Gastrointestinal System

Gastrointestinal System

Functions of the Gastrointestinal System

The digestive system (Fig. 5-1) provides the nutrients needed for cells to replicate themselves continually and build new tissue. This is done through several distinct processes: ingestion, the intake of food; digestion, the breakdown of food; absorption, the process of extracting nutrients; and elimination, the excretion of any waste products. Other names for this system are the gastrointestinal (GI) tract, which refers to the two main parts of the system, and the alimentary (al in MEN tair ee) canal, which refers to the tubelike nature of the digestive system, starting at the mouth and continuing in varying diameters to the anus.

The digestive system begins in the oral cavity, progresses through the mediastinum and the abdominal and pelvic cavities, and finally exits at the anus. The stomach and intestines lie within the peritoneal cavity and are attached to the body wall by a rich vascular membrane termed the mesentery. Internally, the alimentary canal is composed of three layers, or tunics. The inner layer is the tunica mucosa, which secretes gastric juices, absorbs nutrients, and protects the tissue through the production of mucus. The submucosa, the next tunic, holds the blood, lymphatic, and nervous tissue. The deepest layer is the tunica muscularis, which contracts and relaxes around the tube in a wavelike movement termed peristalsis, to move food through the tract.

Anatomy and Physiology

Oral Cavity

Food normally enters the body through the mouth, or oral cavity (Fig. 5-2, A). The function of this cavity initially is to break down the food mechanically by chewing (mastication) and lubricate the food to make swallowing (deglutition dee gloo TIH shun) easier.

The oral cavity begins at the lips, the two fleshy structures surrounding its opening. The inside of the mouth is bounded by the cheeks, the tongue at the floor, and an anterior hard palate (PAL it) and posterior soft palate, which form the roof of the mouth. The upper and lower jaws hold 32 permanent teeth that are set in the flesh of the gums. The uvula (YOO vyoo lah) is the tag of flesh that hangs down from the medial surface of the soft palate. The three pairs of salivary (SAL ih vair ee) glands provide saliva, a substance that moistens the oral cavity, initiates the digestion of starches, and aids in chewing and swallowing. The glands are named for their locations: parotid (pair AH tid), near the ear; submandibular (sub man DIB yoo lur), under the lower jaw; and sublingual (sub LEENG gwul), under the tongue. The upper jaw is called the maxilla, and the lower is called the mandible.


The esophagus (eh SAH fah gus) is a muscular, mucus-lined tube that extends from the throat to the stomach. It carries a masticated lump of food, a bolus (BOH lus), from the oral cavity to the stomach by means of peristalsis. The glands in the lining of the esophagus produce mucus, which aids in lubricating and easing the passage of the bolus to the stomach. The muscle that must relax before the food enters the stomach is known by three names: the lower esophageal (eh sah fah JEE ul) sphincter (SFINK tur) (LES), the gastroesophageal sphincter, or the cardiac sphincter, which gets its name because of its proximity to the heart. Sphincters are ringlike muscles that appear throughout the digestive and other body systems.

image Exercise 1 Oral Cavity, Throat, and Esophagus

Match the combining forms with the following definitions. There may be more than one combining form for a given definition.

Decode the following terms using your knowledge of gastrointestinal word parts.


The stomach, where digestion begins, is an expandable vessel, which is divided into three sections: the top, or fundus (FUN dus); the body; and the muscle between the stomach and first part of the small intestine, or pylorus (pye LORE us) (also called the gastric antrum) (Fig. 5-3). The portion of the stomach that surrounds the esophagogastric connection is the cardia (KAR dee ah). The fundus is the area of the stomach that abuts the diaphragm. This section of the stomach has no acid-producing cells, unlike the remainder of the stomach. The body, or corporis, is the central part of the stomach, and the pylorus (pl. pylori) is at the distal end of the stomach, where the small intestine begins. A small muscle, the pyloric sphincter, regulates the gentle release of food from the stomach into the small intestine. When the stomach is empty, it has an appearance of being lined with many ridges. These ridges, or wrinkles, are called rugae (ROO jee) (sing. ruga).

