Exam 1 Answers BISC 307L - General Physiology February 8, 2010 4 pts. 1. Which one of the following statements regarding an increase in blood osmolarity is true? (d) a. It would tend to trigger an increase in the rate of urine production. b. It can be caused by excessive consumption of water. c. It can cause fatal swelling of brain cells. d. It can occur as a result of dehydration. e. None of the above is true. 2. Background Information: Blood consists of numerous cells (mostly hemoglobin-containing red blood cells, RBCs) suspended in a clear, straw-colored fluid called plasma. RBCs can be separated from the plasma by spinning a blood sample in a centrifuge. Assume, for simplicity, that the RBC membrane is permeable to water but impermeable to any solutes within the RBC. Normal plasma osmolarity is 300 mOsm/L. Scenario: Late at night in the emergency room, the resident doctors took advantage of a quiet period to catch some sleep. They told the undergraduate pre-med volunteer to wake them if a patient arrived. Soon after, a woman who appeared to be seriously dehydrated was brought to the ER. Wanting to impress the residents, the student volunteer decided to handle the case himself. He tried giving the patient water to drink, but she vomited. He then inserted an intravenous catheter into the patient’s arm vein and gave her a liter of sterile distilled water. Her condition quickly deteriorated. 4 pts. 2-1) What happened to the osmolarity of the patient’s plasma immediately after the intravenous infusion of water? (b) a. Plasma osmolarity increased b. Plasma osmolarity decreased c. There was no change in plasma osmolarity 5 pts. 2-2) One of the residents woke up and realized what the student had done. She immediately took a blood sample and spun it in the centrifuge. She was alarmed to see that the plasma was not straw-colored but pink. Briefly explain why the plasma had an abnormal pink color. ANS: The sudden drop in plasma osmolarity caused water to enter RBCs by osmosis, causing them to swell. Some RBCs burst (osmotic lysis), releasing their hemoglobin into the plasma. 4 pts. 2-3) If the resident wanted to intravenously administer 1 liter of a sucrose solution to minimize the damage caused by the student, which one of the following concentrations of sucrose would be the best choice? (c) a. 150 mM b. 300 mM c. 600 mM Page 1 of 5Sweat 3. The drawing at right represents a sweat gland in the skin. Epithelial cells in lower part of the gland, like cell A, secrete Na+, Cl-, and H2O into the lumen, filling the lumen with a NaCl solution that is isotonic with the blood plasma. Epithelial cells in the upper part of the gland, like cell B, transport Na+ and Cl-, but not H2O, out of the lumen to produce sweat, a NaCl solution that is hypotonic to the blood plasma. Assume that in the upper part of the gland, tight junctions are impermeable Na+, Cl-, and H2O. The following questions pertain to cell B. Skin surface Cell 3-1) Where are Na+-K+ pumps located in cell B? (b) a. In the apical membrane b. In the basolateral membrane c. In both apical and basolateral membranes 3-2) Where are CFTR Cl- channels located in cell B? (c) a. In the apical membrane b. In the basolateral membrane c. In both apical and basolateral membranes 3-3) Where are epithelial Na+ channels* located in cell B? (a) (*Epithelial Na+ channels are Na+-selective, always-open leakage channels) a. In the apical membrane b. In the basolateral membrane c. In both apical and basolateral membranes 4. Indicate whether each of the following statements is true or false by writing the word “True” or “False” in the blank (do not mark with T or F). ANS: a-F, b-F, c-T, d-T ________ a. Protein kinase C is activated by cAMP. ________ b. Inhibiting phospholipase A2 would block the synthesis of all eicosanoids. ________ c. Inhibiting lipoxygenase would block the conversion of arachidonic acid to leukotrienes. ________ d. Receptors for inositol trisphosphate (IP3) are located on endoplasmic reticulum membranes. 5. A particular hormone elicits six different responses in a target cell, all mediated completely by the cAMP system. A drug is discovered that eliminates one of these cellular responses, but not the other five. Which of the following, if any, could the drug be blocking? Briefly explain your answer. • the hormone’s receptors • adenylyl cyclase • GS protein • cAMP ANS: The drug could not be blocking any of these. If all 6 responses are mediated by the cAMP system, then blocking any of these 4 steps would eliminate all 6 responses. This is because the signaling cascade for all 6 responses is identical from hormone-receptor binding through the formation of cAMP and activation of protein kinase A. Thus, the drug must be acting at some step beyond the kinase, for example at the level of the phosphorylated protein that mediates the blocked response. Hypotonic NaCl Isotonic NaCl Cell A B 4 pts. 4 pts. 4 pts. 4 pts. 10 pts. Page 2 of 54 pts. 5 pts. 4 pts. 4 pts. 6. Which one of the following statements is correct? The statements pertain to the resting membrane potential in a typical neuron. (d) a. The resting potential is closer to ENa than to EK. b. At the resting potential, there is no movement of ions across the plasma membrane. c. The permeability of the membrane to Cl- is greater than the permeability of the membrane to K+. d. Ion transport by the Na+-K+ pump is equal and opposite to the leakage of ions through Na+ and K+ channels. 7. Some epithelial cells are treated with a drug that blocks Cl- ion channels, and in response, the cells depolarize slightly. Which one of the following is a correct conclusion about the normal state of these cells, before the drug was applied? (c) a. The cells do not actively transport Cl- ions. b. Cl- ions are actively transported into the cells. c. Cl- ions are actively transported out of the cells. d. Insufficient information is given to determine if and how Cl- ions are transported. 8. The length of axon shown below was removed intact from a patient with multiple sclerosis, the most common demyelinating disease. Assume the axon is normal in every way, except that the two myelin segments in the middle have disappeared. In particular, the number, type, and density of ion channels are normal all along the axon, even in the demyelinated segment. When the axon generates action potentials, they travel to the