97 Fun Facts About The Digestive System

At which blind pouch in the lower right abdomen does the large bowel begin?

The cecum is the blind pouch where the large bowel begins; the appendix hangs from it in the right iliac region, which is why appendicitis pain settles in the lower right abdomen.

What enzyme in saliva begins the chemical digestion of carbohydrates?

Amylase starts on starch in the mouth, but food leaves too soon for it to finish, so the pancreas sends more amylase into the small intestine.

Which small fleshy flap at the back of the mouth rises when you swallow to help keep food out of the nose?

The uvula rises with the soft palate when you swallow, and it can also vibrate and add to the sound of snoring.

Which tissue covering the crown of a tooth is the hardest substance in the human body?

Enamel is still vulnerable: bacteria in plaque turn sugar and starch into acids that eat away at it, causing tooth decay.

In a hiatal hernia, the upper part of the stomach bulges through an opening in which muscle?

The diaphragm normally helps keep acid from rising out of the stomach, so a hiatal hernia makes reflux and heartburn more likely.

Which hormone signals the stomach to secrete more acid and increases its muscle contractions?

Gastrin is released as a meal reaches and stretches the stomach, so eating itself switches on more acid secretion.

What is the process of taking food into the body through the mouth called?

Ingestion hands food on to swallowing, which you control only at first; its throat and food-pipe stages then run automatically.

Pepsin is an enzyme primarily responsible for breaking down which type of macromolecule in the stomach?

Pepsin breaks proteins into shorter peptides; the stomach secretes it as inactive pepsinogen, which gastric acid converts into the working enzyme.

Which compound, secreted by cells of its lining, makes the stomach strongly acidic?

Hydrochloric acid kills much of the bacteria swallowed with food and is needed to switch inactive pepsinogen into pepsin.

What is the scientific term for chewing, the process by which teeth crush and grind food?

Mastication breaks food into smaller pieces with more surface area, so digestive enzymes can work on it faster.

Peyer's patches, immune tissue that guards against gut bacteria, are concentrated in which part of the gut?

The ileum is where Peyer's patches are densest, so typhoid, which infects them, can perforate the gut wall there.

Which muscular ring at the stomach's entrance prevents acid reflux?

When the lower esophageal sphincter is weak or relaxes at the wrong time, stomach acid can back up and cause heartburn.

The absorption of vitamin B12 in the small intestine requires the presence of what gastric protein?

Intrinsic factor lets vitamin B12 be absorbed, and a lack of B12 can cause anemia.

What organ stores bile produced by the liver?

The gallbladder concentrates the bile it stores, yet people can live without one because bile has other ways to reach the intestine.

Which vitamin, partly made by bacteria in the colon, is needed for blood clotting?

Newborns have very little vitamin K, so babies usually get a vitamin K shot soon after birth.

The churning action of the stomach walls is a form of what type of digestion?

Mechanical digestion in the stomach relies on an extra inner oblique muscle layer, found nowhere else in the gut, that lets it churn food.

Which simple sugar is the main end product of carbohydrate digestion and the body's chief energy source?

Glucose absorbed from the gut travels first to the liver through the hepatic portal vein, before reaching the rest of the body.

Which Russian physiologist won the 1904 Nobel Prize in medicine for his work on digestion?

Ivan Pavlov's digestion research led him to study conditioned reflexes, including his famous experiments on dogs.

Which duodenal hormone stimulates the pancreas to release bicarbonate-rich fluid?

Secretin is released by S cells of the duodenum when acid arrives; it makes the pancreas secrete a bicarbonate-rich juice that neutralizes stomach acid in the small intestine.

Which lumps of lymphoid tissue at the back of the throat help trap germs coming in through the mouth?

Tonsils and adenoids trap germs, and when the tonsils become inflamed, usually from a virus, the result is tonsillitis.

Bile salts emulsify fats into smaller droplets, increasing the surface area for which enzyme?