Fig. 5-3 The stomach.

The function of the stomach is to temporarily store the chewed food that it receives from the esophagus. This food is mixed with gastric juices and hydrochloric acid to further the digestive process chemically. This mixture is called chyme (kyme). The smooth muscles of the stomach contract to aid in the mechanical digestion of the food. A continual coating of mucus protects the stomach and the rest of the digestive system from the acidic nature of the gastric juices.

Small Intestine

Once the chyme has been formed in the stomach, the pyloric sphincter relaxes a bit at a time to release portions of it into the first part of the small intestine, called the duodenum (doo AH deh num). The small intestine gets its name, not because of its length (it is about 20 feet long), but because of the diameter of its lumen (LOO mun) (a tubular cavity within the body). The second section of the small intestine is the jejunum (jeh JOO num) and the distal part of the small intestine is the ileum (ILL ee um).

Multiple circular folds in the small intestines, called plicae (PLY see), contain thousands of tiny projections called villi (VILL eye) (sing. villus), which contain blood capillaries that absorb the products of carbohydrate and protein digestion. The villi also contain lymphatic vessels, known as lacteals (LACK tee uls), that absorb lipid (LIH pid) substances from the chyme. A lipid is a fatty substance.

The suffix -ase is used to form the name of an enzyme. It is added to the name of the substance upon which the enzyme acts: for example, lipase, which acts on lipids, or amylase, which acts on starches. -ose is a chemical suffix indicating that a substance is a carbohydrate, such as glucose.

Large Intestine

In contrast to the small intestine, the large intestine or colon (Fig. 5-4) is only about 5 feet long, but it is much wider in diameter. The primary function of the large intestine is the elimination of waste products from the body. Some synthesis of vitamins occurs in the large intestine, but unlike the small intestine, the large intestine has no villi and is not well suited for absorption of nutrients. The ileocecal (ILL ee oh SEE kul) valve is the exit from the small intestine and the entrance to the colon. The first part of the large intestine, the cecum (SEE kum), has a wormlike appendage, called the vermiform appendix (VUR mih form ah PEN dicks) (pl. appendices), dangling from it. Although this organ does not seem to have any direct function related to the digestive system, it is thought to have a possible immunologic defense mechanism.

No longer called chyme, whatever has not been absorbed by the small intestines is now called feces (FEE sees). The feces pass from the cecum to the ascending colon (KOH lin), through the transverse colon, the descending colon, the sigmoid colon (the S-shaped part of the large intestine), and on to the rectum (the last straight part of the colon), where they are held until released from the body completely through the anus (the final sphincter in the GI tract.) The process of releasing feces from the body is called defecation, or a bowel movement (BM).

image Exercise 3 The Stomach, Small Intestine, and Large Intestine

Match the following combining forms and body parts with their terms.

Decode the terms.

Accessory Organs (Adnexa)

The accessory organs are the gallbladder (GB), liver, and pancreas (Fig. 5-5). These organs secrete fluid into the GI tract but are not a direct part of the tube itself. Sometimes accessory structures are referred to as adnexa (ad NECK sah).

The two lobes that form the liver (LIH vur) virtually fill the right upper quadrant of the abdomen and extend partially into the left upper quadrant directly inferior to the diaphragm. The liver filters and stores blood and forms a substance called bile, which emulsifies (ee MUL sih fyez), or mechanically breaks down, fats into smaller particles so that they can be chemically digested. Bile is composed of bilirubin (BILL ee roo bin), the waste product formed by the normal breakdown of hemoglobin in red blood cells at the end of their life spans, and cholesterol (koh LESS tur all), a fatty substance found only in animal tissues. Bile is released from the liver through the right and left hepatic ducts, which join to form the hepatic (heh PAT ick) duct. The cystic (SISS tick) duct carries bile to and from the gallbladder. When the hepatic and cystic ducts merge, they form the common bile duct, which empties into the duodenum. Collectively, all of these ducts are termed bile vessels. Bile is stored in the gallbladder (GALL blad ur), a small sac found on the underside of the right lobe of the liver. When fatty food enters the duodenum, a hormone called cholecystokinin (koh lee sis toh KYE nin) is secreted, causing a contraction of the gallbladder to move bile out into the cystic duct, then the common bile duct, and finally into the duodenum.

