BISC 307 – Spring 2009 Exam 3 Answers 5 pts. 1. Match each of the events of the ovarian cycle (on the left) with the day of the cycle (on the right) when that event occurs. Each day should be used only once. _____ 1. Progesterone from the corpus luteum peaks (d) a. Day 1 _____ 2. Estrogen positive feedback peaks (c) b. Day 7 _____ 3. One follicle becomes dominant (b) c. Day 13 _____ 4. Estrogen and progesterone are both decreasing (e) d. Day 21 _____ 5. Increase in FSH stimulates follicles to begin secreting estrogen (1) e. Day 26 7 pts. 2. There are 5 principal reproductive hormones in women: GnRH, FSH, LH, estrogen, and progesterone. State which of these could be used for hormone replacement therapy to treat the symptoms of menopause, and which (if any) could not be used for this purpose. Briefly explain your answer. ANS: Estrogen and progesterone could be used to treat the symptoms of menopause, but GnRH, FHS, and LH could not be used. During menopause, the ovaries no longer contain follicles capable of responding to FSH or LH. Therefore neither of these hormones will have any effect. Likewise GnRH, which stimulates release of FSH and LH, will not have any effect. Since the symptoms of menopause are caused by insufficient estrogen and progesterone, only direct replacement of these hormones would be effective. 5 pts. 3. Which one of the following changes would cause the greatest increase in O2 consumption in cardiac muscle cells? (d) a. a decrease in aortic pressure b. a decrease in heart rate c. a decrease in contractility d. an increase in size of the heart e. a decrease in Na+ influx during the action potential 8 pts. 4. In most places in the body, local hypoxia causes arterioles to dilate, which increases the flow of blood and oxygen to the hypoxic area. In the lung, however, the opposite is true, i.e., hypoxia causes constriction of pulmonary arterioles. Describe how this behavior of pulmonary arterioles helps explain why the foramen ovale in a baby’s heart closes quickly (within a minute) of birth. ANS: Because the lungs are not ventilated during fetal life, tissue there is relatively hypoxic and so pulmonary arterioles are constricted. This causes a high resistance in the pulmonary circulation, so little or no blood flows into the lungs. Instead, the higher pressure of the right side of fetal heart causes blood to pass from the right atrium to the left atrium through the foramen ovale. At birth, when the newborn baby inflates its lungs to take the first breaths, oxygenation of the lung triggers sudden dilation of pulmonary arterioles. The resistance of the pulmonary circulation falls, and so blood from the right ventricle flows into the lungs. The increased return to the left side of the heart through the pulmonary vein increases pressure on the left side. In addition, decreased flow of blood from the placenta causes a decrease in pressure on Page 1 of 5the right side of the heart. This reversal of the pressure gradient between the right and left sides of the heart closes the one-way valve to seal the foramen ovale. 4 pts. 5. In each of the blanks below, clearly write either a “greater than” sign (>) or a “less than” sign (<) as necessary to make the statements read correctly. During ventricular filling, ventricular pressure must be ________ atrial pressure, whereas during ventricular ejection, ventricular pressure must be ________ aortic pressure. During isovolumic ventricular contraction and relaxation, ventricular pressure is ________ than atrial pressure and ________ aortic pressure. ANS: < (less than), > (greater than), > (greater than), < (less than) 6 pts. 6. The upper trace in the diagram on the right shows an action potential in a contractile cardiac muscle cell. On the same time scale, traces a, b, and c show the relative permeabilities for three different ions. Identify the ions in the blanks below. Vm a. Ion a is _____________. a b. Ion b is _____________. c. Ion c is _____________. bcANS: a is K+, b is Na+, c is Ca2+ Time → 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-F, b-F, c-F, d-F _________ a. A drug that increased the open time of G-protein activated, inwardly rectifying K+ channels would increase the frequency of action potentials in pacemaker cells of the sinoatrial node. _________ b. A drug that increased the open time of hyperpolarization-activated, cyclic nucleotide-gated channels would decrease the frequency of action potentials in pacemaker cells of the sinoatrial node. _________ c. If contractile cardiac muscle cells expressed K+ channels similar to those in conventional nerves, the duration of the cardiac muscle action potential would be even longer than it is. _________ d. Under resting conditions, both sympathetic and parasympathetic nerves to the heart are active, and sympathetic influences predominate over parasympathetic influences. Page 2 of 54 pts. 8. Write the word “Increase,” “Decrease,” or “No Change” in the blank to indicate the effect of each of the following changes on venous return to the heart. ANS: a-I, b-D, c-I, d-D ______________ a. increased skeletal muscle activity ______________ b. decreased activity in sympathetic nerves to veins ______________ c. increased rate and depth of breathing ______________ d. increased atrial pressure due to a leaky atrioventricular valve 7 pts. 8 pts. 8 pts. 9. Here’s some useful background information: Occasionally, a Purkinje fiber may become overly excitable and depolarize more rapidly than the SA node. This premature action potential spreads to the ventricles before the SA node can initiate a normal action potential. The result is a PVC, or premature ventricular contraction. The interval between a PVC and the next normal beat is longer than the average interval between heartbeats. Here’s the question: The stroke volume of the next heartbeat after a PVC is usually larger than normal. Briefly explain why. ANS: Because the interval between a PVC and the next normal beat is longer than usual, the heart fills for a longer period of time, resulting in a greater end-diastolic volume. According to the Starling curve, the subsequent stroke volume will be correspondingly larger. 10. A student reported to the health center complaining of weakness and an abnormal heartbeat. In a physical exam, her