ATI TEAS GUIDE TO SCIENCE | THE DIGESTIVE SYSTEM

Bodily Organs and Systems – The Digestive System

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Questions related to the Bodily Organs and Systems will test your knowledge of structures and functions within the ten human organ systems that are essential to life. You may also be tested on vocabulary terms related to your understanding of anatomy. You must understand these vital body systems when caring for patient’s co-morbidities.

Please note that the ATI TEAS will only cover basic knowledge of bodily organs and systems. More in-depth knowledge will be covered in our Anatomy and Physiology Series.

Let’s get started on understanding how the bodily organs and systems are important on the ATI TEAS.

 

THE DIGESTIVE SYSTEM

The digestive system involves a series of processes that break down the food we eat into structures that can be delivered and then used by the cells.

• Food is first ingested into the mouth chewed, and then swallowed.
• Food is then digested through mechanical digestion, the physical breakdown of food through chewing and mixing movements in the stomach.
• Chemical digestion breaks food down further through the use of enzymes so that the nutrients can be absorbed.
• The absorption process transports the digested food through the intestine into the circulatory system.
• Lastly, undigested food is eliminated.

The process of digestion is another complex series of events. The process of digestion begins in the mouth, where the salivary glands secrete saliva as food is chewed and broken down. Enzymes such as lipase and amylase in the saliva begin chemical digestion of lipids and starches. Swallowed food mixed with saliva (bolus) then moves through the esophagus and into the stomach. The gastric sphincter prevents the reflux of food back into the esophagus. The enzyme pepsin initiates chemical digestion in the stomach. Secretions in the stomach further help the food to digest. Once the food is digested in the stomach, the product is called chyme (acidic fluid that passes from the stomach to the small intestines) and it passes through pyloric sphincter into the duodenum, the first part of the small intestine. Absorption of nutrients occurs primarily in the small intestine, where the gallbladder secretes bile made in the liver, and the pancreas secretes additional enzymes essential to digestion. The digested material then passes into the cecum and then into the large intestine. The large intestine performs the role of absorbing water, vitamin K, and salt from the digested food matter and creating solid wastes through bacterial fermentation in the colon. These wastes then pass through the body via the rectum and the anus.

The digestive tract, or gastrointestinal (GI) Tract, is about eight to nine meters long and begins with the mouth, where food enters, and ends at the anus, where waste is eliminated. In between, the GI tract is made up of various organs through which food passes and is broken down. The sequence of the GI tract includes the mouth, throat, esophagus, stomach, small intestine, large intestine. Most digestion takes place in the small intestine.

Hormones play a vital role in digestion as well. They cause the secretions necessary for digestion. They stimulate muscle contraction and relaxation to move digested matter through the small intestine. They regulate the flow of water and electrolytes between the digestive system and the bloodstream and they increase blood flow for the absorption of nutrients. Specific hormones perform other functions as well. For examples, the hormones gherlin stimulates appetite, leptin inhibits hunger, insulin causes the storage of glucose, and glucagon stimulates the breakdown of stored glycogen. Without hormones, the system cannot function.

Other vital organs necessary for the digestion and absorption of food are the pancreas and liver. The pancreas secretes pancreatic juice, which helps to break down fasts into useful nutrients for the body. The liver produces bile, which is important in the digestion of fats. The bile is stored in the gallbladder until it is needed.