Lipase work begins before the stomach: glands on the tongue release lingual lipase, which keeps digesting fat in the stomach.

The small intestine is longer than the large intestine, so why is it called 'small'?

It is narrower: the large intestine is more than twice as wide, even though the small intestine is several times longer.

What is the primary function of the epiglottis during swallowing?

The epiglottis folds down over the larynx to keep food out of the trachea; if food gets in anyway, a cough reflex tries to force it out.

What is the semi-fluid mass of partly digested food and digestive secretions that leaves the stomach?

Chyme takes its name from the Greek for 'juice', and the stomach makes it by churning food with gastric juice in mixing waves.

Which cells in the stomach's glands secrete the acid in gastric juice?

Parietal cells pump out acid with a proton pump, the same pump that proton-pump inhibitor drugs block to cut stomach acid.

What are the fat-absorbing lymphatic capillaries within the villi of the small bowel called?

Sugars and amino acids pass straight into the blood, but digested fats enter the lacteals and reach the blood through the lymphatic system.

What is the small, rounded mass of chewed food mixed with saliva, ready to be swallowed?

While a bolus passes through the throat, breathing stops for a moment.

Which disease is an autoimmune reaction to gluten that damages the small bowel's villi?

Celiac disease is an autoimmune response to gluten in which the immune system flattens the villi of the small bowel, impairing absorption; a strict gluten-free diet is the treatment.

Which section of the large bowel comes immediately after the transverse portion?

Strong waves sweep waste through the descending colon during or soon after meals, which is why eating can bring on the urge to use the toilet.

What are the enzymes anchored on the small bowel's microvilli that finish digesting sugars and peptides called?

Brush border enzymes include enteropeptidase, which switches on trypsin and so activates the pancreas's digestive enzymes.

What is the medical term for difficulty swallowing?

Dysphagia is difficulty swallowing, and it often follows a stroke or a food-pipe problem such as GERD.

Which part of the large bowel holds feces until defecation?

Rectum comes from the Latin for 'straight intestine', yet the human rectum follows the curve of the sacrum.

What are the specialized macrophages found in the liver that remove old blood cells and pathogens?

Kupffer cells are the first cells to meet gut bacteria carried to the liver in portal blood, and they clear old blood cells too.

Which cranial nerve regulates many digestive processes, including gastric secretion and motility?

The vagus nerve is why the sight, smell or thought of food gets the stomach secreting acid before you even take a bite.

Which 'hunger hormone', made mainly by the stomach, stimulates appetite?

Ghrelin, made mainly by the stomach, rises before meals and falls after eating, and it acts on the hypothalamus to stir appetite.

What is the circulation of bile acids from the liver to the small intestine and back to the liver called?

Enterohepatic circulation can be broken by drugs that trap bile acids in the gut, which lowers blood cholesterol.

What is an open sore that develops on the lining of the esophagus, stomach, or small intestine?

The classic sign of a duodenal ulcer is waking at night with upper abdominal pain that eases with eating; most are caused by Helicobacter pylori or heavy NSAID use.

What type of muscle tissue is primarily found in the walls of the alimentary canal, enabling peristalsis?

Smooth muscle does most of the work, but the mouth, throat, upper food pipe and outer anal sphincter use skeletal muscle you control voluntarily.

Which duodenal hormone, formerly called pancreozymin, triggers the release of pancreatic juice and bile?

Cholecystokinin is released when fatty food arrives in the duodenum, bringing on a flow of enzyme-rich pancreatic juice.

Which small bumps on the tongue's surface give it its rough texture?

Not all papillae taste: the thread-like filiform papillae carry no taste buds and instead help the tongue grip and move food.

Which procedure passes a thin tube with a tiny camera through a body opening to look inside organs such as the stomach?

Endoscopy of the stomach usually needs no incision, though a sore throat afterwards is common.

