Another series that was featured early last year which I hope will reinforce the message that every chemical reaction in our bodies is related, and that it is not just what we eat but how we eat and process it that is important.
Top to Toe – The Digestive System – Open Wide
As the purpose of these blogs is to offer you an overview of the body, I am not going to attempt to give you all the specifics about this complex and fascinating process. However, it does serve to illustrate the knock-on effect on our overall health if one part of the operating system, or chemical process, is damaged and off-line for a period of time.
Actually the digestive process starts in the nasal passages – remember how it feels to smell fresh baked bread, the BBQ or a curry. The saliva starts to build up in your mouth – which is why we call it ‘mouth-watering’. As soon as that process begins – we are ready to eat and digest the food. Interestingly enough, people who have a reduced or non-existent ability to smell rarely become obese!
The mouth is much larger than we would imagine from an external view and it contains the tongue and the teeth behind the entrance, which is guarded by the lips and mouth. At the rear of the mouth are the various tubes leading to the lungs or the rest of the digestive tract.
There are two palates within the mouth, the hard and soft palates. The hard palate to the front of the roof of the mouth is used by the tongue to mix and soften food whilst the soft palate (velum) can expand to allow food to pass back into the oesophagus without being forced up into the nasal passages.
The cheeks and soft tissues of the mouth are covered in a mucous membrane that keeps the mouth moist helped by the salivary glands. This membrane is one of the most vulnerable to wear and tear in the body and has remarkable powers of regeneration.
The tongue is triangular, wider at the base than at the tip. It is attached at the base to the lower jaw and to the hyoid bone of the skull. At the sides of the base it is attached to the pharynx which is the cavity at the back of the mouth. The top of the tongue is curved and is home to our taste buds, the front is called the apex and the back of the tongue is called the dorsum.
The tongue is very flexible and is controlled by a complex set of muscles both in the tongue itself and also in the jaw and neck. The styloglossus muscle in the neck is responsible for the upward and backward movement of the tongue and the hyoglossus also in the neck brings it back down into the normal resting position.
Of course one of the main functions of the tongue is its involvement in our speech and its health is therefore vital. Without it our ability to process food in the mouth and to talk would be virtually non-existent.
Food has to be chewed before it is presented to the rest of the digestive tract. The tongue will roll the food around the mouth so that the teeth can begin the process of breaking it down into manageable pieces.
The teeth are very necessary to our digestive process as food needs to be in small enough pieces to pass through the oesophagus into the stomach and also to allow enzymes adequate access to the last crumb. If it is a large chunk of food it will not be processed efficiently and we will lose much of the benefit.
We have two sets of teeth in our lifetime and how we look after the first set can have an effect on the health of the second and adult teeth. I was a dental nurse and in the 60’s we began to see the effect of increased sugars particularly in soft drinks on children’s teeth. My boss who was then in his 60’s was horrified in the difference that had taken place in only 20 or 30 years. As children we have 20 milk teeth that develop from small root structures under the gum at birth appearing around 9 months old to around 6 years old when they are pushed out by the 32 adult teeth as they begin to erupt. The second teeth can be affected by diet when they are still beneath the gums and this can lead to a lifetime of fillings and extractions.
All our teeth have specific roles in digestion and we are given enough so that as we age and lose a few we can still have the ability to process food. Of course in the last hundred years or so we have got very clever and can now replace teeth with dentures or better still implant new artificial teeth into the jaw that last around 15 to 20 years depending on the material used.
The incisors are designed to cut and the pointed canines are perfect for tearing foods such as meat and plant food apart. Our premolars and molars towards the back of the mouth can grind and crush other foods such as nuts, seeds and if necessary even bone.
Teeth are firmly fixed in sockets in the upper and lower jaw by a root system that may have one or two roots depending on tooth type and its role. Gum surrounds the tooth to help protect from decay and act as a buffer while the teeth work on food several times a day for our lifetime. The outer surface is enamel, which is one of the hardest substances in the human body and beneath this is dentine a pulp that protects the sensitive nerve and blood system in the middle of the tooth.
One of the key elements of efficient digestion is how we chew our food. Most of us eat far too quickly, not allowing the teeth to produce small enough pieces of food or our saliva and enzymes to carry out their part in the process.
Chewing slowly has the added benefit of allowing a message to get through from the stomach to the brain to tell it that you are full and to stop eating. This not only helps us maintain a healthy weight but it also reduces the stress and pressure on the digestive system.
The salivary glands –
The salivary glands at the base of the tongue produce an enzyme called ptyalin that digests starch and a chemical called Lysozyme that sanitises the food to prevent infection both in the mouth and the digestive tract. It is hard to believe but the human adult will produce in the region of 1½ litres of saliva per day consisting of mucous and fluid. It is important that the mouth is kept very moist not only for comfort but to enable us to deal with dry foods allowing it to be chewed more easily. It is also essential once food has been chewed, to ease the next stage of the digestive process when food is swallowed.
There are a number of salivary glands positioned in the mouth the largest being the parotids, in the neck, just in front of the ears. The glands that excrete the most saliva are under the jaw. These are the submandibular glands. And finally, under the tongue in the floor of the mouth are the sublinguals. The amylase enzyme produced by these glands converts the carbohydrate we eat into disaccharide sugars for further processing later in the stomach and intestines. (If you want to witness this in action, wave a cooked sausage in front of a dog’s nose and place their jaw over a basin!)
I looked at the respiratory role of the pharynx in the blogs on lungs, but it also is a channel for food. Its upper parts are connected to the nose and the mouth and lower part is connected to the voice box or larynx and leads to the oesophagus for swallowing.
We have all choked on food at one time or another and the reason for this natural and instinctive action is the epiglottis, the flap that prevents food and foreign particles from entering the lungs.
When we swallow this flap tilts backward and the larynx rises up. The cartilage bands around the larynx called the vocal cords come together and close the flap to seal off the entrance to the trachea. As soon as the food has passed safely into the oesophagus on its way to the stomach the epiglottis re-opens to allow air into the windpipe again.
Next time we will move into the oesophagus and the stomach.
©sallycronin Just Food for Health 1998 – 2017
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