How Does Our Digestive System Work?

Gastrointestinal Tract

Gastrointestinal (GI) refers to the stomach and intestines, specifically the large, muscular tube that extends from the mouth to the anus, where the movement of muscles, along with the release of hormones and enzymes, allows for the digestion of food.

Also called the alimentary canal or digestive tract. The GI tract is conventionally divided into upper and lower parts, with associated accessory organs.

Upper GI Tract

This is where ingestion and the first phase of digestion occur and includes the following:

  • Mouth
  • Pharynx
  • Esophagus
  • Stomach

Esophagus is the hollow tube that receives food from the pharynx (throat). Its purpose is to push this food to your stomach by a series of muscular contractions called peristalsis.

Stomach is a large, sac-like organ where food is digested, the stomach receives food from the esophagus, which is connected at its upper segment. The stomach then sends the digested food out to the small intestine, which is connected to its lower segment.

Lower GI Tract

Its primary function is the absorption of leftover water from the waste products of digestion, where it then compacts the remaining waste into faeces for elimination. Lower GI tract components include the following:

Small Intestine

  • Duodenum
  • Jejunum
  • Ileum

Large Intestine

  • Cecum
  • Appendix
  • Colon
  • Rectum
  • Anus

Small Intestine

Primarily responsible for the digestion of food and the absorption of food nutrients into the bloodstream.

There are intestinal glands that are located in the lining of the small intestine that is responsible for secreting intestinal juices that aid in the digestive process. The three main sections of the small intestine are the following:


Duodenum is the first part of the small intestine that connects to the stomach. It helps to further digest food coming from the stomach. Besides, it absorbs nutrients (vitamins, minerals, carbohydrates, fats, proteins) and water from food so they can be used by the body.


Jejunum is the middle part of the small intestine between the duodenum and the ileum. It helps to further digest food coming from the duodenum. Besides, it absorbs nutrients (vitamins, minerals, carbohydrates, fats, proteins) and water from food so they can be used by the body.


Ileum is the last part of the small intestine that connects to the first part of the large intestine. It helps to further digest food coming from the stomach and other parts of the small intestine. 

Besides, it absorbs nutrients (vitamins, minerals, carbohydrates, fats, proteins) and water from food so they can be used by the body, and delivers anything remaining to the large intestine.

Large Intestine

The primary purpose of the large intestine is the removal of digestive waste products called faeces. The four main sections of the large intestine are the following:


Cecum is the beginning section of the large intestine. It receives faecal material from the final section of the small intestine, the ileum. It includes the appendix, a small, fingerlike pouch that sticks out from the cecum.


Colon is a six-foot-long tubular section that connects the cecum to the rectum. Its primary purpose is to remove water from digested food that then results in the conversion to solid waste called stool. Stool then travels through the colon into the rectum.


Rectum is the last six to eight inches of the large intestine where stool is stored before it is evacuated from the anus.


Anus is the opening of the rectum through which the stool is expelled from the body.

Role of bacteria in the large intestine

The gut microbiome plays an active role in the circadian rhythm, nutrient regulation, metabolism, and immunity of hosts through its positive influence on the gut microbiome.

Large intestine bacteria can further digest some material, resulting in gas production. Bacteria in the large intestine also produce some important substances, such as vitamin K, which is essential to blood clotting. Diseases and antibiotics can upset the balance between different types of bacteria in the large intestine, and some types of bacteria are necessary for healthy intestinal function.

In order for your gut to be healthy, it needs a healthy balance of bacteria. That’s why there are so many different probiotic supplements available today. But it’s crucial to pick a supplement with a diverse range of bacterial strains.

The supplement Biofit, for example, claims to contain billions of CFU and diverse types of bacteria. It might benefit those who are bloated or have a lowered immunity, as well as those who are overweight or underweight. However, you should read some Biofit reviews before making any purchase.

Additional Digestive System Components

The digestive system converts the food you eat into nutrients that are used by the body for energy, repairing cells, and growth.


Begins the initial breakdown of food through chewing and aids in digestion by releasing saliva.


A digestive juice that is 99.5 percent water located in the mouth and manufactured by the salivary glands. The remaining 0.5 percent contains an enzyme known as ptyalin.

Saliva also moistens the mouth to help a person chew, swallow food, and control bacteria that could cause mouth infection and tooth decay.

Salivary Glands

There are three pairs of salivary glands in the mouth that produce saliva:

  • Parotid glands: located in the mouth and in front of the ear
  • Submandibular glands: located in the mouth and under the jaw
  • Sublingual glands: located under the tongue, on the floor of the mouth


An enzyme found in the saliva is used in the digestive process to break down the starches and glycogens that you put into your mouth.

