Digestive System

The primary function of the digestive system is to break down the food we eat into smaller parts so the body can use them to build and nourish cells and provide energy.

The digestive system is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. Inside this tube is a lining called the mucosa. In the mouth, stomach, and small intestine, the mucosa contains tiny glands that produce juices to help digest food.
Stomach- The stomach is a hollow organ composed of several strong, muscular layers. It is located protected under the rib cage and connected at each opening to the esophagus and the small intestine. The stomach stores, mixes, and digests the food that we eat. It also acts to protect us from infectious organisms that we might ingest.
After food is chewed and moistened in the mouth, it passes through the esophagus into the stomach. This is the second step in the digestion of everything you consume. Food is mixed with stomach acid and enzymes to break the food down into smaller pieces. This combination of food and stomach "juices" is called chyme. The stomach also stores food temporarily, releasing chyme in small amounts into the small intestine, where it is further broken down into nutrients to be absorbed into the body.
In addition to breaking down food, stomach acid and enzymes also help to kill bacteria or other infectious organisms that you may have eaten. The stomach is protected from corrosive stomach acid by a layer of mucus lining its walls. This mucus layer also protects other internal organs from stomach acid. When the mucus lining is damaged, stomach acids can burn through the lining of the stomach and damage other organs in the body.


Liver- The liver is located in the upper right-hand portion of the abdominal cavity, beneath the diaphragm, and on top of the stomach, right kidney, and intestines. Shaped like a cone, the liver is a dark reddish-brown organ that weighs about 3 pounds.

There are two distinct sources that supply blood to the liver, including the following:
  • oxygenated blood flows in from the hepatic artery
  • nutrient-rich blood flows in from the hepatic portal vein
The liver holds about one pint (13 percent) of the body's blood supply at any given moment. The liver consists of two main lobes, both of which are made up of thousands of lobules. These lobules are connected to small ducts that connect with larger ducts to ultimately form the hepatic duct. The hepatic duct transports the bile produced by the liver cells to the gallbladder and duodenum (the first part of the small intestine).

The liver regulates most chemical levels in the blood and excretes a product called bile, which helps carry away waste products from the liver. All the blood leaving the stomach and intestines passes through the liver. The liver processes this blood and breaks down the nutrients and drugs into forms that are easier to use for the rest of the body. More than 500 vital functions have been identified with the liver. Some of the more well-known functions include the following:
  • production of bile, which helps carry away waste and break down fats in the small intestine during digestion
  • production of certain proteins for blood plasma
  • production of cholesterol and special proteins to help carry fats through the body
  • conversion of excess glucose into glycogen for storage (glycogen can later be converted back to glucose for energy)
  • regulation of blood levels of amino acids, which form the building blocks of proteins
  • processing of hemoglobin for use of its iron content (the liver stores iron)
  • conversion of poisonous ammonia to urea (urea is an end product of protein metabolism and is excreted in the urine)
  • clearing the blood of drugs and other poisonous substances
  • regulating blood clotting
  • resisting infections by producing immune factors and removing bacteria from the bloodstream




Enzymes are large protein molecules that act as catalysts or inducers of chemical changes. They can trigger or speed up the chemical reactions included in digestion so food substances are broken down to simpler substances. A human being is not maintained by their intake, but rather by what is ingested. Enzymes are involved in every process of the body. Life would not exist without them. Enzymes digest all our food and make it small enough to pass through the small pores of the intestines into the blood. Enzymes in the blood take readily digested food and build muscles, nerves, blood, and glands. They also assist in storing sugar in the liver and muscles, turn fat into fatty tissue, aid in the formation of urea to be eliminated as urine, and also eliminate carbon dioxide in the lungs.

