Problem 5
Oxygen Consumption during Exercise A sedentary adult consumes about \(0.05 \mathrm{~L}\) of \(\mathrm{O}_{2}\) in 10 seconds. A sprinter running a \(100 \mathrm{~m}\) race consumes about \(1 \mathrm{~L}\) of \(\mathrm{O}_{2}\) in 10 seconds. After finishing the race, the sprinter continues to breathe at an elevated (but declining) rate for some minutes, consuming an extra \(4 \mathrm{~L}\) of \(\mathrm{O}_{2}\) above the amount consumed by the sedentary individual. a. Why does the need for \(\mathrm{O}_{2}\) increase dramatically during the sprint? b. Why does the demand for \(\mathrm{O}_{2}\) remain high after the sprinter finishes the race?
Problem 6
Thiamine Deficiency and Brain Function Individuals with thiamine deficiency show some characteristic neurological signs and symptoms, including loss of reflexes, anxiety, and mental confusion. Why might thiamine deficiency manifest as changes in brain function?
Problem 7
Potency of Hormones Under normal conditions, the human adrenal medulla secretes epinephrine \(\left(\mathrm{C}_{9} \mathrm{H}_{13} \mathrm{NO}_{3}\right)\) at a rate sufficient to maintain a concentration of \(10^{-10} \mathrm{M}\) in circulating blood. To appreciate what that concentration means, calculate the volume of water that you would need to dissolve \(1.0 \mathrm{~g}\) (about 1 teaspoon) of epinephrine to a concentration equal to that in blood.
Problem 8
Regulation of Hormone Levels in the Blood The half-life of most hormones in the blood is relatively short. For example, when researchers inject radioactively labeled insulin into an animal, half of the labeled hormone disappears from the blood within \(30 \mathrm{~min}\). a. What is the importance of the relatively rapid inactivation of circulating hormones? b. In what ways can the organism make rapid changes in the level of a circulating peptide hormone?
Problem 9
Water-Soluble versus Lipid-Soluble Hormones On the basis of their physical properties, hormones fall into one of two categories: those that are very soluble in water but relatively insoluble in lipids (e.g., epinephrine) and those that are relatively insoluble in water but highly soluble in lipids (e.g., steroid hormones). In their role as regulators of cellular activity, most water-soluble hormones do not enter their target cells. The lipid-soluble hormones, by contrast, do enter their target cells and ultimately act in the nucleus. What is the relationship between solubility, the location of receptors, and the mode of action of these two classes of hormones?
Problem 10
Metabolic Differences between Muscle and Liver in a "Fight-or-Flight" Situation When an animal confronts a "fightor-flight" situation, the release of epinephrine promotes glycogen breakdown in the liver and skeletal muscle. The end product of glycogen breakdown in the liver is glucose; the end product in skeletal muscle is pyruvate. a. What is the reason for the different products of glycogen breakdown in the two tissues? b. What is the advantage of these specific glycogen breakdown routes to an animal that must fight or flee?
Problem 11
Excessive Amounts of Insulin Secretion: cause excessive production of insulin by \(\beta\) cells. Affected individuals exhibit shaking and trembling, weakness and fatigue, sweating, and hunger. a. What is the effect of hyperinsulinism on the metabolism of carbohydrates, amino acids, and lipids by the liver? b. What are the causes of the observed symptoms? Suggest why this condition, if prolonged, leads to brain damage.
Problem 12
Thermogenesis Caused by Thyroid Hormones Thyroid hormones are intimately involved in regulating the basal metabolic rate. Liver tissue of animals given excess thyroxine shows an increased rate of \(\mathrm{O}_{2}\) consumption and increased heat output (thermogenesis), but the ATP concentration in the tissue is normal. Different explanations have been offered for the thermogenic effect of thyroxine. One is that excess thyroxine causes uncoupling of oxidative phosphorylation in mitochondria. How could such an effect account for the observations? Another explanation suggests that thermogenesis is due to an increased rate of ATP utilization by the thyroxine-stimulated tissue. Is this a reasonable explanation? Why or why not?
Problem 13
Function of Prohormones What are the possible advantages of synthesizing hormones as prohormones?
Problem 14
Sources of Glucose during Starvation The typical human adult uses about \(160 \mathrm{~g}\) of glucose per day. Of this, the brain alone uses \(120 \mathrm{~g}\). The body's available reserve of glucose \((\sim 20 \mathrm{~g}\) of circulating glucose and \(\sim 190 \mathrm{~g}\) of glycogen) is adequate for about one day. After the glucose reserve has been depleted during starvation, how does the body obtain more glucose?
