The digestive system

The digestive system

By
Dale Pinnock
Contains
0 recipes
Published by
Quadrille Publishing
ISBN
978 184949 543 1

I feel that the best way to understand your health concerns is to find out more about the way in which your body works, and how things can begin to change when problems arise. This is a recurrent theme throughout my work, and justifiably so. This knowledge will help you to develop that kind of understanding of your body that will allow you to make better, more informed choices in the long term and get a better handle of what may be going on inside you. We are going to explore how the digestive system works, so you can get the full picture of what is happening where, and what may be becoming problematic for you. Obviously, if this is all familiar to you, then move on. If not, do take the time to read through this section, as it will really help you make sense of everything. It is only the basics so don’t worry, it won’t be reams of science, just an overview to help you put all the pieces together.

What is the digestive system? Well, in the simplest of terms, it is there to convert the food we eat into substances that can actually enter our body safely and perform a myriad of functions. When food is first eaten, it cannot enter the body beyond the digestive tract; indeed, if it did, it would trigger an allergic reaction the extent of which you wouldn’t believe. The food has to go through a series of transformations in order to extract individual nutrients and nutrient complexes that can leave the digestive tract safely and make their way to cells and tissues where they can be put to use.

The mouth

This is obviously the first stage in the digestive process, as our food makes its way through the digestive system, subject to all manner of processes in order for us to glean nutrients from what we eat. The first element that takes place here is, of course, mechanical digestion: chewing. This breaks the food down into small pieces so there is more surface area exposed for digestive secretions – enzymes and other compounds – to begin working on. This increasing of surface area to maximise digestive capacity is a recurring theme throughout our digestive system. Digestion is quite a taxing activity for the body, so it has to make it as efficient as possible to save energy and be sure it doesn’t miss out on important nutrients. Chewing is a vital part of the process, but you’d be amazed at how few people actually chew their food properly. It is definitely worthwhile making an effort to chew food better. Now, don’t worry, I’m not going to start sounding like a lot of those other ‘health’ books and tell you to chew every mouthful 30 times. I tried. It is boring, impossible to stay mindful of and really quite unpleasant, unless of course you want to look like one of Pavlov’s dogs and drool uncontrollably! Just a conscious effort not to wolf food down or inhale it is enough.

Mechanical digestion isn’t the only thing to take place in the mouth. There is some subtle chemical digestion going on as well. In the mouth, we produce saliva. This is around 90 per cent water, but it does contain some mild digestive enzymes, too. The main player here is salivary amylase. This can begin to break down some of the more simple sugars that can be absorbed very quickly. You can experience this first hand when you eat something like a piece of bread or potato. Chew it a few times and you will see it starts to get sweeter. This is salivary amylase in action, liberating the simple sugars that we detect as sweetness. Saliva is also used to lubricate the food to make it easier to swallow. The food-saliva mixture, called the bolus, moves from the mouth down to the oesophagus.

The oesophagus

The oesophagus is a flexible, muscular tube that runs between the mouth and the stomach. It has no role to play in physical digestion or absorption. It is merely a transport system that connects two regions of the digestive tract. This adequate spacing of the stomach and mouth is for a good reason, because stomach secretions are very corrosive and could quickly damage membranes in the mouth – and of course our teeth – so the two are best kept apart. The inner surfaces of the oesophagus secrete a thin mucus to aid in the movement of the bolus from the mouth to the stomach.

The stomach

The stomach is a J-shaped bag-like organ that lies beneath the diaphragm. Its main function is to carry out specific mechanical and chemical digestion of food. But it also serves as a holding chamber. It can be viewed as an intermediary between the oesophagus and the small intestine, which is where most digestion and absorption takes place. As a meal can very easily be eaten much faster than the intestine is able to break it down and digest it, the stomach holds the meal in its chamber and releases it a little at a time into the small intestine at regular intervals. The stomach is a basically acidic environment, with cells lining its internal surface that both measure the acidity and that secrete hydrochloric acid into the stomach. The main food group to really undertake significant chemical digestion here is protein, but we will come to that a little later.

