The Digestive System Pages ,

The Digestive System Pages 676-685, 691-711
23 PART 1 The Digestive System Pages ,

Overview of the Digestive System
Organs are divided into two groups Alimentary canal Mouth, pharynx, and esophagus Stomach, small intestine, and large intestine Accessory digestive organs Teeth and tongue Gallbladder, salivary glands, liver, and pancreas Accessory organs are connected to the alimentary canal by ducts Secretions contribute to breakdown of foodstuffs

The Alimentary Canal and Accessory Digestive Organs
Mouth (oral cavity) Tongue Esophagus Liver Gallbladder Anus Duodenum Jejunum Ileum Small intestine Parotid gland Sublingual gland Submandibular gland Salivary glands Pharynx Stomach Pancreas (Spleen) Transverse colon Descending colon Ascending colon Cecum Sigmoid colon Rectum Vermiform appendix Anal canal Large intestine Figure 23.1

Ingestion—occurs in the mouth Propulsion—movement of food
Digestive Processes Ingestion—occurs in the mouth Propulsion—movement of food Peristalsis—major means of propulsion Mechanical digestion—prepares food for chemical digestion Chewing, churning food in stomach, segmentation Segmentation is rhythmic local constrictions of intestine

Absorption—transport of digested nutrients
Digestive Processes Chemical digestion—complex molecules broken down to chemical components Mouth Stomach Small intestine Absorption—transport of digested nutrients Defecation—elimination of indigestible substances as feces

Digestive Processes Figure 23.5 Food Ingestion Propulsion Esophagus
Stomach Pharynx • Swallowing (oropharynx) Mechanical digestion Chemical • Chewing (mouth) • Churning (stomach) • Segmentation (small intestine) Small intestine Large Defecation Anus Feces Mainly H2O Blood vessel Lymph Absorption • Peristalsis (esophagus, stomach, small intestine, large intestine) Figure 23.5

Major means of propulsion
Peristalsis Major means of propulsion Adjacent segments of the alimentary canal relax and contract Figure 23.6

Rhythmic local contractions of the intestine
Segmentation Rhythmic local contractions of the intestine Mixes food with digestive juices Figure 23.6

The Peritoneal Cavity and Peritoneum
Peritoneum—a serous membrane Visceral peritoneum—surrounds digestive organs Parietal peritoneum—lines the body wall Peritoneal cavity—a slit-like potential space

Mesentery—a double layer of peritoneum Holds organs in place Sites of fat storage Provides a route for circulatory vessels and nerves

Parietal peritoneum Visceral Ventral mesentery Abdominopelvic Mesentery resorbed and lost Dorsal Vertebra Alimentary canal organ (a) Schematic cross sections of abdominal cavity illustrating the peritonea and mesenteries (c) Some organs lose their mesentery and become retroperitoneal during development. Alimentary canal organ in a retroperitoneal position Liver Wall of body trunk Kidney (retroperitoneal) cavity (with serous fluid) Stomach (b) Illustration of the peritonea in a cross section through the superior abdomen, inferior view Posterior Anterior Falciform ligament

Retroperitoneal organs Behind the peritoneum Peritoneal organs Digestive organs that keep their mesentery

Superficial view of abdominal organs
Mesenteries Superficial view of abdominal organs (a) Falciform ligament Liver Gallbladder Spleen Stomach Ligamentum teres Greater omentum Small intestine Cecum Figure 23.4

Lesser omentum attaches to lesser curvature of stomach
Mesenteries Lesser omentum attaches to lesser curvature of stomach (b) Liver Lesser omentum Gallbladder Stomach Duodenum Transverse colon Small intestine Cecum Urinary bladder Figure 23.4

Greater omentum—a “fatty apron” of peritoneum
Mesenteries Transverse colon Greater omentum Descending colon Jejunum Mesentery Transverse mesocolon Sigmoid Sigmoid colon Ileum (c) Greater omentum—a “fatty apron” of peritoneum Greater omentum and transverse colon reflected Figure 23.4

Sagittal section through the abdominopelvic cavity
Mesenteries Sagittal section through the abdominopelvic cavity Mesenteries attach to posterior abdominal wall Pancreas Liver Lesser omentum Stomach Duodenum Transverse mesocolon Greater omentum Mesentery Jejunum Visceral peritoneum Urinary bladder Transverse colon Ileum Parietal peritoneum Rectum (d)

Secondarily Retroperitoneal Organs
Initially formed within peritoneum Become retroperitoneal Fuse to posterior abdominal wall

Summary of Intraperitoneal and Secondarily Retroperitoneal Organs
Table 23.1

Histology of the Alimentary Canal Wall
Same four layers from esophagus to anus The mucosa—innermost layer Consists of Epithelium Lamina propria Muscularis mucosae The submucosa—external to the mucosa Contains blood and lymphatic vessels, nerve fibers

