BISC 307 – Spring 2009 Exam 4 Answers 6 pts. 1. Write a 1, 2, or 3 in each blank to indicate whether these characteristics of acquired immunity apply to 1) antibody-mediated immunity, 2) cell-mediated immunity, or 3) both. ________ a. involved in rejection of transplanted tissue ANS: a-2, b-1, c-3, d-3, e-2, f-1 ________ b. requires binding of a lymphocyte to a free extracellular antigen ________ c. triggered by binding specific antigens to complementary lymphocyte receptors ________ d. involves formation of memory cells in response to initial exposure to antigen ________ e. primarily defends against virus-infected host cells ________ f. protects primarily against bacterial invaders 3 pts. 2. Which one of the following statements about class II MHC proteins is false? (c) a. They are found on the surface of B lymphocytes. b. They are found on the surfaces of dendritic cells. c. They are required for B-cells to bind foreign antigens. d. They are used by macrophages to present foreign antigens to helper T-cells. e. They are required for helper T-cells to stimulate the activity of cytotoxic T-cells. 4 pts. 3. Indicate whether each of the following statements is true or false by writing the word “True” or “False” in the blank. Do not write T or F. ANS: a-T, b-T, c-T, d-F ________ a. Activated helper T-cells stimulate cytotoxic T-cells by secretion of interleukin-2. ________ b. Plasma membranes of macrophages contain class I MHC proteins, class II MHC proteins, and CD28 proteins. ________ c. Macrophages secrete interleukin-1 to activate helper T-cells. ________ d. CD8-positive cells bind to antigens presented by class II MHC proteins. 4 pts. 4. Which of the following immune system defects would you expect to see in a strain of mutant mice with defective Fas receptors? Write as many numbers in the box as you think apply. Do not guess; points will be deducted for wrong answers. ANS: a, c, d, f a. abnormally high secretion of IgG b. low numbers of activated CD4-positive cells c. enlarged lymph nodes d. low production of sperm e. reduced secretion of IgM f. symptoms of autoimmune disease 4 pts. 5. If blood flow to the left lung is completely blocked by an embolism in the pulmonary artery, which one of the following would most likely occur? (d) a. Systemic arterial PO2 will be normal. b. Plasma pH will be higher than normal. c. Systemic arterial PCO2 will be lower than normal. d. PO2 in alveoli in the right lung will be approximately equal to PO2 in the inspired air. e. PO2 in alveoli in the right lung will be approximately equal to PO2 in the pulmonary vein. 16 pts. 6. Trophoblast cells in the fetal part of the placenta come into close contact with maternal cells in the endometrium of the uterus. About 10 years ago, researchers in Virginia reported that these trophoblast cells express FAS ligand. What might be accomplished by this expression of FAS ligand, and why may this be necessary? ANS: The FAS ligand on the fetal trophoblast cells could bind to FAS receptors on the surface of lymphocytes, triggering apoptosis of the lymphocytes. This may be necessary because the genetic makeup of fetal tissue is different than that of the mother, and thus the fetal tissue should be subject to attack by the mother’s immune system. Expression of FAS ligand on trophoblastic cells would neutralize this immune attack, helping to make the fetal placenta an immunologically privileged site. 4 pts. 7. Indicate whether each of the following statements is true or false by writing the word “True” or “False” in the blank. Do not write T or F. ANS: a-T, b-T, c-T, d-F ________ a. Surface tension in the alveolar fluid of the lung is less at the end of expiration than it is at the end of inspiration. ________ b. Near the end of inspiration, intrapleural pressure is more negative than it is near the end of expiration. ________ c. During acidosis, the affinity of hemoglobin for O2 is decreased. ________ d. Central chemoreceptors in the respiratory center in the medulla are directly stimulated by CO2 in the cerebrospinal fluid, not H+ ions. 3 pts. 8. Which one of the following would most likely cause an increase in the reabsorption of isosmotic fluid in the proximal tubule? (e) a. oxygen deprivation b. increased blood pressure in peritubular capillaries c. decreased protein concentration in peritubular capillaries d. increased extracellular fluid volume due to infusion of isotonic NaCl e. increased percentage of plasma volume filtered out of glomerular capillaries 3 pts. 9. In the hemoglobin-O2 dissociation curve shown on the right, the shift from curve A to curve B could most likely be caused by… (d) a. an increase in pH. b. a decrease in concentration of 2,3-diphosphoglycerate. c. replacing β chains with γ chains. d. strenuous exercise. e. a decrease in temperature. 8 pts. 10. A 12-year-old boy is brought to the emergency department because of a severe asthmatic attack. He is breathing rapidly, making wheezing sounds, and his fingertips and lips are blue. As the attending physician takes an arterial blood sample for respiratory gas measurements, you (an undergraduate volunteer) impress her by correctly predicting that both arterial PO2 and PCO2 will be low. She invites you to briefly explain, to the medical students in attendance, the sequence 2of events by which a severe asthmatic attack would cause low arterial PO2 and PCO2. Having just studied the respiratory system for Exam 4, you confidently say… ANS: During an asthmatic attack, bronchoconstriction increases airway resistance, leading to hypoventilation of alveoli and decreased arterial PO2. The hypoxemia stimulates peripheral chemoreceptors in the carotid and aortic bodies, which provide excitatory input to the respiratory center in the medulla. This excitation causes rapid breathing (hyperventilation), which removes CO2 from the body faster than it is produced by metabolism, so PCO2 decreases. 4 pts. 11. Items a-d below refer to the drawing of the juxtamedullary nephron on the right. In each blank, write the letter or letters that identify the appropriate part of the nephron. Each lettered item may be used once, more than once, or not at all. Note that in some cases, the correct answer may include more than one letter. ANS: a-B; b-A,D,E,F; c-D; d-E,F; (0.5 pts. each) _______________ a. Site(s) at which tubular fluid osmolarity exceeds plasma osmolarity by the greatest amount. _______________