BIO169-Acid/Base
| Description: | Acid/Base Balance |
| Category: | Biology |
| Created by: | debmurph on 2006-03-03 |
| 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+ |
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The renal system regulates alkalosis by reabsorbing H+ and excreting bicarbonate in the urine by combining it with Na+. The weak base component of the bicarbonate system is NaHCO3. The renal system regulates free H+ over hours or days, but is very powerful. It is particularly important for non-volatile acids (by combining with NaHCO3). The renal system regulates acid/base balance by secreting H+ or reabsorbing HCO3-. CO2 is detected in the blood by central chemoreceptors in the medulla and peripheral chemoreceptors in the aortic arch and carotid sinus. The phosphate buffer system works with HPO4 as the weak base to become H2PO4 and then combines with Na to form NaH2CO4 which is then excreted; H2PO4 is the weak acid. |
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