PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 23 The Digestive System: Part B
Copyright © 2010 Pearson Education, Inc. Pharynx Oropharynx and laryngopharynx Allow passage of food, fluids, and air Stratified squamous epithelium lining Skeletal muscle layers: inner longitudinal, outer pharyngeal constrictors
Copyright © 2010 Pearson Education, Inc. Esophagus Flat muscular tube from laryngopharynx to stomach Pierces diaphragm at esophageal hiatus Joins stomach at the cardiac orifice
Copyright © 2010 Pearson Education, Inc. Esophagus Esophageal mucosa contains stratified squamous epithelium Changes to simple columnar at the stomach Esophageal glands in submucosa secrete mucus to aid in bolus movement Muscularis: skeletal superiorly; smooth inferiorly Adventitia instead of serosa
Copyright © 2010 Pearson Education, Inc. Figure 23.12a Mucosa (contains a stratified squamous epithelium) Submucosa (areolar connective tissue) Lumen Muscularis externa Adventitia (fibrous connective tissue) (a) Circular layer Longitudinal layer
Copyright © 2010 Pearson Education, Inc. Figure 23.12b Mucosa (contains a stratified squamous epithelium) (b)
Copyright © 2010 Pearson Education, Inc. Digestive Processes: Mouth Ingestion Mechanical digestion Mastication is partly voluntary, partly reflexive Chemical digestion (salivary amylase and lingual lipase) Propulsion Deglutition (swallowing)
Copyright © 2010 Pearson Education, Inc. Deglutition Involves the tongue, soft palate, pharynx, esophagus, and 22 muscle groups Buccal phase Voluntary contraction of the tongue Pharyngeal-esophageal phase Involuntary Control center in the medulla and lower pons
Copyright © 2010 Pearson Education, Inc. Figure Tongue Trachea Pharynx Epiglottis Glottis Bolus of food Epiglottis Esophagus Uvula Bolus Relaxed muscles Circular muscles contract Bolus of food Longitudinal muscles contract Stomach Relaxed muscles Gastroesophageal sphincter opens Gastroesophageal sphincter closed Upper esophageal sphincter is contracted. During the buccal phase, the tongue presses against the hard palate, forcing the food bolus into the oropharynx where the involuntary phase begins. Food is moved through the esophagus to the stomach by peristalsis. The gastroesophageal sphincter opens, and food enters the stomach. The uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after entry
Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 1 Tongue Trachea Pharynx Epiglottis Glottis Bolus of food Upper esophageal sphincter is contracted. During the buccal phase, the tongue presses against the hard palate, forcing the food bolus into the oropharynx where the involuntary phase begins. 1
Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 2 Epiglottis Esophagus Uvula Bolus The uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. 2
Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 3 Bolus The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after entry. 3
Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 4 Relaxed muscles Bolus of food Stomach Circular muscles contract Longitudinal muscles contract Gastroesophageal sphincter closed Food is moved through the esophagus to the stomach by peristalsis. 4
Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 5 Relaxed muscles Gastroesophageal sphincter opens The gastroesophageal sphincter opens, and food enters the stomach. 5
Copyright © 2010 Pearson Education, Inc. Figure Tongue Trachea Pharynx Epiglottis Glottis Bolus of food Epiglottis Esophagus Uvula Bolus Relaxed muscles Circular muscles contract Bolus of food Longitudinal muscles contract Stomach Relaxed muscles Gastroesophageal sphincter opens Gastroesophageal sphincter closed Upper esophageal sphincter is contracted. During the buccal phase, the tongue presses against the hard palate, forcing the food bolus into the oropharynx where the involuntary phase begins. Food is moved through the esophagus to the stomach by peristalsis. The gastroesophageal sphincter opens, and food enters the stomach. The uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after entry
Copyright © 2010 Pearson Education, Inc. Stomach: Gross Anatomy Cardiac region (cardia) Surrounds the cardiac orifice Fundus Dome-shaped region beneath the diaphragm Body Midportion
Copyright © 2010 Pearson Education, Inc. Stomach: Gross Anatomy Pyloric region: antrum, pyloric canal, and pylorus Pylorus is continuous with the duodenum through the pyloric valve (sphincter) Greater curvature Convex lateral surface Lesser curvature Concave medial surface
Copyright © 2010 Pearson Education, Inc. Figure 23.14a Cardia Esophagus Pyloric sphincter (valve) at pylorus Pyloric canal Pyloric antrum Rugae of mucosa Body Lumen Serosa Fundus Lesser curvature Greater curvature Muscularis externa Longitudinal layer Circular layer Oblique layer (a) Duodenum
