23 The Digestive System.

23 The Digestive System

Two groups of organs Digestive System
1. Alimentary canal (gastrointestinal or GI tract) Mouth to anus Digests food and absorbs fragments Mouth, pharynx, esophagus, stomach, small intestine, and large intestine © 2013 Pearson Education, Inc.

2. Accessory digestive organs
Digestive System 2. Accessory digestive organs Teeth, tongue, gallbladder Digestive glands Salivary glands Liver Pancreas © 2013 Pearson Education, Inc.

Mouth (oral cavity) Parotid gland Sublingual gland Salivary Tongue*
Figure Alimentary canal and related accessory digestive organs. Mouth (oral cavity) Parotid gland Sublingual gland Salivary glands* Tongue* Submandibular gland Pharynx Esophagus Stomach Pancreas* (Spleen) Liver* Gallbladder* Transverse colon Duodenum Descending colon Small intestine Jejunum Ascending colon Ileum Cecum Large intestine Sigmoid colon Rectum Appendix Anus Anal canal © 2013 Pearson Education, Inc.

Six essential activities
Digestive Processes Six essential activities Ingestion Propulsion Mechanical breakdown Digestion Absorption Defecation © 2013 Pearson Education, Inc.

Ingestion Food Mechanical breakdown Pharynx Esophagus Chewing (mouth)
Figure Gastrointestinal tract activities. Ingestion Food Mechanical breakdown Pharynx Esophagus Chewing (mouth) Churning (stomach) Propulsion Segmentation (small intestine) • Swallowing (oropharynx) • Peristalsis (esophagus, stomach, small intestine, large intestine) Digestion Stomach Absorption Lymph vessel Small intestine Blood vessel Large intestine Mainly H2O Feces Anus Defecation © 2013 Pearson Education, Inc.

Figure 23.3 Peristalsis and segmentation.
From mouth Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, moving food along the tract distally. Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving food forward then backward. Food mixing and slow food propulsion occur. © 2013 Pearson Education, Inc.

GI Tract Regulatory Mechanisms
Mechanoreceptors and chemoreceptors Respond to stretch, changes in osmolarity and pH, and presence of substrate and end products of digestion Initiate reflexes that Activate or inhibit digestive glands Stimulate smooth muscle to mix and move lumen contents © 2013 Pearson Education, Inc.

GI Tract Regulatory Mechanisms
Intrinsic and extrinsic controls Short reflexes - enteric nerve plexuses (gut brain) respond to stimuli in GI tract Long reflexes respond to stimuli inside or outside GI tract; involve CNS centers and autonomic nerves Hormones from cells in stomach and small intestine stimulate target cells in same or different organs to secrete or contract © 2013 Pearson Education, Inc.

Central nervous system
Figure Neural reflex pathways initiated by stimuli inside or outside the gastrointestinal tract. External stimuli (sight, smell, taste, thought of food) Central nervous system Long reflexes Visceral afferents Extrinsic visceral (autonomic) efferents Chemoreceptors, osmoreceptors, or mechanoreceptors Local (intrinsic) nerve plexus ("gut brain") Internal (GI tract) stimuli Effectors: Smooth muscle or glands Short reflexes Gastrointestinal wall (site of short reflexes) Response: Change in contractile or secretory activity Lumen of the alimentary canal © 2013 Pearson Education, Inc.

Peritoneum and Peritoneal Cavity
Peritoneum - serous membrane of abdominal cavity Visceral peritoneum on external surface of most digestive organs Parietal peritoneum lines body wall Peritoneal cavity Between two peritoneums Fluid lubricates mobile organs © 2013 Pearson Education, Inc.

Two schematic cross sections of abdominal cavity illustrate
Figure 23.5a The peritoneum and the peritoneal cavity. Abdominopelvic cavity Vertebra Dorsal mesentery Parietal peritoneum Ventral mesentery Visceral peritoneum Peritoneal cavity Alimentary canal organ Liver Two schematic cross sections of abdominal cavity illustrate the peritoneums and mesenteries. © 2013 Pearson Education, Inc.

Peritoneum and Peritoneal Cavity
Mesentery - double layer of peritoneum Routes for blood vessels, lymphatics, and nerves Holds organs in place; stores fat Retroperitoneal organs posterior to peritoneum Intraperitoneal (peritoneal) organs surrounded by peritoneum © 2013 Pearson Education, Inc.

Alimentary canal organ in a retroperitoneal position
Figure 23.5b The peritoneum and the peritoneal cavity. Mesentery resorbed and lost Alimentary canal organ Alimentary canal organ in a retroperitoneal position Some organs lose their mesentery and move, becoming retroperitoneal, during development. © 2013 Pearson Education, Inc.

Homeostatic Imbalance
Peritonitis Inflammation of peritoneum Causes by e.g., piercing abdominal wound, perforating ulcer, ruptured appendix Peritoneal coverings stick together, localizing infection Dangerous and lethal if widespread Treated with debris removal and antibiotics © 2013 Pearson Education, Inc.

Blood Supply: Splanchnic Circulation
Branches of aorta serving digestive organs Hepatic, splenic, and left gastric arteries Inferior and superior mesenteric arteries Hepatic portal circulation Drains nutrient-rich blood from digestive organs Delivers it to the liver for processing © 2013 Pearson Education, Inc.

Histology of the Alimentary Canal
Four basic layers (tunics) Mucosa Submucosa Muscularis externa Serosa © 2013 Pearson Education, Inc.

Myenteric nerve plexus
Figure Basic structure of the alimentary canal. Intrinsic nerve plexuses Myenteric nerve plexus Submucosal nerve plexus Glands in submucosa Mucosa Epithelium Lamina propria Muscularis mucosae Submucosa Muscularis externa Longitudinal muscle Circular muscle Serosa Epithelium (mesothelium) Nerve Connective tissue Artery Gland in mucosa Lumen Vein Duct of gland outside alimentary canal Mucosa-associated lymphoid tissue Mesentery Lymphatic vessel © 2013 Pearson Education, Inc.

Functions – different layers perform 1 or all 3
Mucosa Lines lumen Functions – different layers perform 1 or all 3 Secretes mucus, digestive enzymes, and hormones Absorbs end products of digestion Protects against infectious disease Three sublayers: epithelium, lamina propria, and muscularis mucosae © 2013 Pearson Education, Inc.

Mucosa Epithelium Simple columnar epithelium and mucus-secreting cells (most of tract) Mucus Protects digestive organs from enzymes Eases food passage May secrete enzymes and hormones (e.g., in stomach and small intestine) © 2013 Pearson Education, Inc.

Muscularis mucosae: smooth muscle  local movements of mucosa
Lamina propria Loose areolar connective tissue Capillaries for nourishment and absorption Lymphoid follicles (part of MALT) Defend against microorganisms Muscularis mucosae: smooth muscle  local movements of mucosa © 2013 Pearson Education, Inc.

Submucosa Submucosa Areolar connective tissue
Blood and lymphatic vessels, lymphoid follicles, and submucosal nerve plexus © 2013 Pearson Education, Inc.

Muscularis Externa Muscularis externa
Responsible for segmentation and peristalsis Inner circular and outer longitudinal layers Circular layer thickens in some areas  sphincters Myenteric nerve plexus between two muscle layers © 2013 Pearson Education, Inc.

Serosa Visceral peritoneum
Areolar connective tissue covered with mesothelium in most organs Replaced by fibrous adventitia in esophagus Retroperitoneal organs have both an adventitia and serosa © 2013 Pearson Education, Inc.

Myenteric nerve plexus
Figure Basic structure of the alimentary canal. Intrinsic nerve plexuses Myenteric nerve plexus Submucosal nerve plexus Glands in submucosa Mucosa Epithelium Lamina propria Muscularis mucosae Submucosa Muscularis externa Longitudinal muscle Circular muscle Serosa Epithelium (mesothelium) Nerve Connective tissue Artery Gland in mucosa Lumen Vein Duct of gland outside alimentary canal Mucosa-associated lymphoid tissue Mesentery Lymphatic vessel © 2013 Pearson Education, Inc.

Enteric Nervous System
Intrinsic nerve supply of alimentary canal – enteric neurons (more than spinal cord) Major nerve supply to GI tract wall; control motility Submucosal nerve plexus Regulates glands and smooth muscle in the mucosa Myenteric nerve plexus Controls GI tract motility © 2013 Pearson Education, Inc.

Enteric Nervous System
Linked to CNS via afferent visceral fibers Long ANS fibers synapse with enteric plexuses Sympathetic impulses inhibit digestive activities Parasympathetic impulses stimulate digestive activities © 2013 Pearson Education, Inc.

