You're working at the medical examiner's office at San Francisco County Hospital. It has been a particularly light day, with only one homicide and a dead chipmunk that you checked over for rabies. The chipmunk didn't have rabies, and you're ready to go home. Just as you're flipping the switch, you get a call from your secretary. "Francesca," he says. "We've got a dead kid up here that you'll want to look at right away. Might be foul play.
Thinking of your four-year old daughter waiting for you at home, you grimace. "OK Jon, I'm heading to the morgue." Performing autopsies on kids is the least favorite part of your job. But you are paid to solve medical mysteries, and it looks like you've got one here.
In the morgue, you find the report from the hospital. Glancing over it, you notice a narrative of the girl's last hours and read it carefully: At 10 AM, mother returns from the store to find girl with dizziness, vomiting, and abdominal pain. Mother put girl to bed. Ten minutes later she sees that the child’s condition has worsened and she calls an ambulance. The EMTs notice that the girls heart beat is very slow (bradycardia) and arrhythmic, and immediately take her to hospital. At noon her heart beat has stopped and she is declared dead.
A police report states the following: The parents discovered that the girl had been playing in the yard and had made a ‘salad’ of leaves that she had found growing there, which she fed to her dolls and stuffed toys.
You are curious. You visit the yard and find the parents had planted a wild flower garden to attract the butterflies. Planted in the garden you find buddleia and milkweeds, but nothing that looks dangerous. You continue your investigation by looking at the autopsy report.
You read that:
The girl died within two hours of first vomiting, immediate cause of death was heart stop.
Before death blood pressure was 89/54 mmHg and a heart rate of 42 beats per minute.
Blood work was unremarkable.
ECG demonstrated complete atrioventricular block.
You order a more detailed analysis of the cellular components in the heart cells of the girl. The report reveals elevated levels of cellular ATP and Na+ and reduced levels of cellular K+. Cellular levels of other ions are unremarkable. Cellular levels of Na+, K+ and ATP are also normal in the lung and in the gut.
You know that cardiac cells have both muscular and neuronal properties, and so you suspect that whatever killed the girl interfered with one of these two activities. You order an electrophysiological analysis of the heart cells and find that their resting membrane potential is elevated, which is known to cause the spontaneous generation of action potentials and misfiring of the cardiac muscles.
Of the following options, choose the one that is the best explanation for your observation and explains why the girl died. Reject all the rest. For full points you must also provide an explanation for each case. Defend the correct choice with adequate justification. For those that are false, explain why they are incorrect.
Accept/Reject: The girl died from ingestion of cardenolides in milkweed leaves, which killed her by interfering with the citric acid cycle, causing the cycle to generate toxic levels of ATP. Accept/Reject: The girl died from ingestion of cardenolides in milkweed leaves, which killed her by inhibiting the Na+/K+-ATPase (Na-K Pump), leading to the accumulation of Na+ in the cells and inhibiting the neuronal activity of the heart, blocking the cardiac cycle.
Accept/Reject: The girl died from ingestion of cardenolides in milkweed leaves, which caused severe gastrointestinal failure, preventing nutrient uptake and killing her through lack of glucose to drive cellular respiration in the heart.
Accept/Reject: The girl died from ingestion of cardenolides in milkweed leaves, which killed her by over-activating the Na+/K+-ATPase (Na-K Pump), pumping excessive Na+ in to the cells and inhibiting the neuronal activity of the heart, blocking the cardiac cycle.
Accept/Reject: The girl died from ingestion of cardenolides in milkweed leaves, which killed her by perforating the membrane of her cells, allowing Na+ to flow freely into the cells and inhibiting the neuronal activity of the heart, blocking the cardiac cycle.