Copyright © 2010 Pearson Education, Inc. Stomach: Gross Anatomy Lesser omentum From the liver to the lesser curvature Greater omentum Drapes from greater curvature Anterior to the small intestine
Copyright © 2010 Pearson Education, Inc. Figure 23.30a Falciform ligament Liver Gallbladder Spleen Stomach Ligamentum teres Greater omentum Small intestine Cecum (a)
Copyright © 2010 Pearson Education, Inc. Figure 23.30b Liver Lesser omentum Gallbladder Stomach Duodenum Transverse colon Small intestine Cecum Urinary bladder (b)
Copyright © 2010 Pearson Education, Inc. Stomach: Gross Anatomy ANS nerve supply Sympathetic via splanchnic nerves and celiac plexus Parasympathetic via vagus nerve Blood supply Celiac trunk Veins of the hepatic portal system
Copyright © 2010 Pearson Education, Inc. Stomach: Microscopic Anatomy Four tunics Muscularis and mucosa are modified Muscularis externa Three layers of smooth muscle Inner oblique layer allows stomach to churn, mix, move, and physically break down food
Copyright © 2010 Pearson Education, Inc. Figure 23.15a Mucosa Surface epithelium Lamina propria Muscularis mucosae Oblique layer Circular layer Longitudinal layer Serosa (a) Layers of the stomach wall (l.s.) Stomach wall Muscularis externa (contains myenteric plexus) Submucosa (contains submucosal plexus)
Copyright © 2010 Pearson Education, Inc. Stomach: Microscopic Anatomy Mucosa Simple columnar epithelium composed of mucous cells Layer of mucus traps bicarbonate-rich fluid beneath it Gastric pits lead into gastric glands
Copyright © 2010 Pearson Education, Inc. Figure 23.15b (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 Gastric gland
Copyright © 2010 Pearson Education, Inc. Gastric Glands Cell types Mucous neck cells (secrete thin, acidic mucus) Parietal cells Chief cells Enteroendocrine cells
Copyright © 2010 Pearson Education, Inc. Figure 23.15c (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
Copyright © 2010 Pearson Education, Inc. Gastric Gland Secretions Glands in the fundus and body produce most of the gastric juice Parietal cell secretions HCl pH 1.5–3.5 denatures protein in food, activates pepsin, and kills many bacteria Intrinsic factor Glycoprotein required for absorption of vitamin B 12 in small intestine
Copyright © 2010 Pearson Education, Inc. Gastric Gland Secretions Chief cell secretions Inactive enzyme pepsinogen Activated to pepsin by HCl and by pepsin itself (a positive feedback mechanism)
Copyright © 2010 Pearson Education, Inc. Gastric Gland Secretions Enteroendocrine cells Secrete chemical messengers into the lamina propria Paracrines Serotonin and histamine Hormones Somatostatin and gastrin
Copyright © 2010 Pearson Education, Inc. Mucosal Barrier Layer of bicarbonate-rich mucus Tight junctions between epithelial cells Damaged epithelial cells are quickly replaced by division of stem cells
Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalance Gastritis: inflammation caused by anything that breaches the mucosal barrier Peptic or gastric ulcers: erosion of the stomach wall Most are caused by Helicobacter pylori bacteria
Copyright © 2010 Pearson Education, Inc. Figure Bacteria Mucosa layer of stomach (a) A gastric ulcer lesion (b) H. pylori bacteria
Copyright © 2010 Pearson Education, Inc. Digestive Processes in the Stomach Physical digestion Denaturation of proteins Enzymatic digestion of proteins by pepsin (and rennin in infants) Secretes intrinsic factor required for absorption of vitamin B 12 Lack of intrinsic factor pernicious anemia Delivers chyme to the small intestine
Copyright © 2010 Pearson Education, Inc. Regulation of Gastric Secretion Neural and hormonal mechanisms Stimulatory and inhibitory events occur in three phases: 1.Cephalic (reflex) phase: few minutes prior to food entry 2.Gastric phase: 3–4 hours after food enters the stomach
Copyright © 2010 Pearson Education, Inc. Regulation of Gastric Secretion 3.Intestinal phase: brief stimulatory effect as partially digested food enters the duodenum, followed by inhibitory effects (enterogastric reflex and enterogastrones)