Functional Anatomy: Mouth
Oral (buccal) cavity Bounded by lips, cheeks, palate, and tongue Oral orifice is anterior opening Lined with stratified squamous epithelium © 2013 Pearson Education, Inc.

Sagittal section of the oral cavity and pharynx
Figure 23.7a Anatomy of the oral cavity (mouth). Soft palate Palatoglossal arch Uvula Hard palate Oral cavity Palatine tonsil Tongue Oropharynx Lingual tonsil Epiglottis Hyoid bone Laryngopharynx Esophagus Trachea Sagittal section of the oral cavity and pharynx © 2013 Pearson Education, Inc.

Contain orbicularis oris and buccinator muscles
Lips and Cheeks Contain orbicularis oris and buccinator muscles Oral vestibule - recess internal to lips (labia) and cheeks, external to teeth and gums Oral cavity proper lies within teeth and gums Labial frenulum - median attachment of each lip to gum © 2013 Pearson Education, Inc.

Upper lip Gingivae (gums) Superior labial frenulum Palatine raphe
Figure 23.7b Anatomy of the oral cavity (mouth). Upper lip Gingivae (gums) Superior labial frenulum Palatine raphe Palatoglossal arch Hard palate Palatopharyngeal arch Soft palate Uvula Palatine tonsil Posterior wall of oropharynx Tongue Sublingual fold with openings of sublingual ducts Lingual frenulum Opening of Submandibular duct Gingivae (gums) Oral vestibule Inferior labial frenulum Lower lip Anterior view © 2013 Pearson Education, Inc.

Hard palate - palatine bones and palatine processes of maxillae
Slightly corrugated to help create friction against tongue Soft palate - fold formed mostly of skeletal muscle Closes off nasopharynx during swallowing Uvula projects downward from its free edge © 2013 Pearson Education, Inc.

Intrinsic muscles change shape of tongue
Skeletal muscle Functions include Repositioning and mixing food during chewing Formation of bolus Initiation of swallowing, speech, and taste Intrinsic muscles change shape of tongue Extrinsic muscles alter tongue's position Lingual frenulum: attachment to floor of mouth © 2013 Pearson Education, Inc.

Surface bears papillae
Tongue Surface bears papillae Filiform—whitish, give the tongue roughness and provide friction; do not contain taste buds Fungiform—reddish, scattered over tongue; contain taste buds Vallate (circumvallate)—V-shaped row in back of tongue; contain taste buds Foliate—on lateral aspects of posterior tongue; contain taste buds that function primarily in infants and children © 2013 Pearson Education, Inc.

Terminal sulcus marks division between
Tongue Lingual lipase Secreted by serous cells beneath foliate and vallate papillae secrete Fat-digesting enzyme functional in stomach Terminal sulcus marks division between Body - anterior 2/3 residing in oral cavity Root - posterior third residing in oropharynx Just posterior to vallate papillae © 2013 Pearson Education, Inc.

Epiglottis Palatopharyngeal arch Palatine tonsil Lingual tonsil
Figure Dorsal surface of the tongue, and the tonsils. Epiglottis Palatopharyngeal arch Palatine tonsil Lingual tonsil Palatoglossal arch Terminal sulcus Foliate papillae Vallate papilla Medial sulcus of the tongue Dorsum of tongue Fungiform papilla Filiform papilla © 2013 Pearson Education, Inc.

Salivary Glands Major salivary glands Minor salivary glands
Produce most saliva; lie outside oral cavity Parotid Submandibular Sublingual Minor salivary glands Scattered throughout oral cavity; augment slightly © 2013 Pearson Education, Inc.

Salivary Glands Function of saliva Cleanses mouth
Dissolves food chemicals for taste Moistens food; compacts into bolus Begins breakdown of starch with enzymes © 2013 Pearson Education, Inc.

Salivary Glands Parotid gland
Anterior to ear; external to masseter muscle Parotid duct opens into oral vestibule next to second upper molar Mumps is inflammation of parotid glands © 2013 Pearson Education, Inc.

Salivary Glands Submandibular gland Sublingual gland
Medial to body of mandible Duct opens at base of lingual frenulum Sublingual gland Anterior to submandibular gland under tongue Opens via 10–12 ducts into floor of mouth © 2013 Pearson Education, Inc.

Figure 23.9 The 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 Mucous cells Serous cells forming demilunes © 2013 Pearson Education, Inc.

Two types of secretory cells
Salivary Glands Two types of secretory cells Serous cells Watery, enzymes, ions, bit of mucin Mucous cells Mucus Parotid, submandibular glands mostly serous; sublingual mostly mucous © 2013 Pearson Education, Inc.

97–99.5% water, slightly acidic
Composition of Saliva 97–99.5% water, slightly acidic Electrolytes—Na+, K+, Cl–, PO4 2–, HCO3– Salivary amylase and lingual lipase Mucin Metabolic wastes—urea and uric acid Lysozyme, IgA, defensins, and a cyanide compound protect against microorganisms PLAY Animation: Rotating head © 2013 Pearson Education, Inc.

Control of Salivation 1500 ml/day
Intrinsic glands continuously keep mouth moist Major salivary glands activated by parasympathetic nervous system when Ingested food stimulates chemoreceptors and mechanoreceptors in mouth  Salivatory nuclei in brain stem send impulses along parasympathetic fibers in cranial nerves VII and IX Strong sympathetic stimulation inhibits salivation and results in dry mouth (xerostomia) © 2013 Pearson Education, Inc.

Tear and grind food for digestion
Teeth Tear and grind food for digestion Primary and permanent dentitions formed by age 21 20 deciduous teeth erupt (6–24 months of age) Roots resorbed, teeth fall out (6–12 years of age) as permanent teeth develop 32 permanent teeth All but third molars in by end of adolescence Third molars at 17–25, or may not erupt © 2013 Pearson Education, Inc.

Premolars (bicuspids) Molars
Classes of Teeth Incisors Chisel shaped for cutting Canines Fanglike teeth that tear or pierce Premolars (bicuspids) Broad crowns, rounded cusps – grind/crush Molars Broad crowns, rounded cusps – best grinders © 2013 Pearson Education, Inc.

Figure 23.10 Human dentition.
Incisors Central (6–8 mo) Lateral (8–10 mo) Canine (eyetooth) (16–20 mo) Molars First molar (10–15 mo) Deciduous (milk) teeth Second molar (about 2 yr) Incisors Central (7 yr) Lateral (8 yr) Canine (eyetooth) (11 yr) Premolars (bicuspids) First premolar (11 yr) Second premolar (12–13 yr) Molars First molar (6–7 yr) Second molar (12–13 yr) Third molar (wisdom tooth) (17–25 yr) Permanent teeth © 2013 Pearson Education, Inc.

Shorthand indicator of number/position of teeth
Dental Formulas Shorthand indicator of number/position of teeth Ratio of upper to lower teeth for 1/2 of mouth Primary: Permanent: © 2013 Pearson Education, Inc.

Crown - exposed part above gingiva (gum)
Tooth Structure Crown - exposed part above gingiva (gum) Covered by enamel—hardest substance in body (calcium salts and hydroxyapatite crystals) Enamel-producing cells degenerate when tooth erupts  no healing if decay or crack Root - portion embedded in jawbone Connected to crown by neck © 2013 Pearson Education, Inc.

Canine, incisor, and premolar  one root
Tooth Structure Canine, incisor, and premolar  one root First upper premolar often has two First two upper molars  three roots First two lower molars  two roots Third molar roots vary; often single fused root © 2013 Pearson Education, Inc.

Cement - calcified connective tissue
Tooth Structure Cement - calcified connective tissue Covers root; attaches it to periodontal ligament Periodontal ligament Forms fibrous joint called gomphosis Anchors tooth in bony socket Gingival sulcus - groove where gingiva borders tooth © 2013 Pearson Education, Inc.

Dentin - bonelike material under enamel
Tooth Structure Dentin - bonelike material under enamel Maintained by odontoblasts of pulp cavity Pulp cavity - surrounded by dentin Pulp - connective tissue, blood vessels, and nerves Root canal - as pulp cavity extends to root Apical foramen at proximal end of root Entry for blood vessels, nerves, etc. © 2013 Pearson Education, Inc.

Enamel Dentin Cement Root canal Bone
Figure Longitudinal section of a canine tooth within its bony socket (alveolus). Enamel Dentin Crown Dentinal tubules Pulp cavity (contains blood vessels and nerves) Neck Gingival sulcus Gingiva (gum) Cement Root canal Root Periodontal ligament Apical foramen Bone © 2013 Pearson Education, Inc.