Once the starches and glycogen are covered with your saliva, they are broken down into maltose and glucose, which are simple sugars that can be used more readily by the body.


The primary function of teeth is to chew (masticate) and to mix food with saliva. Normally there are thirty-two permanent teeth in the adult mouth.

Pharynx (Throat)

Pharynx receives broken-down food particles from the mouth. It is an organ of the respiratory system as well.


Chyme is the partially digested food and the digestive secretions that are formed in the stomach and intestine during digestion.

Gastric Juices

Gastric Juices are digestive fluids secreted from glands located in the stomach.


Organic compounds that are composed mostly of proteins and used in the process of digestion, enzymes act as catalysts because they produce changes in chemical reactions.

These chemical reactions produce a series of chemical breakdowns to the body’s complex compounds that result in the production of simpler substances, and the end result is the production of energy for the body’s needs.


A gland that is located behind and beneath the stomach, the pancreas has a duct portion that secretes a digestive juice known as pancreatic juice.

The ductless portion of the pancreas is known as the Islets of Langerhans (also called the Islands of Langerhans), which produces insulin (a hormone that controls the proper levels of glucose within the cells of the body).


Liver is the largest internal organ in the body that has several functions. It absorbs nutrients and oxygen from the blood.

  • Regulates amino-acid levels in the blood.
  • Regulates glucose levels in the blood.
  • Produces important proteins, including albumin.
  • Produces substances that contribute to the process of blood clotting (coagulation) when bleeding occurs.
  • Helps to break down and remove toxic substances and drugs from the blood.
  • Is responsible for the production of bile, which removes waste from the liver and helps it to break down and absorb fats in the small intestine.
  • Stores sugar in the form of glycogen.


A sac that is attached to the liver, the gallbladder is used to store the bile that the liver produces. When digestion is required, the gallbladder releases the stored bile into the small intestine where it helps in the breakdown and absorption of fats.

Digestive System Injuries and Conditions


Hernia is a condition that occurs when an organ or fatty tissue protrudes, squeezes, pushes, or passes through muscle tissue. There are several types of hernias, and they are classified by the

body location where they occur. The following are four of the most common types.

Inguinal Hernia

When the contents of the abdomen, usually fat or part of the small intestine, bulge through a weak area in the lower abdominal wall, also called the inguinal or groin region. Two types of inguinal hernias are as follows:

  • Indirect inguinal hernias: Caused by a defect in the abdominal wall that is congenital—or present at birth.
  • Direct inguinal hernias: Usually occur only in adult males and are caused by a weakness in the muscles of the abdominal wall that develops over time.

Umbilical Hernia

When part of the small intestine bulges out through the abdominal wall near the belly button or navel.

Femoral Hernia

When the intestine protrudes through the lower abdomen in the area near the upper thigh. This condition is more common in women, particularly those who are obese or pregnant.

Hiatal Hernia

When the opening of the diaphragm lets the upper part of the stomach move up into the chest, which lowers the pressure in the esophageal sphincter.

Peptic Ulcer

Peptic Ulcer is a sore on the lining of your stomach or duodenum. Rarely, a peptic ulcer may develop just above the stomach in the esophagus. Doctors call this type of peptic ulcer an esophageal ulcer.

Causes of peptic ulcers include:

  • Long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin and ibuprofen.
  • An infection with the bacteria Helicobacter pylori.
  • Rare cancerous and noncancerous tumours in the stomach, duodenum, or pancreas—known as Zollinger-Ellison syndrome.

Irritable Bowel Syndrome (IBS)

Irritable Bowel Syndrome (IBS) is a group of symptoms—including pain or discomfort in your abdomen and changes in your bowel movement patterns—that occur together.

Doctors call IBS a functional gastrointestinal (GI) disorder. Functional GI disorders happen when your GI tract behaves in an abnormal way without evidence of damage due to a disease.

In the past, doctors called IBS many other names, including colitis, mucous colitis, spastic colon, nervous colon, and spastic bowel. Experts changed the name to IBS to reflect the understanding that the disorder has both physical and mental causes and isn’t a product of a person’s imagination.

Doctors often classify IBS into one of four types based on stool consistency. Differentiating the types is important because it will affect the types of treatment that are most likely to improve symptoms.

IBS with constipation, or IBS-C

  • Hard or lumpy stools at least 25 percent of the time.
  • Loose or watery stools less than 25 percent of the time.

IBS with diarrhea, or IBS-D

  • Loose or watery stools at least 25 percent of the time.
  • Hard or lumpy stools less than 25 percent of the time.

Mixed IBS, or IBS-M

  • Hard or lumpy stools at least 25 percent of the time.
  • Loose or watery stools at least 25 percent of the time.

