Exam 3 -- Chapter 11 KCQs and Quiz

Quiz #6 According to the Henderson-Hasselbalch equation, the pH of a weak acid solution is determined by

ratio of the concentration of the base in solution to the concentration of the acid.

Quiz #19 Which of the following conditions and/or diseases can result in metabolic acidosis or alkalosis?

- Uncontrolled diabetes - Kidney diseases that result in a loss of acids - Vomiting All of these are correct

Quiz #24 Which of the following statements about a buffer is correct?

- a buffer resists pH change - buffers often consist of a weak acid and its conjugate base - a buffer removes hydrogen ions from solution All of these answers are correct

Quiz #27 Which of the following events occurs during exercise at work rates above 60-80% VO2 max?

- a decrease in blood pH - a decrease in plasma bicarbonate concentration - an increase in blood lactic acid concentration All of these answers are correct

Quiz #10 Acidosis can occur due to

- a decrease in the H+ concentration. - a loss of acids from the blood. - an accumulation of bases in the blood. NONE of these.

Quiz #5 Muscle pH is generally

0.4-0.6 pH units lower than arterial pH.

Quiz #7 Repeated bouts of high intensity exercise (e.g., interval training) can reduce arterial pH to levels as low as

6.8-7.0.

Quiz #4 Using the Henderson-Hasselbalch equation, calculate the pH of blood given: pKa = 6.1 blood concentration of carbonic acid = 1.2 mEq/L blood concentration of bicarbonate = 24 mEq/L Your calculation reveals that the pH of blood is

7.4

Quiz #25 Which of the following track running events would have the greatest risk of acid-base disturbance?

800 meter run

Quiz #13 Which of the following is true of the pH of arterial blood?

A pH of 7.0 would be considered acidosis.

Quiz #14 Which of the following statements about hemoglobin's buffering capacity are true?

Both Hemoglobin has six times the buffering capacity of plasma proteins because of it's concentration and Deoxyhemoglobin is a better buffer than oxyhemoglobin are correct.

Quiz #8 Which of the following statements about skeletal muscle buffer systems is correct?

Both Two monocarboxylate transporters exist in human skeletal muscle fibers and High intensity exercise training has been reported to improve muscle buffer capacity by increasing both carnosine and hydrogen ion transporters in skeletal muscle are correct

Quiz #18 Which of the following transporters in skeletal muscles are responsible for moving hydrogen ions across the sarcolemma?

Both sodium-hydrogen exchanger and monocarboxylate transporter are correct

#7 Briefly outline the way the body resists pH change during exercise. Include both cellular and blood buffering systems.

H+ production depends on: exercise intensity, amount of muscle mass involved, and duration of exercise. Blood pH declines with increasing intensity of exercise. Muscle pH declines with increasing intensity of exercise: muscle pH is lower than blood pH. Muscle is a site of H+ production and has lower buffering capacity. Buffering of H+ in the muscle: 60% by intracellular proteins, 20 to 30% by muscle bicarbonate, and 10 to 20% by intracellular phosphate groups. Buffering of lactic acid in the blood: bicarbonate is a major buffer: Increases in lactic acid accompanied by decreases in bicarbonate and blood pH. Hemoglobin and blood proteins play a minor role. The first line of defense against muscle pH shift during exercise are intracellular buffers: bicarbonate, phosphates, proteins, carnosine, and transport of hydrogen ions out of muscle. The second line of defense against the blood pH shift during exercise are blood buffer systems and respiratory compensation for metabolic acidosis: bicarbonate, phosphates, and proteins. Buffering of lactic acid in the blood include blood buffers and respiratory compensation for exercise-induced metabolic acidosis.

Quiz #15 How do changes in muscle pH affect exercise performance?

Hydrogen ions compete with calcium ions for binding sites on troponin, thereby hindering the contractile process

#5 What are the principle intracellular and extracellular buffers?