Soon after food enters the stomach from the oesophagus, gentle rippling waves start to move through it every 15–25 seconds in a controlled and orchestrated manner. These waves are there to move the food around and continually mix it with the digestive secretions released by the stomach. This action turns the stomach contents into a thinner gloopy mixture called chyme. As chyme makes its way through the stomach, it comes to an area called the pylorus. Here, there is a ring of muscle called the pyloric sphincter which is almost completely closed and controls the exit of food from the stomach into the small intestine. As the chyme reaches the pylorus, the waves of contraction get more forceful and force a few millilitres of chyme at a time out from the stomach and into the intestine. This drip-feeding of chyme into the intestine makes digestion more manageable and effective, as the intestine can only effectively deal with a small amount of food at a time.

The pancreas

The pancreas is a gland around 12–15 cm long that lies just behind the stomach. It produces a whopping 1.2–1.5 litres of pancreatic juices every single day; quite an impressive feat for such a small organ. This juice is a clear, colourless liquid that consists mostly of water, some salts, sodium bicarbonate and an array of enzymes. The sodium bicarbonate content makes it alkaline. Remember that the stomach is an acidic environment, so anything leaving it is going to be very acidic, too, which can potentially damage other areas of the digestive tract. When pancreatic juice mixes with chyme that has just left the stomach via the pyloric sphincter, it neutralises the acidic juices in the chyme. The small intestine is an alkaline environment and this initial mixing prepares it for that environment. The enzymes in pancreatic juices include a carbohydrate-digesting enzyme called pancreatic amylase, protein-digesting enzymes including trypsin and chymotrypsin and the main fat-digesting enzyme called pancreatic lipase, to name but a few.

Pancreatic juice enters the small intestine at the top via the pancreatic duct, which joins with the common bile duct. These two substances flow into the intestine at the same time and in the same location as chyme, as chyme exits the stomach. Bile also increases the alkalinity of chyme.

The liver and gall bladder

The liver is the heaviest gland in the body, weighing in at about 1.5 kg. The gall bladder is a pear-shaped sac that sits in a depression at the rear of the liver. The functions of the liver are incredibly vast and go way beyond the scope of simple digestive function. It manufactures proteins; breaks down, metabolises and removes toxins; and pools nutrients. Second to the brain, the liver is the most important organ in the body. To be honest, the liver’s roles are so vital for survival, that I’d say the liver is of equal importance. In terms of digestive function, the liver is the manufacturing site for bile. The hepatocytes (liver cells) can secrete 800ml–1 litre of bile every single day. This fluid is composed of bile acids, bile salts, cholesterol, a substance called lecithin and other metabolic products. The odd thing about bile is that it is half digestive juice, half excretory substance (it carries waste products out of the liver to the bowel for removal). The salts found in bile help to emulsify fats. This means that it breaks them down into small droplets, which pancreatic lipase then sets to work on. When fats are in smaller droplets like this, it is easier for the body to break them down and digest them, rather than chipping away at one big oil slick. Bile is released into the upper part of the small intestine when chyme enters it after leaving the stomach. The acidity of the chyme stimulates the secretion of a hormone called cholecystokinin, which causes a contraction of the wall of the gall bladder, which in turn squeezes bile out through the duct.

The small intestine

The longest part of the digestive tract, this is a mass of coiled, curled, convoluted folds of tubing. It is made up of three regions: the duodenum, the jejunum and the ileum. It is the part of the digestive tract where most digestion and absorption take place, so the inner surfaces of the small intestine are designed to maximise this effort. The inner surface is made up of millions of finger-like projections. This increases the amount of surface area of the intestine that is available for absorption of nutrients. Inside these finger-like projections are blood vessels that can carry off nutrients, and specialised lymphatic vessels called lacteals that absorb and transport fats. On the surface of each of these finger-like projections are millions of microscopic finger-like projections called microvilli. These extend surface area further, enhancing the extent to which nutrients can be absorbed during their movement through the intestine. As the food moves through the intestine, there are a series of regimented, rhythmical contractions and movements in the intestinal wall. These movements mix chyme with digestive juices and ensure that food particles and nutrients come into contact with the absorbent surfaces of the intestine as much as possible.

