Choose two organs of the digestive system. Explain how the structure of that organ contributes to the function of that organ.

Pancreas produces pancreatic juice that is secreted into the pancreatic duct. Pancreatic juice contains enzymes that can split carbohydrates, proteins, fate, and nucleic acids. pancreatic has a high bicarbonate ion concentration that helps neutralize chyme and causes the intestinal contents to become alkaline. The pancreatic duct leads to the duodenum.
Hole's Human Anatomy and Physiology 8th edition p676-677
Small Intestine
The wall of the small intestine wall is lined with villi that greatly increases the surface area and aids in mixing and absorption. Microvilli on the free ends of the epithelial cells increase the surface area even more. Intestinal glands are located between the villi.. Intestinal glands secrete a watery fluid that lacks digestive enzymes but provides a way for moving chyme to our villi. Circular folds in the lining of our intestinal wall also increase its surface area. Digestive enzymes embedded in the surfaces of microvilli split sugar, protein and fat molecules.
Hole's Human Anatomy and Physiology 8th edition p685-691

The three molecules, carbohydrates, proteins, and lipids, are important molecules in food that need to be physically and chemically digested by the digestive system. For each nutrient (carbohydrates, proteins, and lipids):
Describe where the nutrient is digested in the digestive system
Describe the enzyme that help to hydrolyze the molecules
Describe how the nutrient is absorb
Describe how the body uses the molecule (nutrient)


Carbohydrate digestion begins in the mouth with salivary amylase, and is completed in the small intestine by enzymes from the intestinal mucosa and pancreas. The resulting mono saccharides are absorbed by the villi and enter the blood capillaries. Carbohydrates are a class of natural organic substances that includes sugars, starch and cellulose. The digestion of a particular carbohydrate in the gastrointestinal tract depends upon how complex the structure is. The more complex the harder the digestive system has to work to break it down in order to absorb it into the bloodstream. Carbs are divided into 3 types: mono saccharides, like glucose, fructose and galactose, that are digested rapidly; disaccharides, like sucrose, lactose and maltose, that are digested quickly; polysaccharides, like starch, that take longer to digest; and very complex carbs, like cellulose that cannot be digested at all.
Our digestion system from our mouth to the small intestine is designed to break down disaccharides and polysaccharides into mono saccharides. This metabolism of carbohydrates is achieved through the secretion of a number of digestive enzymes into the gastrointestinal tract where they attack carbohydrates and gradually convert them into simple sugars like glucose so they can be absorbed into the blood. Digestive enzymes are like scissors they chop long starch molecules into simpler ones.
The process of digesting carbohydrates begins in the mouth. Our saliva contains an enzyme called amylase that starts breaking down the more complex carbs into simpler types. Enzyme activity continues in the stomach, but slows down significantly as digestive acids are released into the stomach by the glands. In the Small Intestine Another version of amylase is secreted by the pancreas into the duodenum. This cuts down carbohydrates into simple sugars - maltose, lactose and sucrose. As the carbohydrate passes further into the intestine, the enzymes maltose, lactase and sucrose chop maltose, lactose and sucrose into smaller bits, that are more easily absorbed, which are eventually converted to glucose and absorbed through the intestinal walls into the bloodstream.
After carbohydrates are duly broken down into glucose, in the duodenum and jejunum of the small intestine, the glucose is absorbed into the bloodstream and taken to the liver, where it is stored or distributed to cells throughout the body for energy. In this way, the liver regulates blood glucose levels to provide sufficient energy for the body. For example, excess glucose a cause of hyperglycemia is converted in the liver to glycogen in response to the hormone insulin, and stored. Likewise, if blood sugar levels fall, the glycogen is converted over again to glucose in response to messages that are conveyed by the hormone glucagon, to prevent hypoglycemia. If glycogen levels are exhausted, glucagon can trigger the formation of glucose from some amino acids or glycerol fats - a process called gluconeogenesis.
A simple sugar is much less resistant than a starch, and is digested or metabolized much faster. Things that slow down digestion include: the presence of acid, and the presence of soluble fiber.


An essential macro nutrient, protein is used by the body to build and repair cells, to regulate a huge number of body functions. For example, almost 50 percent of the dietary protein we consume each day goes into making enzymes, the specialized proteins that help to digest food, assemble or divide molecules to make new cells and other chemical substances. Protein is also used to make neurotransmitters, essential for sending nerve messages around the body. Protein is also used in the creation of DNA and RNA, the nucleic acids responsible for determining how our body cells are formed and how they behave.
Enzymes are crucial contributors to protein digestion. Protein digesting enzymes are referred to as protienases or proteases. Protein generally takes the form of very complex molecules arranged in chains of amino acids. So the bonds binding these complex molecules together must firstly be broken down. This digestive process begins in the stomach's gastric acid and attacks the protein molecules separating them and breaking them down into amino acids. Then the gastric enzyme pepsin which is the only protease able to digest collagen starts to digest the amino acids.

