What is the Digestive System?
The human digestive system digests food, absorbs nutrients, and then excretes waste products as poop. It consists of five parts: mouth, pharynx, oesophagus, stomach, small intestine, and large intestine. Accessory organs include the teeth, the tongue, the salivary glands, the liver, the gallbladder, and the pancreas.3
What Does the Digestive System do?
Our digestive system’s job is simple and fundamental: converting food into energy for our survival.4 When we eat an apple, for example, it goes through three different body processes: digestion, absorption, and defecation. And all good things come in threes, right?
The Anatomy of the Digestive System
Several organs and body parts work together like clockwork, each one a part of a well-oiled machine needed to keep the digestive system running smoothly. Let's get to know them.
1. Oral cavity
Digestion starts in the mouth with the mechanical processing of the food by the teeth and tongue. Tasting what we eat, and lubrication of food (so we can swallow it!) also takes place here.3
The pharynx is a passageway that transports food materials to the oesophagus. Common names for it include the gullet, or food pipe.3,6
Through waves of muscular contractions, the oesophagus is primarily responsible for carrying food materials into the stomach.3
In the stomach, food is mechanically and chemically broken down. Muscular contractions and relaxations of the stomach lead to the formation of chyme, which is a mixture of partially digested food particles in a liquid state. Food is then broken down by gastric juices.3
5. Small intestine
90% of nutrients are absorbed in the small intestine. During digestion, the small intestine receives chyme from the stomach and digestive material from the pancreas and liver. The small intestine is the primary site of chemical digestion and absorption.3
6. Large instestine
The large intestine is responsible for absorbing water, vitamins, and salts.25 It then moves faeces into the rectum through waves of muscle contractions. In the rectum, receptors initiate the pooping process, which concludes at the anus.3
The Digestive Process
Six actions take place in the digestive system before the body can use nutrients.6
The digestive process begins with everyone’s favourite pastime; eating! 6
2. Mechanical Digestion
Food pieces must be broken down into smaller pieces for digestion. Mechanical digestion begins in the mouth, with the teeth and tongue, followed by churning and mixing in the stomach.6
3. Chemical Digestion
Chemical digestion breaks down carbohydrates, proteins, and fats into smaller molecules that can be absorbed for use in the body.6
In the stomach, smooth muscle contractions combine food particles with enzymes and other fluids. Further waves of muscle contractions in the intestines also move food particles through the digestive tract.6
During absorption, nutrients enter the blood vessels through the lining of the small and large intestine. The blood can then transport the nutrients around the body to where they are needed. 6
The body eliminates food molecules that cannot be digested or absorbed. This final little process is better known as pooping. 6
Frequently Asked Questions
Gastrointestinal (GI) tract organs have a layer of muscle that allows their walls to move. This movement, called peristalsis, can be compared to an ocean wave moving through a muscle.7 As a result, food and liquid are mixed and pushed through the GI tract.8
As food moves through your digestive tract, it is broken down into smaller pieces through motion (chewing and squeezing) and the mixing of digestive juices. These juices include stomach acid, bile, and enzymes.8
In the small intestine, digested food molecules, water, and other nutrients are absorbed. Most materials enter the bloodstream upon absorption. Here, they are transported to other body parts for storage or chemical modification. The sugars, amino acids, fatty acids, and glycerol in these substances allow your body to produce energy, grow, and repair cells.8
What are Common Conditions Related to the Digestive System?
As much as it should run like a well-oiled machine, and usually does, sometimes the digestive system does encounter problems. Don’t we all?
About one in six hospital admissions are for a primary gastrointestinal disease and about one in six of the main surgical procedures in general hospitals are performed on the digestive tract.11
Here are a few conditions that can affect the digestive system.
