Week 2 Lectures Flashcards
Source of H+ ions in the body
all acids are produced from METABOLISM
carbonic (volatile) acids=H2CO3–produced from metabolism of carbs and fats; oxidized to CO2 and H2O; exhaled by lungs
non-carbonic (non-volatile) acids=HCl, H2SO4–produced by proteins, sulphates and phosphates; comprises the daily acid load that the kidneys excrete
name the volatile acids
carbonic acids
H2CO3
how are volatile acids removed from the body
exhaled by lungs
Name the non-volatile acids
H2SO4, HCl
how are non-volatile acids removed from the body
comprise the daily acid load that the kidneys excrete
What are the three sources of the body’s buffering system?
- extracellular (major source)
- bone
- intracellular
How do extracellular components participate in the buffering system of the body
HCO3-/CO2 system
plasma proteins
inorganic phosphates
How do intracellular components participate in the buffering system of the body
cellular proteins
phosphates
hemoglobin of RBCs
How does bone participate in the buffering system of the body
bone mineral dissolves to release buffer
especially important during ACIDOSIS
What are the two major mechanisms for compensation during acid base disorders?
- respiratory compensation
2. renal compensation
Describe the mechanism of respiratory compensation during acid base disorders
- in metabolic acidosis–>increase alveolar ventilation to blow off more CO2 (Kusmall breathing = fast and deep breathing characteristic of DIABETIC KETOACIDOSIS)
- in metabolic alkalosis–>decrease alveolar ventilation to retain CO2
describe the mechanism of renal compensation during acid base disorders
- in respiratory acidosis–> increases produced of HCO3-
2. in respiratory alkalosis–> decreases production of HCO3-
Which method (renal or respiratory) acts faster? Which method is more effective at restoring normal values?
renal compensation acts SLOWER but is more effective at restoring normal values than respiratory compensation which works faster
What role does plasma buffering play in acid load?
plasma buffering system uses HCO3- to buffer the H+ load, forming H2CO3 which dissociates into CO2 and H2O–>generated CO2 is expired
What equation describes the relationship between pH, H+, bicarb and pCO2?
henderson hasselbach
henderson hasselbach equation
pH = pKa + log([A-]/[HA])
pH = 6.1 + log10 ([HCO3-]/0.03 X PaCO2])
Describe the renal mechanism for H+ secretion
- H+ is not filtered by the kidney as free ions
- secreted into the lumen at the PT and CD (intercalated cells)
- at the PT uses apical Na+/H+ antiporter
- at the CD uses apical H+ ATPase
- secreted H+ combines with filtered HCO3-, titratable acids (Pi), or ammonium (NH4+)
Describe the renal mechanism for HCO3- reabsorption
-kidney filters 4300 mEq/day of HCO3-
-almost all is reabsorbed at three sites: PT (90%), TAL and CD
-All tubular HCO3- reabsorption is the consequence of H+ secretion
HCO3- + H+ –> H2CO3 –> CO2 and H2O which are both passively reabsorbed
Describe the renal mechanism for HCO3- regeneration (new bicarbonate generated)
- titratable acids–> same process as for HCO3- reabsorption, except that secreted H+ combines with a titratable acid such as a phosphate (HPO4-2)–H+ gets thus trapped in the lumen and secreted as H2PO4—net gain of one HCO3- (unfortunately there is a very limited amount of titratable acids in the body)
- NH4+ secretion–> NH4+ production and excretion increases in response to an increased acid load–under normal circumstances, excretion of NH4+ accounts for less than half of the net acid excreted per day–with an acid load, the kidney can increase NH4+ secretion by about 10X normal to 300-350 mmol/day
How does ammonium act as a buffer in the renal mechanism for NCO3- regeneration
Step 1: ammonium formation in the PT–> 2 NH4+ are generated from each molecule of glutamine in the PT; the same Na+/H+ antiporter is involved, except that NH4+ is transported in place of H+; NH3 can freely reenter the cell while NH4+ is trapped in the lumen
Step 2: ammonium reabsorption and recycling in the TAL/LoH–> reabsorption step at the TAL required to prevent NH4+ from being taken up into the blood and metabolized in the liver to form urea at the cost of 2 HCO3-; NH4+ is recycled into NH3+ and moved to the CD, where urine is more acidic, to reformed NH4+; the same Na+/K+/2Cl- co transporter is involved, except NH4+ is transported in place of K+; free H+ is used in the metabolism of glutamate and alpha-ketoglutarate in the Krebs cycle
Step 3: Ammonium finally acts as a buffer in the CT–> H+ secreted from the aldosterone sensitive ATPase in the CD combines with NH3+ to reform NH4+; NH4+ is trapped in lumen and excreted; net gain in one HCO3- per NH4+ excreted
What defines alkalosis and acidoses?
blood pH >7.4 = alkalosis
What pCO2 defines hyperventilation? Hypoventilation?
- Hyperventilation = pCO2 40 mmHG
What use is the amount of HCO3- in the blood?
gives the status of the primary buffering system of the body
Why must some H+ be secreted with urinary buffers in the case of high acid load?
because the kidney cannot excrete urine more acidic than pH 4.0-4.5