CogKnoSys

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Physical

Digestive System

The digestive system breaks food down into small, water-soluble pieces that the body can absorb into the blood and use.

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The idea

The digestive system breaks food down into pieces small enough for the body to absorb and use. It is made of the gastrointestinal tract, a long tube that runs from the mouth to the anus, plus helper organs: the tongue, salivary glands, pancreas, liver and gallbladder. Digestion happens in two ways. Mechanical digestion breaks food into smaller pieces, as when teeth chew it, while chemical digestion uses enzymes to split food into small compounds the body can use.

Digestion starts in the mouth. Chewing mixes food with saliva, which contains an enzyme called amylase that begins to break down starch. The chewed food forms a soft, round mass called a bolus, which is swallowed down the esophagus. Waves of muscle contractions, called peristalsis, push it along into the stomach. There, gastric juice containing hydrochloric acid and an enzyme called pepsin begins to digest protein, while a slimy layer of mucus shields the stomach wall.

Next, the partly digested food, now called chyme, moves into the small intestine. Enzymes from the pancreas and bile from the liver mix with it there. Most digestion takes place in the small intestine, where 95 percent of nutrient absorption happens. The large intestine then takes water and minerals back into the blood, and the leftover waste, called feces, leaves the body through the rectum and anus.

Check yourself

Question 1 of 3

Which enzyme in saliva begins the digestion of starch?

Pick one. The first pick counts.

Composition

what it's made of

  • Mouth and salivary glands — Teeth chew food while saliva wets it and starts breaking down starch.
  • Esophagus — The tube that carries swallowed food to the stomach by peristalsis.
  • Stomach — Mixes food with gastric juice, which starts the digestion of protein.
  • Small intestine — Where most digestion happens and most nutrients are absorbed into the body.
  • Large intestine — Reabsorbs water and minerals and forms the leftover waste.
  • Accessory organs — The tongue, salivary glands, pancreas, liver and gallbladder, which help digestion without food passing through most of them.

Connection

how it relates

Under Human Body

Related

  1. Smooth Musclestrength 70 of 100

    Smooth muscle in the walls of the digestive tract produces the waves of peristalsis that move food along.

  2. Parasympathetic Nervous Systemstrength 60 of 100

    The parasympathetic nervous system speeds up digestion when the body is at rest.

  3. Energy Formsstrength 50 of 100

    Digestion releases nutrients from food that the body's cells use as a source of chemical energy.

Change

how and why it evolves

Past
In 1823, William Prout discovered hydrochloric acid in the gastric juice. In 1825, the army surgeon William Beaumont was able to watch digestion as it took place in the stomach.
Now
Researchers are studying how eating habits affect digestion. Studies suggest that chewing each bite more times raises certain gut hormones and may lower hunger and the amount people eat.
Next
Bacteria in the colon make some vitamins, such as biotin and vitamin K. Research on these gut bacteria will probably reveal more about how digestion affects overall health.

Knowledge you can walk. Read the idea, then step up, across or down.

Digestive System

The digestive system breaks food down into small, water-soluble pieces that the body can absorb into the blood and use.

Learn, discuss, create, buy or invest

The idea

The digestive system breaks food down into pieces small enough for the body to absorb and use. It is made of the gastrointestinal tract, a long tube that runs from the mouth to the anus, plus helper organs: the tongue, salivary glands, pancreas, liver and gallbladder. Digestion happens in two ways. Mechanical digestion breaks food into smaller pieces, as when teeth chew it, while chemical digestion uses enzymes to split food into small compounds the body can use.

Digestion starts in the mouth. Chewing mixes food with saliva, which contains an enzyme called amylase that begins to break down starch. The chewed food forms a soft, round mass called a bolus, which is swallowed down the esophagus. Waves of muscle contractions, called peristalsis, push it along into the stomach. There, gastric juice containing hydrochloric acid and an enzyme called pepsin begins to digest protein, while a slimy layer of mucus shields the stomach wall.

Next, the partly digested food, now called chyme, moves into the small intestine. Enzymes from the pancreas and bile from the liver mix with it there. Most digestion takes place in the small intestine, where 95 percent of nutrient absorption happens. The large intestine then takes water and minerals back into the blood, and the leftover waste, called feces, leaves the body through the rectum and anus.

Check yourself

3 quick questions, instant feedback.