Tooth and Gum Disease Dental caries (cavities) - demineralization of enamel and dentin from bacterial action Dental plaque (film of sugar, bacteria, and debris) adheres to teeth Acid from bacteria dissolves calcium salts Proteolytic enzymes digest organic matter Prevention: daily flossing and brushing © 2013 Pearson Education, Inc.

Tooth and Gum Disease Gingivitis
Plaque calcifies to form calculus (tartar) Calculus disrupts seal between gingivae and teeth Anaerobic bacteria infect gums Infection reversible if calculus removed © 2013 Pearson Education, Inc.

Periodontitis (from neglected gingivitis)
Tooth and Gum Disease Periodontitis (from neglected gingivitis) Immune cells attack intruders and body tissues Destroy periodontal ligament Activate osteoclasts  dissolve bone Possible tooth loss; may promote atherosclerosis and clot formation in coronary and cerebral arteries Risk factors - smoking, diabetes mellitus, oral piercing © 2013 Pearson Education, Inc.

Food passes from mouth  oropharynx  laryngopharynx
Allows passage of food, fluids, and air Stratified squamous epithelium lining; mucus-producing glands Skeletal muscle layers: inner longitudinal, outer pharyngeal constrictors © 2013 Pearson Education, Inc.

Flat muscular tube from laryngopharynx to stomach
Esophagus Flat muscular tube from laryngopharynx to stomach Pierces diaphragm at esophageal hiatus Joins stomach at cardial orifice Gastroesophageal (cardiac) sphincter Surrounds cardial orifice © 2013 Pearson Education, Inc.

Heartburn Stomach acid regurgitates into esophagus Likely with excess food/drink, extreme obesity, pregnancy, running Also with hiatal hernia - structural abnormality Part of stomach above diaphragm Can  esophagitis, esophageal ulcers, esophageal cancer © 2013 Pearson Education, Inc.

Esophageal mucosa contains stratified squamous epithelium
Esophagus Esophageal mucosa contains stratified squamous epithelium Changes to simple columnar at stomach Esophageal glands in submucosa secrete mucus to aid in bolus movement Muscularis externa - skeletal superiorly; mixed in middle; smooth inferiorly Adventitia instead of serosa © 2013 Pearson Education, Inc.

(stratified squamous epithelium)
Figure 23.12a Microscopic structure of the esophagus. Mucosa (stratified squamous epithelium) Submucosa (areolar connective tissue) Lumen Muscularis externa • Circular layer • Longitudinal layer Adventitia (fibrous connective tissue) © 2013 Pearson Education, Inc.

(stratified squamous epithelium)
Figure 23.12b Microscopic structure of the esophagus. Esophagus-stomach junction Mucosa (stratified squamous epithelium) Simple columnar epithelium of stomach © 2013 Pearson Education, Inc.

Digestive Processes: Mouth
Ingestion Mechanical breakdown Chewing Propulsion Deglutition (swallowing) Digestion (salivary amylase and lingual lipase) ~ No absorption, except for few drugs © 2013 Pearson Education, Inc.

Cheeks and closed lips hold food between teeth
Mastication Cheeks and closed lips hold food between teeth Tongue mixes food with saliva; compacts food into bolus Teeth cut and grind Partly voluntary Partly reflexive Stretch reflexes; pressure receptors in cheeks, gums, tongue © 2013 Pearson Education, Inc.

Involves tongue, soft palate, pharynx, esophagus
Deglutition Involves tongue, soft palate, pharynx, esophagus Requires coordination of 22 muscle groups Buccal phase Voluntary contraction of tongue Pharyngeal-esophageal phase Involuntary – primarily vagus nerve Control center in the medulla and lower pons © 2013 Pearson Education, Inc.

Figure 23.13 Deglutition (swallowing). Slide 1
Bolus of food Tongue Uvula Pharynx Bolus Epiglottis Epiglottis Glottis Trachea Upper esophageal sphincter Bolus Esophagus During the buccal phase, the upper esophageal sphincter is contracted. The tongue presses against the hard palate, forcing the food bolus into the oropharynx. 1 The pharyngeal-esophageal phase begins as 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 The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after food enters. 3 Relaxed muscles Peristalsis moves food through the esophagus to the stomach. 4 The gastroesophageal sphincter surrounding the cardial oriface opens, and food enters the stomach. 5 Relaxed muscles Circular muscles contract Bolus of food Longitudinal muscles contract Circular muscles contract Gastroesophageal sphincter closed Gastroesophageal sphincter opens Stomach © 2013 Pearson Education, Inc.

Stomach: Gross Anatomy
In upper left quadrant; temporary storage; digestion of bolus to chyme Cardial part (cardia) Surrounds cardial orifice Fundus Dome-shaped region beneath diaphragm Body Midportion © 2013 Pearson Education, Inc.

Cardia Fundus Esophagus Muscularis externa Serosa Longitudinal layer
Figure 23.14a Anatomy of the stomach. Cardia Fundus Esophagus Muscularis externa Serosa Longitudinal layer Circular layer Oblique layer Body Lumen Lesser curvature Rugae of mucosa Greater curvature Pyloric sphincter (valve) at pylorus Pyloric canal Pyloric antrum Duodenum © 2013 Pearson Education, Inc.

Fundus Liver (cut) Body Spleen Lesser curvature Greater curvature
Figure 23.14b Anatomy of the stomach. Liver (cut) Fundus Body Spleen Lesser curvature Greater curvature © 2013 Pearson Education, Inc.

Greater curvature - convex lateral surface Lesser curvature - concave medial surface Mesenteries tether stomach Lesser omentum From liver to lesser curvature Greater omentum – contains fat deposits & lymph nodes Greater curvature  over small intestine  spleen & transverse colon  mesocolon © 2013 Pearson Education, Inc.

Falciform ligament Liver Gallbladder Spleen Stomach Ligamentum teres
Figure 23.30a Mesenteries of the abdominal digestive organs. Falciform ligament Liver Gallbladder Spleen Stomach Ligamentum teres Greater omentum Small intestine Cecum © 2013 Pearson Education, Inc.

Liver Gallbladder Lesser omentum Stomach Duodenum Transverse colon
Figure 23.30b Mesenteries of the abdominal digestive organs. Liver Gallbladder Lesser omentum Stomach Duodenum Transverse colon Small intestine Cecum Urinary bladder © 2013 Pearson Education, Inc.

Greater omentum Transverse colon Transverse mesocolon Descending colon
Figure 23.30c Mesenteries of the abdominal digestive organs. Greater omentum Transverse colon Transverse mesocolon Descending colon Jejunum Mesentery Sigmoid mesocolon Sigmoid colon Ileum © 2013 Pearson Education, Inc.

ANS nerve supply Sympathetic from thoracic splanchnic nerves via celiac plexus Parasympathetic via vagus nerve Blood supply Celiac trunk (gastric and splenic branches) Veins of hepatic portal system © 2013 Pearson Education, Inc.

Stomach: Microscopic Anatomy
Four tunics Muscularis and mucosa modified Muscularis externa Three layers of smooth muscle Inner oblique layer allows stomach to churn, mix, move, and physically break down food © 2013 Pearson Education, Inc.

Layers of the stomach wall
Figure 23.15a Microscopic anatomy of the stomach. Surface epithelium Mucosa Lamina propria Muscularis mucosae Submucosa (contains submucosal plexus) Oblique layer Muscularis externa (contains myenteric plexus) Circular layer Longitudinal layer Serosa Stomach wall Layers of the stomach wall © 2013 Pearson Education, Inc.

Stomach: Microscopic Anatomy
Mucosa Simple columnar epithelium composed of mucous cells Secrete two-layer coat of alkaline mucus Surface layer traps bicarbonate-rich fluid beneath it Dotted with gastric pits  gastric glands Gastric glands produce gastric juice © 2013 Pearson Education, Inc.

Enlarged view of gastric pits and gastric glands
Figure 23.15b Microscopic anatomy of the stomach. Gastric pits Surface epithelium (mucous cells) Gastric pit Mucous neck cells Parietal cell Gastric gland Chief cell Enteroendocrine cell Enlarged view of gastric pits and gastric glands © 2013 Pearson Education, Inc.

Gastric Glands Cell types
Mucous neck cells (secrete thin, acidic mucus of unknown function) Parietal cells Chief cells Enteroendocrine cells © 2013 Pearson Education, Inc.

Location of the HCl-producing parietal cells
Figure 23.15c Microscopic anatomy of the stomach. Pepsinogen Pepsin HCI Mitochondria Parietal cell Chief cell Enteroendocrine cell Location of the HCl-producing parietal cells and pepsin-secreting chief cells in a gastric gland © 2013 Pearson Education, Inc.