Which layer of the alimentary canal wall contains blood vessels, nerves, and lymphatic tissue?

The submucosa carries the blood and lymphatic vessels that transport absorbed nutrients away from the gut lining.

Which common condition means the body can't properly digest the sugar found in milk?

People with lactose intolerance often manage it by eating less lactose or taking lactase pills or drops.

Which pigment from broken-down red blood cells turns the skin and eyes yellow when it builds up?

Gut bacteria turn bilirubin into stercobilin, the brown pigment that gives stool its colour.

Which sphincter controls how quickly the stomach empties into the small intestine?

The pyloric sphincter stays mostly closed, letting only liquids and small particles through, so the stomach empties a little at a time.

What are live 'good' microbes in foods like yogurt, taken to support gut health, called?

Probiotics rest on a reversal: many bacteria are helpful, not germs, and some in the gut help digest food or make vitamins.

What mainly stops the stomach from digesting its own lining?

A layer of mucus rich in acid-neutralising bicarbonate coats the stomach wall, and drugs such as aspirin can weaken it.

About 90% of which mood-regulating chemical messenger is made in the gut rather than in the brain?

Serotonin made by cells in the gut lining sets how fast the intestines move. When an irritant arrives in food, they release more of it to hurry the contents out.

Stretched out at autopsy, about how long is the whole human digestive tract from mouth to anus?

30 feet is the autopsy figure, but the gut is considerably shorter in a living body because its muscular walls stay half-tensed.

Which everyday item is wrongly said to sit in the stomach for seven years if it is swallowed?

Chewing gum is mostly indigestible, yet it travels through the gut at the same rate as any other matter instead of lingering.

Which gas, present only in traces, gives human flatulence its rotten-egg smell?

Hydrogen sulfide and its sulfur cousins do the damage: over 99% of passed gas is odourless nitrogen, hydrogen, carbon dioxide and methane.

Which small organ, long dismissed as useless, may act as a reservoir for helpful gut bacteria?

The appendix may restock the gut with its usual bacteria after an illness has flushed them out. Its formal label, vermiform, comes from the Latin for 'worm-shaped'.

Which mesh of neurons in the gut wall is often called the body's 'second brain'?

The enteric nervous system can run the gut on its own: it keeps working even when the vagus nerve, its main link to the brain, has been cut.

Which segmented parasite, caught from undercooked beef, can grow several metres long inside the gut?

A beef tapeworm is normally 4 to 10 metres long as an adult, and specimens of more than 22 metres have been reported.

Which English city gives its name to the seven-type medical chart that sorts human stool by shape?

Bristol Royal Infirmary doctors devised the scale in 1997. It runs from type 1, separate hard lumps like nuts, to type 7, entirely liquid.

Which US Army surgeon studied digestion through an unhealed gunshot hole in a man's stomach?

William Beaumont tied food to a string, lowered it through the hole in fur-company worker Alexis St. Martin, and pulled it out every few hours to see how far it had digested.

Which medical term, from a Greek word thought to imitate the sound, names a rumbling stomach?

Borborygmus is the noise of gas and fluid being pushed through the gut, and an empty stomach amplifies it, which is why hunger rumbles are the loudest.

Which fire-stealing Titan had his liver eaten by an eagle each day, only for it to regrow each night?

Prometheus's punishment holds a grain of truth: the liver is the only internal organ able to regrow to full size after part of it is lost.

Which tough plant carbohydrate passes through people undigested, adding bulk as insoluble fibre?

Cellulose defeats human enzymes, but cows and termites can live on it because microbes in their guts break it down for them.

Which molecules, nine of them essential in the diet, are the end product of digesting meat and eggs?

Amino acids are small enough to be absorbed through the gut wall; the nine 'essential' ones are those the body cannot build for itself.

Which teeth, eight in a full adult set, are shaped for cutting food rather than tearing or crushing?

Incisors do the cutting, canines the tearing and molars the crushing. The name comes from the Latin incidere, 'to cut'.

