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PowerPoint® Lecture Slides prepared by Barbara Heard, Atlantic Cape Community College CHAPTER 23 The Digestive System: Part B © Annie Leibovitz/Contact Press Images © 2013 Pearson Education, Inc. Pharynx • Food passes from mouth oropharynx laryngopharynx – Allows passage of food, fluids, and air – Stratified squamous epithelium lining; mucusproducing glands – Skeletal muscle layers: inner longitudinal, outer pharyngeal constrictors © 2013 Pearson Education, Inc. 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. Homeostatic Imbalance • 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. 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. 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. Figure 23.12b Microscopic structure of the esophagus. Mucosa (stratified squamous epithelium) © 2013 Pearson Education, Inc. Esophagus-stomach junction Simple columnar epithelium of stomach Digestive Processes: Mouth • Ingestion • Mechanical digestion – Chewing • Propulsion – Deglutition (swallowing) • Chemical digestion (salivary amylase and lingual lipase) • ~ No absorption, except for few drugs © 2013 Pearson Education, Inc. 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. 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 Esophagus 1 During the buccal phase, the upper esophageal sphincter is contracted. The tongue presses against the hard palate, forcing the food bolus into the oropharynx. 2 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. 4 Peristalsis moves food through the esophagus to the stomach. Relaxed muscles Circular muscles contract Upper esophageal sphincter 3 The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after food enters. Relaxed muscles 5 The gastroesophageal sphincter surrounding the cardial oriface opens, and food enters the stomach. Bolus of food Longitudinal muscles contract Circular muscles contract Gastroesophageal sphincter closed Gastroesophageal sphincter opens Stomach © 2013 Pearson Education, Inc. Bolus Figure 23.13 Deglutition (swallowing). Slide 2 Bolus of food Tongue Pharynx Epiglottis Glottis Trachea © 2013 Pearson Education, Inc. 1 During the buccal phase, the upper esophageal sphincter is contracted. The tongue presses against the hard palate, forcing the food bolus into the oropharynx. Figure 23.13 Deglutition (swallowing). Slide 3 Uvula Bolus Epiglottis Esophagus 2 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. © 2013 Pearson Education, Inc. Figure 23.13 Deglutition (swallowing). Upper esophageal sphincter © 2013 Pearson Education, Inc. Slide 4 Bolus 3 The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after food enters. Figure 23.13 Deglutition (swallowing). Slide 5 4 Peristalsis moves Relaxed muscles food through the esophagus to the stomach. Circular muscles contract Bolus of food Longitudinal muscles contract Gastroesophageal sphincter closed Stomach © 2013 Pearson Education, Inc. Figure 23.13 Deglutition (swallowing). Slide 6 Relaxed muscles 5 The gastroesophageal sphincter surrounding the cardial oriface opens, and food enters the stomach. Circular muscles contract Gastroesophageal sphincter opens © 2013 Pearson Education, Inc. Figure 23.13 Deglutition (swallowing). Slide 7 Bolus of food Tongue Uvula Pharynx Bolus Epiglottis Epiglottis Glottis Trachea Esophagus 1 During the buccal phase, the upper esophageal sphincter is contracted. The tongue presses against the hard palate, forcing the food bolus into the oropharynx. 2 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. 4 Peristalsis moves food through the esophagus to the stomach. Relaxed muscles Circular muscles contract Upper esophageal sphincter 3 The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after food enters. Relaxed muscles 5 The gastroesophageal sphincter surrounding the cardial oriface opens, and food enters the stomach. Bolus of food Longitudinal muscles contract Circular muscles contract Gastroesophageal sphincter closed Gastroesophageal sphincter opens Stomach © 2013 Pearson Education, Inc. Bolus Stomach: Gross Anatomy • In upper left quadrant; temporary storage; chemical digestion of bolus to chyme • Cardial part (cardia) – Surrounds cardial orifice • Fundus – Dome-shaped region beneath diaphragm • Body – Midportion © 2013 Pearson Education, Inc. Stomach: Gross Anatomy • Pyloric part – Antrum (superior portion) pyloric canal pylorus – Pylorus continuous with duodenum through pyloric valve (sphincter controlling stomach emptying) © 2013 Pearson Education, Inc. Figure 23.14a 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 © 2013 Pearson Education, Inc. Pyloric sphincter (valve) at pylorus Pyloric canal Pyloric antrum Figure 23.14b Anatomy of the stomach. Liver (cut) Fundus Body Spleen Lesser curvature Greater curvature © 2013 Pearson Education, Inc. Stomach: Gross Anatomy • 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. 