The Gastrointestinal System
Kim Maryniak, PhD, RNC-NIC, NEA-BC
What is the gastrointestinal tract?
The gastrointestinal tract is essentially a tube that extends from the mouth to the anus. It has generally the same structure throughout. There is a hollow portion of the tube known as the lumen, a muscular layer in the middle, and a layer of epithelial cells. These layers are responsible for maintaining the mucosal integrity of the tract.
What are the funcions of the gastrointestinal tract?
There are three main functions of the gastrointestinal tract, including transportation, digestion, and absorption of food. The mucosal integrity of the gastrointestinal tract and the functioning of its accessory organs are vital in maintaining the health of your patient. Components of the gastrointestinal system include the mouth, esophagus, stomach, small intestine, and large intestine. The gastrointestinal tract’s accessory organs include the liver, pancreas, and gallbladder (Jarvis, 2015 & Scanlon, 2015).
The mouth functions to break down food into smaller parts. The esophagus is the tube that allows the passage of the food bolus from the mouth to the stomach. It plays no part in the digestive process (Jarvis, 2015 & Scanlon, 2015).
The stomach functions to store, churn, and puree food into a substance known as chime. Gastric juices are secreted by the cells of the stomach, contributing to chemical digestion (Jarvis, 2015 & Scanlon, 2015).
The small intestine extends from the pylorus to the ileocecal valve. The small intestine is composed of the duodenum, jejunum, and ileum. The primary function of the small intestine is the absorption of vitamins and nutrients, including electrolytes, iron, carbohydrates, proteins, and fats. Most digestion of nutrients happens here (Jarvis, 2015 & Scanlon, 2015).
The large intestine extends from the terminal ileum at the ileocecal valve to the rectum. At the terminal ileum, the large intestine becomes the ascending colon, the transverse colon, and then the descending colon. Following the descending colon is the sigmoid colon and the rectum. The main function of the large intestine is water absorption. Typically, the large intestine absorbs about one and one-half liters of water per day. It can, however, absorb up to six liters (Jarvis, 2015 & Scanlon, 2015).
The gallbladder is a pear-shaped, sac-like organ attached to the liver that serves as a storage facility for bile. When a large or fatty meal is consumed, nerve and chemical signals (release of the enzyme CCK) cause the gallbladder to contract. This contraction releases bile into the digestive system (Jarvis, 2015 & Scanlon, 2015).
The liver is a very large organ located in the upper right abdomen. Blood supply to the liver arises from both the portal vein and hepatic artery. Nearly one-quarter of our cardiac output is delivered through the liver per minute, most of which travels through the portal vein. The blood is filtered through the liver, which destroy debris and unwanted organisms (Jarvis, 2015 & Scanlon, 2015).
The pancreas is both an endocrine and exocrine gland. The exocrine function of the pancreas is mainly digestive in nature and involves the secretion of pancreatic enzymes and bicarbonate (Jarvis, 2015 & Scanlon, 2015).
Having knowledge of the structure and functions of the gastrointestinal system will assist in the recognition and interpretation of assessment findings related to the patient’s history and physical exam.
For more information about the gastrointestinal system, refer to the RN.com course Gastrointestinal Anatomy and Physiology.
Jarvis, C. (2015). Physical examination and health assessment (7th ed.). St. Louis, MO: W.B. Saunders.
Scanlon, V. (2015). Essentials of anatomy and physiology (7th ed.). Philadelphia, PA: F.A. Davis Co.
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