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PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 23 The Digestive System:

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Presentation on theme: "PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 23 The Digestive System:"— Presentation transcript:

1 PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 23 The Digestive System: Part B

2 Copyright © 2010 Pearson Education, Inc. Pharynx Oropharynx and laryngopharynx Allow passage of food, fluids, and air Stratified squamous epithelium lining Skeletal muscle layers: inner longitudinal, outer pharyngeal constrictors

3 Copyright © 2010 Pearson Education, Inc. Esophagus Flat muscular tube from laryngopharynx to stomach Pierces diaphragm at esophageal hiatus Joins stomach at the cardiac orifice

4 Copyright © 2010 Pearson Education, Inc. Esophagus Esophageal mucosa contains stratified squamous epithelium Changes to simple columnar at the stomach Esophageal glands in submucosa secrete mucus to aid in bolus movement Muscularis: skeletal superiorly; smooth inferiorly Adventitia instead of serosa

5 Copyright © 2010 Pearson Education, Inc. Figure 23.12a Mucosa (contains a stratified squamous epithelium) Submucosa (areolar connective tissue) Lumen Muscularis externa Adventitia (fibrous connective tissue) (a) Circular layer Longitudinal layer

6 Copyright © 2010 Pearson Education, Inc. Figure 23.12b Mucosa (contains a stratified squamous epithelium) (b)

7 Copyright © 2010 Pearson Education, Inc. Go to GI Diseases (Esophagus)

8 Copyright © 2010 Pearson Education, Inc. Digestive Processes: Mouth Ingestion Mechanical digestion Mastication is partly voluntary, partly reflexive Chemical digestion (salivary amylase and lingual lipase) Propulsion Deglutition (swallowing)

9 Copyright © 2010 Pearson Education, Inc. Deglutition Involves the tongue, soft palate, pharynx, esophagus, and 22 muscle groups Buccal phase Voluntary contraction of the tongue Pharyngeal-esophageal phase Involuntary Control center in the medulla and lower pons

10 Copyright © 2010 Pearson Education, Inc. Figure 23.13 Tongue Trachea Pharynx Epiglottis Glottis Bolus of food Epiglottis Esophagus Uvula Bolus Relaxed muscles Circular muscles contract Bolus of food Longitudinal muscles contract Stomach Relaxed muscles Gastroesophageal sphincter opens Gastroesophageal sphincter closed Upper esophageal sphincter is contracted. During the buccal phase, the tongue presses against the hard palate, forcing the food bolus into the oropharynx where the involuntary phase begins. Food is moved through the esophagus to the stomach by peristalsis. The gastroesophageal sphincter opens, and food enters the stomach. The uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after entry. 12 4 3 5

11 Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 1 Tongue Trachea Pharynx Epiglottis Glottis Bolus of food Upper esophageal sphincter is contracted. During the buccal phase, the tongue presses against the hard palate, forcing the food bolus into the oropharynx where the involuntary phase begins. 1

12 Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 3 Bolus The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after entry. 3

13 Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 2 Epiglottis Esophagus Uvula Bolus The uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. 2

14 Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 4 Relaxed muscles Bolus of food Stomach Circular muscles contract Longitudinal muscles contract Gastroesophageal sphincter closed Food is moved through the esophagus to the stomach by peristalsis. 4

15 Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 5 Relaxed muscles Gastroesophageal sphincter opens The gastroesophageal sphincter opens, and food enters the stomach. 5

16 Copyright © 2010 Pearson Education, Inc. Figure 23.13 Tongue Trachea Pharynx Epiglottis Glottis Bolus of food Epiglottis Esophagus Uvula Bolus Relaxed muscles Circular muscles contract Bolus of food Longitudinal muscles contract Stomach Relaxed muscles Gastroesophageal sphincter opens Gastroesophageal sphincter closed Upper esophageal sphincter is contracted. During the buccal phase, the tongue presses against the hard palate, forcing the food bolus into the oropharynx where the involuntary phase begins. Food is moved through the esophagus to the stomach by peristalsis. The gastroesophageal sphincter opens, and food enters the stomach. The uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after entry. 12 4 3 5

17 Copyright © 2010 Pearson Education, Inc. Stomach: Gross Anatomy Cardiac region (cardia) Surrounds the cardiac orifice Fundus Dome-shaped region beneath the diaphragm Body Midportion

18 Copyright © 2010 Pearson Education, Inc. Stomach: Gross Anatomy Cardiac region (cardia) Surrounds the cardiac orifice Fundus Dome-shaped region beneath the diaphragm Body Midportion

19 Copyright © 2010 Pearson Education, Inc. Stomach: Gross Anatomy Pyloric region: antrum, pyloric canal, and pylorus Pylorus is continuous with the duodenum through the pyloric valve (sphincter) Greater curvature Convex lateral surface Lesser curvature Concave medial surface

20 Copyright © 2010 Pearson Education, Inc. Figure 23.14a Cardia Esophagus Pyloric sphincter (valve) at pylorus Pyloric canal Pyloric antrum Rugae of mucosa Body Lumen Serosa Fundus Lesser curvature Greater curvature Muscularis externa Longitudinal layer Circular layer Oblique layer (a) Duodenum

21 Copyright © 2010 Pearson Education, Inc. Stomach: Gross Anatomy Lesser omentum From the liver to the lesser curvature Greater omentum Drapes from greater curvature Anterior to the small intestine The omenta have fat deposits and lots of lymph nodes. The immune cells and macrophages in the omenta police the peritoneal cavity. The omenta can wall off peritoneal infections.

