Digestive System-- Procedures

Biliary System

The biliary, or excretory, system of the liver consists of the bile ducts and gallbladder. Beginning within the lobules as bile capillaries, the ducts unite to form larger and larger passages as they converge, finally forming two main ducts, one leading from each major lobe. The two main hepatic ducts emerge at the porta hepatis and join to form the common hepatic duct, which unites with the cystic duct to form the common bile duct.

Parts of the stomach

The cardia of the stomach is the section immediately surrounding the esophageal opening. The fundus is the superior portion of the stomach that expands superiorly and fills the dome of the left hemidiaphragm. When the patient is in the upright position, the fundus is usually filled with gas; in radiography, this is referred to as the gas bubble. Descending from the fundus and beginning at the level of the cardiac notch is the body of the stomach. The inner mucosal layer of the body of the stomach contains numerous longitudinal folds called rugae. Distal to this plane is the pyloric portion of the stomach, which consists of the pyloric antrum, to the immediate right of the angular notch, and the narrow pyloric canal, which communicates with the duodenal bulb.

Body habitus with the large intestines

In hypersthenic patients, the large intestine is positioned around the periphery of the abdomen and may require more images to show its entire length. The large intestine of asthenic patients, which is bunched together and positioned low in the abdomen, is at the other extreme.

The location of the esophagus

It originates at the level of the sixth cervical vertebra, or the upper margin of the thyroid cartilage. The esophagus enters the thorax from the superior portion of the neck. In the thorax, the esophagus passes through the mediastinum, anterior to the vertebral bodies and posterior to the trachea and heart. In the lower thorax, the esophagus passes through the diaphragm at T10. Inferior to the diaphragm, the esophagus curves sharply left, increases in diameter, and joins the stomach at the esophagogastric junction, which is at the level of the xiphoid tip (T11). The expanded portion of the terminal esophagus, which lies in the abdomen, is called the cardiac antrum

Peristalsis

Peristalsis is the term applied to the contraction waves by which the digestive tube propels its contents toward the rectum. Normally three or four waves per minute occur in the filled stomach. The waves begin in the upper part of the organ and travel toward the pylorus. The average emptying time of a normal stomach is 2 to 3 hours. Peristaltic action in the intestines is greatest in the upper part of the canal and gradually decreases toward the lower portion. In addition to peristaltic waves, localized contractions occur in the duodenum and the jejunum. These contractions usually occur at intervals of 3 to 4 seconds during digestion. The first part of a "barium meal" normally reaches the ileocecal valve in 2 to 3 hours, and the last portion reaches the ileocecal valve in 4 to 5 hours. The barium usually reaches the rectum within 24 hours.

Alimentary Canal

The alimentary canal is a musculomembranous tube that extends from the mouth to the anus. The regions of the alimentary canal vary in diameter according to functional requirements. The greater part of the canal, which is about 29 to 30 ft (8.6 to 8.9 m) long, lies in the abdominal cavity.

Alimentary Canal

The component parts of the alimentary canal are the mouth, in which food is masticated and converted into a bolus by insalivation; the pharynx and esophagus, which are the organs of swallowing; the stomach, in which the digestive process begins; the small intestine, in which the digestive process is completed; and the large intestine, which is an organ of egestion and water absorption that terminates at the anus.

3 portions of the small intestine

The duodenum is 8 to 10 inches (20 to 24 cm) long and is the widest portion of the small intestine. It is retroperitoneal and is relatively fixed in position. Beginning at the pylorus, the duodenum follows a C-shaped course. The segment of the first portion is called the duodenal bulb because of its radiographic appearance when it is filled with an opaque contrast medium. The second portion is about 3 or 4 inches (7.6 to 10 cm) long. This segment passes inferiorly along the head of the pancreas and in close relation to the undersurface of the liver. The common bile duct and the pancreatic duct usually unite to form the hepatopancreatic ampulla, which opens on the summit of the greater duodenal papilla in the duodenum. The third portion passes toward the left at a slight superior inclination for a distance of about 2 1/2 inches and continues as the fourth portion on the left side of the vertebrae. This portion joins the jejunum at a sharp curve called the duodenojejunal flexure and is supported by the suspensory muscle of the duodenum (ligament of Treitz). The duodenal loop, which lies in the second portion, is the most fixed part of the small intestine and normally lies in the upper part of the umbilical region of the abdomen; however, its position varies with body habitus and with the amount of gastric and intestinal contents. The remainder of the small intestine is arbitrarily divided into two portions, with the upper two fifths referred to as the jejunum and the lower three fifths referred to as the ileum. The jejunum and the ileum are gathered into freely movable loops, or gyri, and are attached to the posterior wall of the abdomen by the mesentery. The loops lie in the central and lower part of the abdominal cavity within the arch of the large intestine.

Esophagus

The esophagus is a long, muscular tube that carries food and saliva from the laryngopharynx to the stomach. The adult esophagus is approximately 10 inches (24 cm) long and image inch (1.9 cm) in diameter. Similar to the rest of the alimentary canal, the esophagus has a wall composed of four layers. Beginning with the outermost layer and moving in, the layers are as follows: • Fibrous layer • Muscular layer • Submucosal layer • Mucosal layer

Gallbladder

The gallbladder is a thin-walled, more or less pear-shaped, musculomembranous sac with a capacity of approximately 2 oz. The gallbladder concentrates bile through absorption of the water content; stores bile during interdigestive periods; and, by contraction of its musculature, evacuates the bile during digestion. The The gallbladder consists of a narrow neck that is continuous with the cystic duct; a body or main portion; and a fundus, which is its broad lower portion. The gallbladder is usually lodged in a fossa on the visceral (inferior) surface of the right lobe of the liver, where it lies in an oblique plane inferiorly and anteriorly. Measuring about 1 inch (2.5 cm) in width at its widest part and 3 to 4 inches (7.5 to 10 cm) long, the gallbladder extends from the lower right margin of the porta hepatis to a variable distance below the anterior border of the liver.

