Digestion

What is Digestion?

Digestion comprises a complex series of steps by which your body transforms the food you consume into smaller, water-soluble compounds that enter the bloodstream and reach every cell. Depending on each cell’s needs, these compounds serve as fuel, support tissue growth and repair, or help maintain the immune system. The organs that carry out this transformation collectively form the digestive system. At times, digestive discomfort may be linked to conditions like gastroenteritis or constipation.

Digestive system

The digestive system consists of the gastrointestinal tract (GI tract) plus the liver, pancreas and gallbladder. The GI tract spans roughly 8 metres and includes these hollow organs:

• Mouth
• Oesophagus
• Stomach
• Small intestine
• Large intestine
• Anus

As food moves through these hollow passageways, the liver, pancreas and gallbladder (the “solid” organs) release enzymes and fluids that aid digestion.

What is the digestion process?

Digestion starts in the mouth when chewing breaks food into smaller pieces and mixes it with saliva, which contains enzymes that begin carbohydrate breakdown. The softened mass, or bolus, then travels down the oesophagus once swallowed. Mouth

• Chewing grinds food into smaller pieces and mixes it with saliva, which contains the enzyme amylase to begin breaking down carbohydrates.
• The tongue shapes the chewed mass into a soft ball called a bolus, ready for swallowing.

Oesophagus

• Once you swallow, the bolus enters the oesophagus, a muscular tube that uses rhythmic contractions (peristalsis) to propel food downward.
• A flap called the epiglottis closes over the windpipe to ensure the bolus moves safely into the digestive tract.

Stomach

• In the stomach, the bolus is mixed with gastric juices, hydrochloric acid and pepsin, to further break down proteins and kill potential pathogens.
• Stomach muscles churn the mixture into a semi-liquid slurry called chyme, which is gradually released into the small intestine.

Small intestine

• The chyme enters the small intestine, where pancreatic enzymes and bile from the liver and gallbladder complete the digestion of proteins, fats, and carbohydrates.
• The inner walls of the small intestine are lined with villi and microvilli, tiny finger-like projections that dramatically increase surface area and absorb nutrients into the bloodstream.

Large intestine

• Remaining indigestible material moves into the large intestine, where water and electrolytes are absorbed, converting the mix into more solid waste.
• Beneficial gut bacteria ferment some of the leftovers, producing vitamins (such as vitamin K) and gases as byproducts.

Rectum and anus

• Solid waste (feces) is stored in the rectum until pressure stimulates the defecation reflex.
• When you choose to expel, the anal sphincters relax and feces pass out through the anus, completing the digestive journey.

How long does it take to digest food?

Digestion times vary by individual. On average, food spends about six to eight hours in the stomach and small intestine. It then takes around 36 hours to pass through the large intestine. Overall, from swallowing to elimination, the process can range from two to five days, depending on the person and the types of food eaten.

Common digestive problems

Following are some Common digestive problems: Gas Gas is a normal byproduct of digestion, released as burps or flatulence. Swallowed air or the breakdown of certain foods, and even some medications such as aspirin, antacids, anti-diarrhoeal drugs, opioids, fibre supplements, and iron supplements, can increase gas. Bloating When gas builds up in the stomach or intestines, it can cause abdominal swelling and a sensation of fullness or discomfort. Heartburn Heartburn (also known as reflux or GORD) presents as a burning or aching sensation behind the breastbone, typically after eating and worsening when bending or lying down. It happens when stomach acid flows back into the oesophagus. Diverticulitis Small pouches (diverticula) can form in the intestinal wall, becoming inflamed or infected and causing severe pain, fever, nausea, and changes in bowel habits. Irritable bowel syndrome (IBS) IBS is marked by abdominal pain before or after bowel movements, along with diarrhoea, constipation, or both. Factors such as gut microbe imbalances, stress, and diet may contribute. Stomach ulcers Gastric ulcers are tears in the stomach lining that can become inflamed and painful, often due to Helicobacter pylori infection or prolonged use of anti-inflammatory medications. Gastroenteritis Often called “gastro,” this is a short-lived infection or inflammation of the stomach and intestines, producing cramps, vomiting, and/or diarrhoea. Diarrhoea Characterized by loose, watery stools and frequent bowel movements, diarrhoea may result from food intolerances, infections, or medication side effects. Constipation Constipation involves hard, dry stools or difficulty passing them. It can stem from factors like diet, inactivity, certain medications, dehydration, or illness. Other conditions that can affect digestion include coeliac disease (an autoimmune response to gluten), lactose intolerance (difficulty digesting lactose), and inflammatory bowel diseases such as ulcerative colitis and Crohn’s disease.

When to see a doctor?

Occasional indigestion, heartburn, or minor digestive issues are common. However, consult your doctor if you experience any of the following:

• Persistent or worsening heartburn, frequent vomiting, or need medication for relief over several weeks
• Vomiting blood
• Unexplained, ongoing abdominal pain
• A sensation of food being stuck in your chest
• Unintended weight loss
• Pain or difficulty when swallowing
• Chronic hoarseness or sore throat
• Black or bloody stools
• Persistent diarrhoea
• Fewer than two bowel movements per week or significant changes in bowel habits