Human Digestive System & Nutrition

What is the digestive system?

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Browse Articles By Category Browse an area of study or degree level. Zip Code Zip code is required. Your body uses sugars, amino acids, fatty acids, and glycerol to build substances you need for energy, growth, and cell repair. Depending on your students' ability, this article can be read online or printed out and read in class. This process creates conditions that help the bacteria grow but also adds nutrients, enzymes and other beneficial compounds Fats and oils are turned into fatty acids and glycerol, needed to insulate our bodies and make cell membranes.

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Digestive System

Bacteria in your GI tract, also called gut flora or microbiome, help with digestion. Parts of your nervous and circulatory systems also help. Working together, nerves, hormones , bacteria, blood, and the organs of your digestive system digest the foods and liquids you eat or drink each day.

Digestion is important because your body needs nutrients from food and drink to work properly and stay healthy. Proteins , fats , carbohydrates , vitamins , minerals , and water are nutrients. Your digestive system breaks nutrients into parts small enough for your body to absorb and use for energy, growth, and cell repair.

MyPlate offers ideas and tips to help you meet your individual health needs. Each part of your digestive system helps to move food and liquid through your GI tract, break food and liquid into smaller parts, or both.

Once foods are broken into small enough parts, your body can absorb and move the nutrients to where they are needed. Your large intestine absorbs water, and the waste products of digestion become stool.

Nerves and hormones help control the digestive process. Food moves through your GI tract by a process called peristalsis. The large, hollow organs of your GI tract contain a layer of muscle that enables their walls to move.

The movement pushes food and liquid through your GI tract and mixes the contents within each organ. The muscle behind the food contracts and squeezes the food forward, while the muscle in front of the food relaxes to allow the food to move. Food starts to move through your GI tract when you eat. When you swallow, your tongue pushes the food into your throat.

A small flap of tissue, called the epiglottis, folds over your windpipe to prevent choking and the food passes into your esophagus. Once you begin swallowing, the process becomes automatic. Your brain signals the muscles of the esophagus and peristalsis begins. When food reaches the end of your esophagus, a ringlike muscle—called the lower esophageal sphincter —relaxes and lets food pass into your stomach.

After food enters your stomach, the stomach muscles mix the food and liquid with digestive juices. The stomach slowly empties its contents, called chyme , into your small intestine. The muscles of the small intestine mix food with digestive juices from the pancreas, liver, and intestine, and push the mixture forward for further digestion. The walls of the small intestine absorb water and the digested nutrients into your bloodstream. As peristalsis continues, the waste products of the digestive process move into the large intestine.

Waste products from the digestive process include undigested parts of food, fluid, and older cells from the lining of your GI tract. The large intestine absorbs water and changes the waste from liquid into stool.

Peristalsis helps move the stool into your rectum. The lower end of your large intestine, the rectum, stores stool until it pushes stool out of your anus during a bowel movement. Watch this video to see how food moves through your GI tract. As food moves through your GI tract, your digestive organs break the food into smaller parts using:. The digestive process starts in your mouth when you chew.

Your salivary glands make saliva , a digestive juice, which moistens food so it moves more easily through your esophagus into your stomach. Saliva also has an enzyme that begins to break down starches in your food. After you swallow, peristalsis pushes the food down your esophagus into your stomach. Glands in your stomach lining make stomach acid and enzymes that break down food. Muscles of your stomach mix the food with these digestive juices.

Your pancreas makes a digestive juice that has enzymes that break down carbohydrates, fats, and proteins. The pancreas delivers the digestive juice to the small intestine through small tubes called ducts. Your liver makes a digestive juice called bile that helps digest fats and some vitamins. Bile ducts carry bile from your liver to your gallbladder for storage, or to the small intestine for use.

Your gallbladder stores bile between meals. When you eat, your gallbladder squeezes bile through the bile ducts into your small intestine. Your small intestine makes digestive juice, which mixes with bile and pancreatic juice to complete the breakdown of proteins, carbohydrates, and fats.

Bacteria in your small intestine make some of the enzymes you need to digest carbohydrates. Your small intestine moves water from your bloodstream into your GI tract to help break down food. Your small intestine also absorbs water with other nutrients.

