I have already covered the most important of our survival mechanisms which was the respiratory system since the most urgent requirement that we have as humans is for oxygen. Fluids and food are the next priority so in this series of blogs it is the turn of the digestive system.
There is much evidence to suggest that the indigestion pills that millions of people consume daily because their digestive systems are in overload, are causing more harm than good. When I went to the US in 1985 – the first advert I saw on TV was for a preparation to consume before you went out to eat to prevent later acid problems. Take a good look at the adverts today – most are implying that they are a preventative measure so that you can eat exactly what you like and to hell with the consequences. Not true.
Honestly, it was not until I studied nutrition and the human body that I had any interest in what happened to lunch after I had eaten it. I expected that it would pass through my body and really only thought about it when it gave me indigestion. The fact that these foods on a plate were vital to my survival was far less pressing than extinguishing my hunger pangs.
The process is fascinating – well for some of us! However, it is I believe this lack of connection with the food we put in our mouths, and the magnificent processing power of out bodies to turn this hotchpotch of foods into energy, nutrients to feed a fetus, boost our immune system, repair cells, keep our brain alive, that is fuelling our obesity crisis. So I hope you will enjoy this journey that we will follow along with your breakfast this morning. It is a couple of thousand words but about 24 hours in real time. Perhaps not as exciting as 24 hours with Jack Bauer but the digestive system’s mission is just as vital to our survival as is his.
This system is sophisticated and complex, with a combination of organs, glands and chemicals involved in the process that turns raw materials into the specific nutrients that the body needs to survive. In this first blog I will take a quick trip down the digestive system as far as the intestines. Buckle your seat belt!
The Digestive system
Our bodies are not designed to take a piece of meat, apple or carrot and use it immediately in that form. So, it is necessary for the body to make enzymes that are capable of converting the original food into the optimum fuel for energy, growth, health and repair.
Enzymes are produced at various stages along the digestive tract by organs and glands such as salivary glands in the mouth, the stomach and the intestines. Enzymes are protein molecules that speed up the chemical processes in the body and they also work with, and alter, molecules of other chemical substances to ensure that the body is nourished, energised and healed.
The chemical process
The alimentary canal is over 30 feet long and starts in the mouth and ends at the anus and it is divided into two operating systems; the digestive system and the excretory system, both of which are vital to our health. The food is kept moving through the alimentary canal by smooth muscular contractions called peristalsis
The first stop for food is the mouth, where our tongues, teeth and salivary glands (that produce enzymes like amylase) begin the digestive process before passing the food into the pharynx at the back of the throat.
Amylase, for example, converts our carbohydrates into pairs of sugars, or dissacharides.
From here food passes into the oesophagus through to the stomach where stomach acid will continue the digestive process. Hydrochloric acid in the stomach modifies pepsinogen secreted by the stomach lining to form an enzyme called pepsin. Pepsin breaks down the protein in food into smaller units called polypeptides and lipase will break the fatty globules present in the food into glycerol and fatty acids. The acid in the stomach will also kill as much harmful bacteria as possible before it moves further into the body. The end result of this part of the process is a highly acidic liquid that is then passed into the duodenum.
Here it will be mixed with mucous secreted by the duodenum in response to two hormones that are released to neutralise the acid. One of the hormones, secretin, stimulates the release of alkaline juices and pancreatic enzymes are released in response to the second hormone pancreozymin. Bile is also passed into the duodenum either directly from the liver or from the gallbladder, where it has been stored.
Bile is a complex fluid containing water, electrolytes and organic molecules. These molecules include bile acids, cholesterol, phospholipids and bilirubin all essential in the digestive process. Bile acids help digest fats and allow for the absorption of fats, and fat soluble vitamins, as they pass through the small intestine. Bile also collects waste products that have accumulated in the liver and need to be passed through to the colon for elimination.
Cholesterol levels are affected by the efficiency of this bile process. Cholesterol comes not only from ingested food; it is also manufactured in the liver. It is virtually insoluble in most fluids – except for bile – where the acids and fats such as lecithin do the job. If these components are not effective cholesterol can collect into stones that block the ducts and cause problems with the digestion of fats.
Levels of bile in the body are lowest when we are fasting, which is why cholesterol tests are carried out at least 12 hours after your last meal. Most of the bile that is secreted during this period is diverted into the gallbladder, to be concentrated until it is needed when you have your next meal. As bile is not passing into the ileum, less passes into the bloodstream and the blood levels of cholesterol are stabilised and can be measured.