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. 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. 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. Stomach: Gross Anatomy • 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. Figure 23.15a Microscopic anatomy of the stomach. Surface epithelium Mucosa Lamina propria Muscularis mucosae Submucosa (contains submucosal Oblique plexus) layer Muscularis Circular externa layer (contains Longitudinal myenteric layer plexus) Stomach wall Serosa 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. 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 © 2013 Pearson Education, Inc. Enlarged view of gastric pits and gastric glands Gastric Glands • Cell types – Mucous neck cells (secrete thin, acidic mucus of unknown function) – Parietal cells – Chief cells – Enteroendocrine cells © 2013 Pearson Education, Inc. Figure 23.15c Microscopic anatomy of the stomach. Pepsinogen Pepsin HCI Mitochondria Parietal cell Chief cell Enteroendocrine cell © 2013 Pearson Education, Inc. Location of the HCl-producing parietal cells and pepsin-secreting chief cells in a gastric gland 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. Gastric Gland Secretions • Chief cell secretions – Pepsinogen - inactive enzyme • Activated to pepsin by HCl and by pepsin itself (a positive feedback mechanism) – Lipases • Digest ~15% of lipids © 2013 Pearson Education, Inc. Gastric Gland Secretions • 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. Mucosal Barrier • 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. Homeostatic Imbalance • 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. Figure 23.16 Photographs of a gastric ulcer and the H. pylori bacteria that most commonly cause it. Bacteria Mucosa layer of stomach A gastric ulcer lesion © 2013 Pearson Education, Inc. H. pylori bacteria Digestive Processes in the Stomach • Physical digestion • Denaturation of proteins by HCl • Enzymatic digestion of proteins by pepsin (and milk protein by rennin in infants) • Lingual lipase digests some triglycerides before digested as any other protein • 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 ® 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. Regulation of Gastric Secretion • 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 secondmessenger systems – All three are necessary for maximum HCl secretion © 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. Figure 23.19 Deglutition (swallowing). Pyloric valve closed 1 Propulsion: Peristaltic waves move from the fundus toward the pylorus. © 2013 Pearson Education, Inc. Slide 1 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 23.19 Deglutition (swallowing). Pyloric valve closed 1 Propulsion: Peristaltic waves move from the fundus toward the pylorus. © 2013 Pearson Education, Inc. Slide 2 Figure 23.19 Deglutition (swallowing). Pyloric valve closed 1 Propulsion: Peristaltic waves move from the fundus toward the pylorus. © 2013 Pearson Education, Inc. Slide 3 Pyloric valve closed 2 Grinding: The most vigorous peristalsis and mixing action occur close to the pylorus. Figure 23.19 Deglutition (swallowing). Pyloric valve closed 1 Propulsion: Peristaltic waves move from the fundus toward the pylorus. © 2013 Pearson Education, Inc. Slide 4 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. 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. Figure 23.20 Neural and hormonal factors that inhibit gastric emptying. Presence of fatty, hypertonic, acidic chyme in duodenum Duodenal enteroendocrine cells Chemoreceptors and stretch receptors Secrete Enterogastrones (secretin, cholecystokinin, vasoactive intestinal peptide) Target Via short reflexes Enteric neurons Duodenal stimuli decline Via long reflexes CNS centers sympathetic activity; parasympathetic activity Contractile force and rate of stomach emptying decline © 2013 Pearson Education, Inc. Initial stimulus Stimulate Physiological response Inhibit Result Homeostatic Imbalance • 