In your large intestine, more water moves from your GI tract into your bloodstream. Bacteria in your large intestine help break down remaining nutrients and make vitamin K. They contain the digestive enzyme lipase. This enzyme helps digest fat molecules into smaller molecules, such as fatty acids and glycerol, which are easier for the body to absorb However, taking a lipase supplement can help ease digestion, especially after a high-fat meal Avocados also contain other enzymes, including polyphenol oxidase.

This enzyme is responsible for turning green avocados brown in the presence of oxygen 24 , Kefir is a fermented milk beverage that is popular in the natural health community.

During fermentation, bacteria digest the natural sugars in milk and convert them into organic acids and carbon dioxide. This process creates conditions that help the bacteria grow but also adds nutrients, enzymes and other beneficial compounds Kefir contains many digestive enzymes, including lipase, proteases and lactase 28 , 29 , Lactase aids the digestion of lactose, a sugar in milk that is often poorly digested.

A study found that kefir improved lactose digestion in people with lactose intolerance Sauerkraut is a type of fermented cabbage that has a distinct sour taste. The fermentation process also adds digestive enzymes, which makes eating sauerkraut a great way to increase your intake of digestive enzymes In addition to containing digestive enzymes, sauerkraut is also considered a probiotic food , as it contains healthy gut bacteria that boost your digestive health and immunity 33 , Just make sure to eat raw or unpasteurized sauerkraut rather than cooked sauerkraut.

High temperatures may deactivate its digestive enzymes. As with sauerkraut and kefir, the fermentation process adds healthy bacteria, which provide nutrients, enzymes and other benefits Kimchi contains bacteria of the Bacillus species, which produce proteases, lipases and amylases.

These enzymes digest proteins, fats and carbs, respectively 40 , Aside from aiding digestion, kimchi has been linked to many other health benefits.

It may be especially effective at lowering cholesterol and other heart disease risk factors In a study in young, healthy participants, scientists found that those who ate the most kimchi experienced the greatest reduction in total blood cholesterol. Elevated total blood cholesterol is a risk factor for heart disease Miso is a popular seasoning in Japanese cuisine. Koji adds a variety of digestive enzymes, including lactases, lipases, proteases and amylases 46 , 47 , In fact, studies have shown that the bacteria in miso can reduce symptoms linked to digestive problems, such as irritable bowel disease IBD Moreover, fermenting soybeans helps improve their nutritional quality by reducing their antinutrient content.

Antinutrients are compounds found naturally in foods that may hinder the absorption of nutrients by binding to them The kiwifruit is an edible berry that is often recommended to ease digestion This enzyme helps digest proteins and is commercially used to tenderize tough meats 52 , Additionally, kiwifruit contains many other enzymes that help ripen the fruit An animal study found that adding kiwifruit to the diet improved the digestion of beef, gluten and soy protein isolates in the stomach.

This was thought to be due to its actinidain content Another animal study analyzed the effects of actinidain on digestion. It fed some animals kiwifruit with active actinidain and other animals kiwifruit without active actinidain. Results showed that animals fed kiwifruit with active actinidain digested meat more efficiently. The meat also moved faster through the stomach Many human-based studies have also found that kiwifruit aids digestion, reduces bloating and helps relieve constipation 57 , 58 , 59 , Ginger contains the protease zingibain, which digests proteins into their building blocks.

Zingibain is used commercially to make ginger milk curd, a popular Chinese dessert Studies in healthy adults and those with indigestion show that ginger helped food move faster through the stomach by promoting contractions 63 , Animal studies have also shown that spices, including ginger, helped increase the body's own production of digestive enzymes like amylases and lipases Digestive enzymes are proteins that break down larger molecules like fats, proteins and carbs into smaller molecules that are easier to absorb across the small intestine.

Without sufficient digestive enzymes, the body is unable to digest food particles properly, which may lead to food intolerances.

Foods that contain natural digestive enzymes include pineapples, papayas, mangoes, honey, bananas, avocados, kefir, sauerkraut, kimchi, miso, kiwifruit and ginger. Fermented foods contain beneficial probiotics, which can improve digestion, immunity and even weight loss.

Here are 8 healthy fermented foods. The gut microbiome refers to the trillions of bacteria, viruses and fungi that live in your gut. Here's why your gut microbiome is so important for….

Nutrition & the Digestive System - Chapter Summary