Histology of the Alimentary Canal
Glands in submucosa Submucosa Lumen Mucosa-associated lymphoid tissue Duct of gland outside alimentary canal Gland in mucosa Nerve Artery Vein Lymphatic vessel Mesentery Intrinsic nerve plexuses Mucosa Muscularis externa Serosa (a) Longitudinal and cross-sectional views through the small intestine Myenteric nerve plexus Submucosal nerve plexus Epithelium Lamina propria Muscularis mucosae Longitudinal muscle Circular muscle Connective tissue Figure 23.7a

Histology of the Alimentary Canal Wall
The muscularis externa—external to the submucosa Two layers Circular muscularis—inner layer Longitudinal muscularis—outer layer The serosa—the outermost layer Is the visceral peritoneum

Histology of the Alimentary Canal
(b) Light micrograph cross section through the small intestine (30) Submucosa Mucosa Muscularis externa Serosa Figure 23.7b

Primarily found in walls of viscera Fibers elongated
Smooth Muscle Primarily found in walls of viscera Fibers elongated Have one centrally located nucleus Grouped into sheets Longitudinal layer—parallel to long axis of organ Circular layer—deeper layer, fibers run around circumference of organ

Smooth Muscle Figure 23.8a, b Small intestine
(a) Location and plane of section shown in (b) (b) Cross section of the intestine showing the smooth muscle layers (one circular and the other longitudinal) running at right angles to each other Mucosa Longitudinal layer of smooth muscle (shows smooth muscle fibers in cross section, 145) Circular layer of smooth muscle (shows longitudinal views of smooth muscle fibers, 145) Figure 23.8a, b

The Salivary Glands Produce saliva Parotid glands Submandibular glands
Parotid duct—parallel to zygomatic arch Submandibular glands Lie along medial surface of mandible Sublingual glands Lie in floor of oral cavity

Figure 23.15 The major salivary glands.
Tongue Teeth Parotid gland Ducts of sublingual gland Parotid duct Masseter muscle Frenulum of tongue Body of mandible (cut) Sublingual gland Posterior belly of digastric muscle Mylohyoid muscle (cut) Submandibular duct Anterior belly of digastric muscle Submandibular gland

Oropharynx and laryngopharynx
The Pharynx Oropharynx and laryngopharynx Passages for air and food Lined with stratified squamous epithelium External muscle layer Consists of superior, middle, and inferior pharyngeal constrictors

Gross anatomy—muscular tube
The Esophagus Gross anatomy—muscular tube Begins as a continuation of the pharynx Joins the stomach inferior to the diaphragm Cardiac sphincter—closes lumen to prevent stomach acid from entering esophagus

Diaphragm Figure 11.13b Foramen for esophagus-esophageal hiatus
Costal cartilage Lumbar vertebra Diaphragm Quadratus lumborum Psoas major Xiphoid process of sternum Foramen for inferior vena cava Central tendon of diaphragm Foramen for aorta 12th rib (b) Figure 11.13b

Cardia Esophagus Pyloric sphincter (valve) at pylorus Pyloric canal
antrum Rugae of mucosa Body Lumen Serosa Fundus Lesser curvature Greater Muscularis externa (a) Duodenum Longitudinal layer Circular layer Oblique layer Figure 23.17a

The Esophagus Microscopic anatomy
Epithelium is stratified squamous epithelium When empty, mucosa and submucosa in longitudinal folds Mucous glands—extends from submucosa to lumen Muscularis externa Skeletal muscle first third of length Adventitia—most external layer

Figure 23.16 Microscopic structure of the esophagus.
Mucosa (stratified squamous epithelium) Esophagus- stomach junction Submucosa (areolar connective tissue) Lumen Muscularis externa Simple columnar epithelium of stomach Circular layer Longitudinal layer Adventitia (fibrous connective tissue) Cross section through esophagus (3) Esophagus-stomach junction, longitudinal section (85)

Site where food is churned into chyme
The Stomach Site where food is churned into chyme Secretion of pepsin begins protein digestion Functions under acidic conditions Food remains in stomach approximately 4 hours Regions of the stomach Cardiac region Fundus Body Pyloric region

The Stomach Cardia Esophagus Pyloric sphincter (valve) at pylorus
canal antrum Rugae of mucosa Body Lumen Serosa Fundus Lesser curvature Greater Muscularis externa (a) Duodenum Longitudinal layer Circular layer Oblique layer Figure 23.17a

The Stomach Fundus Liver (cut) Body Spleen Lesser curvature Greater
Figure 23.17b

