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The familiar sounds of your heart are made by the heart's valves as they open and close.
On average, the stomach produces 2 L of hydrochloric acid per day.
Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
Acute bronchitis is an inflammation of the breathing tubes (bronchi), which causes increased mucus production and other changes. It is usually caused by bacteria or viruses, can be serious in people who have pulmonary or cardiac diseases, and can lead to pneumonia.
Bacteria have flourished on the earth for over three billion years. They were the first life forms on the planet.