Large Intestine

The large intestine begins in the right iliac region, where it joins the ileum of the small intestine, forms an arch surrounding the loops of the small intestine, and ends at the anus. The large intestine has four main parts, as follows: • Cecum • Colon • Rectum • Anal canal The large intestine is about 5 ft (1.5 m) long and is greater in diameter than the small intestine. The main functions of the large intestine are reabsorption of fluids and elimination of waste products. The cecum is the pouchlike portion of the large intestine that is below the junction of the ileum and the colon.

Liver

The liver, the largest gland in the body, is an irregularly wedge-shaped gland. It is situated with its base on the right and its apex directed anteriorly and to the left The portal vein and the hepatic artery, both of which convey blood to the liver, enter the porta hepatis and branch out through the liver substance The liver has numerous physiologic functions. The primary consideration from the radiographic standpoint is the formation of bile. Bile, the channel of elimination for the waste products of red blood cell destruction, is an excretion and a secretion. As a secretion, it is an important aid in the emulsification and assimilation of fats. The bile is collected from the liver cells by the ducts and is carried to the gallbladder for temporary storage or is poured directly into the duodenum through the common bile duct.

Pancreas and Spleen

The pancreas is an elongated gland situated across the posterior abdominal wall. Extending from the duodenum to the spleen, the pancreas is about 5 1/2 inches (14 cm) long and consists of a head, neck, body, and tail. The head, which is the broadest portion of the organ, extends inferiorly and is enclosed within the curve of the duodenum at the level of the second or third lumbar vertebra. The body and tail of the pancreas pass transversely behind the stomach and in front of the left kidney, with the narrow tail terminating near the spleen.

Rectum

The rectum extends from the sigmoid colon to the anal canal. The anal canal terminates at the anus, which is the external aperture of the large intestine. The rectum is approximately 6 inches (15 cm) long. The distal portion, which is about 1 inch (2.5 cm) long, is constricted to form the anal canal. Just above the anal canal is a dilatation called the rectal ampulla. Following the sacrococcygeal curve, the rectum passes inferiorly and posteriorly to the level of the pelvic floor and bends sharply anteriorly and inferiorly into the anal canal, which extends to the anus. The rectum and anal canal have two AP curves; this fact must be remembered when an enema tube is inserted.

Small Intestine

The small intestine extends from the pyloric sphincter of the stomach to the ileocecal valve, where it joins the large intestine at a right angle. Digestion and absorption of food occur in this portion of the alimentary canal. The length of the adult small intestine averages about 22 ft The wall of the small intestine contains the same four layers as the walls of the esophagus and stomach. The mucosa of the small intestine contains a series of fingerlike projections called villi, which assist the processes of digestion and absorption.

Spleen

The spleen is included in this section only because of its location; it belongs to the lymphatic system. The spleen is a glandlike but ductless organ that produces lymphocytes and stores and removes dead or dying red blood cells. The spleen is more or less bean-shaped and measures about 5 inches (13 cm) long, 3 inches wide Situated obliquely in the left upper quadrant, the spleen is just below the diaphragm and behind the stomach. It is in contact with the abdominal wall laterally, with the left suprarenal gland and left kidney medially, and with the left colic flexure of the colon inferiorly. The spleen is visualized with and without contrast media.

Stomach

The stomach is the dilated, saclike portion of the digestive tract extending between the esophagus and the small intestine The stomach is divided into the following four parts: • Cardia • Fundus • Body • Pyloric portion

Functions of the stomach in the digestive process

The stomach serves as a storage area for food until it can be digested further. It is also where food is broken down. Acids, enzymes, and other chemicals are secreted to break food down chemically. Food is also mechanically broken down through churning and peristalsis. Food that has been mechanically and chemically altered in the stomach is transported to the duodenum as a material called chyme.

The colon

colon is subdivided into ascending, transverse, descending, and sigmoid portions. The ascending colon passes superiorly from its junction with the cecum to the undersurface of the liver, where it joins the transverse portion at an angle called the right colic flexure (formerly hepatic flexure). The transverse colon, which is the longest and most movable part of the colon, crosses the abdomen to the undersurface of the spleen. The transverse portion makes a sharp curve, called the left colic flexure (formerly splenic flexure), and ends in the descending portion. The descending colon passes inferiorly and medially to its junction with the sigmoid portion at the superior aperture of the lesser pelvis. The sigmoid colon curves to form an S-shaped loop and ends in the rectum at the level of the third sacral segment.

The entrance and exit from stomach are controlled by

muscle sphincter. The esophagus joins the stomach at the esophagogastric junction through an opening termed the cardiac orifice. The muscle controlling the cardiac orifice is called the cardiac sphincter. The opening between the stomach and the small intestine is the pyloric orifice, and the muscle controlling the pyloric orifice is called the pyloric sphincter.

Accessory Glands

salivary glands, liver, gallbladder, and pancreas, secrete digestive enzymes into the alimentary canal.

The digestive system consist of two parts:

the accessory glands and the alimentary canal