The Gastrointestinal (GI) system:

Stomach, Liver, Gallbladder, Pancreas and Bowels:

The GI system contains all of the organs we need to take in nutrients and eliminate waste. The mouth is connected to the stomach by a passage called the esophagus. The stomach does not absorb a lot of nutrients, but it helps to start breaking them down by churning and adding chemicals that break down the food.

From the stomach food travels into the small bowel, or intestine. This is where most nutrients are absorbed. The liver makes a substance called bile that is released as needed into the small bowel through the gallbladder. The pancreas also makes substances that help break down food so the body can use it. It also creates insulin that helps keep our blood sugar in a normal range.

After having most of the nutrients absorbed in the small bowel, the large bowel then takes back most of the water from the digested food. The large bowel also contains a lot of bacteria that make some vitamins that our body needs. After the water and remaining vitamins and minerals have been absorbed, the now-digested food is eliminated as feces.

The liver, gallbladder, and pancreas all help with digestion, but do other things for the body as well.

Potential Problems:

Gastric reflux

Stomach contents travelling back up the esophagus. This can be a complication of feeding tubes, because the gate (sphincter) between the esophagus and the stomach is being kept open by the tube.

Gastrointestinal (GI) bleeding

Bleeding in the GI system can happen in the stomach and esophagus or lower down in the bowels. Upper GI bleeding may be caused by ulcers, blood backing up from an injured liver, or the physical stress of critical illness. Lower GI bleeding can be a result of inflammation, infection, disease, or injury.


Ileus happens when the contents in the GI system stop moving. Food is usually kept moving along by smooth muscle contractions controlled automatically by the brain. If this motion stops in one area or along the whole GI tract, a build-up of wastes can occur. This makes it more difficult for the bowels to get moving again.


Jaundice a yellowing of the whites of the eyes and the skin. It is caused by a buildup of bilirubin in the blood and may mean the liver is not working properly.


A condition of the liver as the result of many different diseases, such as hepatitis. The surface of the liver becomes scarred and does not function well.

Portal hypertension

The portal vein is a large vessel going into the liver from the vessels around the bowels. It carries everything that has been absorbed by the intestines to the liver for cleaning and processing. This includes nutrients as well as medications and toxins. If the liver becomes scarred, the pressure of the blood in the portal vein goes up. The fluid can then back up causing higher blood pressures in the veins connected to this system, such as those that line the esophagus.

Hepatic encephalopathy

If the liver does not process toxins out of the blood, they can build up. The brain is very sensitive to toxins and can be effected by the breakdown of liver function. The result is impaired thinking, a decreased level of consciousness, cerebral edema and coma.


The collecting of fluid in the abdomen can be a sign of liver disease.


The GI system can become blocked in a number of different ways. The gall bladder can be blocked by a gall stone or narrowing of the tube that feeds bile into the small bowel. The bowels can become blocked up by wastes if they are not stimulated to keep moving. The duct from the pancreas to the small intestine can be blocked as well, leading to pancreatitis.


The inflammation of the pancreas. This is usually the result of a block in the duct leading to the small intestine. It is problematic because the pancreas makes substances that help digest all kinds of foods. When these substances have no way out, they start to digest the pancreas.


The inability to absorb enough nutrients from food. There are many situations that can cause malabsorption. If a person has nausea, vomiting, and diarrhea, their bowels are not given enough time to take nutrients out of the food. If the bowel has been damaged by disease (i.e., Crohn’s) or shortened by surgery or trauma it is less effective at pulling nutrients from food. Malabsorption can lead to short supplies of essential nutrients, vitamins, and minerals in the body.


Diabetes is the inability of the pancreas to make enough insulin to process the blood glucose so the cells of the body can use it. Sometimes the body makes no insulin (type I). More commonly, the body makes some insulin but either it is not making enough, or the body is not able to use it (type II). Some diabetes can be managed with a change in diet. Other times people need to take insulin.


Low blood sugar. Hypoglycemia has a number of causes. It is treated by raising the level of glucose in the blood to the normal range.


High blood sugar. People with diabetes often struggle to keep their blood sugar down in the normal range. It can be treated with diet control or insulin.

Prevention and Therapies:

Basics of Nutritional Support

People who are admitted to the intensive care unit have unique nutritional needs. Sometimes they will need more protein or other nutrients to help them heal from illness or injury. If there are imbalances in fluid or mineral salts, they will need to be corrected as well.

Often patients cannot eat normally and need alternative ways to get the nutrients their bodies need.

