- The Mouth: The First Step in Digestion
- The Stomach: Where Food Is Digested
- The Small Intestine: Where Most of the Digestion and Absorption Occurs
- The Large Intestine: The Final Step in Digestion
- The Liver: An Important Organ in Digestion
- The Gallbladder: Stores Bile Used in Digestion
- The Pancreas: Produces enzymes essential for digestion
- Digestive enzymes: Important players in digestion
- The gut microbiota: An important but often overlooked player in digestion
- Digestive disorders: When things go wrong
How is the food we eat digested?
The human digestive system is a complex series of organs and glands that breaks down the food we eat. In order to better understand how this system works, let’s take a closer look at the process of digestion.
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The Mouth: The First Step in Digestion
The mouth is the first step in the digestive process. When you eat, your teeth break food down into small pieces that can be more easily digested. At the same time, your salivary glands produce saliva, which contains enzymes that begin to break down carbohydrates in your food.
Once food has been chewed and mixed with saliva, it forms a bolus, or a small round ball, that is swallowed and travels down your esophagus to your stomach.
The Stomach: Where Food Is Digested
The stomach is a J-shaped organ in the digestive system that stores food and helps to break it down. The stomach has three main functions: to store food, to break down food, and to move food along the digestive tract.
When you eat, the stomach muscles contract and push the food into the stomach. The stomach muscles then churn the food to help break it down. Once the food is broken down, it is mixed with acids and enzymes that help to further break down the food.
The walls of the stomach are lined with mucus that protects it from the acids and enzymes. The mucus also forms a barrier between the food and the lining of the stomach, which prevents ulcers from forming.
Once the food has been sufficiently broken down, it is pushed into the small intestine where it is further digested and absorbed into the bloodstream.
The Small Intestine: Where Most of the Digestion and Absorption Occurs
The small intestine is the workhorse of the digestive system. Most of the digestion and absorption of food occurs in the small intestine. The small intestine is a long, coiled tube about 20 feet (6 meters) long. It has three parts. The first part is called the duodenum. The duodenum is where most chemical digestion occurs. Bile (a greenish-yellow fluid) and pancreatic juice enter the duodenum through special ducts. These fluids help to break down food chemically.
The next part of the small intestine is called the jejunum (jee-JOO-num). This section of the small intestine is about 8 feet (2.4 meters) long. In the jejunum, most of the absorption of nutrients takes place.
The last part of the small intestine is called ileum (ILL-ee-um). The ileum is about 12 feet (3.6 meters) long. The ileum absorbs vitamin B12 and bile salts.
The small intestine gets its name from its smaller diameter than the large intestine. The walls of the small intestine contain many tiny, fingerlike projections called villi (VILL-eye). Each villus is covered with even tinier fingerlike projections called microvilli (MYE-kroh-VILL-eye). Villi and microvilli greatly increase the surface area of the small intestine so that more nutrients can be absorbed into the bloodstream through their walls than would be possible if they were smooth like those of most other tubes in our bodies.
The Large Intestine: The Final Step in Digestion
The large intestine is the final stage of digestion. Here, water and electrolytes (sodium, potassium, and chloride) are absorbed from food that is passing through the colon (large intestine). The intestine propels feces towards the rectum where they are eventually eliminated.
The large intestine is divided into several sections: the cecum, ascending colon, transverse colon, descending colon, and sigmoid colon. The cecum is a small pouch where the small intestine empties into the large intestine. The ascending colon runs up the right side of the abdomen. The transverse colon runs across the abdomen. The descending colon runs down the left side of the abdomen. The sigmoid colon is a S-shaped section that connects the descending colon to the rectum.
Most absorption of water and electrolytes occurs in the large intestine. In addition, bacteria in the large intestine help to break down indigestible food matter (such as cellulose) into short-chain fatty acids, which are then absorbed into the bloodstream. These short-chain fatty acids provide a small amount of energy for animals (including humans).
The Liver: An Important Organ in Digestion
The liver is a large,reddish-brown organ that sits on the right side of the abdomen,Just below the ribs. It has many important functions,including filtering toxins out of the blood, storing energy and nutrients, and producing bile. Bile is a yellowish-green liquid that helps to digest fats. The liver secretes bile through small tubes called ducts into the small intestine, where it emulsifies fats and makes them easier to absorb.