Which name is given to the third molars, which usually erupt between the late teens and early twenties?

Wisdom teeth earned the name by arriving so late, at an age when people are presumably wiser than when their other teeth came through.

Which condition, a common result of heavy drinking, replaces working liver tissue with scar tissue?

Cirrhosis typically creeps up over months or years, and the liver shrinks as the scarring spreads. Chronic hepatitis B and C are other leading causes.

Which muscular passage behind the nose and mouth carries both breathed air and swallowed food?

The pharynx belongs to both the digestive and the respiratory systems, and anatomists divide it into three sections named for the nose, mouth and voice box.

Which branch of medicine, whose doctors perform colonoscopies, covers the gut, liver and pancreas?

Gastroenterology takes its name from the Greek for 'belly' and 'intestine'; its practitioners are often just called GI doctors.

Which almond-sized region of the brain controls hunger, thirst and body temperature?

The hypothalamus sits just below the thalamus, and it also governs sleep, fatigue and the body's daily rhythms.

Which mostly harmless gut bacterium is named after the paediatrician Escherich, who first described it?

E. coli is a tiny minority in the gut: it and similar bacteria make up only about 0.1% of the microbes there. Most strains are harmless, though a few bring on serious food poisoning.

Which stretch of gut is named from the Latin for 'fasting' because it was often found empty after death?

The jejunum is the middle section of the small bowel, and its unusually vigorous muscular squeezing is what clears food out of it so quickly.

Which folds in the lining of the empty stomach flatten out to let it expand as it fills with food?

Rugae let the stomach take in a large meal by increasing its volume without increasing the pressure inside.

Which pancreatic enzyme is made in an inactive form and switched on only once it reaches the gut?

Trypsin is stored as inactive trypsinogen because the working enzyme would severely damage the pancreas's own tissue. An enzyme in the gut wall switches it on.

Which starch-like carbohydrate does the liver store after meals and break down to steady blood sugar?

Glycogen is packed more densely into the liver than into any other tissue. Muscles hold more of it in total, but they keep theirs for their own use.

Into which less toxic compound does the liver convert ammonia so that the kidneys can excrete it?

Urea is made mainly in the liver by the first metabolic cycle ever discovered, worked out by Hans Krebs and Kurt Henseleit five years before the better-known Krebs cycle.

Which thin membrane lines the abdominal cavity and wraps around most of the organs inside it?

The peritoneum does more than wrap: it holds the abdominal organs in place and is the route by which blood vessels, lymph vessels and nerves reach them.

Which fold of tissue, now counted as a single organ, anchors the intestines to the abdomen's back wall?

The mesentery was long treated as a set of separate membranes, although a description of it as one structure goes back at least to Leonardo da Vinci.

Which term describes glands, such as the salivary glands, that release secretions through a duct?

Exocrine glands deliver through ducts, while endocrine glands secrete straight into the bloodstream. The liver and the pancreas manage to be both.

Which hormone, made by fat cells, signals the brain that energy stores are full and dampens hunger?

Leptin takes its name from the Greek for 'thin', yet in obesity the body grows less sensitive to it and stops registering that it is full.

Which Australian Nobel laureate drank a broth of bacteria to prove they infect the stomach?

Barry Marshall felt nauseous within three days of swallowing Helicobacter pylori. He and Robin Warren shared the 2005 Nobel Prize for discovering the bacterium's role in stomach disease.

Which largest pair of salivary glands swells painfully during mumps?

The parotid glands, whose name means 'beside the ear', are the biggest of the three main pairs yet supply only about a quarter of the mouth's saliva.

Which chronic bowel condition, named after a New York doctor, can strike anywhere from mouth to anus?

Crohn's disease was described in 1932 by Burrill Crohn and two colleagues at Mount Sinai Hospital. Smoking raises the risk of it, yet lowers the risk of its cousin, ulcerative colitis.

