Digestive System Explained ~ Briefly!

The Gastrointesintal System, or GIT as we call it in the biz:

Let's get to the guts of the matter.

Let’s get to the guts of the matter.

This kind of image once brought confusion and as such, fear into my heart. But it’s been many moons since I first sat with my new pens and highlighters poised in Nutrition 1A and I now view the digestive system with familiarity and comfort. It’s the part of the body that I deal with.

Feet or anuses I’m not sure I’d be down with. But kudos to the people who spend their days perusing those parts of the human body. I hope they wash their hands before making dinner is all.

I digress.

I got to thinking about how often I consider the function of the digestive system and the relationships between the individual organs, because it’s often. And how this is really the backbone of my work as a nutritionist. It’s like learning the alphabet and then being able to spell and read words.

One of my goals for this blog is to educate and so here we are in Katie180 1A ~ !

The gastrointestinal system begins at the mouth and ends at the anus and is connected all the way down via the pharynx, esophagus, stomach, small and large intestines. On the wings are the pancreas, liver and gallbladder.

You put food and drink in: it is chewed, churned, broken down by digestive acids and enzymes, the good stuff is sent around the body by the blood to be used or stored and the leftover stuff is excreted.

Each organ of the digestive system has an important role to play and I’m going to summarise them here for you.

Check the look on my face after four years of studying. I'm all "Hell yeah, bring it biatches!"

Check the look on my face after five years of studying. I’m all “Hell yeah, bring it biatches!”

~In the beginning, there is the mouth~

Inside the mouth is the tongue, teeth and salivary glands which kick start digestion.

Teeth tear and crush food into smaller bits, enabling maximal exposure to saliva and ease of swallowing and further, maximal availability to digestive enzymes.

Saliva is totally important, containing water, mucous, proteins, mineral salts, enzymes and antibodies. It dissolves food and then the taste buds are stimulated to respond accordingly, it coats food to ease its transition into the pharynx/esophagus, digests starches and it kills harmful microbes that may enter via the mouth.

The tongue pushes food around the mouth, participating in chewing action as well as takes charge of taste.

So chew thoroughly and as slowly as you can, be mindful of how you chew and swallow: really taste your food, make the most of every mouthful. Not only does this promote optimal digestion and nutrient absorption, but it allows for accurate satiety. The faster you eat, the more you eat and eventually the more uncomfortably full you feel (and extra kilojoules you’ve consumed.)

~Down the right pipe thank you very much~

Ever found yourself spluttering and coughing on a mouthful “Urgh, it’s gone down the wrong pipe!”? This is likely because your food almost did go down the wrong pipe!, the trachea. You see the passage that food enters when it leaves the mouth, the pharynx is shared by both the digestive and respiratory systems, with a flap closure system between them called the epiglottis (epi = upon, glottis = back of tongue.)

The epiglottis closes micro-momentarily in order to keep us from taking food into our trachea, it’s pretty nifty how we can effectively stop breathing in order to eat. But if you’ve ever hoovered into a super tasty meal, all the while yakking your head off excitedly… not me! and found yourself out of breath, this is why.

So after the teeth and tongue treatment, chewed, mixed up and wet food passes through the pharynx, past the epiglottis and down the esophagus (the right pipe for food) into the stomach. In a little blob called a bolus.

~I churn for you~

Via a hole at the end of the esophagus, the bolus enters the top portion of the stomach (the pink, curvy organ at the top) and then the hole closes to prevent the bolus moving back upwards. If you’ve ever experienced the burning pain of reflux, you know why this happens. Gastric acids are powerful, so much so that if you stuck your finger directly into your stomach it’d fizzle away like a body disposed of by the Mafia.

The stomach itself is protected from these flesh-eating acids by mucous secreting cells.

The stomach is comprised of three separate layers of muscle, which all run in different directions and it contracts around the food, gradually transferring it from its upper to lower portion, where it is mixed with gastric acid and enzymes and turned into a semi-liquid called chyme (kime.)

Chyme is released bit by bit into the small intestine via another hole which also closes behind the chyme.

For the record, these holes I am referring to are actually called sphincters. But I’m using hole instead because sphincter will make some people think of bottoms. Again… not me!

~Small intestine, large absorption~

The small intestine (the pink long, twisty sausage-like organs in the middle) is where most of our nutrient absorption takes place, via teeny tiny little hair-like structures called villi. The villi provide a huge surface area for nutrient absorption.