The Gallbladder: Stores Bile Used in Digestion
The gallbladder is a small, pouch-like organ located just below the liver in the right upper abdomen. The main function of the gallbladder is to store and concentrate bile produced by the liver. Bile is a yellowish-brown fluid that helps break down fats in the small intestine during digestion.
The liver produces about a pint of bile each day, which is stored in the gallbladder. The concentration of bile can be as much as 20 times higher in the gallbladder than it is in the liver. When fat enters the small intestine, muscle contractions squeeze the gallbladder, causing it to empty and release bile into the small intestine through a duct called the common bile duct. Bile breaks down fat into fatty acids that can be absorbed and used by the body for energy.
The Pancreas: Produces enzymes essential for digestion
The pancreas is located behind the stomach and is about 6 inches long. It produces enzymes essential for digestion, including amylase that breaks down carbohydrates, lipase that breaks down fats, and protease that breaks down proteins. The pancreas also produces bicarbonate that neutralizes acids in the duodenum (the upper section of the small intestine). Pancreatic juice flows through a system of ducts into the intestine.
Digestive enzymes: Important players in digestion
Digestive enzymes are important players in digestion, as they help to break down the food we eat into smaller, more easilyabsorbed particles. There are different types of digestive enzymes, each with a specific role to play in the digestive process.
Proteases break down proteins into smaller amino acids, which can then be used by the body to build new proteins or to be used for energy. Lipases break down fats into small fatty acids, which can be used for energy or for building new cells. Amylases break down carbohydrates into simple sugars, which can be used for energy or stored in the liver for use later.
The digestive process begins in the mouth, where saliva contains amylase, an enzyme that begins the breakdown of carbohydrates. As food moves through the digestive system, it is acted upon by different enzymes that complete the process of breaking it down into its component parts. Once food has been completely digested, the nutrients are absorbed into the bloodstream and distributed to the cells of the body.
The gut microbiota: An important but often overlooked player in digestion
The gut microbiota is a constantly evolving community of trillions of microbes that reside in the gastrointestinal tract. This microbiome is crucial for maintaining human health, as it performs a variety of functions including aiding in food digestion, synthesizing vitamins and minerals, and protecting against pathogens.
While the gut microbiota is essential for human health, it is often overlooked in discussions of digestion. This is because the microbiota does not directly participate in the digestive process; rather, it helps to break down food after it has been ingested. The microbiota does this by producing enzymes that break down complex carbohydrates, proteins, and other nutrients that our bodies cannot digest on their own.
In addition to its role in digestion, the gut microbiota also plays an important role in immunity and metabolism. For example, the gut microbiota synthesizes vitamins K and B12, which are essential for blood clotting and cell metabolism, respectively. The gut microbiota also protects against pathogens by producing chemicals that kill or inhibit the growth of bacteria, viruses, and other harmful microorganisms.
While the gut microbiota is a crucial player in digestion, it is only one part of a complex digestive system that includes the gastrointestinal tract, liver, pancreas, and other organs. This system works together to turn food into nutrients that our bodies can use for energy, growth, and repair.
Digestive disorders: When things go wrong
There are many different types of digestive disorders that can affect people of all ages. Some disorders, such as celiac disease, are more common in certain age groups or populations. Other disorders, such as Crohn’s disease, can affect people of any age.
Digestive disorders can be classified into three main categories:
* Malabsorption disorders: These disorders prevent the body from properly absorbing nutrients from food. Celiac disease is an example of a malabsorption disorder.
* Motility disorders: These disorders prevent the digestive system from moving food and waste through the gastrointestinal (GI) tract in a normal way. Crohn’s disease and irritable bowel syndrome (IBS) are examples of motility disorders.
* Inflammatory bowel diseases (IBD): These diseases involve inflammation of the GI tract. Crohn’s disease and ulcerative colitis are examples of IBDs.
While some digestive disorders can be mild and easily treated, others can be more severe and life-threatening. It is important to see a doctor if you think you or your child may have a digestive disorder.