Chapter 4.4, Problem 1HYEW

Over the years, scientists have wondered how many cells are in the human body. They don't yet agree, but 10 trillion seems a reasonable estimate. There is a consensus, however, that there are at least 10 times as many prokaryotic cells associated with the body, residing in a community called the microbiome. We each host a unique community consisting of about 3 pounds (1.4 kilograms) of prokaryotic life, which includes roughly 100 different types of bacteria. These cells colonize the nose, skin, vagina, and the digestive tract from mouth to anus.

  Because the digestive tract is a tube open to the outside at both ends, our microbiome occupies a unique niche that is simultaneously integral to—yet outside of—our bodies. With recent advances allowing identification of microorganisms by their unique DMA sequences, scientists are increasingly studying our relationships with our microbial residents. Our gut microbiome helps digest food and synthesize vitamins, and it allows the immune system to develop properly. Even though our bacterial populations changes in response to food intake and states of disease and health, one thing is clear: We would not be ourselves without them.