D313 Anatomy and Physiology II - Set 4 - Part 3

Correct Answer: Carbonic anhydrase

Option d is correct because carbonic anhydrase is the enzyme inside red blood cells that catalyzes the dissociation of carbonic acid into hydrogen ions and bicarbonate ions for carbon dioxide transport. Option a is incorrect because hemoglobin is a transport protein that carries oxygen and can bind some carbon dioxide as carbaminohemoglobin, but it does not catalyze the bicarbonate-forming reaction. Option b is incorrect because prothrombin is a clotting factor in the coagulation cascade and has no role in carbon dioxide transport or bicarbonate ion formation inside red blood cells. Option c is incorrect because pancreatic lipase is a digestive enzyme that breaks down triglycerides in the small intestine and has no involvement in gas transport or bicarbonate production.

Correct Answer: Carbaminohemoglobin

Option c is correct because carbaminohemoglobin is the specific compound formed when carbon dioxide molecules bind directly to hemoglobin proteins inside red blood cells for transport to the lungs. Option a is incorrect because bicarbonate is an ion formed from the chemical conversion of carbon dioxide inside red blood cells and transported in plasma, not a compound bound to hemoglobin. Option b is incorrect because oxyhemoglobin is the compound formed when oxygen binds to hemoglobin, not carbon dioxide, and it represents the oxygen-loaded state of the hemoglobin molecule. Option d is incorrect because carbonic acid is an intermediate molecule formed when carbon dioxide combines with water inside red blood cells, and it quickly dissociates into hydrogen and bicarbonate ions.

Correct Answer: The concentration gradient as bicarbonate accumulates inside the cell

Option a is correct because as carbonic anhydrase produces bicarbonate ions inside red blood cells, the concentration builds until the gradient drives bicarbonate out into the plasma passively. Option b is incorrect because the movement of bicarbonate out of red blood cells follows its concentration gradient and does not require active transport pumps consuming ATP for this process. Option c is incorrect because the chloride shift and bicarbonate movement are driven by local chemical gradients within the blood, not by hormonal signals from distant endocrine glands. Option d is incorrect because osmotic pressure differences relate to water movement across membranes, not the specific ion exchange of bicarbonate leaving and chloride entering red blood cells.

Correct Answer: Bicarbonate ions first, then carbaminohemoglobin, then dissolved in plasma

Option c is correct because bicarbonate ions in plasma carry the most carbon dioxide, followed by carbaminohemoglobin bound to hemoglobin, with dissolved gas in plasma being the least common method. Option a is incorrect because dissolved carbon dioxide in plasma actually accounts for the smallest portion of total carbon dioxide transport, not the largest as this ordering suggests. Option b is incorrect because carbaminohemoglobin carries a moderate amount of carbon dioxide but is not the most common method, as bicarbonate ions transport the largest proportion overall. Option d is incorrect because this places dissolved plasma gas first and bicarbonate second, which reverses the actual proportions since bicarbonate ions are the dominant transport form.

Correct Answer: Hydrogen ions and bicarbonate ions

Option d is correct because carbonic anhydrase catalyzes the dissociation of carbonic acid into hydrogen ions and bicarbonate ions inside red blood cells, enabling carbon dioxide transport as bicarbonate. Option a is incorrect because oxygen and water are not the products of carbonic anhydrase activity; the enzyme specifically acts on carbonic acid to produce hydrogen ions and bicarbonate ions. Option b is incorrect because hemoglobin subunits and iron atoms are structural components of the hemoglobin protein and are not produced by any enzymatic reaction involving carbonic anhydrase. Option c is incorrect because carbonic anhydrase does not produce carbon dioxide gas and plasma proteins; instead it processes carbonic acid that was formed from carbon dioxide and water combining.

Correct Answer: Higher temperature and lower pH

Option c is correct because active muscles generate heat and produce acidic byproducts that raise temperature and lower pH, both of which reduce hemoglobin's oxygen affinity and promote oxygen release. Option a is incorrect because lower temperature would actually increase hemoglobin's affinity for oxygen, making it hold on tighter rather than releasing it to the tissues that need it. Option b is incorrect because while higher temperature is correct, higher pH means more alkaline conditions which would increase oxygen affinity rather than promoting the release that active muscles require. Option d is incorrect because while lower pH is correct for promoting oxygen release, lower temperature would counteract this by increasing hemoglobin's grip on oxygen molecules in the opposite direction.

Correct Answer: The Bohr effect

Option a is correct because the Bohr effect specifically describes how decreases in pH and increases in carbon dioxide concentration reduce hemoglobin's affinity for oxygen, promoting release to active tissues. Option b is incorrect because the Haldane effect describes how oxygen binding affects hemoglobin's ability to carry carbon dioxide, which is a related but distinct phenomenon from pH-driven oxygen release. Option c is incorrect because the Frank-Starling mechanism describes how the heart adjusts its stroke volume based on venous return, a cardiac function unrelated to hemoglobin oxygen binding dynamics. Option d is incorrect because the Henderson-Hasselbalch principle is a chemistry equation relating pH to acid-base buffer systems and does not describe the oxygen-hemoglobin dissociation relationship directly.

Correct Answer: Hemoglobin loads oxygen in the lungs and releases it in the tissues

Option c is correct because hemoglobin picks up oxygen in the lungs where oxygen concentration is high and releases it in the tissues where oxygen is being consumed and concentration is lower. Option a is incorrect because this reverses the correct pattern; hemoglobin does not load oxygen at the tissue level since tissues consume oxygen rather than providing it for hemoglobin binding. Option b is incorrect because the liver and kidneys are not the primary sites of oxygen loading and unloading; the lungs are where oxygen enters the blood and tissues are where it gets delivered. Option d is incorrect because while the heart pumps oxygenated blood, hemoglobin does not selectively load oxygen in the heart or release it exclusively in the brain during normal circulation.

Correct Answer: Resting muscles create conditions where hemoglobin holds oxygen more tightly

Option c is correct because resting muscles are cooler and have a higher pH than active muscles, conditions that increase hemoglobin's affinity for oxygen so it holds on more tightly. Option a is incorrect because resting muscles produce less heat and fewer acidic byproducts, creating conditions that reduce oxygen release from hemoglobin rather than increasing it compared to active tissue. Option b is incorrect because temperature and pH always influence hemoglobin's oxygen binding behavior, and the conditions in resting versus active tissue create measurably different oxygen delivery patterns. Option d is incorrect because hemoglobin never completely stops binding oxygen under normal physiological conditions; resting muscles simply shift the balance toward tighter binding rather than total cessation.

Correct Answer: Hemoglobin would release oxygen more readily throughout the body due to low pH

Option a is correct because the Bohr effect dictates that lower blood pH reduces hemoglobin's oxygen affinity, causing it to release oxygen more readily even in tissues that may not need extra delivery. Option b is incorrect because blood pH is one of the most significant factors affecting hemoglobin's oxygen affinity, and changes in acidity always produce measurable shifts in oxygen delivery patterns. Option c is incorrect because hemoglobin does not permanently lose its oxygen-carrying ability due to acidosis; the reduced affinity is a reversible change that corrects when pH returns to normal levels. Option d is incorrect because acidic conditions decrease hemoglobin's grip on oxygen rather than strengthening it, so more oxygen would be released to tissues, not less, under low pH conditions.