Microscopic Anatomy of the Stomach
Muscularis has three layers Circular and longitudinal layers and oblique layer Epithelium is simple columnar epithelium Mucosa dotted with gastric pits Gastric glands—deep to gastric pits

Microscopic Anatomy of the Stomach
Gastric glands of fundus and body Mucous neck cells Secrete a special mucus Parietal (oxyntic) cells Secrete hydrochloric acid and gastric intrinsic factor Chief (zymogenic) cells Secrete pepsinogen Pepsinogen is activated to pepsin when it encounters acid in the gastric glands

The Stomach—Microscopic Anatomy
Mucosa Surface epithelium Lamina propria Muscularis mucosae Oblique layer Circular layer Longitudinal layer Serosa (a) Layers of the stomach wall, longitudinal section Stomach wall Muscularis externa (contains myenteric plexus) Submucosa (contains submucosal plexus) (b) Enlarged view of gastric pits and gastric glands Mucous neck cells Parietal cell Surface epithelium (mucous cells) Gastric pits Chief cell Enteroendocrine cell Gastric pit gland (c) Location of the HCl-producing parietal cells and pepsin-secreting chief cells in a gastric gland Pepsinogen Mitochondria Pepsin HCl Chief cell Enteroendocrine cell Parietal cell Figure 23.18

Figure 23.18 Microscopic anatomy of the stomach.
Gastric pits Surface epithelium (mucous cells) Gastric pit Surface epithelium Mucous neck cells Parietal cell Mucosa Gastric gland Lamina propria Chief cell Muscularis mucosae Submucosa (contains submucosal plexus) Oblique layer Enteroendocrine cell Pepsinogen Pepsin HCl Muscularis externa (contains myenteric plexus) Circular layer Enlarged view of gastric pits and gastric glands Longitudinal layer Mitochondria Serosa Stomach wall Parietal cell Layers of the stomach wall, longitudinal section Mucus-secreting cells Chief cell Gastric pits Surface mucous cell Enteroendocrine cell Mucous neck cells Location of the HCl-producing parietal cells and pepsin-secreting chief cells in a gastric gland HCl-secreting parietal cells Gastric gland Enzyme-secreting chief cells Muscularis mucosae Micrograph of the stomach mucosa, view similar to part (b) (110)

The Small Intestine—Gross Anatomy
Longest portion of the alimentary canal Site of most enzymatic digestion and absorption Three subdivisions Duodenum Jejunum Ileum

Receives digestive enzymes and bile
The Duodenum Receives digestive enzymes and bile Main pancreatic duct and common bile duct enter duodenum Sphincters control entry of bile and pancreatic juices

The Duodenum and Related Organs
Jejunum Mucosa with folds Cystic duct Duodenum Hepatopancreatic ampulla and sphincter Gallbladder Right and left hepatic ducts of liver Bile duct and sphincter Main pancreatic duct and Pancreas Tail of pancreas Head of pancreas Common hepatic duct Major duodenal papilla Accessory pancreatic duct Figure 23.19

The Small Intestine—Microscopic Anatomy
Modifications for absorption Circular folds (plicae circulares) Transverse ridges of mucosa and submucosa Villi Finger-like projections of the mucosa Covered with simple columnar epithelium Microvilli Further increase surface area for absorption

Histology of the Intestinal Wall
Absorptive cells Uptake digested nutrients Goblet cells Secrete mucus that lubricates chyme Enteroendocrine cells Secrete hormones Intestinal crypts Epithelial cells secrete intestinal juice

The Small Intestine—Structural Features
Vein carrying blood to hepatic portal vessel Muscle layers (b) Absorptive cells Lacteal Intestinal crypt Mucosa associated lymphoid tissue Muscularis mucosae Duodenal gland Submucosa Enteroendocrine Venule Lymphatic vessel Microvilli (brush border) Goblet cell Blood capillaries Vilus Lumen Circular folds Villi (c) Intestinal crypt Absorptive cells Villi Goblet cells (a) Figure 23.20

Digested residue contains few nutrients
The Large Intestine Digested residue contains few nutrients Small amount of digestion by bacteria Main functions Absorb water and electrolytes

Gross Anatomy of Large Intestine
Subdivided into Cecum, vermiform appendix, colon, rectum, anal canal Special features of large intestine Teniae coli Thickening of longitudinal muscularis Haustra Puckering created by teniae coli Epiploic appendages Fat-filled pouches of visceral peritoneum

Cecum Blind pouch Beginning of large intestine Vermiform appendix Contains lymphoid tissue Neutralizes pathogens Colon Divided into distinct segments Ascending, transverse, descending, and sigmoid colon

Rectum Descends along the inferior half of the sacrum Anal canal The last subdivision of the large intestine Lined with stratified squamous epithelium