Gastric Gland Secretions
Glands in fundus and body produce most gastric juice Parietal cell secretions Hydrochloric acid (HCl)  pH 1.5–3.5 denatures protein, activates pepsin, breaks down plant cell walls, kills many bacteria Intrinsic factor Glycoprotein required for absorption of vitamin B12 in small intestine © 2013 Pearson Education, Inc.

Enteroendocrine cells Secrete chemical messengers into lamina propria Act as paracrines Serotonin and histamine Hormones Somatostatin (also acts as paracrine) and gastrin © 2013 Pearson Education, Inc.

Harsh digestive conditions in stomach Has mucosal barrier to protect
Thick layer of bicarbonate-rich mucus Tight junctions between epithelial cells Prevent juice seeping underneath tissue Damaged epithelial cells quickly replaced by division of stem cells Surface cells replaced every 3–6 days © 2013 Pearson Education, Inc.

Gastritis Inflammation caused by anything that breaches mucosal barrier Peptic or gastric ulcers Erosions of stomach wall Can perforate  peritonitis; hemorrhage Most caused by Helicobacter pylori bacteria Some by NSAIDs © 2013 Pearson Education, Inc.

Bacteria Mucosa layer of stomach A gastric ulcer lesion
Figure Photographs of a gastric ulcer and the H. pylori bacteria that most commonly cause it. Bacteria Mucosa layer of stomach A gastric ulcer lesion H. pylori bacteria © 2013 Pearson Education, Inc.

Digestive Processes in the Stomach
Mechanical breakdown Denaturation of proteins by HCl Enzymatic digestion of proteins by pepsin (and milk protein by rennin in infants) Delivers chyme to small intestine © 2013 Pearson Education, Inc.

Digestive Processes in the Stomach
Lipid-soluble alcohol and aspirin absorbed into blood Only stomach function essential to life Secretes intrinsic factor for vitamin B12 absorption B12 needed  mature red blood cells Lack of intrinsic factor causes pernicious anemia Treated with B12 injections © 2013 Pearson Education, Inc.

Regulation of Gastric Secretion
Neural and hormonal mechanisms Gastric mucosa  up to 3 L gastric juice/day Vagus nerve stimulation  secretion  Sympathetic stimulation  secretion  Hormonal control largely gastrin  Enzyme and HCl secretion Most small intestine secretions - gastrin antagonists © 2013 Pearson Education, Inc.

Three phases of gastric secretion Cephalic (reflex) phase – conditioned reflex triggered by aroma, taste, sight, thought Gastric phase – lasts 3–4 hours; ⅔ gastric juice released Stimulated by distension, peptides, low acidity, gastrin (major stimulus) Enteroendocrine G cells stimulated by caffeine, peptides, rising pH  gastrin © 2013 Pearson Education, Inc.

Stimuli of Gastric Phase
Gastrin  enzyme and HCl release Low pH inhibits gastrin secretion (as between meals) Buffering action of ingested proteins  rising pH  gastrin secretion Three chemicals - ACh, histamine, and gastrin - stimulate parietal cells through second-messenger systems All three are necessary for maximum HCl secretion © 2013 Pearson Education, Inc.

HCl Formation Parietal cells pump H+ (from carbonic acid breakdown) into stomach lumen K+ goes into cells to balance charge HCO3– from carbonic acid breakdown  blood (via Cl– and HCO3– antiporter)  blood leaving stomach more alkaline  Alkaline tide Cl– (from blood plasma via antiporter) follows H+ HCl © 2013 Pearson Education, Inc.

Gastric gland Blood capillary Chief cell Stomach lumen CO2 CO2 + H2O
Figure Mechanism of HCl secretion by parietal cells. Gastric gland Blood capillary Chief cell Stomach lumen CO2 CO2 + H2O H+-K+ ATPase Carbonic anhydrase H2CO3 H+ H+ K+ K+ HCO3− HCI Alkaline tide Parietal cell HCO3− Cl− Cl− Cl− HCO3−- Cl− antiporter Interstitial fluid © 2013 Pearson Education, Inc.

Intestinal phase Stimulatory component Partially digested food enters small intestine  brief intestinal gastrin release Inhibitory effects (enterogastric reflex and enterogastrones) Chyme with H+, fats, peptides, irritating substances  inhibition © 2013 Pearson Education, Inc.

Enterogastric Reflex Three reflexes act to
Inhibit vagal nuclei in medulla Inhibit local reflexes Activate sympathetic fibers  tightening of pyloric sphincter  no more food entry to small intestine  Decreased gastric activity  protects small intestine from excessive acidity © 2013 Pearson Education, Inc.

Enterogastrones released
Intestinal Phase Enterogastrones released Secretin, cholecystokinin (CCK), vasoactive intestinal peptide (VIP) All inhibit gastric secretion If small intestine pushed to accept more chyme  dumping syndrome Nausea and vomiting Common in gastric reduction for weight loss © 2013 Pearson Education, Inc.

Figure 23.17 Neural and hormonal mechanisms that regulate release of gastric juice.
Stimulatory events Inhibitory events Cephalic phase Sight and thought of food 1 Cerebral cortex Lack of stimulatory impulses to parasympathetic center Cerebral cortex Loss of appetite, depression 1 Conditioned reflex Stimulation of taste and smell receptors 2 Hypothalamus and medulla oblongata Vagus nerve Stomach distension activates stretch receptors 1 Vagovagal reflexes Medulla Vagus nerve Gastrin secretion declines G cells Excessive acidity (pH < 2) in stomach 1 Gastric phase Local reflexes Overrides parasympathetic controls Sympathetic nervous system activation Emotional stress 2 Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors 2 G cells Gastrin release to blood Stomach secretory activity Entero- gastric reflex Local reflexes Distension of duodenum; presence of fatty, acidic, or hypertonic chyme; and/or irritants in the duodenum 1 Presence of partially digested foods in duodenum or distension of the duodenum when stomach begins to empty 1 Intestinal (enteric) gastrin release to blood Vagal nuclei in medulla Brief effect Intestinal phase Pyloric sphincter Release of enterogastrones (secretin, cholecystokinin, vasoactive intestinal peptide) Distension; presence of fatty, acidic, partially digested food in the duodenum 2 Stimulate Inhibit © 2013 Pearson Education, Inc.

Response of the Stomach to Filling
Stretches to accommodate incoming food Pressure constant until 1.5 L food ingested Reflex-mediated receptive relaxation Coordinated by swallowing center of brain stem Gastric accommodation Plasticity (stress-relaxation response) of smooth muscle (see Chapter 9) © 2013 Pearson Education, Inc.

Gastric Contractile Activity
Peristaltic waves move toward pylorus at rate of 3 per minute Basic electrical rhythm (BER) set by enteric pacemaker cells (formerly interstitial cells of Cajal) Pacemaker cells linked by gap junctions  entire muscularis contracts Distension and gastrin increase force of contraction © 2013 Pearson Education, Inc.

Gastric Contractile Activity
Most vigorous near pylorus Chyme is either Delivered in ~3 ml spurts to duodenum, or Forced backward into stomach © 2013 Pearson Education, Inc.

Pyloric Pyloric Pyloric valve valve valve slightly closed closed
Figure Deglutition (swallowing). Slide 1 Pyloric valve slightly opened Pyloric valve closed Pyloric valve closed Propulsion: Peristaltic waves move from the fundus toward the pylorus. 1 Grinding: The most vigorous peristalsis and mixing action occur close to the pylorus. 2 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. 3 © 2013 Pearson Education, Inc.

Regulation of Gastric Emptying
As chyme enters duodenum Receptors respond to stretch and chemical signals Enterogastric reflex and enterogastrones inhibit gastric secretion and duodenal filling Carbohydrate-rich chyme moves quickly through duodenum Fatty chyme remains in duodenum 6 hours or more © 2013 Pearson Education, Inc.

Physiological response
Figure Neural and hormonal factors that inhibit gastric emptying. Presence of fatty, hypertonic, acidic chyme in duodenum Duodenal enteroendocrine cells Chemoreceptors and stretch receptors Secrete Target Enterogastrones (secretin, cholecystokinin, vasoactive intestinal peptide) Via short reflexes Via long reflexes Enteric neurons CNS centers sympathetic activity; parasympathetic activity Duodenal stimuli decline Contractile force and rate of stomach emptying decline Initial stimulus Stimulate Physiological response Inhibit Result © 2013 Pearson Education, Inc.

Vomiting (emesis) caused by Extreme stretching Intestinal irritants, e.g., bacterial toxins, excessive alcohol, spicy food, certain drugs Chemicals/sensory impulses  emetic center of medulla Excessive vomiting  dehydration, electrolyte and acid-base imbalances (alkalosis) © 2013 Pearson Education, Inc.