There are many different enzymes within intestinal secretions that break down different food groups, such as amylase, sucrase and lactase for sugar and carbohydrate digestion, trypsin and chymotrypsin for protein digestion, and lipase for fat digestion. I will give a bit more detail later about how different food groups are digested. Once these nutrients are liberated from the food that we have eaten, they are absorbed in different ways. Simple sugars and fats move through the gut wall by means of simple diffusion, meaning they easily just pass through. Simple sugars go into the bloodstream via tiny veins in the villi, while fats diffuse through into specific lymphatic vessels called lacteals. Amino acids, the building blocks for proteins, get absorbed by ‘active transport’. This means that specialised carrier structures on the surface of the villi bind to them and carry them through, again taking them to the liver.

The large intestine

The large intestine really has a lot less to do with digestion and breakdown in comparison to the other regions of the digestive tract; it is more a site for last-minute absorption and taking what is left behind and moving it on out! When chyme leaves the small intestine and moves to the large, one of the first things that happens is that the remaining water in the chyme begins to get absorbed through the intestinal wall. About 90 per cent of the water will be absorbed in the small intestine, but a great deal of what remains will get absorbed via the large intestine. This makes the chyme more solid and it becomes… you guessed it… faeces. The walls of the large intestine are really geared up for moving things along ready for removal from the body. They are much smoother than those of the small intestine. The most prominent features in the wall of the large intestine are mucus-secreting glands that lubricate its contents, to ease their passage through. The other notable feature is the muscularity of its walls. These muscles contract forcefully, in rhythmical waves called peristalsis (which occurs throughout the whole digestive tract, but more forcefully in the large intestine) which move things along.

The most important aspects of digestion that occur in the large intestine are carried out by things that I personally view as being another digestive organ. These additional unsung heroes of the digestive tract are the gut flora.

‘Gut flora’ refers to the diverse bacterial population that thrives within our digestive system. The digestive tract is not a sterile tube; it is in fact home to a vast network of bacterial life. This may sound a bit horrific, but we actually have an absolutely vital and symbiotic (mutually beneficial/dependent) relationship with this complex bacterial colony. Believe it or not, there can be 300–1,000 different species of bacteria living in the gut. These bugs help us in so many ways. One of the simplest tasks they do is break down certain types of carbohydrate that would otherwise be unusable for the body.

They do this by a process called saccarolytic fermentation, which turns carbohydrates into short chain fatty acids that then go on to help cellular metabolism, nutrient absorption and even localised tissue repair. Encouraging this process is actually a specific therapeutic target for certain digestive issues and you will see that discussed later in this book. There is some evidence to suggest that bacterial production of short chain fatty acids can prevent inflammatory bowel disease, while certain types of bacteria are believed to have a localised anti-inflammatory/inflammatory mediatory function.

The ‘good bacteria’, as they have become known, have a further defensive role to play. For a long time they were known to be a vital part of immunity within the gut, as they were one of the first barriers between pathogens entering via the digestive tract and the inner workings of the body. They offer an immediate and localised defence. However, in recent years we have realised that the effect of gut flora on immunity goes far beyond just a local influence. We now know that the bacterial colony of the gut can influence immunity systemically. Literally, bacteria in your gut can influence a white blood cell in your little toe. We also now know that gut flora is involved in immunological development in infants and children. The gut flora, is in my opinion, one of the most vital aspects of overall gut health and, no matter what digestive issue I am working with, supporting gut flora is always part of my protocol.

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