Only 5% of bile is eliminated from the body on a daily basis whilst the remainder is absorbed back into the bloodstream – during the passage through the ileum in the second part of the small intestine
By the time the liquid reaches the duodenum the particles in the liquid, whilst minute are still too large to be absorbed efficiently and the role of the enzymes is not just to process carbohydrates, proteins and fats but to also break them down into even smaller particles. For example, one of the pancreatic enzymes is trypsin which breaks down peptones, the particles at this stage, into peptides. Amylase will go to work on carbohydrates breaking them down into maltose, which is a disaccharide sugar.
This now digested food is passed down further, into the ileum, where the final chemical processing will take place.
More enzymes called maltase, sucrase and lactase are produced to facilitate the absorption of the food through the villi, which are millions of tiny hair like projections lining the walls of the small intestine. At this point the disaccharide sugars, or pairs, need to be converted into single sugars called monosaccharides for easy absorption by the villi.
Each one of these tiny hairs contains a capillary and a tiny branch of the lymphatic system called a lacteal. When the digestive mix comes in contact with the villi all the glycerol, fatty acids and dissolved vitamins are sucked up into the lymphatic system and then transported into the bloodstream. Other nutrients such as amino acids, sugars and minerals are absorbed directly into the villi capillaries, which connect directly with the hepatic portal vein and into the liver.
In the liver certain nutrients will be extracted and stored for later use whilst the other nutrients are passed on into the body. This is just one role that this vital organ plays in the digestive system and I will cover the liver in more detail later in the book.
How our energy is produced.
Starch based carbohydrates that we eat such as potatoes and bread are broken down into pairs of sugar molecules by the enzyme amylase in saliva in the mouth and further down in the digestive tract. These sugar molecules are broken down even further by other enzymes in the small intestine into single sugar molecules, which are absorbed by the villi capillaries and taken to the liver.
We need glucose to provide energy but it is very important that this is kept in balance. Too much glucose in the system and we can become diabetic and too little and our brain function ceases and we lose consciousness. Once the glucose reaches the liver it will determine if there is too much or too little in the bloodstream and either convert the glucose into glycogen and store it or release it directly into the bloodstream to be used as energy within each individual cell. Energy cannot be used directly by the cell so it is stored in a high energy chemical bond which links to a molecule of ADP (adenosine diphosphate) to a phosphate group, forming ATP (adenosine triphosphate). When this bond is broken energy is released as the ATP converts back to ADP, which begins the process all over again. Carbon dioxide is released as a waste product and is removed in the bloodstream through the lungs and out of the body.
Our glycogen stores in the liver and muscles is not huge and should the body be deprived of glucose producing foods for even short periods of time the body will have to make adjustments to maintain some form of balance. If glucose providing foods such as carbohydrates are not readily available in the diet the body will switch over to emergency power using either fat reserves (not too bad) or failing that, proteins in our muscles and tissues. This is why rapid weight loss is not advisable. Whilst we should burn fat reserves to a normal level it is dangerous to force the body into eating muscle which is extremely difficult to replace.
Insulin is produced by the pancreas and is secreted in response to high levels of glucose in the blood and other hormones such as adrenaline and cortisone can also be released if levels drop too far. In this way we maintain a healthy balance in the bloodstream and we do not develop diabetes. However it puts enormous stress on these organs and glands if we are constantly yo-yo dieting and restricting and bingeing alternately on various foods. The body prefers to receive a regular and staple diet combining the carbohydrates, proteins and fats in exactly the right amounts for its needs. The problem that we have with recent dieting fads is that we were all told twenty years ago to remove all fat from our diet and simply take in carbohydrates. This created excessive amounts of glucose in our bloodstream which if not used by the body is stored as fat. Add in the reduction in physical activity and none of this excess fat has then been used to provide energy but has instead accumulated over a period of time.
The current rates of obesity are the result of too many carbohydrates in the form of sugars and too little exercise.
Unless we all change our lifestyle and diet radically in the next twenty years the current figures for obesity will go from 65% to 85% and our children will be dying before us.
It normally takes ten thousand years for an evolutionary change to take place but humans have managed one in only 300 years since the introduction of excessive refined sugars and carbohydrates entered the food chain.
The second half of the journey – into the excretory system
Once all the nutrients have been extracted and passed into the bloodstream, or liver, any insoluble and undigested food moves into the large intestine. Any water and salt remaining in the mixture is absorbed into the lining of the intestine and the remainder mixes with all the other waste products produced by the body – such as bacteria and dead cells. It is packed and pressed into stool and stored for excretion at periodic times during the day.
Next time – our mouth is so much more than a talking point.
©sallycronin Just Food For Health 2007
Please feel free to share on your own blogs and thanks for dropping by.