I believe the answer is: No, this does not need to be reported since it is unrelated to participation in the study.
Unless a person is induced with chemical substance, The cause of heart attack is most likely diet and lifestyle that has been building up over time.
Since the research is revolved around attitudes towards hygiene and disease prevention, they would only observe the subject's behaviour, not making them digesting any substance.
Answer: tight junction; desmosomes
Explanation: Tight junctions are connected areas of the plasma. They form a water tight seal and acts as barrier against the movement of water, solute and prevents passage of materials between the cells or epithelial layers.
Desmosomes forms a strong connection that joins intermediate filament of adjacent cells, they can be viewed as rivets through the plasma membranes of adjacent cells.
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