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A Step-by-Step Journey Through Your Body's Digestive System

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We at Mental Floss write a lot about poop, but not as often about how our bodies produce the stuff in the first place. Humans eat between two and six pounds of food per day—and as TED-Ed’s latest video explains, this grub passes through an elaborate network of channels, organs, tissues, and nerves that’s commonly known as the human digestive system.

The digestive system is the unsung hero of our torso. Its 10 organs—which include the esophagus, liver, intestines, and stomach—contain over 20 specialized cell types, and the gastrointestinal track alone has an internal surface area of between 320 and 430 square feet. But the digestive process doesn’t begin and end with the esophagus—it starts in our mouths.

The body produces just over six cups of saliva per day, a process that begins when we start salivating over a tasty morsel. This clear substance contains starch-busting enzymes, which break the food we eat into a moist lump (a bolus) that will eventually become the stuff that comes out our other ends. In all, this journey lasts between 30 and 40 hours—and you can follow it step by step by watching TED-Ed’s video below.

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science
The Prehistoric Bacteria That Helped Create Our Cells Billions of Years Ago
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We owe the existence of our cells—the very building blocks of life—to a chance relationship between bacteria that occurred more than 2 billion years ago. Flash back to Bio 101, and you might remember that humans, plants, and animals have complex eukaryotic cells, with nucleus-bound DNA, instead of single-celled prokaryotic cells. These contain specialized organelles such as the mitochondria—the cell’s powerhouse—and the chloroplast, which converts sunlight into sugar in plants.

Mitochondria and chloroplasts both look and behave a lot like bacteria, and they also share similar genes. This isn’t a coincidence: Scientists believe these specialized cell subunits are descendants of free-living prehistoric bacteria that somehow merged together to form one. Over time, they became part of our basic biological units—and you can learn how by watching PBS Eons’s latest video below.

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Stones, Bones, and Wrecks
Buckingham Palace Was Built With Jurassic Fossils, Scientists Find
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The UK's Buckingham Palace is a vestige from another era, and not just because it was built in the early 18th century. According to a new study, the limestone used to construct it is filled with the fossilized remains of microbes from the Jurassic period of 200 million years ago, as The Telegraph reports.

The palace is made of oolitic limestone, which consists of individual balls of carbonate sediment called ooids. The material is strong but lightweight, and is found worldwide. Jurassic oolite has been used to construct numerous famous buildings, from those in the British city of Bath to the Empire State Building and the Pentagon.

A new study from Australian National University published in Scientific Reports found that the spherical ooids in Buckingham Palace's walls are made up of layers and layers of mineralized microbes. Inspired by a mathematical model from the 1970s for predicting the growth of brain tumors, the researchers created a model that explains how ooids are created and predicts the factors that limit their ultimate size.

A hand holding a chunk of oolite limestone
Australian National University

They found that the mineralization of the microbes forms the central core of the ooid, and the layers of sediment that gather around that core feed those microbes until the nutrients can no longer reach the core from the outermost layer.

This contrasts with previous research on how ooids form, which hypothesized that they are the result of sediment gathered from rolling on the ocean floor. It also reshapes how we think about the buildings made out of oolitic limestone from this period. Next time you look up at the Empire State Building or Buckingham Palace, thank the ancient microbes.

[h/t The Telegraph]

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