Nasogastric (NG) tube

The NG tube is fed through the nose, down the back of the throat, and into the stomach. The NG tube is used to remove contents from the stomach.  It can be used to give medications and temporarily feed patients as well.

Orogastric (OG) tube

The OG tube is fed through the mouth, down the throat, and into the stomach. The OG tube is used if an NG tube cannot be placed and can be used to give nutrients and liquid medications in the same way.

Feeding tube past the pylorus

A tube that is fed down through the stomach and into the small bowel. These feeding tubes are used for long term enteral feeding.  Often the patient's stomach is not working well enough to move food and medications from the stomach into the small bowel.  Different kinds of nutrients and medications can be given because it goes right to the place where most nutrients are absorbed into the blood.

Gastric tube (G-tube)

A G-tube is placed through the skin into the stomach. A port is attached that can be sealed off when the G-tube is not being used. It is used to give the same kinds of nutrients and medicines as a nasogastric or orogastric tube.

Jejunal tube (J-tube)

A J-tube is placed through the skin into the small bowel. A port is attached that can be capped off when the J-tube is not being used. It is used to give the same kinds of nutrients and medicines as an orojejunal tube placed through the mouth.

Parenteral feeding

If a patient cannot take in nutrients by their gastrointestinal system, they will be provided with the nutrient they need directly into the bloodstream. TPN is the short form for total parenteral nutrition. It is preferred that TPN is given through a central line into a large blood vessel. A larger amount of the TPN fluid can be delivered through these lines.

Ileostomy and Colostomy

These surgeries make a passage between the bowels and the outside of the body. The passage is fitted with a sealed bag to hold intestinal contents. These may be used if the bowel below the passage is damaged.



Insulin in normally produced by the pancreas. It is essential to allow the body to use sugars for energy. Insulin is used to reduce blood sugar to a normal range if it is too high.

Critically ill patients may need insulin even though they are not diabetic.  The stress of critical illness, fever, and some medications can cause a rise in blood sugar.  The body works better when the blood sugar is kept in a normal range.


Short for total parenteral nutrition. The nutrients the body needs are delivered directly into a central blood vessel in a form the body can use. TPN is used if nutritional needs are not being met by other methods.

IV fluids and electrolytes

The balance of fluid, mineral salts (electrolytes), and blood acidity can be maintained or corrected with intravenous fluids and electrolytes.

Diagnostic Tests and Monitoring:

Blood tests
  • There are many blood tests that can be used to check how the gastrointestinal system is working. Blood sugars are one of the most common and can give a clue to how the pancreas is working and how the body is using energy from sugars. ALT, AST, alkaline phosphatase, and ammonia are some of the tests used to see how the liver is working.
  • As with all body systems, it is important to check the balance of fluids and electrolytes, such as sodium (Na+) and potassium (K+).

A record is kept of the amount of each group of nutrients such as protein, fats, and sugars. The team can monitor how a person is responding to the nutrition and adjust it as needed.


A colonoscopy uses a tube with a camera on it to look at the bowels from the inside. Colonoscopies can be used to both identify and treat some bowel diseases.


Endoscopies use tubes with a camera to look at the esophagus and stomach through the mouth. They can help the team identify and treat some upper GI disorders.

  • Angiograms are used to study the pattern of blood flow in the gastrointestinal system. They can be used to identify areas where there may be a block in blood flow, and help determine how much blood and nutrients are getting to different parts of the system.
  • The picture on the left shows an angiogram of the lower abdomen.  The kidneys are visible in the upper part of the image. The bright white line is the abdominal aorta, an extension of the largest artery in the body.
Abdominal Ultrasound

Ultrasounds are helpful for identifying the collection of blood or fluid in the abdomen. They use sound waves that produce an image when they are reflected back and interpreted by the machine.

CT Scan
  • A CT or CAT Scan is a specialized kind of X-ray. A person is scanned and the pictures gathered are turned into a 3D image by the machine’s computer. CT scans are good at picking up collections of fluid.
  • Sometimes a patient is injected with an x-ray dye that will show up under the CT scan. This is called a CT with contrast. It can help determine problems with the vessels such as bleeding or blockages. Patients are taken to the radiology department for CT scans.
  • MRIs are used to get a very detailed picture of the body tissues and organs. MRIs use a strong electromagnetic field to make two- and three-dimensional images of the area scanned. The use of a strong magnet means it is important to remove all metal before an MRI. The scanner is loud, so patients and staff are given ear plugs.
  • Sometimes a patient will be given a substance to increase the contrast and sharpen the details of certain body parts, such as the blood vessels. Like a CT scan, an MRI is painless. Patients travel to radiology with a nurse to get an MRI.