Right colic (hepatic) flexure Transverse colon Superior mesenteric artery Haustrum Ascending colon IIeum IIeocecal valve Vermiform appendix Cecum Left colic (splenic) flexure Transverse mesocolon Epiploic appendages Descending colon Teniae coli Sigmoid colon Cut edge of mesentery External anal sphincter Rectum Anal canal Figure 23.21a

(b) Rectal valve Rectum Anal canal Levator ani muscle Anus Anal sinuses Anal columns Anal valves Internal anal sphincter External anal Hemorrhoidal veins Pectinate line Figure 23.21b

Microscopic Anatomy of Large Intestine
Villi are absent Contains numerous goblet cells Intestinal crypts with many goblet cells Lined with simple columnar epithelial tissue Epithelium changes at anal canal Becomes stratified squamous epithelium

Figure 23.23 The mucosa of the large intestine.
Colonocytes Goblet cells Lamina propria Intestinal crypt Muscularis mucosae

Figure 23.24 Digestive Processes and Histology of the Alimentary Canal (1 of 2)

Figure 23.24 Digestive Processes and Histology of the Alimentary Canal (2 of 2)

Largest gland in the body
The Liver Largest gland in the body Performs over 500 functions Digestive function Bile production Performs many metabolic functions

The Liver Sternum Bare area Nipple Liver Falciform ligament Left lobe
Right lobe of liver Gallbladder Bare area Falciform ligament Left lobe of liver Round (ligamentum teres) Figure 23.25

Visceral Surface of the Liver
Lesser omentum (in fissure) Left lobe of liver Porta hepatis containing hepatic artery (left) and hepatic portal vein (right) Quadrate lobe of liver Ligamentum teres Gallbladder Hepatic vein (cut) Sulcus for inferior vena cava Caudate lobe Bare area Bile duct (cut) Right lobe Figure 23.26

Visceral Surface of the Liver
(b) Hepatic portal vein Hepatic veins Inferior vena cava Bare area Right hepatic artery duct Cystic duct Gallbladder Right lobe Quadrate lobe Ligamentum teres Falciform ligament Fissure Common hepatic Left hepatic duct Left hepatic artery Porta hepatis Ligamentum venosum in fissure Left lobe Caudate lobe Figure 23.26

Microscopic Anatomy of the Liver
Hepatocyte—functional cells of the liver Portal triad composed of Bile duct Branch of hepatic portal vein Branch of hepatic artery Kupffer cells (hepatic macrophages)—destroy bacteria

Microscopic Anatomy of Liver
(b) Lobule Central vein Connective tissue septum (c) Interlobular veins (to hepatic vein) Central vein Sinusoids Portal triad Plates of hepatocytes Portal vein Bile canaliculi Fenestrated lining (endothelial cells) of sinusoids Bile duct (receives bile from bile canaliculi) Bile duct Portal arteriole Portal venule Hepatic macrophages in sinusoid walls Figure 23.27

Stores and concentrates bile Expels bile into duodenum
The Gallbladder Stores and concentrates bile Expels bile into duodenum Bile emulsifies fats Cholecystokinin—released from enteroendocrine cells in response to fatty chyme

The Gallbladder Jejunum Mucosa with folds Cystic duct Duodenum
Hepatopancreatic ampulla and sphincter Gallbladder Right and left hepatic ducts of liver Bile duct and sphincter Main pancreatic duct and Pancreas Tail of pancreas Head of pancreas Common hepatic duct Major duodenal papilla Accessory pancreatic duct Figure 23.19

Jejunum Mucosa with folds Cystic duct Duodenum Hepatopancreatic ampulla and sphincter Gallbladder Right and left hepatic ducts of liver Bile duct and sphincter Main pancreatic duct and Pancreas Tail of pancreas Head of pancreas Common hepatic duct Major duodenal papilla Accessory pancreatic duct Figure 23.19

The Pancreas Exocrine function Endocrine function
Acinar cells make, store, and secrete pancreatic enzymes Enzymes are activated in the duodenum Endocrine function Produces insulin and glucagon Regulates blood sugar

Figure 23.28 The gross and microscopic anatomy of the pancreas.
Small duct Diaphragm Acinar cell Liver Basement membrane Spleen Zymogen granules Pancreas Tail Rough endoplasmic reticulum Body Duct cell Head One acinus Duodenum Illustration of the pancreatic acinar cells Dissection illustrating the pancreas and its relationship to surrounding organs in the superior abdomen Acinar cells Pancreatic duct Photomicrograph of the exocrine acinar cells of the pancreas (130)

Figure 17.9 Photomicrograph of a pancreatic islet.
Pancreas Pancreatic islet  (Glucagon- producing) cells  (Insulin- producing) cells Pancreatic acinar cells (exocrine)

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