Intracellular buffers: cellular proteins, phosphate groups, histidine-dipeptides (primarily carnosine), and bicarbonate. The presence of bicarbonate in skeletal muscle fiber is a useful buffer during exercise. Several phosphate-containing compounds also serve as intracellular buffers in skeletal muscle fibers, and phosphate buffers are of particular importance at the beginning of exercise. Numerous cellular proteins contain the amino acid histidine, which possesses an ionizable group that can accept (buffer) hydrogen ions. The combination of a hydrogen ion with this cellular protein results in the formation of a weak acid, which protects against a decrease in cellular pH. Muscle fibers also contain several histidine-dipeptides (two linked amino acids) that are capable of buffering hydrogen ions. Extracellular buffers: bicarbonate, hemoglobin, and blood proteins. Blood proteins act as buffers in the extracellular compartment. Like intracellular proteins, these blood proteins contain ionizable groups that are weak acids and therefore act as buffers. However, because blood proteins are found in small quantities, their usefulness as buffers during heavy exercise is limited. Compared to most blood proteins, hemoglobin is a more important protein buffer and is a major blood buffer during resting conditions. Hemoglobin has six times the buffering capacity of plasma proteins due to its high concentration. The bicarbonate buffer system is the most important extracellular buffer system in the body.

Quiz #30 Which of the following events are not primary sources of hydrogen ions during rigorous exercise?

Production of 3-phosphoglucose during glycolysis

#6 Discuss respiratory compensation to metabolic acidosis.

Respiratory compensation is the physiologic mechanism to help normalize a metabolic acidosis, however, compensation never completely corrects an acidemia. It is important to determine if there is adequate respiratory compensation or if there is another underlying respiratory acid-base disturbance. Respiratory control of acid-base balance involves the regulation of blood PCO2. An increase in blood PCO2 lowers pH, whereas a decrease in blood PCO2 increases pH. Increased pulmonary ventilation can remove CO2 from the body and thus eliminate hydrogen ions and increase pH.

#8 Why would someone ingest sodium bicarbonate prior to an athletic event? Would this help?

Supplementation with sodium bicarbonate is an important extracellular buffer. It can increase time to exhaustion during high-intensity exercise (80 to 120% VO2 max). Yes, it may help, but is also associated with nausea and vomiting. If large doses are taken, it can promote alkalosis.

#2 List and briefly describe the 3 major sources of H+ produced in the muscle during exercise.

The exercise-induced decrease in muscle pH is due to multiple factors, including (1) increased production of carbon dioxide; (2) increased production of lactic acid; and (3) the release of H+ ions during the breakdown of ATP. Three important contributors to exercise-induced muscle acidosis are 1. Exercise-induced production of carbon dioxide and carbonic acid in the working skeletal muscles. Carbon dioxide, an end product in the oxidation of carbohydrates, fats, and proteins, is regarded as an acid by virtue of its ability to react with water to form carbonic acid (H2CO3), which in turn dissociates to form H+ and bicarbonate (HCO3-). Because CO2 is a gas and can be eliminated by the lungs, it is often referred to as a volatile acid. During the course of a day, the body produces large amounts of CO2 due to normal metabolism (e.g., oxidative phosphorylation). During exercise, metabolic production of CO2 increases and therefore adds a "volatile acid" load on the body. 2. Exercise-induced production of lactic acid in the working muscle. Although controversy exists, it is likely that the production of lactic acid (lactate) in the muscle during heavy, very heavy, and severe exercise is a key factor that causes the decrease in muscle pH. 3. Exercise-induced ATP breakdown in the working muscles. The breakdown of ATP for energy during muscle contraction results in the release of H+ ions. The breakdown of ATP alone during exercise can be an important source of H+ ions in contracting muscles.

#3 How tightly regulated is the pH of arterial blood?

The pH scale is a measure of the relative concentration of hydrogen ions (H+) and hydroxyl (OH-) ions. A neutral solution has equal amounts of H+ and OH- (i.e., pH - 7.0). The survival range of the pH of arterial blood is 7.0-7.8). If the pH of arterial blood drops below the normal value of 7.4, the resulting condition is termed acidosis. In contrast, if the pH increases above 7.4, blood alkalosis occurs.

#4 Why is the maintenance of acid-base homeostasis important to physical performance?

