sup>+</sup>. This is very useful as:
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| − | * It adds flexibility to renal acid base regulation and can help regulate NH<sub>4</sub><sup>+</sup>
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| − | * It is ionised, fat insoluble and trapped therefore is excreted
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| − | * It is easily replaced so is quite a good method
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| − | * Under physiological control
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| − | =====The Role of Ammonium in the Collecting Ducts=====
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| − | * Very different mechanism
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| − | * No bicarbonate produced
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| − | * See diagram
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| − | ===The Effect of The Buffers on Body pH===
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| − | * When H<sup>+</sup> is binding to buffers other than bicarbonate it is excreted. This means that the reabsorption of bicarbonate represents a net gain of bicarbonate not just a replacement of what was filtered. This results in an increase in plasma pH.
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| − | * Bicarbonate is also produced as part of the secretion of ammonium in the proximal tubule
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| − | ===Regulation===
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| − | * H<sup>+</sup> is important for both HCO<sub>3</sub><sup>-</sup> reabsorption and generation of new HCO<sub>3</sub><sup>-</sup>
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| − | * However the rate of secretion must be carefully regulated
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| − | * There must be enough H<sup>+</sup> secreted to reabsorb all the filtered HCO<sub>3</sub><sup>-</sup>
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| | ==Oxygen== | | ==Oxygen== |