Copyright © 2010 Pearson Education, Inc. Figure Presence of low pH, partially digested foods, fats, or hypertonic solution in duodenum when stomach begins to empty Distension; presence of fatty, acidic, partially digested food in the duodenum Brief effect Intestinal (enteric) gastrin release to blood Entero- gastric reflex Release of intestinal hormones (secretin, cholecystokinin, vasoactive intestinal peptide) Local reflexes Vagal nuclei in medulla Pyloric sphincter Stimulate Inhibit Stomach secretory activity Sight and thought of food Stomach distension activates stretch receptors Stimulation of taste and smell receptors Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors Loss of appetite, depression Emotional upset Lack of stimulatory impulses to parasym- pathetic center Cerebral cortex Cerebral cortex Conditioned reflex Vagovagal reflexes Local reflexes Medulla G cells Hypothalamus and medulla oblongata Vagus nerve Vagus nerve Gastrin release to blood Gastrin secretion declines G cells Overrides parasym- pathetic controls Sympathetic nervous system activation Stimulatory eventsInhibitory events Cephalic phase Gastric phase Intestinal phase Excessive acidity (pH <2) in stomach Distension of duodenum; presence of fatty, acidic, hypertonic chyme, and/or irritants in the duodenum
Copyright © 2010 Pearson Education, Inc. Regulation and Mechanism of HCl Secretion Three chemicals (ACh, histamine, and gastrin) stimulate parietal cells through second-messenger systems All three are necessary for maximum HCl secretion Antihistamines block H 2 receptors and decrease HCl release
Copyright © 2010 Pearson Education, Inc. Figure Stomach lumenChief cell Parietal cell Inter- stitial fluid Carbonic anhydrase Alkaline tide HCO 3 – Blood capillary CO 2 Cl – CO 2 + H 2 O H 2 CO 3 HCO 3 – - Cl – antiporter HCO 3 – H+H+ Cl – l K+K+ K+K+ H+H+ H + -K + ATPase HCI
Copyright © 2010 Pearson Education, Inc. Response of the Stomach to Filling Stretches to accommodate incoming food Reflex-mediated receptive relaxation Coordinated by the swallowing center of the brain stem Gastric accommodation Plasticity (stress-relaxation response) of smooth muscle
Copyright © 2010 Pearson Education, Inc. Gastric Contractile Activity Peristaltic waves move toward the pylorus at the rate of 3 per minute Basic electrical rhythm (BER) initiated by pacemaker cells (cells of Cajal) Distension and gastrin increase force of contraction
Copyright © 2010 Pearson Education, Inc. Gastric Contractile Activity Most vigorous near the pylorus Chyme is either Delivered in ~ 3 ml spurts to the duodenum, or Forced backward into the stomach
Copyright © 2010 Pearson Education, Inc. Figure Propulsion: Peristaltic waves move from the fundus toward the pylorus. 23 Grinding: The most vigorous peristalsis and mixing action occur close to the pylorus. Retropulsion: The pyloric end of the stomach acts as a pump that delivers small amounts of chyme into the duodenum, simultaneously forcing most of its contained material backward into the stomach. Pyloric valve closed Pyloric valve closed Pyloric valve slightly opened
Copyright © 2010 Pearson Education, Inc. Regulation of Gastric Emptying As chyme enters the duodenum Receptors respond to stretch and chemical signals Enterogastric reflex and enterogastrones inhibit gastric secretion and duodenal filling Carbohydrate-rich chyme moves quickly through the duodenum Fatty chyme remains in the duodenum 6 hours or more
Copyright © 2010 Pearson Education, Inc. Figure Presence of fatty, hypertonic, acidic chyme in duodenum Duodenal entero- endocrine cells Chemoreceptors and stretch receptors Enterogastrones (secretin, cholecystokinin, vasoactive intestinal peptide) Duodenal stimuli decline Via short reflexes Via long reflexes Enteric neurons Initial stimulus Physiological response Result Contractile force and rate of stomach emptying decline CNS centers sympathetic activity; parasympathetic activity Stimulate Inhibit SecreteTarget
Copyright © 2010 Pearson Education, Inc. Small Intestine: Gross Anatomy Major organ of digestion and absorption 2–4 m long; from pyloric sphincter to ileocecal valve Subdivisions 1.Duodenum (retroperitoneal) 2.Jejunum (attached posteriorly by mesentery) 3.Ileum (attached posteriorly by mesentery)
Copyright © 2010 Pearson Education, Inc. Figure 23.1 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
Copyright © 2010 Pearson Education, Inc. Duodenum The bile duct and main pancreatic duct Join at the hepatopancreatic ampulla Enter the duodenum at the major duodenal papilla Are controlled by the hepatopancreatic sphincter
Copyright © 2010 Pearson Education, Inc. Figure 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 sphincter Pancreas Tail of pancreas Head of pancreas Common hepatic duct Major duodenal papilla Accessory pancreatic duct
Copyright © 2010 Pearson Education, Inc. Structural Modifications Increase surface area of proximal part for nutrient absorption Circular folds (plicae circulares) Villi Microvilli
Copyright © 2010 Pearson Education, Inc. Structural Modifications Circular folds Permanent (~1 cm deep) Force chyme to slowly spiral through lumen
Copyright © 2010 Pearson Education, Inc. Figure 23.22a Vein carrying blood to hepatic portal vessel Muscle layers Circular folds Villi (a) Lumen
