Digestion- so easy a baby can do it! The digestive system is a key part of our survival-without it we would starve and when it goes wrong (in either direction) it can not only make us miserable but it can kill us. However it can also give us great pleasure not only from the foods we eat but it also contains 95% of the serotonin in the body. So let us take a look of what is actually going on here.
First we start out with mastication- and no that isn’t something you hide from your mother it’s just a fancy word for chewing. Even though you started sticking things in your mouth and chewing on them since you could grab you probably aren’t doing it right. You don’t have to go to crazy town and start counting the number of chews per bite- every food is different based on the macronutrients in it. However if you could still tell what the food was before it went in there chances are you need to keep chewing until it’s a mushy (but still tasty) glob.
You may think that the mouth is a purely mechanical fixture- with all those specialized teeth for cutting and grinding- however there are many important chemical reactions that the mouth is responsible for. Chemical break down of food begins in the mouth with the enzyme amylase that is found in saliva. (For now, think of all enzymes like specialized scissors- or cartoon samarui’s). The action of chewing also starts a whole chemical cascade of signals to the brain and other organs shouting that food is coming.
The wet mushy mass that you just finished chewing.. it’s called a bolus now.. and the oesophagus does a squeezing action known as peristalsis. If you imagine squeezing your tube of toothpaste from the bottom up just to get that last bit out- then you have got the right idea. At the end there is a one way door known as a sphincter which unloads onto the ball of mush into your stomach. I say it’s a one way door- sometimes you need to get food out (or sometimes your body decides this is a good idea on its own) and that door opens wide. If this sphincter muscle isn’t nice and tight you can have leakage of stomach acid onto the soft smooth muscle lining of the oesophagus- this is heart burn, or GERD, or reflux… or last night’s curry.
Here strong acid (with a pH of 2) continues the chemical breakdown of foods and peptidases are released and work to break up the protein. The acid also forms a second function in the fact is it really good at killing bacteria- so that slightly dodgy leftover won’t kill you. In this caustic environment we turn the bolus into chime- most of the long chains of the macronutrients have been broken down into much smaller pieces, readying them for absorption later. Contrary to popular belief you can’t “shrink down” your stomach through eating less. However you can train the stomach-brain connection as to when to stimulate that full feeling and how long that feeling is maintained. Then again this is more helped by the types of food that you are sticking in there.
The small intestines have three parts- duodenum, jejunum, and ileum- or if you want to keep it simple “digest, push and absorb”. The last bit of digestion takes place here with bile and lipases being released to help with the digestion of fat. More importantly is the beginning of the absorption of nutrients- after all we need to get all that goodness to the rest of the body. The details of absorption and transport of nutrients will be discussed later in detail but for now you need to know it’s all about surface area. The small intestines in an adult can be up to 30 feet in length- and have the surface area of a tennis court. This vastness of folds and crevices are known as villi and enable a larger amount of absorption. When things go wrong in the small intestines it can trigger a variety of issues downstream. The small intestines can become coated with thick mucus (Cystic Fibrosis), villi can be damaged and clumped together (Coeliac Disease), bacterial overgrowth (SIBO) or progression can become rushed (IBS)- all resulting in a lack of nutrients being delivered to the body.
Made up of three parts- “up, over, out” or “ascending, transverse, descending.” The main function of the colon is to absorb water to maintain the balance of fluid. Most of us have learned to control the sphincter at the end so we can choose where and when to eliminate- preventing much embarrassment. Your colon (another name for the large intestines) should be filled with bacteria. (FYI did you know that 90% of the DNA in your body doesn’t belong to you- it belongs to these cute little dudes in your intestines) We like these bacteria as they digest some last food making some nutrients available and they fight against the growth of evil yeast. Also they can do some cool tricks- depending on the population you will have little/no gas and farts, really stinky farts or even farts that light on fire.