Your ‘gut’ is a snappy word for your intestines, which we’ll discuss more about later. But really your gut is only a part of a larger system in your body called your ‘GIT’ (or ‘gastrointestinal tract’ for you scientists out there). So what is your GIT and how does it work?
Your GIT is the collection of organs that helps you to absorb or excrete foods, liquids, medicines and anything else that you end up swallowing. It starts in your mouth and ends at your anus (yes, I said anus. It’s the scientific term, so let’s have our laughs and move on). If you think about it, humans are like hollow tubes; if our GIT wasn’t so folded, we would be able to peer down someone’s throat and out the other end. As food is made up of many different things (protein, fats, carbohydrates, vitamins, minerals etc), your GIT needs to break food down into all of these individual parts so that they can be absorbed by the into your body to give you energy. So how does this happen?
The GIT starts in your mouth where food digestion begins. Your teeth start digesting food by breaking it down into smaller pieces. Your saliva also contains an enzyme called amylase that helps digest carbohydrates. After you swallow (remember what your mother told you, always chew your food before swallowing, 15-20 times preferably) this mushy food-ball then makes its way down your oesophagus (the tube leading to your stomach). Not much digestion happens here, but muscles in the oeseophagus help it to wriggle, squirm and push the food down, so that it doesn’t just rely in gravity. That’s why you could still swallow and digest food whilst hanging upside down (DISCLAIMER: don’t eat your food upside down!).
Once in your stomach, the food-ball is bathed in acid that is almost as strong as a car battery acid, and an enzyme called pepsin that breaks down proteins. This acid, alongside other enzymes, helps to break down the food even further before it heads down into your intestines/gut. When the acidified food leaves your stomach and goes into your gut, it goes through another digestion step. Your pancreas makes enzymes and hormones that digest the food further. Then, your gall bladder (a little pocket at the start of the intestines) squirts out a disgusting green liquid called bile, which contains acids that are specifically used for digesting fat (it’s quite useful after that 2am kebab and fries).
Now this broken down food can begin its long journey through the gut. This is where all the magic happens: the gateway to your body, where many different cells communicate with each other to decide what to allow through the gate and into your blood, or what to attack and excrete. There are many different stages to this process however, as your gut has many different sections. Broadly, it can be divided into two main sections: the small intestine and the large intestine. Confusingly, the small intestine is actually much longer than the large intestine (6m vs 1.5m), but the names probably refer to the larger width of the large intestine. The small intestine is where 95% of absorption occurs. This is helped by the millions of finger-like structures inside the small intestine, called villi, which provide a large surface area for food to be absorbed. As your food travels through the different sections of this tube (the duodenum, jejenum and ileum), the cells in your small intestinal villi absorb the sugars, fats, vitamins etc, which travel into your blood, giving your body energy. However, some food and liquids don’t get absorbed and travel all the way to the end of your small intestine to a large pouch called the cecum. The cecum is the beginning of your large intestine which contains trillions of bacteria and other microbes that digest any remaining food that makes it’s way to the depths of the gut. For example, fiber from fruit, vegetables and whole grains can’t be digested and absorbed by our own enzymes in the small intestine so instead makes its way to the large intestine where it is food for the microbes. These microbes continue to digest the remaining food in the colon (the large intestine) before all of the waste passes out into the toilet.
So there you have it, the wonders of the GIT.
Dr. Ruairi Robertson is a postdoctoral researcher examining the role of the gut microbiota (all of the bacteria and other microbes in your gut) in many aspects of human health. He has a B.Sc in Human Nutrition from University College Dublin and a Ph.D in Microbiology from University College Cork, where he conducted his research within the world-renowned APC Microbiome Institute. Ruairi also spent one year as a Fulbright Scholar working in Harvard University and Massachusetts General Hospital in Boston, USA. Ruairi is currently a Postdoctoral Research Fellow in Queen Mary University of London.
Ruairi’s research examines how the trillions of microbes that make up the gut microbiota can influence everything from weight to brain health, and most importantly how our diets influence this relationship.
Check out his TEDx talk here: https://www.youtube.com/watch?v=awtmTJW9ic8&t=110s