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BIO169-Acid/Base
Acid/Base Balance
| Question | Answer |
|---|---|
| what is pH? | a logarithmic scale from 0-14; low end => acidic => high H+ concentration; ph 7 = neutral; pH = -log (H+) = log 1/(H+) |
| what is the normal pH of arterial blood? | 7.35 - 7.45; it is tightly regulated |
| what is the normal pH of urine? | 4.5 - 8.0; it varies widely and reflects the kidney's ability to excrete excess H+ or bicarbonate ions as needed |
| what is the most powerful regulator of pH? | the kidneys are the most powerful long-term regulators of pH |
| how is carbonic acid formed? | when cells make ATP, they produce CO2; CO2 can combine with water from red blood cells to produce carbonic acid (H2CO3) |
| what is the chemical equation for the formation of carbonic acid? | CO2 + H2O <=> (catalyzed by carbonic hydronase) H2CO3 <=> HCO3- + H+; HCO3- is a bicarbonate ion |
| what is a volatile acid? | one that is unstable; after dissociation, it reforms |
| what is the effect of the lungs on the carbonic acid reaction? | in the lungs, the carbonic acid reaction reverses; carbonic acid reforms into H2O & CO2; the CO2 will be removed and exhaled |
| what types of acids are regulated by the lungs? | volatile acids; specifically carbonic acid which dissociates into water and CO2, which is then exhaled |
| what is non-volatile acid? | acids that do not reform once they dissociate; these cannot be removed by the lungs; examples are HCl, sulfuric acid, phosphoric acid, lactic acid |
| how prevalent are non-volatile acids? | they are a significant source of free H+ |
| What are the 3 ways of regulating free H+ concentrations? | 1) buffers 2) kidneys, 3) respiratory system |
| how do buffers regulate free H+ concentrations? | in body fluids (including blood), buffers bind free H+; buffers react almost immediately to sudden, brief changes in pH; buffers do NOT remove free H+; they only bind the free H+ until the renal and respiratory systems reestablish pH balance |
| how does the respiratory system regulate H+ concentration? | the respiratory system can regulate H+ concentration from VOLATILE acids within seconds to minutes |
| how do the kidneys regulate free H+ concentrations? | the kidneys respond more slowly (hours/days) to free H+, but they have an extremely powerful control, particularly from NON-VOLATILE acids |
| what do buffer systems consist of? | 2 chemical components; a weak acid and a weak base |
| what is the function of buffer systems? | to minimize potential pH changes that would result from the addition of strong acids/bases to body fluids |
| what is a buffer? | any molecule that can REVERSIBLY bind or release free H+ |
| what is the general reaction equation of a buffer? | X + H+ <=> XH, where X is the buffer |
| where can free H+ bind with buffers? | in both the intra- and extracellular fluid |
| what are 2 examples of intracellular buffers? | phosphates (primary buffer in urine) and proteins (primary buffer inside cells; hemoglobin primary buffer inside RBC) |
| what is the most powerful extracellular buffer? | bicarbonate |
| what is the weak acid in the bicarbonate buffer system? The weak base? | carbonic acid (H2CO3) is the weak acid; sodium bicarbonate (NaHCO3) is the weak base |
| show the chemical equation how a strong acid is regulated by the bicarbonate system | NaHCO3 + HCl => H2CO3 + NaCl |
| show the chemical equation how a strong base is regulated by the bicarbonate system | H2CO3 + NaOH => NaHCO3 + H2O |
| what makes the bicarbonate buffers system so important? | its weak acid component is regulated by the lungs and its weak base component is regulated by the kidneys |
| why do buffer systems work in pairs? | why do buffebecause the weak acids can donate H+ and the weak base can accept H+; when a strong base is added, the weak acid component will release protons and convert the strong base to a weaker one, minimizing the pH change that results, and vice versa |
| what is acidosis? | presence of excess acid or free H+ ions; the weak base of the pair must be able to bind or remove the free H+ ions |
| what occurs during respiratory acidosis? | there is an increase of CO2 in the blood (which is a weak acid) |
| what is the catalyst that acts to dissociate carbonic acid, as well as to recombine its components back to carbonic acid? | carbonic anhydrase |
| what occurs during metabolic acidosis? | there is a decrease in the amount of bicarbonate in the blood, |
| what are the causes of metabolic acidosis? | most important - loss of bicarbonate in diarrhea; also, kidney failure, formation of excess metabolic acids in body, ingestion of acids (such as aspirin, methyl alcohol) |
| what is alkalosis? What's the difference between respiratory and metabolic alkalosis? | alkalosis is the presence of excess base; the weak acid of the buffer system must be able to release H+ ions; in respiratory alkalosis there is a decrease of CO2 in the blood; in metabolic alkalosis there is an increase of bicarbonate in the blood |
| what are the causes of metabolic alkalosis? | loss of HCl from the stomach from vomiting, or ingestion of alkaline drugs (such as sodium bicarbonate for ulcers) |
| how does hemoglobin function as a buffer? | hemoglobin, aka Hb, can reversibly bind with free H+ to help stabilize acidity inside RBCs; hemoglobin can also bind CO2 to reduce potential acidity |
| why is CO2 considered a weak acid or a potential acid? | it has the potential to release large amounts of H+ if it combines with H2O to form H2CO3 |
| how is CO2 detected in the blood? | central chemoreceptors in the medulla and peripheral chemoreceptors in the aortic arch and carotid sinus |
| what happens if the chemoreceptors detect a rise in CO2 in the blood? | increaes in respiration resulting in an increase in the amount of CO2 removed by lungs |
| how does the respiratory system respond to acidosis and alkalosis? | response to acidosis is increase in respiratory rate (to expel CO2); response to alkalosis is to decrease respirator rate (to retain CO2) |
| how do the respiratory and renal systems work together during alkalosis? | respiratory rate decreases, CO2 is retained in blood and combines with water to form carbonic acid, which becomes free H+ and bicarbonate ions (CO2 + H2O) -> H2CO3 -> H+ + HCO3- |
| what is the role of carbonic anhydrase in the respiratory system? | this enzyme is contained in the tubular epithelial cells to catalyze the reaction between CO2 and H2O to form H2CO3 which then breaks down to H+ and HCO3 (bicarbonate) |
| what is the role of the renal system in the regulation of acid/base balance? | by secreting H+ or by reabsorbing HCO3- |
| what happens in the renal system during acidosis? | during acidosis, H+ is secreted into the renal tubules (for elimination) (the H+ is obtained from non-volatile acids) and bicarbonate is reabsorbed by the blood to raise pH; during alkalosis, H+ is reabsorbed by the blood to lower pH |
| what happens in the renal system during alkalosis? | during alkalosis, H+ is reabsorbed by the blood and bicarbonate is released in the urine (by combining with Na+) to lower pH |
| what is the relationship between bicarbonate and H+ in the renal system? | for every bicarbonate ion absorbed by the blood, there must be one H+ secreted into the renal tubule |
| what is the role of ammonia in the renal system? | ammonia acts as a buffer; NH3 is the hydrogen acceptor, so it is the weak base; NH4 is the weak acid |
| how does phosphate act as a buffer? | HPO4 is the weak base, which accepts hydrogen ions to become H2PO4 (and then combines with sodium to become NaH2CO4) which is excreted; H2PO4 is the weak acid component, as it will donate its H+ |
Created by:
debmurph
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