Constipation is when you have infrequent or uncomfortable bowel movements, and usually means passing only small amounts of hard dry stool, if any at all. As a general rule, you would be considered constipated if you are passing stool less than 3 times a week 16, however, we are all different, and a normal amount of bowel movements could range anywhere from 3 times a day to 3 times a week.16
Acute diarrhoea is the second most commonly reported illness in the United States. Acute diarrhoea refers to diarrhoea lasting less than two weeks. diarrhoea that lasts longer than four weeks is considered chronic. Loose or watery stools are commonly described as a sign of diarrhoea. Viruses are the most common cause of acute diarrhoea. Chronic diarrhoea requires accurate diagnosis due to its multiple causes, including Crohn's disease, parasitic intestinal infections, and irritable bowel syndrome (IBS), to name a few.21
Irritable Bowel Syndrome (IBS)
IBS is a gastrointestinal disorder that affects 17% of people in the UK.27 It is a chronic condition, meaning it is generally long lasting. However, symptoms tend to come and go in bouts, in episodes knows as “flares”. Symptoms can include abdominal pain, diarrhoea, constipation, and/or bloating. The exact cause is unknown, but scientists believe it may relate to the communication between the brain and the gut, known as the gut-brain axis.26
Diverticulosis occurs when tiny sacs in the intestinal tract wall become inflamed or infected. There is a high incidence of diverticulosis among older adults. Most patients with diverticulosis don't know they have the condition, and it doesn't cause them any trouble.12
Peptic ulcers affect around 5–10% of the global population.13 An “ulcer” is an open sore and the word “peptic” means the acid is at the root of the problem. The two most common types of peptic ulcers are “gastric ulcers” and “duodenal” ulcers referring to the location where it is found.14
Haemorrhoids are veins in the rectum or anal canal. Swollen or dilated blood vessels can cause symptoms such as rectal bleeding. Haemorrhoids usually go away on their own or with simple measures. These measures include avoidance of straining and treatment of constipation.15
About 20% of the UK population suffers from GERD. It’s a condition in which stomach contents flow upwards into the oesophagus. Heartburn and regurgitation are the most common symptoms.22
Coeliac disease (CD) is a digestive condition characterised by inflammation of the small intestine precipitated by eating gluten-containing foods. About one in every 100 people may have coeliac disease in the UK and numbers are higher in women than men.23
When to Contact Medical Professionals About Digestive Issues
Improving your intestinal health requires action, but the results are well worth it. The benefits of treating constipation, for example, extend to all aspects of life. You feel ready to face a new day after a good morning poop.
If dietary and lifestyle adjustments don’t help, you can try laxatives.
Consult your GP if you experience symptoms like constipation, diarrhoea, vomiting, stomach cramps, excessive gas, or heartburn on a regular basis.
Taking care of your digestive system is taking care of yourself, so don’t neglect it, listen closely to the hum and whir of something not feeling right, and do what you need to make sure your digestive system keeps on and carries on running smoothly.
MAT-XU-2304716 (v1.0) November 2023
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- Stanford Medicine (2022) The Digestive Process: How Does the Esophagus Work? , The Digestive Process: How Does the Esophagus Work? Stanford Medicine . https://www.stanfordchildrens.org/en/topic/default?id=the-digestive-process-how-does-the-esophagus-work-134-195 (Accessed: December 5, 2022).
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- National Cancer Institute (2022) Introduction to the digestive system, Introduction to the Digestive System . National Cancer Institute. https://training.seer.cancer.gov/anatomy/digestive/ (Accessed: December 5, 2022).
- International Foundation for Gastrointestinal Disorders (2022) The digestive system, IFFGD. International Foundation for Gastrointestinal Disorders. Available at: https://iffgd.org/gi-disorders/the-digestive-system/ (Accessed: December 6, 2022).
- National Institute of Diabetes and Digestive and Kidney Diseases (2017) Your digestive system & how it works, National Institute of Diabetes and Digestive and Kidney Diseases. U.S. Department of Health and Human Services. Available at: https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-system-how-it-works (Accessed: December 6, 2022).
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- Kienzle-Horn S, Vix JM, Schuijt C, Peil H, Jordan CC, Kamm MA. Efficacy and safety of bisacodyl in the acute treatment of constipation: a double-blind, randomized, placebo-controlled study. Aliment Pharmacol Ther. 2006 May 15;23(10):1479-88. doi: 10.1111/j.1365-2036.2006.02903.x. PMID: 16669963.
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- Abbasi-Kangevari M, Ahmadi N, Fattahi N, Rezaei N, Malekpour M-R, Ghamari S-H, et al. (2022) Quality of care of peptic ulcer disease worldwide: A systematic analysis for the global burden of disease study 1990–2019. PLoS ONE 17(8): e0271284. https://doi.org/10.1371/journal.pone.0271284 (Accessed September 2023
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