Small Intestine: Gross Anatomy
Major organ of digestion and absorption 2-4 m long; from pyloric sphincter to ileocecal valve Subdivisions Duodenum (retroperitoneal) Jejunum (attached posteriorly by mesentery) Ileum (attached posteriorly by mesentery) © 2013 Pearson Education, Inc.

Mouth (oral cavity) Parotid gland Sublingual gland Salivary Tongue*
Figure Alimentary canal and related accessory digestive organs. Mouth (oral cavity) Parotid gland Sublingual gland Salivary glands* Tongue* Submandibular gland Pharynx Esophagus Stomach Pancreas* (Spleen) Liver* Gallbladder* Transverse colon Duodenum Descending colon Small intestine Jejunum Ascending colon Ileum Cecum Large intestine Sigmoid colon Rectum Appendix Anus Anal canal © 2013 Pearson Education, Inc.

Curves around head of pancreas; shortest part – 25 cm
Duodenum Curves around head of pancreas; shortest part – 25 cm Bile duct (from liver) and main pancreatic duct (from pancreas) Join at hepatopancreatic ampulla Enter duodenum at major duodenal papilla Entry controlled by hepatopancreatic sphincter © 2013 Pearson Education, Inc.

Bile duct and sphincter Accessory pancreatic duct
Figure The duodenum of the small intestine, and related organs. Right and left hepatic ducts of liver Common hepatic duct Bile duct and sphincter Accessory pancreatic duct Tail of pancreas Pancreas Jejunum Main pancreatic duct and sphincter Head of pancreas Hepatopancreatic ampulla and sphincter Duodenum Mucosa with folds Gallbladder Major duodenal papilla Cystic duct © 2013 Pearson Education, Inc.

Jejunum and Ileum Jejunum Ileum Extends from duodenum to ileum
About 2.5 m long Ileum Joins large intestine at ileocecal valve About 3.6 m long © 2013 Pearson Education, Inc.

Gross Anatomy of Small Intestine
Vagus nerve (parasympathetic) and sympathetics from thoracic splanchnic nerves serve small intestine Superior mesenteric artery brings blood supply Veins (carrying nutrient-rich blood) drain into superior mesenteric veins  hepatic portal vein  liver © 2013 Pearson Education, Inc.

Structural Modifications
Increase surface area of proximal part for nutrient absorption Circular folds (plicae circulares) Villi Microvilli © 2013 Pearson Education, Inc.

Structural Modifications
Circular folds Permanent folds (~1 cm deep) that force chyme to slowly spiral through lumen  more nutrient absorption Villi Extensions (~1 mm high) of mucosa with capillary bed and lacteal for absorption Microvilli (brush border) – contain enzymes for carbohydrate and protein digestion © 2013 Pearson Education, Inc.

Vein carrying blood to hepatic portal vessel Muscle layers Lumen
Figure 23.22a Structural modifications of the small intestine that increase its surface area for digestion and absorption. Vein carrying blood to hepatic portal vessel Muscle layers Lumen Circular folds Villi © 2013 Pearson Education, Inc.

Villus Venule Lymphatic vessel Submucosa
Figure 23.22b Structural modifications of the small intestine that increase its surface area for digestion and absorption. Microvilli (brush border) Absorptive cells Lacteal Villus Goblet cell Blood capillaries Mucosa- associated lymphoid tissue Intestinal crypt Enteroendocrine cells Venule Muscularis mucosae Lymphatic vessel Duodenal gland Submucosa © 2013 Pearson Education, Inc.

Absorptive cells Villi Intestinal crypt
Figure 23.22c Structural modifications of the small intestine that increase its surface area for digestion and absorption. Absorptive cells Goblet cells Villi Intestinal crypt © 2013 Pearson Education, Inc.

Mucus granules Microvilli forming the brush border Absorptive cell
Figure Microvilli of the small intestine. Mucus granules Microvilli forming the brush border Absorptive cell © 2013 Pearson Education, Inc.

Intestinal crypt epithelium renewed every 2-4 days
Intestinal Crypts Intestinal crypt epithelium renewed every 2-4 days Most - secretory cells that produce intestinal juice Enteroendocrine cells  enterogastrones Intraepithelial lymphocytes (IELs) Release cytokines that kill infected cells Paneth cells Secrete antimicrobial agents (defensins and lysozyme) Stem cells divide to produce crypt cells © 2013 Pearson Education, Inc.

Peyer's patches protect especially distal part against bacteria
Mucosa Peyer's patches protect especially distal part against bacteria May protrude into submucosa B lymphocytes leave intestine, enter blood, protect intestinal lamina propria with their IgA Duodenal (Brunner's) glands of the duodenum secrete alkaline mucus to neutralize acidic chyme © 2013 Pearson Education, Inc.

1-2 L secreted daily in response to distension or irritation of mucosa
Intestinal Juice 1-2 L secreted daily in response to distension or irritation of mucosa Slightly alkaline; isotonic with blood plasma Largely water; enzyme-poor (enzymes of small intestine only in brush border); contains mucus Facilitates transport and absorption of nutrients © 2013 Pearson Education, Inc.

The Liver and Gallbladder
Accessory organs Liver Many functions; only digestive function  bile production Bile – fat emulsifier Gallbladder Chief function  bile storage © 2013 Pearson Education, Inc.

Four lobes—right, left, caudate, and quadrate
Liver Largest gland in body Four lobes—right, left, caudate, and quadrate © 2013 Pearson Education, Inc.

Round ligament (ligamentum teres)
Liver Falciform ligament Separates larger right and smaller left lobes Suspends liver from diaphragm and anterior abdominal wall Round ligament (ligamentum teres) Remnant of fetal umbilical vein along free edge of falciform ligament © 2013 Pearson Education, Inc.

Sternum Bare area Nipple Liver Right lobe of liver Gallbladder
Figure 23.24a Gross anatomy of the human liver. Sternum Bare area Nipple Liver Falciform ligament Left lobe of liver Right lobe of liver Round ligament (ligamentum teres) Gallbladder © 2013 Pearson Education, Inc.

Bare area Lesser omentum (in fissure) Caudate lobe of liver
Figure 23.24b Gross anatomy of the human liver. Bare area Lesser omentum (in fissure) Caudate lobe of liver Sulcus for inferior vena cava Left lobe of liver Porta hepatis containing hepatic artery (left) and hepatic portal vein (right) Hepatic vein (cut) Bile duct (cut) Quadrate lobe of liver Right lobe of liver Ligamentum teres Gallbladder © 2013 Pearson Education, Inc.

Liver: Associated Structures
Lesser omentum anchors liver to stomach Hepatic artery and vein enter at porta hepatis Bile ducts Common hepatic duct leaves liver Cystic duct connects to gallbladder Bile duct formed by union of common hepatic and cystic ducts © 2013 Pearson Education, Inc.

Bile duct and sphincter Accessory pancreatic duct
Figure The duodenum of the small intestine, and related organs. Right and left hepatic ducts of liver Cystic duct Common hepatic duct Bile duct and sphincter Accessory pancreatic duct Mucosa with folds Tail of pancreas Pancreas Gallbladder Jejunum Major duodenal papilla Main pancreatic duct and sphincter Hepatopancreatic ampulla and sphincter Duodenum Head of pancreas © 2013 Pearson Education, Inc.

Liver: Microscopic Anatomy
Liver lobules Hexagonal structural and functional units Composed of plates of hepatocytes (liver cells) Filter and process nutrient-rich blood Central vein in longitudinal axis © 2013 Pearson Education, Inc.

Lobule Central vein Connective tissue septum
Figure 23.25a–b Microscopic anatomy of the liver. Lobule Central vein Connective tissue septum © 2013 Pearson Education, Inc.

Portal triad at each corner of lobule Branch of hepatic artery supplies oxygen Branch of hepatic portal vein brings nutrient-rich blood Bile duct receives bile from bile canaliculi Liver sinusoids - leaky capillaries between hepatic plates Stellate macrophages (hepatic macrophages or Kupffer cells) in liver sinusoids remove debris & old RBCs © 2013 Pearson Education, Inc.

Interlobular veins (to hepatic vein) Central vein Sinusoids
Figure 23.25c Microscopic anatomy of the liver. Interlobular veins (to hepatic vein) Central vein Sinusoids Plates of hepatocytes Portal vein Stellate macrophages in sinusoid walls Bile canaliculi Bile duct (receives bile from bile canaliculi) Fenestrated lining (endothelial cells) of sinusoids Bile duct Portal venule Portal arteriole Portal triad © 2013 Pearson Education, Inc.

