The first section of the digestive tract is made up of our mouth, teeth, tongue, salivary glands, our throat, oesophagus and stomach.
SO HOW DOES IT WORK?
It all starts with spit. Spit is the business!
We produce two types of spit or saliva. Unstimulated
spit is the thick and sticky kind that is continually present in our mouth. It protects our gums and teeth from acid and traps bacteria which are later destroyed in the acidic environment of the stomach. Stimulated saliva is what we release when we smell, see or even think about food. It is 90% water and 10% digestive enzymes, mainly an enzyme called amylase which
breaks down starchy food like bread and rice and pasta.
The tongue pushes food around our mouth, mixing it with saliva and positioning it for teeth to grind. When food is sufficiently soft, the tongue shapes it into a soft ball called a bolus and moves it to the back of the mouth where we swallow. This is the oral phase of digestion and we can consciously control it. From now on food is entirely under the control of our gut.
Next is the pharyngeal phase. Because our throat (the pharynx) contains both our windpipe (the trachea) and food pipe (the oesophagus), a series of movements automatically close our respiratory passages when we swallow. This allows food to pass into our oesophagus
without us choking. We probably all know what this feels like if it fails; it makes us cough and splutter.
Then, the muscles of the oesophagus relax and contract, squeezing the bolus towards the entrance of the stomach. Usually, this movement is in one direction only – down – but the gut muscles are so strong that theoretically we could eat whilst doing a headstand!
At the junction to the stomach, there is a ring of muscles called the lower oesophageal sphincter (LOS) which relaxes to allow the food to drop into the stomach and then closes to prevent it coming back up.
This next stage of the journey is where the serious process of digestion of food really gets going. Our stomach is not located where most of us believe it is. It starts just below our left nipple and ends below our right ribcage, much higher than we usually think.
When the stomach is empty, it folds up but it can more than double in size to hold food and has amazing stretch receptors to tell us when we are full.
The stomach produces digestive acids to kill off harmful bacteria and start to breakdown proteins while the muscles squeeze and churn food into a lumpy liquid called chyme. Chyme is what we see when we vomit; it is the acid in it that makes our mouth burn and taste
The stomach is protected by a thick coating of mucus. This mucus is always adjusting its pH value and replaces itself every 3 days. A pH value is a measure of how strongly acid or alkaline something is (pH values from 0–7 are acidic and those from 7–14 are alkaline). The
stomach should have a pH value of roughly 2. Blood and water should have a neutral pH value of 7.
It takes between 2 to 6 hours for food to leave the stomach depending on what we have eaten. A meal higher in fats like steak and chips will take roughly 6 hours, whereas most fruit and vegetables move on in under 2 hours.
The first stage of our journey is over and when the chyme is in just the right state, the ring of muscles at the bottom of the stomach called the pylorus relaxes to allow it to pass through on the next stage of its journey into the small intestine.
This is an extract from Gut Feeling. I wrote Gut Feeling as an easy to read, illustrated guide especially designed for parents whose children have significant digestive conditions.
The booklet describes some of the challenges parents face, the impact these may have on day to day life and ways to help deal with them.
The illustrations and fun facts to share with a child will foster a family's understanding of the gut and will engage a child more positively with what is happening inside them.