Chapter 22
The Digestive System
I. Overview of the Digestive System (pp. 645–648, Figs. 22.1–22.4)
A.The digestive system consists of the alimentary canal and several accessory organs. (p. 645, Fig. 22.1)
B.The digestive processes of the digestive system are ingestion, propulsion, mechanical digestion, chemical digestion, absorption, and defecation. (pp. 646–647, Figs. 22.2–22.3)
C.The abdominopelvic cavity is divided into four quadrants and nine regions to aid in location of abdominopelvic organs. (pp. 647–648, Fig. 22.4)
II. Anatomy of the Digestive System (pp. 648–678, Figs. 22.5–22.29, Table 22.1)
A.Many of the digestive organs are associated with the peritoneal cavity; peritoneum is the serous membrane that covers many digestive organs and lines the abdominopelvic cavity. (p. 648, Fig. 22.5)
B.Histologically, the walls of the alimentary canal have the same four tissue layers. (p. 648, Fig. 22.5)
1.The mucosa is a mucous membrane and is the innermost lining epithelium.
2.The submucosa is a layer of fibrous connective tissue external to the mucosa that contains blood vessels, lymph vessels, and nerves.
3.The muscularis externa contains layers of smooth muscle.
4.The serosa is the visceral peritoneum.
C.Smooth muscle layers form the muscularis externa in the wall of the alimentary canal. Smooth muscle cells are elongated with tapering ends and one central nucleus. Smooth muscle in the alimentary canal is arranged in sheets; usually an outer longitudinal layer and an inner circular layer. The stomach contains an additional oblique layer of smooth muscle. Smooth muscle contracts more slowly than skeletal muscle and is under the control of involuntary nerve fibers. (pp. 649–651, Figs. 22.7–22.8)
D.The myenteric plexus and submucosal nerve plexus are the visceral nerve plexuses supplying the wall of the alimentary canal. Parasympathetic, sympathetic, visceral sensory fibers, and enteric neurons comprise these plexuses. (pp. 651–652)
E.Mesenteries are formed from a double layer of peritoneum. Mesenteries function to hold abdominal organs in place, store fat, and allow passage of blood vessels and nerves to and from digestive organs. (pp. 652–654, Figs. 22.9–22.11)
F.The mouth is the oral cavity and is lined by mucosa; lips and cheeks help keep food in mouth while chewing; the palate forms the roof of the mouth. (pp. 655–659, Figs. 22.12–22.16)
1.The tongue is mostly a mucosa-covered skeletal muscle with taste buds. (p. 656, Fig. 22.13)
2.Teeth tear and grind food; humans have distinct dentitions (deciduous and permanent), a specific dental formula, and structure consisting of a crown and root. (pp. 656–658, Figs. 22.14–22.15)
3.Salivary glands produce saliva to initiate the chemical breakdown of food and moisten the mouth. (pp. 658–659, Fig. 22.16)
G.The pharynx is a common passageway for food and air. (p. 659, Fig. 22.12)
H.The esophagus is a collapsible tube that connects the pharynx to the stomach; microscopic anatomy reveals several unique histological features. (p. 660, Figs. 22.1, 22.12, and 22.17–18)
I.The stomach churns food into chyme; it extends from the esophagus to the duodenum; microscopically, the muscularis externa shows special features. (pp. 660–665, Figs. 22.18–22.19)
J.The small intestine is the longest part of the alimentary canal; its subdivisions are the duodenum, the jejunum, and the ileum; microscopic anatomy reveals modifications for nutrient absorption and typical wall structure. (pp. 665–668, Figs. 22.20–22.21)
K.The large intestine has several subdivisions: cecum, vermiform appendix, colon, rectum, and anal canal; superior and inferior mesenteric blood vessels serve the large intestine; sympathetic and parasympathetic fibers, and some somatic nerves innervate this organ; defecation occurs when rectal wall muscles contract; microscopic anatomy reveals the lack of villi. (pp. 668–672, Figs. 22.22–22.24)
L.The liver is the largest gland in the body; it secretes bile along with 100’s of other functions; gross anatomical features are the diaphragmatic and visceral surfaces, four lobes, and the bare area; microscopic anatomy reveals the classical liver lobule. (pp. 672–676, Figs. 22.25–22.27)
M.The gallbladder functions to store and concentrate bile produced by the liver. (p. 676, Figs 22.20 and 22.28)
N.The pancreas runs horizontally between the duodenum and spleen. (pp. 677–678, Figs. 22.28–22.29)
III. Disorders of the Digestive System (pp. 678–679)
A.Disorders of the digestive system include hiatal hernia of the esophagus, gastroesophageal reflux disease. (p. 660), peptic ulcers. (pp. 664–665), intestinal obstruction, inflammatory bowel disease, viral hepatitis, and the effects of cystic fibrosis on the pancreas. (pp. 678–679)
IV. The Digestive System Throughout Life (pp. 679–680)
A.The week 3 primitive gut is a tube of endoderm covered by splanchnic mesoderm; the embryonic gut is divided into a foregut, midgut, and hindgut, which form distinct regions of the digestive system. (p. 679, Fig. 22.30)
B.In later life, many disorders of the digestive system include appendicitis, gastroenteritis, food poisoning, ulcers, and gallstones; the efficiency of digestive processes decline in the elderly. (p. 680)
SUPPLEMENTAL STUDENT MATERIALS to Human Anatomy, Fifth Edition
Chapter 22: The Digestive System
To the Student
The digestive system is responsible for the food-processing activities of ingestion, digestion, absorption, and elimination of feces. Because of the external openings, you will be presented with the unique concept that food “inside” the alimentary canal (the GI tract) is actually “outside” of the body. The structural plan of the alimentary canal includes digestive organs: the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. In addition, it contains several accessory digestive organs: the teeth, tongue, gallbladder, salivary glands, liver, and pancreas. A clear understanding of the peritoneum, peritoneal cavity, and associated mesenteries is essential to your study. The general arrangement, location, gross anatomy, microscopic anatomy, and functions of all the aforementioned structures are part of your study of the digestive system.