The pancreas (PAN kree us) is a gland located in the upper left quadrant. It is involved in the digestion of the three types of food molecules: carbohydrates, proteins, and lipids. The pancreatic enzymes are carried through the pancreatic duct, which empties into the common bile duct. Pancreatic involvement in food digestion is an exocrine (ECK soh krin) function because the secretion is into a duct. Pancreatic endocrine (EN doh krin) functions (secretion into blood and lymph vessels) are discussed in Chapter 15.

Case Study

Peter Jacobs

Peter Jacobs is a 62-year-old CEO of a large international company, who has come to see his physician today because he has been experiencing nausea and persistent heartburn. His physician, Dr. Wellemeyer, knows that Peter’s job is stressful and has required him to travel frequently and eat a variety of unusual foods. In the past, Dr. Wellemeyer has prescribed an antacid and an antianxiety medication, which helped relieve Peter’s symptoms. Today, however, Peter says that he is no longer getting relief. He has lost weight and sleep over the past 2 months.

After lab and stool tests turn out normal, Dr. Wellemeyer refers Peter to a gastroenterologist, who schedules an upper GI endoscopy, which reveals erosion and narrowing of the esophagus. He is diagnosed with Barrett esophagus, a moderate hiatal hernia, and gastritis. Peter is placed on a special antacid and is told that if his symptoms do not improve, surgery may be necessary to repair his hiatal hernia.



image Exercise 7 Operative Report

Using the operative report above, answer the following questions. Use a dictionary as needed for this exercise.

Combining and Adjective Forms for the Anatomy of the GI System

Meaning Combining Form Adjective Form
abdomen abdomin/o, celi/o, lapar/o abdominal, celiac
accessory adnex/o adnexal
anus an/o anal
appendix appendic/o, append/o appendicular
bile chol/e, bil/i biliary
bile vessel cholangi/o  
bolus bol/o  
cecum cec/o cecal
cheek bucc/o buccal
cholesterol cholesterol/o  
common bile duct choledoch/o choledochal
corporis, body corpor/o corporeal
duodenum duoden/o duodenal
esophagus esophag/o esophageal
fat, lipid lip/o, lipid/o lipid
feces fec/a fecal
fold, plica plic/o plical
fundus fund/o fundal
gallbladder cholecyst/o cholecystic
glucose, sugar gluc/o  
gums gingiv/o gingival
ileum ile/o ileal
intestines intestin/o intestinal
jejunum jejun/o jejunal
large intestine, colon col/o, colon/o colonic
lips cheil/o, labi/o labial
liver hepat/o hepatic
lobe lob/o lobular
lower jaw mandibul/o mandibular
lumen lumin/o luminal
mouth, oral cavity or/o, stom/o, stomat/o oral, stomal, stomatic
nose nas/o, rhin/o nasal
nutrition aliment/o alimentary
palate palat/o palatine
pancreas pancreat/o pancreatic
pharynx, throat pharyng/o pharyngeal
pylorus pylor/o pyloric
rectum rect/o rectal
rectum and anus proct/o  
rugae rug/o rugous
saliva sial/o salivary
salivary gland sialaden/o  
sigmoid colon sigmoid/o sigmoidal
small intestine enter/o enteral
starch amyl/o  
stomach gastr/o gastric
teeth dent/i, odont/o dental
tongue gloss/o, lingu/o lingual, glossal
upper jaw maxill/o maxillary
uvula uvul/o uvular
villus vill/o villous

Oct 6, 2017 | Posted by in GENERAL SURGERY | Comments Off on Gastrointestinal System
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