The enzymes in raw food actually digest up to 75% of the food without the help of the enzymes secreted by the body. There are three major classes of enzymes: metabolic enzymes (enzymes which work in blood, tissues, and organs), food enzymes from raw food, and digestive enzymes. We inherited an enzyme reserve at birth and this quantity can be decreased as we age by eating an enzyme-deficient diet. Nature has placed enzymes in food to aid in the digestive process instead of forcing the body's enzymes to do all of the work. Once we cook food at high temperatures, the enzyme is destroyed. It no longer carries on its designated function. By eating most of our food cooked, our digestive systems have to produce all of the enzymes, thus causing an enlargement of the digestive organs. To supply such enzymes, the body draws on its reserve from all organs and tissues, causing a metabolic deficit. One can live for many years on a cooked food diet but eventually this will cause cellular enzyme exhaustion which lays the foundation for a weak immune system and disease. Although the physical protein molecule is still present, it has lost its life force. Much like a battery that has lost its power, the physical structure remains but the electrical energy which once animated it is no longer present. A protein molecule is actually only the carrier of enzyme activity.


Digestion of Protein, Fats, and Carbohydrates
Watch this You Tube video! Very interesting and good explanation as to where your food is being digested and absorbed.

Most digested molecules of food, as well as water and minerals, are absorbed through the small intestine. The mucosa of the small intestine contains many folds that are covered with tiny fingerlike projections called villi. In turn, the villi are covered with microscopic projections called microvilli. These structures create a vast surface area through which nutrients can be absorbed. Specialized cells allow absorbed materials to cross the mucosa into the blood, where they are carried off in the bloodstream to other parts of the body for storage or further chemical change. This part of the process varies with different types of nutrients.

Carbohydrates such as starch and sugar—are broken into simpler molecules by enzymes in the saliva, in juice produced by the pancreas, and in the lining of the small intestine. Starch is digested in two steps. First, an enzyme in the saliva and pancreatic juice breaks the starch into molecules called maltose. Then an enzyme in the lining of the small intestine splits the maltose into glucose molecules that can be absorbed into the blood. Glucose is carried through the bloodstream to the liver, where it is stored or used to provide energy for the work of the body.
Sugars are digested in one step. An enzyme in the lining of the small intestine digests sucrose, also known as table sugar, into glucose and fructose, which are absorbed through the intestine into the blood. Milk contains another type of sugar, lactose, which is changed into absorbable molecules by another enzyme in the intestinal lining.
Fiber is undigestible and moves through the digestive tract without being broken down by enzymes. Many foods contain both soluble and insoluble fiber. Soluble fiber dissolves easily in water and takes on a soft, gel-like texture in the intestines. Insoluble fiber, on the other hand, passes essentially unchanged through the intestines.

Protein. Foods such as meat, eggs, and beans consist of giant molecules of protein that must be digested by enzymes before they can be used to build and repair body tissues. An enzyme in the juice of the stomach starts the digestion of swallowed protein. Then in the small intestine, several enzymes from the pancreatic juice and the lining of the intestine complete the breakdown of huge protein molecules into small molecules called amino acids. These small molecules can be absorbed through the small intestine into the blood and then be carried to all parts of the body to build the walls and other parts of cells.

Fats. Fat molecules are a rich source of energy for the body. The first step in digestion of a fat such as butter is to dissolve it into the watery content of the intestine. The bile acids produced by the liver dissolve fat into tiny droplets and allow pancreatic and intestinal enzymes to break the large fat molecules into smaller ones. Some of these small molecules are fatty acids and cholesterol. The bile acids combine with the fatty acids and cholesterol and help these molecules move into the cells of the mucosa. In these cells the small molecules are formed back into large ones, most of which pass into vessels called lymphatics near the intestine. These small vessels carry the reformed fat to the veins of the chest, and the blood carries the fat to storage depots in different parts of the body.

The digestive system is very fascinating and we could not function without all those organs working together. As a nurse, you will need to know every part of the digestive system and its functions. There are many people with digestive issues that need the help of doctors and nurses to find and diagnose their problems.

For me, working with a pediatric Gastroenterologist was a great experience for me! I saw many patients that had digestive disorders from Celiac disease to Crohn's disease. Those patients were very sick at the time upon coming into the clinic. If they would not have seeked medical attention, a good number of those kids would not be living today. Without a functioning digestive system, we would not be able to absorb the nutrients needed to maintain life.

Human Physiology Stuart Ira Fox 10th edition