Hepatocytes – increased rough & smooth ER, Golgi, peroxisomes, mitochondria Hepatocyte functions Process bloodborne nutrients Store fat-soluble vitamins Perform detoxification Produce ~900 ml bile per day © 2013 Pearson Education, Inc.

Regenerative capacity
Liver Regenerative capacity Restores full size in 6-12 months after 80% removal Injury  hepatocytes  growth factors  endothelial cell proliferation © 2013 Pearson Education, Inc.

Hepatitis Usually viral infection, drug toxicity, wild mushroom poisoning Cirrhosis Progressive, chronic inflammation from chronic hepatitis or alcoholism Liver  fatty, fibrous  portal hypertension Liver transplants successful, but livers scarce © 2013 Pearson Education, Inc.

Yellow-green, alkaline solution containing
Bile Yellow-green, alkaline solution containing Bile salts - cholesterol derivatives that function in fat emulsification and absorption Bilirubin - pigment formed from heme Bacteria break down in intestine to stercobilin  brown color of feces Cholesterol, triglycerides, phospholipids, and electrolytes © 2013 Pearson Education, Inc.

Enterohepatic circulation
Bile Enterohepatic circulation Recycles bile salts Bile salts  duodenum  reabsorbed from ileum  hepatic portal blood  liver  secreted into bile © 2013 Pearson Education, Inc.

Thin-walled muscular sac on ventral surface of liver
The Gallbladder Thin-walled muscular sac on ventral surface of liver Stores and concentrates bile by absorbing water and ions Muscular contractions release bile via cystic duct, which flows into bile duct © 2013 Pearson Education, Inc.

High cholesterol; too few bile salts  gallstones (biliary calculi)
The Gallbladder High cholesterol; too few bile salts  gallstones (biliary calculi) Obstruct flow of bile from gallbladder May cause obstructive jaundice Gallbladder contracts against sharp crystals  pain Treated with drugs, ultrasound vibrations (lithotripsy), laser vaporization, surgery © 2013 Pearson Education, Inc.

Pancreas Endocrine function Exocrine function
Pancreatic islets secrete insulin and glucagon Exocrine function Acini (clusters of secretory cells) secrete pancreatic juice To duodenum via main pancreatic duct Zymogen granules of acini cells contain proenzymes © 2013 Pearson Education, Inc.

Small duct Acinar cell Basement membrane Zymogen granules Rough
Figure 23.26a Structure of the enzyme-producing tissue of the pancreas. Small duct Acinar cell Basement membrane Zymogen granules Rough endoplasmic reticulum Duct cell One acinus © 2013 Pearson Education, Inc.

Acinar cells Pancreatic duct
Figure 23.26b Structure of the enzyme-producing tissue of the pancreas. Acinar cells Pancreatic duct © 2013 Pearson Education, Inc.

Watery alkaline solution (pH 8) neutralizes chyme
Pancreatic Juice 1200 – 1500 ml/day Watery alkaline solution (pH 8) neutralizes chyme Electrolytes (primarily HCO3–) Enzymes Amylase, lipases, nucleases secreted in active form but require ions or bile for optimal activity Proteases secreted in inactive form © 2013 Pearson Education, Inc.

Protease activation in duodenum
Pancreatic Juice Protease activation in duodenum Trypsinogen activated to trypsin by brush border enzyme enteropeptidase Procarboxypeptidase and chymotrypsinogen activated by trypsin © 2013 Pearson Education, Inc.

Figure 23.27 Activation of pancreatic proteases in the small intestine.
Stomach Pancreas Epithelial cells Membrane-bound enteropeptidase Trypsinogen (inactive) Chymotrypsinogen Procarboxypeptidase Trypsin Chymotrypsin Carboxypeptidase © 2013 Pearson Education, Inc.

Regulation of Bile Secretion
Bile secretion stimulated by Bile salts in enterohepatic circulation Secretin from intestinal cells exposed to HCl and fatty chyme Hepatopancreatic sphincter closed unless digestion active  bile stored in gallbladder Released to small intestine ~ only with contraction © 2013 Pearson Education, Inc.

Regulation of Bile Secretion
Gallbladder contraction stimulated by Cholecystokinin (CCK) from intestinal cells exposed to acidic, fatty chyme Vagal stimulation (minor stimulus) CCK also causes Secretion of pancreatic juice Hepatopancreatic sphincter to relax © 2013 Pearson Education, Inc.

Regulation of Pancreatic Secretion
CCK induces secretion of enzyme-rich pancreatic juice by acini Secretin causes secretion of bicarbonate-rich pancreatic juice by duct cells Vagal stimulation also causes release of pancreatic juice (minor stimulus) © 2013 Pearson Education, Inc.

Chyme enter -ing duodenum causes duodenal
Figure Mechanisms promoting secretion and release of bile and pancreatic juice. Slide 1 Chyme enter -ing duodenum causes duodenal enteroendocrine cells to release cholecystokinin (CCK) and secretin. 1 4 Bile salts and, to a lesser extent, secretin transported via bloodstream stimulate Liver to produce bile more rapidly. 5 CCK (via blood stream) causes gallbladder to contract and Hepatopancreatic Sphincter to relax. Bile Enters duodenum. CCK (red dots) and secretin (yellow dots) enter the bloodstream. 2 CCK induces secretion of enzyme-rich pancreatic juice. Secretin causes secretion of HCO3− -rich pancreatic juice. 3 During cephalic and gastric phases, vagal Nerve stimulates gallbladder to contract weakly. 6 CCK secretion Secretin secretion © 2013 Pearson Education, Inc.

Digestion in the Small Intestine
Chyme from stomach contains Partially digested carbohydrates and proteins Undigested fats 3–6 hours in small intestine Most water absorbed ~ All nutrients absorbed Small intestine, like stomach, no role in ingestion or defecation © 2013 Pearson Education, Inc.

Requirements for Digestion and Absorption in the Small Intestine
Slow delivery of acidic, hypertonic chyme Delivery of bile, enzymes, and bicarbonate ions from liver and pancreas Mixing © 2013 Pearson Education, Inc.

Motility of the Small Intestine
Segmentation Most common motion of small intestine Initiated by intrinsic pacemaker cells Mixes/moves contents toward ileocecal valve Intensity altered by long & short reflexes; hormones Parasympathetic  ; sympathetic  Wanes in late intestinal (fasting) phase © 2013 Pearson Education, Inc.

Mucus granules Microvilli forming the brush border Absorptive cell
Figure Microvilli of the small intestine. Mucus granules Microvilli forming the brush border Absorptive cell © 2013 Pearson Education, Inc.

Peristalsis Initiated by rise in hormone motilin in late intestinal phase; every 90–120 minutes Each wave starts distal to previous Migrating motor complex Meal remnants, bacteria, and debris moved to large intestine From duodenum  ileum ~ 2 hours © 2013 Pearson Education, Inc.

Figure 23.3a Peristalsis and segmentation.
From mouth Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, moving food along the tract distally. © 2013 Pearson Education, Inc.

Local enteric neurons coordinate intestinal motility Cholinergic sensory neurons may activate myenteric plexus Causes contraction of circular muscle proximally and of longitudinal muscle distally Forces chyme along tract © 2013 Pearson Education, Inc.

Ileocecal sphincter relaxes, admits chyme into large intestine when Gastroileal reflex enhances force of segmentation in ileum Gastrin increases motility of ileum Ileocecal valve flaps close when chyme exerts backward pressure Prevents regurgitation into ileum © 2013 Pearson Education, Inc.

Large Intestine Unique features Teniae coli Haustra
Three bands of longitudinal smooth muscle in muscularis Haustra Pocketlike sacs caused by tone of teniae coli Epiploic appendages Fat-filled pouches of visceral peritoneum © 2013 Pearson Education, Inc.

External anal sphincter
Figure 23.29a Gross anatomy of the large intestine. Left colic (splenic) flexure Transverse mesocolon Right colic (hepatic) flexure Epiploic appendages Transverse colon Superior mesenteric artery Descending colon Haustrum Ascending colon IIeum Cut edge of mesentery IIeocecal valve Tenia coli Sigmoid colon Cecum Appendix Rectum Anal canal External anal sphincter © 2013 Pearson Education, Inc.

Subdivisions of the Large Intestine
Cecum – first part of large intestine Appendix – masses of lymphoid tissue Part of MALT of immune system Bacterial storehouse  recolonizes gut when necessary Twisted  enteric bacteria accumulate and multiply © 2013 Pearson Education, Inc.

