Why do we need to break down the food we eat

The physical breakdown of food is a physiological process known as digestion. To benefit your body, the foods you eat must be broken down so the nutrients they contain can move from your gut through the cells of your intestines and into your bloodstream. While some nutrients, such as vitamins and minerals, are already small enough for your small intestine to absorb, the larger carbohydrate, fat and protein molecules require digestion into smaller nutrient units.

Carbohydrate

The carbohydrates your body digests are made up of single-sugar units, or monosaccharides, linked together. Disaccharides are pairs of monosaccharides joined as one, while starch molecules consist of a large number of bonded monosaccharides. The goal of carbohydrate digestion is to break them down into individual sugars so that your bloodstream can absorb them from intestinal cells. The process starts in your mouth but occurs mostly in your small intestine, where carbohydrate-specific digestive enzymes clip off sugars from the larger carbohydrate molecules.

Lipids

The digestion of dietary lipids, or fats, reduces them to fatty acids and monoglycerides. Similar to carbohydrate digestion, digestive enzymes act on these nutrients in your small intestine; however, fats need to become water soluble before these enzymes can work on them. Your liver secretes into your small intestine a fluid called bile, which mixes with the fat in such a way that the fat droplets become very small and water soluble. Then the fat is better able to interact with enzymes that can break them down. As this happens, the fatty acids and monoglyceride molecules can move into the absorptive cells lining your intestine.

Protein

Food proteins comprise long chains of amino acids, linked together and folded into a three-dimensional shape. Digestion unfolds the protein and breaks them down into amino acids so they can enter your bloodstream and travel to the cells where they are needed. Unlike carbohydrate and lipid digestion, protein digestion begins in your stomach, where gastric acid relaxes the protein molecule and a preliminary digestive enzyme breaks down the protein into smaller pieces. As these pieces move on to your small intestine, additional enzymes snip off specific individual amino acids in preparation for absorption.

Considerations

In addition to mechanical breakdown of food in your mouth, your digestive tract organs, and the fluids and enzymes involved in digestion, the process of reducing the foods you eat into smaller components requires the action of hormones. The physical presence of food in your stomach, for instance, stimulates a hormone that releases acid into your stomach and starts protein digestion. Food moving into your small intestine then activates a hormone that causes your pancreas to secrete digestive enzymes and another hormone that turns off acid production in your stomach. Together, all these processes accomplish the breakdown of food so you can benefit from its nutrients.

The digestive system breaks down the food we eat into tiny parts to give us fuel and the nutrients we need to live. As food breaks down, we get amino acids from protein, simple sugars from starches, and fatty acids and glycerol from fats.

What Are the Parts of the Digestive System?

The digestive system is made up of:

• the alimentary canal (also called the digestive tract). This long tube of organs makes a pathway for food to travel through the body. It runs from the mouth to the anus (where poop comes out) and includes the esophagus, stomach, and intestines. An adult's digestive tract is about 30 feet (about 9 meters) long.
• other organs that help the process by adding enzymes and chemicals to break down the food. Important organs that help with digestion include the salivary glands, liver, gallbladder, and pancreas.

How Does the Digestion System Work?

Here’s how digestion happens:

The mouth: Digestion begins even before we taste food. When we see, smell, taste, or even imagine a tasty meal, our salivary glands (located in front of the ears, under the tongue, and near the lower jaw) begin making saliva (spit).

Teeth tear and chop the food. Spit moistens it for easy swallowing. A digestive enzyme in saliva called amylase (AH-meh-lace) starts to break down some carbohydrates (starches and sugars) in the food.

Muscles in the tongue and mouth work together to swallow the food and move it into the throat (pharynx). The pharynx (FAIR-inks) is a passageway for food and air. A soft flap of tissue called the epiglottis (ep-ih-GLAH-tus) closes over the windpipe when we swallow to keep food and liquid out of the lungs.

The esophagus: Food travels down a muscular tube in the chest called the esophagus (ih-SAH-fuh-gus). Waves of muscle contractions called peristalsis (per-uh-STALL-sus) force food down through the esophagus to the stomach. A person usually isn't aware of the muscle movements that push food through the digestive tract.

The stomach: At the end of the esophagus is a muscular ring or valve called a sphincter (SFINK-ter). The sphincter lets food enter the stomach, then squeezes shut to keep food and liquids from flowing back up into the esophagus. The stomach muscles churn and mix the food with digestive juices that have acids and enzymes. These juices help break up food into much smaller pieces.

By the time food is ready to leave the stomach, it has been turned into a thick liquid called chyme (kime). A small muscular valve called the pylorus (pie-LOR-is) controls when chyme is released into the small intestine.

The small intestine: The small intestine is where many nutrients (like protein, carbohydrates, and fats) get absorbed into the bloodstream. It has three parts:

• The duodenum (due-uh-DEE-num). This C-shaped first part is where enzymes from the pancreas and bile from the liver are added to the chyme.
• The jejunum (jih-JU-num). This coiled middle part further digests the chyme and absorbs nutrients.
• The ileum (IH-lee-um). The final section that leads into the large intestine absorbs nutrients, vitamin B12, and bile acids.

Millions of microscopic, finger-like projections called villi (VIH-lie) line the inside of the small intestine. The villi make lots of surface area for nutrients to get absorbed into the blood. Then blood brings the nutrients to the rest of the body.

While food works its way through the small intestine, three organs that are not part of the alimentary canal help the digestion process:

• The liver makes bile, which helps the body absorb fat. It’s located in the top right of the belly. 
• The gallbladder stores bile until it is needed. It’s hidden just below the liver.
• The pancreas makes enzymes that help digest proteins, fats, and carbs. It’s found below the stomach.

Enzymes and bile travel through small pathways (called ducts) into the small intestine, where they help to break down food.

Undigested food and some water travels to the large intestine through a muscular ring called the ileocecal (ill-ee-oh-SEE-kul) valve. This valve prevents food from returning to the small intestine. By the time food reaches the large intestine, the work of absorbing nutrients is nearly finished.

The large intestine: The large intestine's main job is to remove water from the undigested matter and form solid waste (poop) to be excreted. The large intestine includes three parts: