Transcript Document
Figure 22.17 Neural and hormonal mechanisms that regulate release of gastric juice. Inhibitory events Stimulatory events Cephalic phase 1 Sight and thought of food Cerebral cortex Conditioned reflex 2 Stimulation of taste and smell receptors Gastric phase 1 Stomach distension activates stretch receptors Hypothalamus and medulla oblongata Vagovagal reflexes Intestinal phase Stimulate Inhibit © 2014 Pearson Education, Inc. Vagus nerve Vagus nerve Local reflexes 2 Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors 1 Presence of partially digested foods in duodenum or distension of the duodenum when stomach begins to empty Medulla Lack of stimulatory impulses to parasympathetic center G cells Intestinal (enteric) gastrin release to blood Gastrin release to blood Gastrin secretion declines G cells Overrides parasympathetic controls Sympathetic nervous system activation 1 Loss of appetite, depression 1 Excessive acidity (pH < 2) in stomach 2 Emotional stress Stomach secretory activity Enterogastric reflex Brief effect Cerebral cortex Local reflexes Vagal nuclei in medulla Pyloric sphincter Release of enterogastrones (secretin, cholecystokinin, vasoactive intestinal peptide) 1 Distension of duodenum; presence of fatty, acidic, or hypertonic chyme; and/or irritants in the duodenum 2 Distension; presence of fatty, acidic, partially digested food in the duodenum Figure 22.17 Neural and hormonal mechanisms that regulate release of gastric juice. Inhibitory events Stimulatory events Cephalic phase 1 Sight and thought of food Cerebral cortex Conditioned reflex 2 Stimulation of taste and smell receptors Gastric phase 1 Stomach distension activates stretch receptors Hypothalamus and medulla oblongata Vagovagal reflexes Intestinal phase Stimulate Inhibit © 2014 Pearson Education, Inc. Vagus nerve Vagus nerve Local reflexes 2 Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors 1 Presence of partially digested foods in duodenum or distension of the duodenum when stomach begins to empty Medulla Lack of stimulatory impulses to parasympathetic center G cells Intestinal (enteric) gastrin release to blood Gastrin release to blood Gastrin secretion declines G cells Overrides parasympathetic controls Sympathetic nervous system activation 1 Loss of appetite, depression 1 Excessive acidity (pH < 2) in stomach 2 Emotional stress Stomach secretory activity Enterogastric reflex Brief effect Cerebral cortex Local reflexes Vagal nuclei in medulla Pyloric sphincter Release of enterogastrones (secretin, cholecystokinin, vasoactive intestinal peptide) 1 Distension of duodenum; presence of fatty, acidic, or hypertonic chyme; and/or irritants in the duodenum 2 Distension; presence of fatty, acidic, partially digested food in the duodenum Figure 22.15b Microscopic anatomy of the stomach. Gastric pits Surface epithelium (mucous cells) Gastric pit Mucous neck cells Parietal cell Gastric gland Chief cell Enteroendocrine cell © 2014 Pearson Education, Inc. Enlarged view of gastric pits and gastric glands Figure 22.15c Microscopic anatomy of the stomach. Pepsinogen HCI Pepsin Mitochondria Parietal cell Chief cell Enteroendocrine cell Location of the HCl-producing parietal cells and pepsin-secreting chief cells in a gastric © 2014 Pearson Education, Inc. gland Figure 22.18 Mechanism of HCl secretion by parietal cells. Gastric gland Blood capillary CO2 Chief cell Stomach lumen CO2 + H2O H+-K+ ATPase H2CO3 Carbonic anhydrase H+ K+ HCO3− Alkaline tide Parietal cell H+ K+ HCI HCO3− Cl− Interstitial fluid © 2014 Pearson Education, Inc. HCO3−- Cl− antiporter Cl− Cl− Figure 22.15c Microscopic anatomy of the stomach. Pepsinogen HCI Pepsin Mitochondria Parietal cell Chief cell Enteroendocrine cell Location of the HCl-producing parietal cells and pepsin-secreting chief cells in a gastric © 2014 Pearson Education, Inc. gland Figure 22.16 Photographs of a gastric ulcer and the H. pylori bacteria that most commonly cause it. Bacteria Mucosa layer of stomach A gastric ulcer lesion © 2014 Pearson Education, Inc. H. pylori bacteria Figure 22.17 Neural and hormonal mechanisms that regulate release of gastric juice. Inhibitory events Stimulatory events Cephalic phase 1 Sight and thought of food Cerebral cortex Conditioned reflex 2 Stimulation of taste and smell receptors Gastric phase 1 Stomach distension activates stretch receptors Hypothalamus and medulla oblongata Vagovagal reflexes Intestinal phase Stimulate Inhibit © 2014 Pearson Education, Inc. Vagus nerve Vagus nerve Local reflexes 