Retroperitoneal except for transverse and sigmoid regions
Colon Retroperitoneal except for transverse and sigmoid regions Ascending colon (right side – to level of right kidney)  right colic (hepatic) flexure  Transverse colon  left colic (splenic) flexure  Descending colon (left side)  Sigmoid colon in pelvis  rectum © 2013 Pearson Education, Inc.

Greater omentum Transverse colon Transverse mesocolon Descending colon
Figure 23.30c Mesenteries of the abdominal digestive organs. Greater omentum Transverse colon Transverse mesocolon Descending colon Jejunum Mesentery Sigmoid mesocolon Sigmoid colon Ileum © 2013 Pearson Education, Inc.

Liver Lesser omentum Pancreas Stomach Duodenum Transverse mesocolon
Figure 23.30d Mesenteries of the abdominal digestive organs. Liver Lesser omentum Pancreas Stomach Duodenum Transverse mesocolon Transverse colon Mesentery Greater omentum Jejunum Ileum Visceral peritoneum Parietal peritoneum Urinary bladder Rectum © 2013 Pearson Education, Inc.

Rectum and Anus Rectum Anal canal Sphincters
Three rectal valves stop feces from being passed with gas (flatus) Anal canal Last segment of large intestine Opens to body exterior at anus Sphincters Internal anal sphincter—smooth muscle External anal sphincter—skeletal muscle © 2013 Pearson Education, Inc.

Anal columns Pectinate line Anal sinuses Anus
Figure 23.29b Gross anatomy of the large intestine. Rectal valve Rectum Hemorrhoidal veins Levator ani muscle Anal canal External anal sphincter Internal anal sphincter Anal columns Pectinate line Anal sinuses Anus © 2013 Pearson Education, Inc.

Large Intestine: Microscopic Anatomy
Thicker mucosa of simple columnar epithelium except in anal canal (stratified squamous to withstand abrasion) No circular folds, villi, digestive secretions Abundant deep crypts with goblet cells Superficial venous plexuses of anal canal form hemorrhoids if inflamed © 2013 Pearson Education, Inc.

Enter from small intestine or anus
Bacterial Flora Enter from small intestine or anus Colonize colon Synthesize B complex vitamins and vitamin K Metabolize some host-derived molecules (mucin, heparin, hyaluronic acid) Ferment indigestible carbohydrates Release irritating acids and gases (~500 ml/day) © 2013 Pearson Education, Inc.

Viruses and protozoans
Intestinal Flora Viruses and protozoans Bacteria prevented from breaching mucosal barrier Epithelial cells recruit dendritic cells to mucosa  sample microbial antigens  present to T cells of MALT  IgA antibody-mediated response  restricts microbes © 2013 Pearson Education, Inc.

Digestive Processes in the Large Intestine
Residue remains in large intestine 12–24 hours No food breakdown except by enteric bacteria Vitamins (made by bacterial flora), water, and electrolytes (especially Na+ and Cl–) reclaimed Major functions - propulsion of feces to anus; defecation Colon not essential for life © 2013 Pearson Education, Inc.

Motility of the Large Intestine
Most contractions of colon Haustral contractions Slow segmenting movements Haustra sequentially contract in response to distension © 2013 Pearson Education, Inc.

Motility of the Large Intestine
Gastrocolic reflex Initiated by presence of food in stomach Activates three to four slow powerful peristaltic waves per day in colon (mass movements) © 2013 Pearson Education, Inc.

Low fiber diet  narrowed colon  strong contractions  increased pressure on walls  diverticula (herniations of mucosa) Diverticulosis commonly in sigmoid colon Affects ½ people > 70 years Diverticulitis Inflamed diverticula; may rupture and leak into peritoneal cavity; may be life threatening © 2013 Pearson Education, Inc.

Irritable bowel syndrome Functional GI disorder Recurring abdominal pain, stool changes, bloating, flatulence, nausea, depression Stress common precipitating factor Stress management important in treatment © 2013 Pearson Education, Inc.

Mass movements force feces toward rectum
Defecation Mass movements force feces toward rectum Distension initiates spinal defecation reflex Parasympathetic signals Stimulate contraction of sigmoid colon and rectum Relax internal anal sphincter Conscious control allows relaxation of external anal sphincter © 2013 Pearson Education, Inc.

Muscles of rectum contract to expel feces
Defecation Muscles of rectum contract to expel feces Assisted by Valsalva's maneuver Closing of glottis, contraction of diaphragm and abdominal wall muscles  increased intra-abdominal pressure Levator ani muscle contracts  anal canal lifted superiorly  feces leave body © 2013 Pearson Education, Inc.

stimulating stretch receptors there. The receptors transmit
Figure Defecation reflex. Slide 1 Impulses from cerebral cortex (conscious control) Sensory nerve fibers Feces move into and distend the rectum, stimulating stretch receptors there. The receptors transmit signals along afferent fibers to spinal cord neurons. 1 Voluntary motor nerve to external anal sphincter Sigmoid colon Stretch receptors in wall A spinal reflex is initiated in which parasympathetic motor (efferent) fibers stimulate contraction of the rectum and sigmoid colon, and relaxation of the internal anal sphincter. 2 Rectum External anal sphincter (skeletal muscle) Involuntary motor nerve (parasympathetic division) Internal anal sphincter (smooth muscle) If it is convenient to defecate, voluntary motor neurons are inhibited, allowing the external anal sphincter to relax so feces may pass. 3 © 2013 Pearson Education, Inc.

Digestion Digestion Enzymes Hydrolysis
Catabolic; macromolecules  monomers small enough for absorption Enzymes Intrinsic and accessory gland enzymes break down food Hydrolysis Water is added to break bonds © 2013 Pearson Education, Inc.

Digestion of Carbohydrates
Only monosaccharides can be absorbed Monosaccharides absorbed as ingested Glucose, fructose, galactose Digestive enzymes Salivary amylase, pancreatic amylase, and brush border enzymes (dextrinase, glucoamylase, lactase, maltase, and sucrase) Break down disaccharides sucrose, lactose, maltose; polysaccharides glycogen and starch © 2013 Pearson Education, Inc.

Digestion of Carbohydrates
Starch digestion Salivary amylase (saliva)  oligosaccharides at pH 6.75 – 7.00 Pancreatic amylase (small intestine)  breaks down any that escaped salivary amylase  oligosaccharides Brush border enzymes (dextrinase, glucoamylase, lactase, maltase, sucrase)  oligosaccharides  monosaccharides © 2013 Pearson Education, Inc.

Starch and disaccharides
Figure Flowchart of digestion and absorption of foodstuffs. (1 of 4) Foodstuff Enzyme(s) and source Site of action Path of absorption Starch and disaccharides Glucose and galactose are absorbed via cotransport with sodium ions. Fructose passes via facilitated diffusion. All monosaccharides leave the epithelial cells via facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein. Salivary amylase Mouth Pancreatic amylase Small intestine Oligosaccharides and disaccharides Carbohydrate digestion Brush border enzymes in small intestine (dextrinase, glucoamylase, lactase, maltase, and sucrase) Small intestine Lactose Maltose Sucrose Galactose Glucose Fructose © 2013 Pearson Education, Inc.

Digestion of Proteins Source is dietary, digestive enzymes, mucosal cells; digested to amino acid monomers Begins with pepsin in stomach at pH 1.5 – 2.5 Inactive in high pH of duodenum Pancreatic proteases Trypsin, chymotrypsin, and carboxypeptidase Brush border enzymes Aminopeptidases, carboxypeptidases, and dipeptidases © 2013 Pearson Education, Inc.

Amino acids of protein fragments
Figure Protein digestion and absorption in the small intestine. Slide 1 Lumen of intestine Amino acids of protein fragments Brush border enzymes Pancreatic proteases Apical membrane (microvilli) Na+ Proteins and protein fragments are digested to amino acids by pancreatic proteases (trypsin, chymotrypsin, and carboxypeptidase), and by brush border enzymes (carboxypeptidase, aminopeptidase, and dipeptidase) of mucosal cells. 1 Absorptive epithelial cell Na+ The amino acids are then absorbed by active transport into the absorptive cells, and move to their opposite side. 2 Amino acid carrier The amino acids leave the villus epithelial cell by facilitated diffusion and enter the capillary via intercellular clefts. 3 Capillary © 2013 Pearson Education, Inc.

