Digestion

Your body turns food into tiny bits.

First, you chew food in your mouth. This makes food small. Saliva helps make it soft.

Next, food goes to your stomach. It mixes with juices there. These juices break food down more.

Then, food moves to the small tube. Most of the food goes into your blood here. This gives you strength.

Finally, your body takes what it needs. The rest leaves your body as waste. It is a big job!

Digestion is how your body breaks down food. It turns large pieces of food into tiny parts. These tiny parts can then move into your blood.

There are two main ways this happens. First is mechanical digestion. This is the physical breaking of food into smaller pieces. You start this by chewing in your mouth. This is called mastication. Your tongue helps roll food into a small ball. We call this ball a bolus.

Next is chemical digestion. This uses enzymes to break food down. Enzymes are special tools that change food. In your mouth, saliva has an enzyme called amylase. It starts to break down starch.

Food then travels to your stomach. It moves through a tube using muscle waves. This is called peristalsis. In the stomach, gastric juice breaks down proteins. It uses a chemical called pepsin. The stomach also makes mucus to protect its walls.

Most digestion happens in the small intestine. Here, food mixes with juices from the liver and pancreas. About 95% of nutrients are absorbed here. Finally, the colon takes back water and minerals. The rest leaves your body as waste.

Digestion is the way living things break down food. It turns large, insoluble food pieces into tiny, water-soluble parts. These small parts are then absorbed into the blood plasma. This is a type of catabolism, which is a way of breaking things down. There are two main ways this happens. One way is mechanical digestion, which is the physical breaking of food. The other way is chemical digestion, which uses enzymes to change food.

In humans, the process starts in the mouth. Mechanical digestion begins with mastication, which is the act of chewing. Saliva helps by wetting the food and adding mucus for lubrication. Saliva also contains an enzyme called salivary amylase. This enzyme starts breaking down starch into disaccharides. About 30% of starch is broken down right in the mouth. The tongue helps roll the food into a small mass called a bolus.

After the mouth, the bolus travels down the esophagus. It moves using peristalsis, which is a series of muscular contractions. The food then enters the stomach to meet gastric juice. This juice contains hydrochloric acid and an enzyme called pepsin. In infants and toddlers, a chemical called rennin also helps digest milk. The stomach makes a layer of mucus to protect its own walls from the acid. This keeps the strong chemicals from damaging the stomach.

Next, the partially digested food is called chyme. It moves through a valve called the pyloric sphincter into the duodenum. Here, it mixes with bile from the liver and enzymes from the pancreas. Most of the work happens in the small intestine. In fact, 95% of nutrient absorption occurs in this part of the body. After this, the food moves to the colon, also known as the large intestine.

The colon has a slightly acidic pH between 5.6 and 6.9. It absorbs water and minerals back into the blood. Some bacteria in the colon even produce vitamins like biotin and vitamin K. Finally, any waste material is called feces. This waste is eliminated from the rectum through a process called defecation. This entire system ensures that living things get the energy they need to grow.

Digestion is the biological process of breaking down large, insoluble food compounds. This process turns them into small, water-soluble components. Once these components are small enough, they can be absorbed into the blood plasma. Digestion is a form of catabolism, which is the breakdown of complex molecules. In many organisms, these nutrients are absorbed through the small intestine into the bloodstream. This process is vital for life because it provides the energy and materials needed for growth.

There are two distinct ways that food is broken down: mechanical and chemical digestion. Mechanical digestion is the physical breakdown of large food pieces into smaller parts. This makes it easier for digestive enzymes to access the food. Chemical digestion uses enzymes to break food down into small compounds the body can use. In humans, mechanical digestion begins in the mouth through mastication, which is the act of chewing. At the same time, saliva wets the food and provides lubrication through mucus. Saliva also contains salivary amylase, an enzyme that starts breaking down starch. About 30% of starch is hydrolyzed into disaccharides right in the oral cavity. The tongue then rolls the food into a small, round mass called a bolus.

After mastication, the bolus travels down the esophagus. It moves via peristalsis, which is a series of wave-like muscular contractions. The food then enters the stomach to meet gastric juice. This juice contains hydrochloric acid and the enzyme pepsin, which starts protein digestion. In infants and toddlers, gastric juice also contains rennin to help digest milk proteins. Because these chemicals are very strong, the stomach secretes mucus and bicarbonates. These substances create a slimy shield to protect the stomach wall from the concentrated hydrochloric acid. While proteins are being broken down, peristalsis also provides mechanical mixing in the stomach. This ensures the food mass mixes thoroughly with the digestive enzymes.

Once the food is partially digested, it is called chyme. The pyloric sphincter, a valve at the bottom of the stomach, opens to let the chyme enter the duodenum. In the duodenum, the chyme mixes with bile juice from the liver and enzymes from the pancreas. The small intestine is where the most important work happens. In fact, 95% of all nutrient absorption occurs in the small intestine. Here, pepsin breaks proteins into peptides or proteoses. These are further broken down into dipeptides and amino acids by enzymes in the small intestine.

After the small intestine, the remaining material moves into the colon, also called the large intestine. The colon has a slightly acidic pH, ranging from about 5.6 to 6.9. Its main job is to reabsorb water and minerals back into the blood. Some vitamins, such as biotin and vitamin K, are also absorbed here. These vitamins are produced by bacteria living in the colon. Finally, any waste material, known as feces, is held in the rectum. This waste is eliminated from the body during a process called defecation.

Different organisms use very different digestive strategies. Some organisms use external digestion, which developed early in evolutionary history. In this method, enzymes are secreted into the environment to break down organic material. The products then diffuse back into the organism. Most fungi rely on this method. In contrast, animals use a gastrointestinal tract for internal digestion. This is much more efficient because the animal can better control the chemical environment. It can also capture more of the broken-down products.

Some specialized organisms have unique ways of getting nutrients. The Venus flytrap is a plant that lives in boggy, acidic habitats. It does not eat for energy, but it uses prey to mine for nitrogen and phosphorus. Some animals have evolved specialized tools like beaks, tongues, or teeth. For example, the squid has a robust beak made of cross-linked proteins to tear prey. Birds have beaks shaped for their specific diets, like macaws that use theirs to open tough seeds. Even bacteria have complex systems, such as the type III secretion system, which acts like a molecular syringe to inject nutrients into other cells.