Unsubtyped IBS, or IBS-U

  • Hard or lumpy stools less than 25 percent of the time.
  • Loose or watery stools less than 25 percent of the time.


Hemorrhoids are also called piles, hemorrhoids are swollen and inflamed veins around your anus or in your lower rectum.

The two types of hemorrhoids are:

  • External hemorrhoids, which form under the skin around the anus.
  • Internal hemorrhoids, which form in the lining of the anus and lower rectum.

Hemorrhoids are common in both men and women, and affect about one in twenty Americans. About half of adults older than age fifty have hemorrhoids. High-risk triggers for hemorrhoids include the following:

  • Straining during bowel movements
  • Sitting on the toilet for long periods of time
  • Having chronic constipation or diarrhea
  • Eating foods that are low in fiber
  • Pregnancy
  • Lifting heavy objects

Complications of hemorrhoids can include the following:

  • Blood clots in an external hemorrhoid
  • Skin tags—extra skin left behind when a blood clot in an external hemorrhoid dissolves
  • Infection of a sore on an external hemorrhoid
  • Strangulated hemorrhoid—when the muscles around the anus cut off the blood supply to an internal hemorrhoid that has fallen through the anal opening.

Crohn’s Disease

Crohn’s Disease is a chronic disease that causes inflammation and irritation in your digestive tract. Most commonly, Crohn’s affects the small intestine and the beginning of the large intestine. However, the disease can affect any part of the digestive tract, from mouth to anus.

Crohn’s disease is an inflammatory bowel disease (IBD). Ulcerative colitis and microscopic colitis are other common types of IBD.

Crohn’s disease most often begins gradually and can become worse over time. There may be periods of remission that can last for weeks or years.

Researchers estimate that more than half a million people in the United States have Crohn’s disease. Studies show that, over time, Crohn’s disease has become more common in the United States and other parts of the world. Experts do not know the reason for this increase.

Crohn’s disease can develop in people of any age, though it’s more likely to develop in people between the ages of twenty and twenty- nine.

Those who have a family member with IBD, most often a sibling or parent, are at higher risk of developing an IBD themselves.

Cigarette smokers are at high risk for Crohn’s disease as well. Possible complications from Crohn’s Disease include the following:

Intestinal obstruction

Crohn’s disease can thicken the wall of the intestines. Over time, the thickened areas of the intestines can narrow, which can cause blockage.

A partial or complete intestinal obstruction, also called a bowel blockage, can block the movement of food or stool through the intestines.


Abnormal passages between two organs, or between an organ and the outside of the body. In Crohn’s disease, inflammation can go through the wall of the intestines and create fistulas that may become infected.


Painful, swollen, pus-filled pockets of infection. Anal fissures Small tears in the anus that may cause itching, pain, or bleeding.


Open sores in your mouth, intestines, anus, or perineum. 


Develops when the body does not get the right amounts of vitamins, minerals, and nutrients it needs to maintain healthy tissues and organ function.

Additional inflammation

Inflammation of the digestive tract may develop into inflammation of the joints, eyes, and skin as well.

Colon cancer

If Crohn’s disease is in the large intestine, it may be more likely to develop into colon cancer.

Ongoing treatment for Crohn’s disease and remission may reduce the chances of it developing into colon cancer.

Screening for colon cancer, which can include a colonoscopy with biopsies, may help to find cancer at an early stage in the absence of symptoms and improve the chance of curing cancer.

Acid Reflux

Gastroesophageal Reflux (GER)

Gastroesophageal reflux (GER) happens when your stomach contents come back up into your esophagus causing heartburn (also called acid reflux).

Gastroesophageal Reflux Disease (GERD)

GERD is a more serious and long-lasting form of GER, specifically GER that occurs more than twice a week for a few weeks could be GERD.

GERD can lead to more serious health problems over time. Medical attention is recommended.

GERD affects about 20 percent of the US population. Anyone can develop GERD; some for unknown reasons. A person is more likely to develop GERD if he or she is:

  • Overweight or obese
  • Pregnant
  • Taking certain medicines
  • A smoker or regularly exposed to secondhand smoke

Without treatment, GERD can sometimes cause serious complications over time, such as:

Inflamed esophagus

Adults who have chronic esophagitis over many years are more likely to develop precancerous changes in the esophagus.

Esophageal stricture

An esophageal stricture happens when your esophagus becomes too narrow. Esophageal strictures can lead to problems with swallowing.

Respiratory problems

There is a risk of breathing stomach acid into the lungs, which can irritate the throat and lungs, causing respiratory problems.

Barrett’s esophagus

A small number of people with Barrett’s esophagus develop a rare yet often deadly type of cancer of the esophagus.

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