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Digestive system: how it works

The digestive system is a tube that runs from the mouth to the anus and it is approximately 9 metres in length.


Food that we eat is, generally, made up of a variety of large molecules such as proteins, fats and carbohydrates. 

The digestive system consists of all the organs that are responsible for chewing, swallowing, digestion and absorption of food and also the elimination of waste products from the body. Each of these has a distinct role to play in the process of digestion and absorption.

The mouth is where we start breaking down food by chewing.

We also add saliva to food in the first stage of the digestive process. When you eat, chemical messages from the mouth are sent to your stomach to warn it that food is on its way. 

Eating too fast adds to the risk of bloating after a meal. The remedy is simple, eat more slowly. Satiety signals can take up to 20 minutes to reach the brain and dampen appetite. Many weight loss experts believe that eating slowly helps prevent overeating.

Eating too quickly and not allowing enough time to chew means that food arrives in the stomach before the stomach acid (HCl) and digestive enzymes can be produced to break it down. The result is that not enough time is given for the stomach enzymes to work, and the partially digested proteins cause havoc as they move through the rest of the digestive tract. HCl arriving late on the scene may attack the stomach wall, causing indigestion and a tendency to ulcers.

The oesophagus is a tube connecting the mouth to the stomach.

Food moves through the oesophagus by a wave of contraction known as peristalsis.
Heartburn or gastro-oesophagal reflux is an inflammation caused by reflux of the acid contents of the stomach into the lower part of the oesophagus. This gives an irritation, inflammation and ulceration of the oesophagus, termed oesophagitis.

The stomach is where the main part of digestion occurs

Food lies in the stomach for a few hours. This time allows the digestion of proteins to begin and food is turned into liquid form at the end of this process. The main agent responsible for digestion in the stomach is the enzyme pepsin, which digests proteins. In infants, rennin is another important enzyme found in the stomach. It acts on milk proteins. The stomach lining secretes both these enzymes. 

Enzymes in the stomach require an acidic medium in which to work. This is provided by hydrochloric acid (HCl), which is also secreted by the stomach lining.

Poor production of stomach acid means that food cannot be properly acidified. The stomach enzymes do not work properly in this situation. Matters are made worse if the muscles in the stomach wall do not work enough to mix food with digestive juices. This can lead to food lying ‘like a stone’ in the stomach. 

In certain cases, the muscle at the entrance of the stomach (known as the oesophageal sphincter and which normally prevents food from moving backwards into the oesophagus) loses its tone and stomach acid can escape into the oesophagus. This is known as ‘reflux’ and is often described as heartburn.

Gastroenteritis, often referred to as “stomach flu” or “gastric flu” is typically caused by viruses, bacteria or parasites in water or in contaminated food, or through contact with an infected person.

The liver is responsible for many chemical processes.

In the digestive system, its main role is to secrete bile into the small intestine. Bile is important for the digestion and absorption of fats.

Stress, alcohol, medication, excess of processed foods and a lack of dietary fibers are unduly detrimental to liver health. An inadequate amount of fibers reduces the liver’s ability to eliminate toxins, since fibers transport toxic substances out of the body. It is important to avoid processed food and consume food in its most natural state

Gallstones look very much like their name says, stones. They are the most common gallbladder problem, often causing colic and jaundice. The usual symptoms are: pain (from light pressure to intense) under the ribcage on the right sometimes rising all the way into the right shoulder or back, nausea, fever with chills, yellow and itchy skin and indigestion.

The pancreas secretes a mixture of enzymes

The pancreas secretes a mixture of enzymes for the digestion of proteins, fats and carbohydrates. These are trypsinogen, amylase and lipase.
A blockage near the end of the bile duct is the most frequent cause of acute pancreatitis.

The small intestine

The final stages of chemical digestion occur in the small intestine where all the nutrients from food are absorbed. The small intestine is about 6 metres long and is divided into 3 parts known as the duodenum, the jejunum and the ileum.

Production of the digestive enzymes in the stomach usually triggers the production of chemical substances by the pancreas and liver. If the digestive function in the stomach is not right, production of pancreatic juices and bile may be delayed. Food is then poorly digested in the small intestines and this in turn leads to poor absorption of nutrients and even nutritional deficiencies, despite nutritious foods being eaten.

The large intestine

The large intestine completes the process of digestion. It is about 1.5 metres long and divided into sections known as the caecum, the colon and the rectum. Water is absorbed and waste material, known as faeces, is formed and eliminated.

The production of bile triggers the peristaltic action that moves waste matter through the large intestine before too much water is absorbed. If this does not happen, faeces become dry, hard and difficult to pass – giving rise to constipation. Waste matter hanging around in the large intestine tends to putrefy and ferment, leading to bloating, wind and general discomfort. Toxins that should have been expelled can be reabsorbed into the bloodstream, returning to the liver, putting an extra burden on that organ. Skin problems and fatigue are some of the resulting symptoms.

What do you think?

Have you found what you read useful? If so, I would love if you would leave your comment below. Thanks Sonia Chartier

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