The Digestive System: Beyond the Stomach

The Digestive System: Beyond the Stomach

The processes that happen to our digested food once it leaves the stomach are the most important as this is where the nutrients from the food we eat is absorbed.

human_digestive_systemBelow explains how all of the components beyond the stomach fit together and their roles within digestion. I have put words in bold that refer to the picture above.

 

The duodenum (pictured in between the gall bladder and pancreas)

is the start of the small intestine and regulates the entering of chyme (stomach contents). As chyme enters it stimulates the release of cholecystokinin (no idea how to pronounce this one but all we need to know is that it is a hormone) secreted by cells in the duodenum.

As a result of this hormone the gall bladder, which stores bile that has been made in the liver, empties itself almost completely when it gets this message that food is arriving from the stomach. Between meals, it only lets out a dribble of bile. The bile travels down the bile duct to the duodenum. The pancreatic duct meets it there through a ring of muscle, or sphincter, controlling the release of bile pancreatic fluid into the duodenum.

The duodenum occupies a key position in the digestive system, linking the upper part of the mouth, gullet and stomach with the bowels. It lies just above the navel in a circle hugging the head of the pancreas. It also has a key role in the digestive process, as food arriving from the stomach is only half-digested so this is where essential digestion takes place. This includes starches and fats in particular but proteins are also incompletely digested. Fats at this point are virtually unchanged, it is only when it reaches the duodenum the digestion of fats can actually begin.

Digestive enzymes made in the pancreas, and bile manufactured by the liver, are both poured onto the part-digested food in the intestine, in response to an electro-chemical signal that fatty food is on its way.

First, bile acts on the fats in the food, breaking them down, then pancreatic enzymes, complete the digestion of the remaining starches, fats and proteins.

The enzyme lipase from the pancreas emulsifies the fats, breaking down the fat globules (known as lipids made up of fats and oils) into smaller globules (these are known as fatty acids and glycerol). Bile completes this process. It is only when globules are microscopically small that they can be absorbed into the bloodstream. If this does not happen fatty diarrhoea will be a result.

Which brings us onto the middle part of the small intestine is the jejunum. Villi increase the surface area inside the jejunum, these finger-like projection are one cell thick with a good blood supply, designed to easily absorb digested food molecules quickly into the blood stream by diffusion. (Going back to my GCSE Science here!)

The final section of the small intestine is the ileum. Any further products of digestion are absorbed here and due to the bigger pores so can vitamins such as vitamin B12, minerals and salts. The main difference is the high abundance of lymphoid tissue, this is part of the immune system to protect the body from invasion in the gut. Our digestive tract has the largest mass of lymphoid tissue in the body and is key to protecting us from infection.

Fibre, water and vitamins carry onto be broken down further in the large intestine. Water that has been used in the digestion process is now reabsorbed in the colon and any undigested food and fibre is sorted in the rectum which is then eliminated through the anus (and we all know what happens here).


There’s a ton of more processes and I have tried to keep it as informative but also understandable for anyone to read as well. I hope this gives you an insight into how amazing our digestive system is and how important it is to treat it well and with respect.

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The Digestive System: The Stomach

We continue our journey through the digestive system, we have already learnt about processes in inside the mouth and in the oesophagus.

human_digestive_system

The Stomach

This is where our food now a bolus is exposed to hydrochloric acid produced by the stomach for further digestion. Our saliva is slightly alkaline, so why this change in pH? In this case not only does the acidity destroy potentially harmful microorganisms which could have been swallowed with our food but also different enzymes, which breakdown food, are more effective at different pH values.

The enzyme pepsin for example is produced in the stomach and works best at a low pH level, thriving in an acidic environment. Pepsin breaks down protein into smaller peptides, it is known as a protease enzyme because it does this process by hydrolysis of peptide bonds. The resulting product: peptides, short chains of amino acids (the basic building blocks of the human body and essential for a healthy body). Protein found in meat, eggs, dairy and seeds are broken down by the enzyme pepsin.

This mixture of acid and enzymes are mixed thoroughly by the stomach muscles, softening, sterilising and digesting protein, making the bolus into chyme.

The stomach has three types of contractions:
Rhythmic, 3 per minute, synchronized contractions in the lower part of the stomach which create waves of food particles and juice which splash against a closed sphincter muscle to grind the food down into small particles.
Slow relaxations in the upper part of the stomach lasting a minute or more that follow each swallow and that allow the food to enter the stomach; at other times the upper part of the stomach shows slow contractions which help to empty the stomach.
Between meals, after all the digestible food has left the stomach, there are occasional bursts of very strong, synchronized contractions that are accompanied by opening of the sphincter muscle. The function is to sweep any indigestible particles out of the stomach. Another name for them is the migrating motor complex.

Chyme can stay in the stomach for up to 2-4 hours, this depends on dilution of the stomach acid (this is why it is best to avoid having a drink while eating your meal) and the amount of food you have eaten.

There are certain types of foods you may want to avoid, to decrease the chance of inflammation to the stomach lining. These irritants include:

  • Acidic and Spicy Foods
  • Animal Milks – Milk products are thought to increase acid production.
  • Coffee, Carbonated Beverages, Alcohol and Certain Fruit Juices, such as Citrus Juices
  • High-Fat Foods
  • Highly Salted Foods – can damage the gastric mucosa: the mucous membrane layer of your stomach.
  • Junk Foods and Processed Foods – often contain chemicals that irritate the stomach lining as the are hard to digest and increase acid production

If you are experiencing gastritis (an inflamed stomach lining), causing symptoms of indigestion, stomach pain, vomiting and feeling bloated, you may want to take Antacids. These come in chewable and liquid form and counteract / neutralise the acid build up in your stomach to relive pain, but these shouldn’t be taken on a regular basis.

The best thing is to try and avoid the type of foods above.

I hope this helps and explains the complex processes that are happening within your stomach, if you have a question or would like me to expand on any part please let me know in the comments section below and I will do my best to answer.