Copyright © 2010 Pearson Education, Inc. Structural Modifications Villi Motile fingerlike extensions (~1 mm high) of the mucosa Villus epithelium Simple columnar absorptive cells (enterocytes) Goblet cells
Copyright © 2010 Pearson Education, Inc. Structural Modifications Microvilli Projections (brush border) of absorptive cells Bear brush border enzymes
Copyright © 2010 Pearson Education, Inc. Intestinal Crypts Intestinal crypt epithelium Secretory cells that produce intestinal juice Enteroendocrine cells Intraepithelial lymphocytes (IELs) Release cytokines that kill infected cells Paneth cells Secrete antimicrobial agents (defensins and lysozyme) Stem cells
Copyright © 2010 Pearson Education, Inc. Figure 23.22b (b) Absorptive cells Lacteal Intestinal crypt Mucosa associated lymphoid tissue Muscularis mucosae Duodenal gland Submucosa Enteroendocrine cells Venule Lymphatic vessel Goblet cell Blood capillaries Vilus Microvilli (brush border)
Copyright © 2010 Pearson Education, Inc. Submucosa Peyer’s patches protect distal part against bacteria Duodenal (Brunner’s) glands of the duodenum secrete alkaline mucus
Copyright © 2010 Pearson Education, Inc. Intestinal Juice Secreted in response to distension or irritation of the mucosa Slightly alkaline and isotonic with blood plasma Largely water, enzyme-poor, but contains mucus Facilitates transport and absorption of nutrients
Copyright © 2010 Pearson Education, Inc. Liver Largest gland in the body Four lobes—right, left, caudate, and quadrate
Copyright © 2010 Pearson Education, Inc. Liver Falciform ligament Separates the (larger) right and (smaller) left lobes Suspends liver from the diaphragm and anterior abdominal wall Round ligament (ligamentum teres) Remnant of fetal umbilical vein along free edge of falciform ligament
Copyright © 2010 Pearson Education, Inc. Figure 23.24a Sternum Nipple Liver Right lobe of liver Gallbladder (a) Bare area Falciform ligament Left lobe of liver Round ligament (ligamentum teres)
Copyright © 2010 Pearson Education, Inc. Figure 23.24b Lesser omentum (in fissure) Left lobe of liver (b) 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 of liver Bare area Bile duct (cut) Right lobe of liver Sternum Nipple Liver
Copyright © 2010 Pearson Education, Inc. Liver: Associated Structures Lesser omentum anchors liver to stomach Hepatic artery and vein at the porta hepatis Bile ducts Common hepatic duct leaves the liver Cystic duct connects to gallbladder Bile duct formed by the union of the above two ducts
Copyright © 2010 Pearson Education, Inc. Figure 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 sphincter Pancreas Tail of pancreas Head of pancreas Common hepatic duct Major duodenal papilla Accessory pancreatic duct
Copyright © 2010 Pearson Education, Inc. Liver: Microscopic Anatomy Liver lobules Hexagonal structural and functional units Filter and process nutrient-rich blood Composed of plates of hepatocytes (liver cells) Longitudinal central vein
Copyright © 2010 Pearson Education, Inc. Figure 23.25a, b (a)(b) Lobule Central veinConnective tissue septum
Copyright © 2010 Pearson Education, Inc. Liver: Microscopic Anatomy Portal triad at each corner of lobule Bile duct receives bile from bile canaliculi Portal arteriole is a branch of the hepatic artery Hepatic venule is a branch of the hepatic portal vein Liver sinusoids are leaky capillaries between hepatic plates Kupffer cells (hepatic macrophages) in liver sinusoids
Copyright © 2010 Pearson Education, Inc. Figure 23.25c (c) Interlobular veins (to hepatic vein) Central vein Sinusoids Portal triad Plates of hepatocytes Portal vein Fenestrated lining (endothelial cells) of sinusoids Bile duct (receives bile from bile canaliculi) Bile duct Portal arteriole Portal venule Hepatic macrophages in sinusoid walls Bile canaliculi
Copyright © 2010 Pearson Education, Inc. Liver: Microscopic Anatomy Hepatocyte functions Process bloodborne nutrients Store fat-soluble vitamins Perform detoxification Produce ~900 ml bile per day
Copyright © 2010 Pearson Education, Inc. Bile Yellow-green, alkaline solution containing Bile salts: cholesterol derivatives that function in fat emulsification and absorption Bilirubin: pigment formed from heme Cholesterol, neutral fats, phospholipids, and electrolytes
Copyright © 2010 Pearson Education, Inc. Bile Enterohepatic circulation Recycles bile salts Bile salts duodenum reabsorbed from ileum hepatic portal blood liver secreted into bile
Copyright © 2010 Pearson Education, Inc. The Gallbladder Thin-walled muscular sac on the ventral surface of the liver Stores and concentrates bile by absorbing its water and ions Releases bile via the cystic duct, which flows into the bile duct