Exam 4 Physio: Renal 4

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EXAM 4 PHYSIO: RENAL 4

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EXAM 4 PHYSIO: RENAL 4

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Two major sets of biological buffers:

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1. intracellular (proteins)
2. extracellular (CO2/ bicarb system)

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Definition of buffer

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Utilizes weak acid or base that does not completely dissociate. Leads to an efficient pH buffer.

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When is the buffer capacity the greatest?

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When pH = pK

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The more widely the different pKs present,

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The broader the buffer capacity of a protein.

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Why is carbonic acid an efficient physiological buffer?

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Because pCO2 is kept constant through respiration.

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GFR per day?

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180 L/day

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How is bicarb recovered?

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Occurs at the proximal tubule.

Coupled to Na reab. through the Na-H exchange.

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Outline the Na-H exchanger:

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At the proximal tubule:
1. Na goes in, H is extruded
2. H is neutralized by luminal bicarb to form H2CO3 thus forming CO2 and H2O
3. BUT in cytoplasm, eexported H is replenished leaving behind a bicarb.

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Overall result of Na-H exchanger:

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Uptake of Na and EQUIVALENT HCO3.

NOTE: most of filtered bicarb is reab. in proximal tubule.

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Bicarb in proximal tubule

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Overall effect:

1. protons and CO2 move through apical membrane
2. one bicarb reabsorbed from lumen to serosa

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Bicarb in the COLLECTING DUCT

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Generation of new bicarb

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Phosphate buffer

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Urinary buffer

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Ammonium buffer

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Another way to buffer hydrogen ions.

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Glutamine

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Glutamine synthesis consume equimolar of NH4 and HCO3.

Metabolized in liver and produces equimolar of NH4 and HCO3.

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Metabolism of glutamine coupled to NH4 and HCO3 transport results in?

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Acid excretion in the form of NH4.