Teeny tiny little villi with a big ass job to do.

Microvilli on the outer surface of the cell of a villi.

Each villi is in turn covered by microvilli which project from the membrane of the villi. The microvilli houses enzymes and pumps (that assist nutrient transport into the blood stream) which respond accordingly to individual nutrients. It’s HA-MAZING!

I mean, c’mon nutrient X goes into the blood via enzyme X and pump X… kinda turns food combining on its head doesn’t it?!

The villi are constantly in motion, waving and wriggling about like Nemo’s house. Nutrients are absorbed and small, partially digested food particles get trapped and further digested before also being absorbed into the blood stream.

→Diseases that result in a lack of integrity in the small intestine, such as Coeliac, Chron’s and leaky gut lead to nutrient malabsorption and associated diseases as well as the entry into the blood stream of foreign particles that cause havoc. This is why we see great results in children with behavioral disorders, Autism and the spectrum of Autistic disorders when we remove offending foods and work to heal their gut. As well as all others with allergies and intolerances. It’s the brain-gut connection being rebooted.

~This is good shit~

After traveling along the small intestine, the chyme makes its way via another hole into the large intestine (the grey-blue fat bumpy tube) where water is extracted from it, leaving a semi-solid material that is eventually excreted.

Some fluid and nutrients are reabsorbed at this final stage also.

The beneficial bacteria that live within the large intestine feed on some of the partially digested fibrous material.

→So drink water, eat fibre (fresh fruit and veg as well as whole grains and legumes) and MOVE your body to make good, healthy turds. Did you know that dry and hard to budge poo can make its way back into the system causing toxicity, and literally “poo breath” in those with sluggish bowel movements? Ewww.

~Accessories are a must~

The Liver (labelled) has many important roles in digestion and metabolism including the breakdown and conversion of nutrients,  conversion of glucose into glycogen for storage, and then back into glucose when needed; the storage of vitamin A and iron and the synthesis of bile.

→It detoxifies toxic by-products of digestion as well as harmful substances we ingest via our mouth or bloodstream, and unfortunately for our health, toxins such as alcohol, drugs and highly processed food crap “displace” nutrients by hogging the function of the liver for their excretion, rather than its role in assimilation of nutrients.

It does awholelotta other things too, but we’re here today to talk about digestion.

The Gallbladder (the green pear shaped organ underneath the liver) receives the bile that the liver makes and concentrates it then releases it back to the liver when needed, for fat digestion.

The Pancreas (the yellow arrow-shaped organ behind the stomach) participates in the digestive system by producing enzymes that are responsible for for breaking down fats, proteins and starches. It also produces bicarbonate to neutralise stomach acids that come with the chyme into the small intestine.

The pancreas also has an endocrine function (it secretes hormones.)

You have reached the end of my brief introduction to the digestive system. I hope that this has been enlightening?! and if anyone out there is an ass-doctor and wants to share their own “Bungholes for Dummies” with me, feel free. Just maybe use fuzzy filters on the pictures mkay?

~Yours digesting, K180, x

{Images: Whitney and Rolfes, Understanding Nutrition, 10th ed. 2005, Thomson Wadsworth.}



  1. I’m a food tech teacher. It’s OK to link my kids to this post, right? Amazing.

  2. Lynne Stone says:

    Hi Katie, I’ve been meaning to contact you for ages. I love what you do, I have been banging on for years pretty much everything you post! I’m not a nutritionist….would have loved to be one in another life!….I’ve even fallen for some of the so called weight loss crap that’s out there but it’s people like you that we need to see and hear, so please keep up the great work you do. I was hoping you could possibly suggest some ideas for my sister. She has Chrons and the arthritis some people also get with it. I saw that slippery elm was good for arthritis but not sure how it would effect her tummy. After reading this blog I thought you would be the one to ask. Thanks. Lynne Stone.

    • Hi Lynne. SORRY it’s taken me AGES to reply. My administration bad. Slippery elm bark is not irritating to the gut lining or the intestines. It is in fact, soothing, healing and nourishing. I think it would be OK to introduce it perhaps in 1/2 teaspoons measures to begin with as it is still fibre and could bulk up stools somewhat. LOTS of water when taking slippery elm bark powder! I have written a post on slippery elm bark powder: http://www.katie180.com.au/top5/top5-slippery-elm-bark-powder/
      Cheers, Katie.

Leave a comment