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. Figure 23.1 Alimentary canal and related accessory digestive organs. Mouth (oral cavity) Tongue* Parotid gland Sublingual gland Submandibular gland Salivary glands* Pharynx Esophagus Stomach Pancreas* (Spleen) Liver* Gallbladder* Transverse colon Small intestine Anus © 2013 Pearson Education, Inc. Duodenum Jejunum Ileum Descending colon Ascending colon Cecum Sigmoid colon Rectum Appendix Anal canal Large intestine 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. Figure 23.21 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 © 2013 Pearson Education, Inc. Main pancreatic duct and sphincter Duodenum Head of pancreas Jejunum and Ileum • Jejunum – 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 intesting • 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. 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 Circular folds Villi © 2013 Pearson Education, Inc. Lumen Figure 23.22b Structural modifications of the small intestine that increase its surface area for digestion and absorption. Microvilli (brush border) Absorptive cells Lacteal Goblet cell Blood capillaries Mucosaassociated lymphoid tissue Intestinal crypt Muscularis mucosae Duodenal gland © 2013 Pearson Education, Inc. Villus Enteroendocrine cells Venule Lymphatic vessel Submucosa Figure 23.22c Structural modifications of the small intestine that increase its surface area for digestion and absorption. Absorptive cells Goblet cells Villi © 2013 Pearson Education, Inc. Intestinal crypt Figure 23.23 Microvilli of the small intestine. Mucus granules Microvilli forming the brush border Absorptive cell © 2013 Pearson Education, Inc. 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. Homeostatic Imbalance • Chemotherapy targets rapidly dividing cells – Kills cancer cells – Kills rapidly dividing GI tract epithelium nausea, vomiting, diarrhea © 2013 Pearson Education, Inc. 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. 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. Liver • Largest gland in body • Four lobes—right, left, caudate, and quadrate © 2013 Pearson Education, Inc. 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. Figure 23.24a Gross anatomy of the human liver. Sternum Nipple Bare area Liver Falciform ligament Left lobe of liver Right lobe of liver Gallbladder © 2013 Pearson Education, Inc. Round ligament (ligamentum teres) Figure 23.24b Gross anatomy of the human liver. Lesser omentum (in fissure) Left lobe of liver Porta hepatis containing hepatic artery (left) and hepatic portal vein (right) Quadrate lobe of liver Ligamentum teres Bare area Caudate lobe of liver Sulcus for inferior vena cava Hepatic vein (cut) Bile duct (cut) Right lobe of liver 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. Figure 23.21 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 © 2013 Pearson Education, Inc. Main pancreatic duct and sphincter Duodenum Head of pancreas 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. Figure 23.25a–b Microscopic anatomy of the liver. Lobule © 2013 Pearson Education, Inc. Central Connective vein tissue septum Liver: Microscopic Anatomy • 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 • Kupffer cells (hepatic or stellate macrophages) in liver sinusoids remove debris & old RBCs © 2013 Pearson Education, Inc. Figure 23.25c Microscopic anatomy of the liver. Interlobular veins (to hepatic vein) Central vein Sinusoids Bile canaliculi Plates of hepatocytes Bile duct (receives bile from bile canaliculi) Fenestrated lining (endothelial cells) of sinusoids Stellate macrophages in sinusoid walls Portal vein © 2013 Pearson Education, Inc. Bile duct Portal venule Portal arteriole Portal triad Liver: Microscopic Anatomy • 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. Liver • Regenerative capacity – Restores full size in 6-12 months after 80% removal – Injury hepatocytes growth factors endothelial cell proliferation © 2013 Pearson Education, Inc. Homeostatic Imbalance • 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. 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, neutral fats, phospholipids, and electrolytes © 2013 Pearson Education, Inc. Bile • Enterohepatic circulation – Recycles bile salts – Bile salts duodenum reabsorbed from ileum hepatic portal blood liver secreted into bile © 2013 Pearson Education, Inc. 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. 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.