GERD
Acidic stomach contents repeatedly rise into the esophagus because the sphincter between them does not close properly, irritating the lining.
Main symptoms
- Burning rising from the chest
- Regurgitation of acid or food
- Dry night-time cough
- +2
The journey
Our body
The digestive tract is a continuous nine-metre corridor running through the body. Walk it stretch by stretch and see what each chamber does.
Full journey: 24 to 72 hours
- 15–30 s
Mouth
Where it all begins
Digestion starts before the first bite: the smell and sight of food already switch on the salivary glands. As you chew, your teeth break food into small particles and saliva moistens it, while salivary amylase begins breaking down starches. The tongue shapes the food into a bolus and pushes it toward the pharynx to be swallowed.
Did you know
We produce 1 to 1.5 litres of saliva a day. Chewing slowly is not empty advice: it improves digestion and your sense of fullness.
- 5–10 s
Esophagus
The muscular corridor
A tube about 25 centimetres long connecting the throat to the stomach. It absorbs no nutrients: its job is transport. It moves food by peristalsis, coordinated muscular waves that push the bolus downward even if you are lying down. At its lower end, the lower esophageal sphincter opens to let food through and closes again so acid cannot come back up.
Did you know
When that sphincter does not close properly, acid rises and reflux appears. It is the origin of GERD, the most common digestive disease.
- 2–4 h
Stomach
The acid cauldron
A muscular pouch that can expand to hold nearly a litre and a half. Here food mixes with hydrochloric acid and pepsin until it becomes chyme, a semi-liquid paste. The acid does two jobs: it denatures proteins so they can be digested, and it kills most of the microorganisms that arrive with food. A layer of mucus protects the stomach wall itself from that acid.
Did you know
Gastric juice has a pH of 1.5 to 3.5, acidic enough to dissolve metal. When the mucus barrier fails, gastritis and ulcers appear.
- 3–6 h
Small intestine
Where life is absorbed
Seven metres coiled into three sections: duodenum, jejunum and ileum. This is the real centre of nutrition. Its wall is carpeted with villi and microvilli that multiply the absorptive surface to around 250 square metres, comparable to a tennis court. Sugars, amino acids, fats, vitamins and minerals are absorbed here and pass into the bloodstream.
Did you know
90% of nutrient absorption happens here. When the villi are damaged, as in celiac disease, nutritional deficiencies appear even with a good diet.
- 24/7
Liver, pancreas and gallbladder
The chemical laboratory
These three organs never receive the food itself, yet without them digestion would be impossible. The liver produces bile and processes everything that is absorbed, filtering toxins and regulating blood sugar. The gallbladder stores and concentrates that bile, releasing it into the duodenum when fat arrives. The pancreas supplies enzymes that digest proteins, fats and carbohydrates, plus the insulin that controls glucose.
Did you know
The liver is the only internal organ able to regenerate: it can regain its full size after losing up to 70% of its mass.
- 12–48 h
Large intestine
Home of the microbiome
About a metre and a half long, its main job is to recover water and electrolytes from what remains. This is where the gut microbiome lives: trillions of bacteria that ferment the fibre we could not digest, produce short-chain fatty acids that feed the colon cells, and synthesise vitamins such as K and several B vitamins. That ecosystem shapes immunity, metabolism and even mood.
Did you know
You host roughly 100 trillion microorganisms, with more bacterial cells than your own human cells. Dietary fibre is their main food.
- variable
Rectum and anus
The end of the road
The rectum stores waste until the defecation reflex signals that it is time to eliminate it. Two sphincters, one involuntary and one under voluntary control, let you decide when. Repeatedly ignoring that signal is one of the most common causes of chronic constipation, and excessive straining encourages hemorrhoids and fissures.
Did you know
The full journey, mouth to anus, takes 24 to 72 hours in a healthy person. Transit that is much faster or much slower is a signal worth watching.
The 20 profiles
When something goes wrong
The 20 most common digestive diseases, grouped by the stretch they affect.
Esophagus
01Stomach
05
Gastritis
Inflammation of the stomach lining. It can be acute and short-lived or chronic, and in many cases the bacterium Helicobacter pylori is behind it.
Main symptoms
- Pain or burning in the upper abdomen
- Feeling full very early
- Nausea
- +2
Peptic ulcer
An open sore in the wall of the stomach or the first part of the small intestine, where acid has eroded the tissue.
