Chapter 18: Digestive System
Chapter 18: Digestive System
Introduction to the Digestive System (pp. 615-616)
- The digestive system mechanically and chemically
breaks down food to forms that can be absorbed through the intestinal wall
and transported by the blood and lymph for use at the cellular level.
- The digestive system consists of a gastrointestinal
(GI) tract and accessory digestive organs.
Serous Membranes and Tunics of the Gastrointestinal
Tract (pp. 616-620)
- Peritoneal membranes line the abdominal wall
and cover the visceral organs. The GI tract is supported by a double layer
of peritoneum called the mesentery.
- The lesser omentum and greater omentum are
folds of peritoneum that extend from the stomach.
- Retroperitoneal organs are positioned behind
the parietal peritoneum.
- The layers (tunics) of the abdominal GI tract
are, from the inside outward, the mucosa, submucosa, tunica muscularis, and
- The mucosa consists of a simple columnar
epithelium, a thin layer of connective tissue called the lamina propria,
and thin layers of smooth muscle called the muscularis mucosae.
- The submucosa is composed of connective
tissue; the tunica muscularis consists of layers of smooth muscle; and
the serosa is composed of connective tissue covered with the visceral
- The submucosa contains the submucosal plexus,
and the tunica muscularis contains the myenteric plexus of autonomic nerves.
Mouth, Pharynx, and Associated Structures (pp.
- The oral cavity is formed by the cheeks, lips,
and hard palate and soft palate. The tongue and teeth are contained in the
- Lingual tonsils and papillae with taste
buds are located on the tongue.
- Structures of the palate include palatal
folds, a cone-shaped projection called the palatine uvula, and palatine
- The incisors and canines have one root each;
the bicuspids and molars have two or three roots.
- Humans are diphyodont; they have deciduous
and permanent sets of teeth.
- The roots of teeth fit into sockets called
dental alveoli that are lined with a periodontal membrane. Fibers in the
periodontal membrane insert into the cementum covering the roots, firmly
anchoring the teeth in the sockets.
- Enamel forms the outer layer of the tooth
crown; beneath the enamel is dentin.
- The interior of a tooth contains a pulp
cavity, which is continuous through the apical foramen of the root with
the connective tissue around the tooth.
- The major salivary glands are the parotid glands,
the submandibular glands, and the sublingual glands.
- The muscular pharynx is a passageway connecting
the oral and nasal cavities to the esophagus and larynx.
Esophagus and Stomach (pp. 628-632)
- Swallowing (deglutition) occurs in three phases
and involves structures of the oral cavity, pharynx, and esophagus.
- Peristaltic waves of contraction push food through
the lower esophageal sphincter into the stomach.
- The stomach consists of a cardia, fundus, body,
and pylorus. It displays greater and lesser curvatures, and contains a pyloric
sphincter at its junction with the duodenum.
- The mucosa of the stomach is thrown into
distensible gastric folds; gastric pits and gastric glands are present
in the mucosa.
- The parietal cells of the gastric glands
secrete HCl, and the principal cells secrete pepsinogen.
Small Intestine (pp. 632-635)
- Regions of the small intestine include the duodenum,
jejunum, and ileum; the bile duct and pancreatic duct empty into the duodenum.
- Fingerlike extensions of mucosa, called villi,
project into the lumen, and at the bases of the villi the mucosa forms intestinal
- New epithelial cells are formed in the intestinal
- The membrane of intestinal epithelial cells
is folded to form microvilli; this brush border of the mucosa increases
the absorptive surface area.
- Movements of the small intestine include rhythmic
segmentation, pendular movement, and peristalsis.
Large Intestine (pp. 636-639)
- The large intestine absorbs water and electrolytes
from the chyme and passes fecal material out of the body through the rectum
and anal canal.
- The large intestine is divided into the cecum,
colon, rectum, and anal canal.
- The appendix is attached to the inferior
medial margin of the cecum.
- The colon consists of ascending, transverse,
descending, and sigmoid portions.
- Haustra are bulges in the walls of the large
- Movements of the large intestine include peristalsis,
haustral churning, and mass movement.
Liver, Gallbladder, and Pancreas (pp. 639-648)
- The liver is divided into right, left, quadrate,
and caudate lobes. Each lobe contains liver lobules, the functional units
of the liver.
- Liver lobules consist of plates of hepatic
cells separated by modified capillaries called sinusoids.
- Blood flows from the periphery of each lobule,
where branches of the hepatic artery and hepatic portal vein empty, through
the sinusoids and out the central vein.
- Bile flows within the hepatic plates, in
bile canaliculi, to the biliary ductules at the periphery of each lobule.
- The gallbladder stores and concentrates the
bile; it releases the bile through the cystic duct and common bile duct into
- The pancreas is both an exocrine and an endocrine
- The endocrine portion, consisting of the
pancreatic islets, secretes the hormones insulin and glucagon.
- The exocrine acini of the pancreas produce
pancreatic juice, which contains various digestive enzymes.
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