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Chapter 23A Digestive System Slides by Barbara Heard and W. Rose.
HESC310 4/19/2017 Chapter 23A Digestive System Slides by Barbara Heard and W. Rose. figures from Marieb & Hoehn 9th ed. Portions copyright Pearson Education Axial Skeleton
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Introduction/Overview Functional Anatomy
HESC310 4/19/2017 Ch. 23: Digestive System Introduction/Overview Functional Anatomy Physiology of Digestion & Absorption Axial Skeleton
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Digestive System Introduction/Overview Functional Anatomy
HESC310 4/19/2017 Digestive System Introduction/Overview Digestive System Organs Digestive Processes Basic Concepts Relations & Common Features of Digestive Organs Functional Anatomy Physiology of Digestion & Absorption Axial Skeleton
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Digestive System Organs (Fig 23.1)
HESC310 4/19/2017 Digestive System Organs (Fig 23.1) Alimentary Canal = path through Mouth to anus Digests food and absorbs fragments Mouth, pharynx, esophagus, stomach, small intestine, and large intestine Accessory organs = "off-to-the-side" helpers Teeth, tongue, gallbladder Digestive glands Salivary glands Liver Pancreas Axial Skeleton
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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.
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Six essential activities
Digestive Processes Six essential activities Ingestion Propulsion Mechanical breakdown Digestion Absorption Defecation © 2013 Pearson Education, Inc.
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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.
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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.
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© 2013 Pearson Education, Inc.
Basic Concepts Gut lumen is "outside" Digestion control mechanisms try to control chemical environment in lumen to optimize absorption Digestion is provoked by mechanical & chemical stimuli (sensors in walls): stretch, pH, osmolarity, which can cause secretion and propulsion via reflexes (Fig. 23.4) Control by local as well as remote reflexes (Fig 23.4) Short reflexes: via enteric nerve plexus Long: via CNS © 2013 Pearson Education, Inc.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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© 2013 Pearson Education, Inc.
Histology: all alimentary canal organs have same basic 4 layers From lumen out (Fig 23.6): Mucosa = mucous membrane = epithelial layer of cells Secrete: mucus, digestive enz, hormones Absorb broken down compounds into blood Protect against infection Submucosa Connective tissie with blood vessels & lymphatics for absorption, lymph nodes, elastic fibers (shape retention) Muscularis externa Inner circular muscles Outer longitudinal muscles Serosa The peritoneum already mentioned © 2013 Pearson Education, Inc.
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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.
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Enteric nervous system
Submucosal plexus In submucosa Controls glandular secretions & thin submucosal muscular layer Myenteric nerve plexus Between circular & longitudinal muscle layers Controls GI tract motility © 2013 Pearson Education, Inc.
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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.
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