2 Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors 1 Presence of partially digested foods in duodenum or distension of the duodenum when stomach begins to empty Medulla Lack of stimulatory impulses to parasympathetic center G cells Intestinal (enteric) gastrin release to blood Gastrin release to blood Gastrin secretion declines G cells Overrides parasympathetic controls Sympathetic nervous system activation 1 Loss of appetite, depression 1 Excessive acidity (pH < 2) in stomach 2 Emotional stress Stomach secretory activity Enterogastric reflex Brief effect Cerebral cortex Local reflexes Vagal nuclei in medulla Pyloric sphincter Release of enterogastrones (secretin, cholecystokinin, vasoactive intestinal peptide) 1 Distension of duodenum; presence of fatty, acidic, or hypertonic chyme; and/or irritants in the duodenum 2 Distension; presence of fatty, acidic, partially digested food in the duodenum Figure 22.14a Anatomy of the stomach. Cardia Fundus Esophagus Muscularis externa • Longitudinal layer • Circular layer • Oblique layer Serosa Body Lumen Lesser curvature Rugae of mucosa Greater curvature Duodenum © 2014 Pearson Education, Inc. Pyloric sphincter (valve) at pylorus Pyloric canal Pyloric antrum Figure 22.19 Peristaltic waves in the stomach. Pyloric valve closed 1 Propulsion: Peristaltic waves move from the fundus toward the pylorus. © 2014 Pearson Education, Inc. Pyloric valve closed 2 Grinding: The most vigorous peristalsis and mixing action occur close to the pylorus. Pyloric valve slightly opened 3 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. Figure 22.30c Mesenteries of the abdominal digestive organs. Greater omentum Transverse colon Transverse mesocolon Descending colon Jejunum Mesentery Sigmoid mesocolon Sigmoid colon Ileum © 2014 Pearson Education, Inc. Figure 22.22a Structural modifications of the small intestine that increase its surface area for digestion and absorption. Vein carrying blood to hepatic portal vessel Muscle layers Circular folds Villi © 2014 Pearson Education, Inc. Lumen Figure 22.22b 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 Mucosaassociated lymphoid tissue Intestinal crypt Muscularis mucosae Duodenal gland © 2014 Pearson Education, Inc. Enteroendocrine cells Venule Lymphatic vessel Submucosa Figure 22.22c Structural modifications of the small intestine that increase its surface area for digestion and absorption. Absorptive cells Goblet cells Villi © 2014 Pearson Education, Inc. Intestinal crypt Figure 22.21 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 Jejunum Gallbladder Major duodenal papilla Hepatopancreatic ampulla and sphincter © 2014 Pearson Education, Inc. Main pancreatic duct and sphincter Duodenum Head of pancreas Figure 22.28 Mechanisms promoting secretion and release of bile and pancreatic juice. 1 Chyme enter -ing duodenum causes duodenal enteroendocrine cells to release cholecystokinin (CCK) and secretin. 2 CCK (red dots) and secretin (yellow dots) enter the bloodstream. 3 CCK induces secretion of enzyme-rich pancreatic juice. Secretin causes secretion of HCO3− -rich pancreatic juice. © 2014 Pearson Education, Inc. 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. 6 During cephalic and gastric phases, vagal Nerve stimulates gallbladder to contract weakly. CCK secretion Secretin secretion Figure 22.29a Gross anatomy of the large intestine. Left colic (splenic) flexure Transverse mesocolon Right colic (hepatic) flexure Transverse colon Epiploic appendages Superior mesenteric artery Haustrum Descending colon Ascending colon IIeum Cut edge of mesentery IIeocecal valve Tenia coli Sigmoid colon Cecum Appendix Rectum Anal canal © 2014 Pearson Education, Inc. External anal sphincter Figure 22.29b 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 © 2014 Pearson Education, Inc. Figure 22.31 Defecation reflex. Impulses from cerebral cortex (conscious control) Sensory nerve fibers Voluntary motor nerve to external anal sphincter Sigmoid colon Rectum External anal sphincter (skeletal muscle) Stretch receptors in wall 2 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. Involuntary motor nerve (parasympathetic division) Internal anal sphincter (smooth muscle) 3 If it is convenient to defecate, voluntary motor neurons are inhibited, allowing the external anal sphincter to relax so feces may pass. © 2014 Pearson Education, Inc. 1 Feces move into and distend the rectum, stimulating stretch receptors there. The receptors transmit signals along afferent fibers to spinal cord neurons.