Step 1: Describe an overview of the digestive system.
-Differentiate the alimentary canal from the accessory digestive organs.
-List and describe specific and essential food-processing activities of the digestive system.
-Draw a simple diagram distinguishing between peristalsis and segmentation.
-Identify the anatomical abdominal regions and quadrants, locating the positions of the abdominopelvic organs.
Step 2: Explain the peritoneum and peritoneal cavity.
-Review the difference between serous membranes and mucous membranes.
-Define peritoneum, distinguishing between visceral peritoneum, parietal peritoneum, and the peritoneal cavity.
-Define mesentery. (Note: Refer to end of this exercise for more details.)
-Explain the difference between retroperitoneal organs and intraperitoneal organs and give several examples.
Step 3: Describe the alimentary canal.
-Describe the histology of the alimentary canal wall, including structure and function of smooth muscle.
-Draw a cross section and label the four layers of the alimentary canal wall at the level of the esophagus.
-Draw a cross section and label the four layers of the alimentary canal wall at the level of the small intestine.
-Name the visceral nerve plexuses that occur in the wall of the alimentary canal, and list the types of fibers and neurons present.
-Describe the effects of sympathetic and parasympathetic innervation to the stomach.
Step 4: Describe the mouth (oral cavity) and its associated organs.
-Describe the gross anatomy of the oral cavity.
-Identify the type of epithelium that lines the oral cavity.
-Explain the function of lips and cheeks, also explaining why lips are reddish.
-Describe the structure and function of the tongue, including papillae and taste buds.
-Name and identify locations of salivary glands.
-Describe the structure and function of teeth, distinguish between permanent and deciduous teeth, and identify classification types of teeth.
Step 5: Describe the pharynx, esophagus, and stomach as digestive system organs.
-Explain the role of the pharynx during swallowing.
-Describe the location and gross anatomy of the pharynx, including openings.
-Describe the location, gross structure, and function of the esophagus.
-Explain how the outer layer of the wall of the esophagus differs from the rest of the digestive tract.
-Describe the location, gross anatomy, and functions of the stomach.
-Compare and contrast the microscopic structure of the esophagus and stomach.
Step 6: Describe the small intestine and the large intestine as digestive system organs.
-Describe the location and functions of the small intestine, identifying its individual segments.
-Explain why the duodenum is retroperitoneal.
-Identify major ducts and their contents that empty into the duodenum.
-Describe the features of the small intestine that increase its surface area.
-Describe the location and functions of the large intestine, identifying its subdivisions.
-Describe and identify special anatomical features on the external surface of the colon.
-Compare the lining of the large intestine to the lining of the small intestine.
-Describe defecation.
Step 7: Describe the liver, gallbladder, and pancreas as accessory digestive organs.
-Identify the location and list the functions of the liver.
-Describe the gross anatomy of the liver, including its lobes, mesenteries, and vessels.
-Describe classic liver lobules.
-Outline the flow of blood through the liver. (Reminder: It has two blood supply sources.)
-Explain the function of hepatocytes.
-Identify the location, structure, and function of the gallbladder.
-Trace the movement of bile from its point of secretion all the way to the duodenum.
-Explain the function of bile.
-Identify the location, structure, and function of the pancreas.
Step 8: Describe the mesenteries associated with abdominal digestive organs.
-Name several specific examples of mesenteries, describing their locations and indicating if each example is dorsal or ventral. (Note: Some mesenteries are called “ligaments”; do not confuse terminology with fibrous ligaments that connect bone to bone.)
-Explain the functions of mesenteries.
-Refer to Figure 22.5 and apply specific names to the two ventral mesenteries indicated in the diagram.