This is because acidosis can impair exercise performance. It can contribute to muscle fatigue. Although increasing blood buffering capacity may improve performance in some events. High-intensity exercise lasting 45 seconds produces large amounts of H+. In some sports, the risk of acid-base disturbance is directly linked to the effort of the competitor. Playing at 100% effort increases the risk of acidosis. Sprint to finish in distance events also increases the risk of acidosis. High intensity exercise also results in the production of lactic acid and increased H+ in muscle fibers and blood. Increased H+ can impair performance. It inhibits glycolytic and TCA enzyme activity (ATP production). H+ can also impair muscle contraction by competing with Ca2+ for binding sites on troponin. Acid-base balance is maintained by buffers: release H+ ions when pH is high and accept H+ ions when pH is low.

#1 Define buffer.

a compound that resists pH change. A buffer resists pH change by removing hydrogen ions when the hydrogen ion concentration increases, and releasing hydrogen ions when the hydrogen ion concentration falls. Buffers often consist of a weak acid and its associated base (called a conjugate base). The ability of individual buffers to resist pH change is dependent upon two factors. First, individual buffers differ in their intrinsic physiochemical ability to act as buffers. Simply stated, some buffers are better than others. A second factor influencing buffering capacity is the concentration of the buffer present. The greater the concentration of a particular buffer, the more effective the buffer can be in preventing pH change.

#1 Define pH.

a measure of the acidity of a solution; calculated as the negative log10 of the [H+] in which 7 is neutral; values that are >7 are basic and <7 are acidic. The pH of a solution is defined as the negative logarithm of the hydrogen ion concentration (H+).

Quiz #22 Metabolic acidosis can result from the overproduction of ketoacids, which can occur

in uncontrolled diabetes.

#1 Define alkalosis.

an abnormal increase in blood concentration of OH- ions, resulting in a rise in arterial pH above 7.45. As the hydrogen ion concentration decreases, pH increases and the solution becomes more basic (alkalotic), this condition is alkalosis.

#1 Define acidosis.

an abnormal increase in blood hydrogen ion concentration (i.e., arterial pH below 7.35). When the H+ concentration of the blood increases, pH decreases resulting in the condition of acidosis.

Quiz #11 The ability of histidine to buffer hydrogen ions is because histidine contains

an ionizable group.

Quiz #12 The respiratory system works in the regulation of acid-base balance by regulating

arterial PCO2.

Quiz #16 Which of the extracellular buffers contributes the most to the cell's buffering capacity?

bicarbonate

Quiz #9 The most important of the blood buffers is/are

bicarbonate.

#1 Define acid.

compounds capable of giving up hydrogen ions into solution. An acid is defined as a molecule that releases hydrogen ions and thus can raise the hydrogen ion concentration of a solution above that of pure water. Acids that give up hydrogen ions (ionize) more completely are called strong acids (e.g., lactic acid).

#1 Define base.

compounds that ionize in water to release hydroxyl ions (OH-) or other ions that are capable of combining with hydrogen ions. In contrast to acids, a base is a molecule that is capable of combining with hydrogen ions, which would lower the hydrogen ion concentration of the solution. Bases that ionize more completely are defined as strong bases (e.g., bicarbonate "HCO3-").

Quiz #20 Athletes involved in sports that require high intensity exercise have experimented with numerous supplements to improve buffering capacity and enhance performance. Which of the following supplements has NOT been shown to improve muscle buffering capacity?

hydrogen peroxide

Quiz #29 Studies reveal that exercise training improves muscle buffering capacity. Which of the following exercise-induced changes is NOT responsible for training-induced improvements in muscle buffering capacity?

increased muscle levels of citrate synthase

Quiz #23 Sodium bicarbonate has been ingested by athletes before competition in an effort to improve performance by

increasing blood buffering capacity.

Quiz #17 The first line of defense in protecting against pH change during exercise is

intracellular buffers within muscle fibers.

Quiz #21 The most common and strongest acid produced in skeletal muscle during heavy exercise is ________________ acid.

lactic

Quiz #2 Acids are defined as

molecules that release hydrogen ions (H+).

Quiz #1 An increase in blood levels of carbon dioxide results in a decrease in blood pH because an increase in PCO2

reacts with water to form carbonic acid, which dissociates to release H+.

Quiz #26 At rest, voluntary hyperventilation can result in ___________ due to ____________.

respiratory alkalosis; decreased blood levels of carbon dioxide

Quiz #28 Which of the following organs plays an important role in acid-base balance during exercise?

respiratory system

Quiz #3 The pH scale is a measure of

the relative concentration of hydrogen ions and hydroxyl ions in a solution.