NATIONAL UNIVERSITY OF SINGAPORE
FACULTY OF MEDICINE
First Professional Examination for the degrees of M.B.,B.S.
Systems Biology
Wednesday, 26 April 2000 Time: 9.00am - 12 noon
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Instructions to Candidates
There are 9 questions in this paper. Questions 1-6 (Section A) are short questions while questions 7-9 (Section B) are long questions. Each long question carries 20 marks and each short question carries 10 marks. All questions must be answered.
Section A: Answer all six questions (1 hr 30 mins)
1. Answer both parts of the question:
a. Discuss briefly the similarities and differences between eicosanoids and hormones.
b. What are the effects of anti-inflammatory steroids and aspirin on prostaglandin biosynthesis? Where
do they act along the biosynthetic pathway?
2. Write a concise account of the role of vitamin K in blood coagulation and explain how its deficiency would
affect the coagulation process.
3. Explain concisely how the kidney is capable of producing urine having an osmolality greater than that of
plasma. How does this help in the regulation of plasma osmolality?
4. Discuss the regulation of respiration by central and peripheral chemoreceptors.
5. Give a concise account of how gastric acid secretion is regulated physiologically. Explain, giving examples,
how acid secretion may be reduced or blocked to treat peptic ulcer disease.
6. Answer both parts of the question:
a. Olestra is an indigestible oil used as a fat substitute in certain foods. It has been observed to decrease
the absorption of vitamin E and beta-carotene from the gut but not the absorption of vitamin B2 or
vitamin C. Suggest an explanation for this observation.
b. Outline the roles of 2 of the above vitamins in metabolism.
Section B: Answer all three questions (1 hr 30 mins)
7. A patient, lying supine and strapped to a tilt table, had a blood pressure of 120/80 mmHg and a heart rate
of 70/min. Immediately after assuming a vertical position, the blood pressure was found to be 100/70 mm
Hg and the heart rate was 70/min. Fifteen minutes later, the blood pressure was still 100/70 and heart rate
was 70/min.
a. Explain why the blood pressure dropped immediately when the patient assumed a vertical position.
b. What changes in the heart rate would be expected in a normal individual after assumption of a vertical
posture from a supine position? What possible reasons could explain why the heart rate of the
patient did not change.
c. What changes in the blood pressure would be expected in a normal individual 15 minutes after
assuming a vertical posture from a supine position? Explain your answer.
8. A 35 year old woman stops menstruating after having had fairly normal menses for 21 years.
a. If her amenorrhea is due to estrogen deficiency, what hormonal measurement(s) would help
distinguish between estrogen deficiency due to ovarian disease from that due to pituitary disease?
Explain your answer.
b. If the amenorrhea is due to uterine disease, what functional changes, if any, may exist in the patient's
hypothalamic-pituitary-ovarian axis? Suggest how sex steroids (estrogens and progestins) may be
used to confirm that the uterus is indeed the organ where the problem lies.
c. If the menstrual disturbance is accompanied by lactation, suggest a probable cause for the patient's
problem and explain why pregnancy is not a likely cause.
9. A 15 year old girl was admitted to hospital for shortness of breath, excessive thirst, and excessive
urination. She was found to be breathless, with a pulse rate of 110/min and a blood pressure of 80/50.
Plasma glucose level was high at 20 mmol/L, plasma bicarbonate was low at 13 mmol/L, and arterial pH
was low at 7.24. Glucose and ketones were present in large amounts in the urine.
a. Assuming that she had insulin deficiency, briefly describe the biochemical basis of her acidosis and
ketosis.
b. Explain her shortness of breath, high pulse rate, and low blood pressure.
c. Do you think an agent that stimulates insulin secretion would be effective treatment for this patient?
Explain your answer.
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