Digestion of proteins continues in the duodenum, the first segment of the small intestine. As in fat digestion, the pancreas helps the process by secreting the pancreatic protease enzymes trypsin and chymotrypsin. Like pepsin, trypsin breaks down a protein into single amino acid molecules, through a process called hydrolysis. During hydrolysis, a water molecule is inserted between the two amino acids which are bonded together. This breaks the bond between them. After breakdown, the amino acids are small enough to pass through the intestinal lining into tiny veins capillaries in the villi the finger-like projections on the wall of the small intestine. Once in the bloodstream, the amino acids are distributed by both red blood cells and by the liquid blood plasma to tissues throughout the body where they are used in the creation and repair of cell structures. Such is the demand for protein, the body maintains a constant balance of amino acids in the blood.

If protein requirements are exceeded by protein intake, the surplus amino acids may be converted to glucose for energy use, or converted to fatty acids and stored as adipose tissue.

If we eat insufficient protein, the body may break down stored protein in the muscles and transport the amino acids to the more vital organs, as required. Alternatively, if our energy intake falls dangerously low, protein amino acids will be taken from the muscles and sent to the liver to be converted into glucose.


Dietary fats, like those in butter, meat or cooking oils, are basically organic compounds composed of carbon, hydrogen, and oxygen. They consist of complex molecules and are the most highly concentrated source of energy in our daily diet. They belong to a class of substances called lipids. Unfortunately, dietary fats do not dissolve in water, as a result they are not easily broken down by fat-digesting enzymes (lipase) in the watery content of the gastrointestinal tract. Thus fats tend to take longer to digest than carbohydrates or proteins.
Although a small amount of lipase is secreted by glands on the tongue, and by the stomach, these digestive actions are not significant, as almost no real breakdown of fat occurs until the fats reach the duodenum in the form of gastric chyme.

Fat digestion and absorption requires that the complex fat molecules be broken down into smaller more manageable molecules. This is done by mixing the fat with the digestive enzyme lipase, which enters the duodenum from the pancreas - the main source of enzymes for digesting fats and proteins. Lipase chops up lipid molecules into fatty acid molecules and glycerol molecules. However, because fat does not dissolve in water, the fat molecules enter the duodenum in a congealed mass, which makes it impossible for the pancreatic lipase enzymes to attack them, since lipase is a water soluble enzyme and can only attack the surface of the fat molecules. To overcome this problem the digestive system uses a substance called bile, produced in the liver but stored in the gallbladder, which enters the duodenum via the bile duct. Bile emulsifies fats - meaning, it disperses them into small droplets which then become suspended in the watery contents of the digestive tract. Emulsification allows lipase to gain easier access to the fat molecules and thus accelerates their breakdown and digestion.
Lipase and other digestive juices break down the fat molecules into fatty acids and types of glycerol. Absorption of fat into the body, which takes 10-15 minutes, occurs in the villi - the millions of finger-like projections which cover the walls of the small intestine. Inside each villus is a series of lymph vessels and blood vessels. The lacteal absorb the fatty acids and glycerol into the lymphatic system which eventually drains into the bloodstream. The fatty acids are transported via the bloodstream to the membranes of adipose cells or muscle cells, where they are either stored or oxidized for energy. Since glucose rather than fat is the body's preferred source of energy, and since only about 5 percent of absorbed fat called glycerol's can be converted into glucose, a significant proportion of digested fat is typically stored as body fat in the adipose cells. The glycerol part is absorbed by the liver and is either converted into glucose, and used to help breakdown glucose into energy.

Content Summary

Digestion is the process of mechanically and chemically breaking down foods so that they can be absorbed. The digestive system consists of an alimentary canal and many accessory organs. The mouth is adapted to receive food and begin preparing it for digestion. It also serves as an organ of speech and sensory perception. Salivary glands secrete saliva, that moistens food and helps bind food particles that begins chemical digestion of carbohydrates and makes taste possible. The pharynx and esophagus serve as passage ways. The stomach receives food, mixes it with gastric juice and carries a limited amount of absorption, and moves food into the small intestine. The pancreas is closely associated with the duodenum. The liver is located in the upper right quadrant of the abdominal cavity. The small intestine extends from our pyloric sphincter to the large intestine. It receives secretions from the pancreas and liver, completes the digestion of nutrients and absorbs the products of digestion and transports the residue to the large intestine. The large intestine absorbs water and electrolytes and forms and stores our waste.

How Digestion applies to us and our careers as Nurses

Digestion is how food gets broken down in the body and absorbed into the bloodstream. How well nourished an individual is has everything to do with digestion and proper homeostasis. There are all sorts of chemical processes that take place in order for your body to use the nutrition in our foods. The nurse must have a superb understanding of nutrition and how to apply it to all conditions and diagnosis. When the body doesn’t digest correctly the nurse will use the symptoms from the patient to determine how to treat him or her.