Figure 23. 32 Flowchart of digestion and absorption of foodstuffs
Figure Flowchart of digestion and absorption of foodstuffs. (2 of 4) Foodstuff Enzyme(s) and source Site of action Path of absorption Proteins Amino acids are absorbed via cotransport with sodium ions. Some dipeptides and tripeptides are absorbed via cotransport with H+ and hydrolyzed to amino acids within the cells. Infrequently, transcytosis of small peptides occurs. Amino acids leave the epithelial cells by facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein. Pepsin (stomach glands) in presence of HCl Stomach Large polypeptides Pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase) Small intestine Protein digestion Small polypeptides, small peptides Brush border enzymes (aminopeptidase, carboxypeptidase, and dipeptidase) Small intestine Amino acids (some dipeptides and tripeptides) © 2013 Pearson Education, Inc.

Pre-treatment—emulsification by bile salts Enzymes—pancreatic lipases
Digestion of Lipids Pre-treatment—emulsification by bile salts Does not break bonds Enzymes—pancreatic lipases  Fatty acids and monoglycerides © 2013 Pearson Education, Inc.

with bile salts to form micelles which
Figure Emulsification, digestion, and absorption of fats. Slide 1 Fat globule Bile salts in the duodenum emulsify large fat globules (physically break them up into smaller fat droplets). 1 Bile salts Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides. These then associate with bile salts to form micelles which “ferry” them to the intestinal mucosa. 2 Fat droplets coated with bile salts Micelles made up of fatty acids, monoglycerides, and bile salts Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. There they are recombined and packaged with other fatty substances and proteins to form chylomicrons. 3 Chylomicrons are extruded from the epithelial cells by exocytosis. The chylomicrons enter lacteals and are carried away from the intestine in lymph. 4 Epithelial cells of small intestine Lacteal © 2013 Pearson Education, Inc.

Figure Flowchart of digestion and absorption of foodstuffs. (3 of 4) Foodstuff Enzyme(s) and source Site of action Path of absorption Unemulsified triglycerides Fatty acids and monoglycerides enter the intestinal cells via diffusion. Fatty acids and monoglycerides are recombined to form triglycerides and then combined with other lipids and proteins within the cells. The resulting chylomicrons are extruded by exocytosis. The chylomicrons enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic duct. Some short-chain fatty acids are absorbed, move into the capillary blood in the villi by diffusion, and are transported to the liver via the hepatic portal vein. Lingual lipase Mouth Gastric lipase Stomach Emulsification by the detergent action of bile salts ducted in from the liver Small intestine Fat digestion Pancreatic lipases Small intestine Monoglycerides (or diglycerides with gastric lipase) and fatty acids © 2013 Pearson Education, Inc.

Digestion of Nucleic Acids
Enzymes Pancreatic ribonuclease and deoxyribonuclease  nucleotide monomers Brush border enzyme nucleosidases and phosphatases  free bases, pentose sugars, phosphate ions © 2013 Pearson Education, Inc.

Figure Flowchart of digestion and absorption of foodstuffs. (4 of 4) Foodstuff Enzyme(s) and source Site of action Path of absorption Nucleic acids Units enter intestinal cells by active transport via membrane carriers. Units are absorbed into capillary blood in the villi and transported to the liver via the hepatic portal vein. Pancreatic ribonuclease and deoxyribonuclease Small intestine Nucleic acid digestion Brush border enzymes (nucleosidases and phosphatases) Small intestine Pentose sugars, N-containing bases, phosphate ions © 2013 Pearson Education, Inc.

~ All food; 80% electrolytes; most water absorbed in small intestine
Absorption ~ All food; 80% electrolytes; most water absorbed in small intestine Most prior to ileum Ileum reclaims bile salts Most absorbed by active transport  blood Exception - lipids © 2013 Pearson Education, Inc.

Absorption of Carbohydrates
Glucose and galactose Secondary active transport (cotransport) with Na+  epithelial cells Move out of epithelial cells by facilitated diffusion  capillary beds in villi Fructose Facilitated diffusion to enter and exit cells © 2013 Pearson Education, Inc.

Absorption of Carbohydrates
Glucose and galactose Secondary active transport (cotransport) with Na+  epithelial cells Move out of epithelial cells by facilitated diffusion  capillary beds in villi Fructose Facilitated diffusion to enter and exit cells © 2013 Pearson Education, Inc. 193

Amino acids transported by several types of carriers
Absorption of Protein Amino acids transported by several types of carriers Most coupled to active transport of Na+ Dipeptides and tripeptides actively absorbed by H+-dependent cotransport; digested to amino acids within epithelial cells Enter capillary blood by diffusion © 2013 Pearson Education, Inc.

Whole proteins not usually absorbed Can be taken up by endocytosis/exocytosis Most common in newborns  food allergies Usually disappear with mucosa maturation Allows IgA antibodies in breast milk to reach infant's bloodstream  passive immunity © 2013 Pearson Education, Inc.

Absorption of Lipids Absorption of monoglycerides and fatty acids
Cluster with bile salts and lecithin to form micelles Released by micelles to diffuse into epithelial cells Combined with lecithin, phospholipids, cholesterol, & coated with proteins to form chylomicrons Enter lacteals; transported to systemic circulation Hydrolyzed to free fatty acids and glycerol by lipoprotein lipase of capillary endothelium Cells can use for energy or stored fat Absorption of short chain fatty acids Diffuse into portal blood for distribution © 2013 Pearson Education, Inc.

Absorption of Vitamins
In small intestine Fat-soluble vitamins (A, D, E, and K) carried by micelles; diffuse into absorptive cells Water-soluble vitamins (vitamin C and B vitamins) absorbed by diffusion or by passive or active transporters. Vitamin B12 (large, charged molecule) binds with intrinsic factor, and is absorbed by endocytosis © 2013 Pearson Education, Inc.

Absorption of Vitamins
In large intestine Vitamin K and B vitamins from bacterial metabolism are absorbed © 2013 Pearson Education, Inc.

Absorption of Electrolytes
Most ions actively along length of small intestine Iron and calcium are absorbed in duodenum Na+ coupled with active absorption of glucose and amino acids Cl– transported actively K+ diffuses in response to osmotic gradients; lost if poor water absorption Usually amount in intestine is amount absorbed © 2013 Pearson Education, Inc.

Absorption of Electrolytes
Iron and calcium absorption related to need Ionic iron stored in mucosal cells with ferritin When needed, transported in blood by transferrin Ca2+ absorption regulated by vitamin D and parathyroid hormone (PTH) © 2013 Pearson Education, Inc.

9 L water, most from GI tract secretions, enter small intestine
Absorption of Water 9 L water, most from GI tract secretions, enter small intestine 95% absorbed in the small intestine by osmosis Most of rest absorbed in large intestine Net osmosis occurs if concentration gradient established by active transport of solutes Water uptake coupled with solute uptake © 2013 Pearson Education, Inc.

Malabsorption of Nutrients
Causes Anything that interferes with delivery of bile or pancreatic juice Damaged intestinal mucosa (e.g., bacterial infection; some antibiotics) © 2013 Pearson Education, Inc.

Malabsorption of Nutrients
Gluten-sensitive enteropathy (celiac disease) Immune reaction to gluten Gluten causes immune cell damage to intestinal villi and brush border Treated by eliminating gluten from diet (all grains but rice and corn) © 2013 Pearson Education, Inc.

Developmental Aspects
Oral membrane  mouth opening Cloacal membrane  anus By week 5 alimentary canal continuous tube from mouth to anus Shortly after, accessory organs bud from mucosa © 2013 Pearson Education, Inc.

Figure 23.36 Embryonic development of the digestive system.
Lung bud Stomodeum Brain Foregut Oral membrane Liver Stomach Heart Site of liver development Bile duct Yolk sac Midgut Spinal cord Gall- bladder Dorsal pancreatic bud Cloacal membrane Hindgut Cystic duct Duodenum Body stalk Ventral pancreatic bud Proctodeum Endoderm © 2013 Pearson Education, Inc.

Fetal nutrition via placenta, but GI tract stimulated to mature by amniotic fluid swallowed in utero Newborn's rooting reflex helps infant find nipple; sucking reflex aids in swallowing Newborns double birth weight in six months; adult diet by 2 years Cholecystitis, ulcers – problems of middle age © 2013 Pearson Education, Inc.

During old age GI tract activity declines, less digestive juice, absorption less efficient, peristalsis slows  less frequent bowel movements Taste/smell less acute; periodontal disease often develops Diverticulosis, fecal incontinence, and cancer of GI tract fairly common © 2013 Pearson Education, Inc.

Stomach and colon cancers rarely have early signs or symptoms
Metastasized colon cancers frequently cause secondary liver cancer Prevention Regular dental and medical examination © 2013 Pearson Education, Inc.

23 The Digestive System.

Similar presentations

Presentation on theme: "23 The Digestive System."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

23 The Digestive System.

Similar presentations

Presentation on theme: "23 The Digestive System."— Presentation transcript:

Similar presentations

About project

Feedback