Digestion Series: Part 6 - Small intestine

The small intestine is where most of the final #digestion (break down) and absorption of #nutrients takes place. It is long (~20 feet/6 meters) with a variety of microstructures including mucosa folds and villi which increase the small intestine's surface area by over 600 times the surface area of a straight tube!

When discussing the small intestine, it is usually divided into three sections: the duodenum, the jejunum and the ileum.

The #duodenum is the first ~1 foot (~0.3 meter) section. It receives the #chyme from the stomach as well as secretions from the pancreas, liver and gall bladder.

As chyme from the stomach enters the duodenum, the acid in the chyme stimulates special cells called enteroendocrine S cells, which then secrete a hormone called #secretin. This secretin stimulates the pancreas to produce an alkaline (basic, pH ~8) substance.

What happens when you add a base to an acid in the right proportions? They #neutralize each other!

When you add this #pancreatic alkaline secretion to the acidic chyme from the stomach, this now-neutral condition stimulates another system of processes where several hormones and enzymes (including amylase, lipases, and others) are produced in the pancreas and delivered to the duodenum.

These pancreatic enzymes are most active when the pH is neutral, and they begin to facilitate the digestion of nutrients in preparation for them to be used by our #bodies.

In the next part of the series, we will talk about how these nutrients are #absorbed.