Main symptoms
- Burning pain in the centre of the abdomen
- Discomfort that wakes you at night
- Relief or worsening when eating
- +2
H. pylori
A bacterium able to survive in stomach acid. It colonises the gastric lining and is the main cause of chronic gastritis and peptic ulcer.
Main symptoms
- Often none
- Burning or pain in the upper abdomen
- Early fullness
- +2
Functional dyspepsia
Persistent upper abdominal discomfort with no lesion to explain it. The stomach is not damaged, but it functions and perceives abnormally.
Main symptoms
- Uncomfortable fullness after eating
- Very early satiety
- Burning or pain in the epigastrium
- +2
Gastroparesis
The stomach empties too slowly with no obstruction present, because the muscle or the nerves coordinating it are not working properly.
Main symptoms
- Nausea and vomiting, sometimes of food eaten hours earlier
- Fullness after only a few bites
- Upper abdominal bloating
- +2
Small intestine
03
Celiac disease
An autoimmune disease in which gluten triggers the immune system to attack the villi of the small intestine.
Main symptoms
- Chronic diarrhea or greasy stools
- Bloating and abdominal pain
- Weight loss
- +3
Lactose intolerance
The gut produces little lactase, the enzyme that splits milk sugar, and undigested lactose ferments in the colon.
Main symptoms
- Gas and bloating after dairy
- Cramping
- Diarrhea
- +2
SIBO
An excess of bacteria in the small intestine, which should host few. They ferment food before it is absorbed, producing gas and malabsorption.
Main symptoms
- Bloating that builds through the day
- Abundant gas
- Diarrhea or, less often, constipation
- +2
Liver, pancreas and gallbladder
04
Gallstones
Stones that form in the gallbladder when bile becomes too concentrated. Many cause no symptoms; others block the bile duct and trigger an attack.
Main symptoms
- Intense pain under the right ribs
- Pain radiating to the shoulder or back
- Nausea and vomiting
- +2
Hepatitis
Inflammation of the liver. It can be caused by viruses (A, B, C, D, E), alcohol, medications, or metabolic or autoimmune causes.
Main symptoms
- Marked fatigue
- Jaundice: yellow skin and eyes
- Dark urine and pale stools
- +2
Fatty liver
Fat accumulating in liver cells, almost always linked to insulin resistance, excess weight, diabetes or cholesterol abnormalities.
Main symptoms
- Often none at all
- Fatigue
- Dull discomfort in the right side
- +1
Pancreatitis
Inflammation of the pancreas, occurring when its own digestive enzymes activate inside the organ and damage it. It can be acute or chronic.
Main symptoms
- Severe upper abdominal pain boring through to the back
- Pain that eases when leaning forward
- Persistent vomiting
- +2
Large intestine
06
IBS
A disorder of gut-brain interaction: the bowel works abnormally and is more sensitive, even though there is no visible damage to its structure.
Main symptoms
- Abdominal pain relieved by bowel movements
- Bloating and gas
- Diarrhea, constipation or alternating between them
- +2
Chronic constipation
Infrequent, hard or difficult-to-pass bowel movements for at least three months, with straining and a sense of not being finished.
Main symptoms
- Fewer than three bowel movements a week
- Hard or pellet-like stools
- Excessive straining
- +2
Chronic diarrhea
Loose or liquid stools most of the time for more than four weeks. It is a symptom, not a diagnosis: the point is to find the cause.
Main symptoms
- Persistent loose or watery stools
- Increased number of bowel movements
- Urgency
- +2
IBD
Chronic immune-driven inflammation of the digestive tract, running in flares and periods of remission. It includes Crohn disease and ulcerative colitis.
Main symptoms
- Prolonged diarrhea, sometimes with blood
- Recurrent abdominal pain
- Urgency and tenesmus
- +3
Diverticulosis and diverticulitis
Small pouches that form in the colon wall. Having them is diverticulosis; when one becomes inflamed or infected, it is diverticulitis.
Main symptoms
- Diverticulosis usually causes no symptoms
- In diverticulitis: pain in the lower left abdomen
- Fever
- +2
Colorectal cancer
One of the most common cancers and, at the same time, one of the most preventable: it almost always begins as a polyp that takes years to transform.
Main symptoms
- In early stages, none
- Blood in the stool or very dark stools
- Persistent change in bowel habit
- +3