Which gut hormone, mimicked by the weight-loss drug semaglutide, slows the emptying of the stomach?

GLP-1 released by the gut has a half-life of only about two minutes, whereas the modified copy in the drug lasts about seven days.

By which process do bacteria in the colon break down dietary fibre into short-chain fatty acids?

Fermentation of fibre produces butyrate, the main energy source of the cells lining the colon, so fibre feeds the gut even though people cannot digest it.

From which lipid, better known for building up in artery walls, do liver cells make bile acids?

Cholesterol is the raw material: roughly half of what the body makes each day is turned into bile acids, which also help carry it out of the body.

Which reaction, the reverse of condensation, do digestive enzymes use to split large food molecules?

Hydrolysis means 'unbinding with water': every bond cut in a large food molecule uses up one water molecule.

Which dark, tar-like first stool of a newborn is made of material swallowed in the womb?

Meconium is a very dark olive green and almost odourless, a mix of amniotic fluid, shed cells and fine body hair taken in before birth.

Which vessel carries nutrient-rich blood from the gut to the liver before it returns to the heart?

The portal vein delivers about 75% of the liver's blood, and strictly it is not a true vein, because it runs between two capillary beds instead of straight to the heart.

Which metal's sulfate is swallowed as a milky 'meal' so that the stomach and bowel show up on X-rays?

Barium is highly toxic in its water-soluble compounds, but the sulfate dissolves so poorly that the patient absorbs no harmful amount of the metal.

Which phenomenon describes the liver breaking down much of a swallowed drug before it can circulate?

The first-pass effect can greatly cut how much of a swallowed medicine becomes available to the body, which is why some drugs are infused straight into a vein instead.

Which muscle, running from cheekbone to lower jaw, is one of the strongest used for grinding food?

The masseter is found only in mammals and is particularly powerful in herbivores, which need it to grind down tough plant matter.

Which cell type in the stomach's glands releases pepsinogen, the inactive forerunner of the enzyme pepsin?

Chief cells release pepsinogen in a harmless form, and it becomes working pepsin only when acid from neighbouring cells converts it. They also make a fat-digesting enzyme.

Which small sac-like pouches give the wall of the colon its distinctive segmented appearance?

Haustra pass the colon's contents along slowly: as one fills and stretches, its muscle contracts and pushes the load into the next pouch.

Which pigment, an end product of the breakdown of old red blood cells, makes human feces brown?

Stercobilin was first isolated from feces in 1932, and it is now measured in rivers as a chemical marker of sewage pollution.

Which German scientist, famous for extending cell theory to animals, discovered the enzyme pepsin?

Theodor Schwann found pepsin in 1836 and named it from the Greek for 'digestion'. He also invented the term 'metabolism'.

The stomach has an extra muscle layer, found nowhere else in the gut, whose fibres run in which direction?

Oblique fibres make up the innermost of the stomach's three muscle coats, lying at an angle to the circular and lengthwise layers that the rest of the gut also has.

Which apron-like fatty fold hanging from the stomach did a surgeon dub the 'abdominal policeman'?

The greater omentum got the nickname in 1906 from the surgeon James Rutherford Morison, because it wraps itself around infected areas and walls them off from the rest of the abdomen.

Which germ-killing enzyme in saliva and tears was named by Alexander Fleming, of penicillin fame?

Lysozyme got its name in 1922, when Fleming showed that secretions from the nose could rapidly dissolve bacteria. It is also abundant in human milk.

Which bodily response, most active in the morning, triggers the urge to empty the bowels after a meal?

The gastrocolic reflex answers the stretching of a filling stomach with strong contractions of the colon, clearing space for the incoming meal.

Which back-and-forth squeezing by the gut's circular muscles mixes food with digestive juices?

Segmentation shoves the gut's contents in both directions at once, whereas peristalsis is a one-way wave that carries them onward.