22 Copyright © 2010 Pearson Education, Inc. Greater and Lesser Omentums

23 Copyright © 2010 Pearson Education, Inc. ANS nerve supply to stomach Sympathetic via splanchnic nerves and celiac plexus Parasympathetic via vagus nerve

24 Copyright © 2010 Pearson Education, Inc. Blood supply to Stomach Celiac trunk – branches go to liver, stomach, spleen, pancreas Veins of the hepatic portal system

25 Copyright © 2010 Pearson Education, Inc. Figure 19.29c (c) The hepatic portal circulation. Hepatic veins Liver Spleen Gastric veins Inferior vena cava (not part of hepatic portal system) Splenic vein Right gastroepiploic vein Inferior mesenteric vein Superior mesenteric vein Large intestine Hepatic portal vein Small intestine Rectum

26 Copyright © 2010 Pearson Education, Inc. Figure 19.24a (a) Schematic flowchart. Abdominal aorta Inferior phrenic arteries Celiac trunk Superior mesenteric artery Middle suprarenal arteries Renal arteries Inferior mesenteric artery Lumbar arteries Median sacral artery Superior rectal artery L. colic artery Sigmoidal arteries R. colic artery L. gastroepiploic artery R. gastroepiploic artery Ileocolic artery Intestinal arteries Common iliac arteries Gonadal arteries Gastro- duodenal artery Hepatic artery proper Common hepatic artery Splenic artery R. gastric artery L. gastric artery L Middle colic artery R Diaphragm Celiac Trunk

27 Copyright © 2010 Pearson Education, Inc. Figure 19.24b Liver (cut)Diaphragm Esophagus Left gastric artery Superior mesenteric Left gastroepiploic artery Spleen Stomach Pancreas (major portion lies posterior to stomach) Splenic artery Inferior vena cava Celiac trunk Hepatic artery proper Common hepatic artery Gastroduodenal artery Right gastric artery Gallbladder Abdominal aorta Right gastroepiploic artery Duodenum (b) The celiac trunk and its major branches. The left half of the liver has been removed.

28 Copyright © 2010 Pearson Education, Inc. Figure 23.30a Falciform ligament Liver Gallbladder Spleen Stomach Ligamentum teres Greater omentum Small intestine Cecum (a) The Ligamentum Teres Hepatis is the remnant of the umbilical vein

29 Copyright © 2010 Pearson Education, Inc. Stomach: Microscopic Anatomy Four tunics Muscularis and mucosa are modified Muscularis externa Three layers of smooth muscle Inner oblique layer allows stomach to churn, mix, move, and physically break down food

30 Copyright © 2010 Pearson Education, Inc. Figure 23.30b Liver Lesser omentum Gallbladder Stomach Duodenum Transverse colon Small intestine Cecum Urinary bladder (b)

31 Copyright © 2010 Pearson Education, Inc. Figure 23.15a Mucosa Surface epithelium Lamina propria Muscularis mucosae Oblique layer Circular layer Longitudinal layer Serosa (a) Layers of the stomach wall (l.s.) Stomach wall Muscularis externa (contains myenteric plexus) Submucosa (contains submucosal plexus)

32 Copyright © 2010 Pearson Education, Inc. Stomach: Microscopic Anatomy Mucosa Simple columnar epithelium composed of mucous cells – they produce a cloudy two layer coat of alkaline mucus which the surface layer consists of a viscous-insoluble mucus that traps bicarbonate-rich fluid beneath it The smooth lining is lined with dotted Gastric pits that lead into gastric glands that produce the various gastric juices

33 Copyright © 2010 Pearson Education, Inc. The cells forming the walls of the gastric pits are primarily mucous cells – but the gastric gland cells differ in the different regions of the stomach. Cardia (entrance) and pylorus (exit) are primarily mucus secreting cells Pyloric Antrum produce mucus and hormones (enteroendocrine cells) Fundus and body – where most chemical digestion occurs produce the majority of stomach secretions

34 Copyright © 2010 Pearson Education, Inc. Figure 23.15b (b) Enlarged view of gastric pits and gastric glands Mucous neck cells Parietal cell Surface epithelium (mucous cells) Gastric pits Chief cell Enteroendocrine cell Gastric pit Gastric gland

35 Copyright © 2010 Pearson Education, Inc. Gastric Glands Cell types Mucous neck cells (secrete thin, acidic mucus) Parietal cells Chief cells Enteroendocrine cells

36 Copyright © 2010 Pearson Education, Inc. Figure 23.15c (c) Location of the HCl-producing parietal cells and pepsin-secreting chief cells in a gastric gland Pepsinogen Mitochondria Pepsin HCl Chief cell Enteroendocrine cell Parietal cell

37 Copyright © 2010 Pearson Education, Inc. Gastric Gland Secretions Glands in the fundus and body produce most of the gastric juice Parietal cell secretions HCl  pH 1.5–3.5 denatures protein in food, activates pepsin, and kills many bacteria Intrinsic factor Glycoprotein required for absorption of vitamin B 12 in small intestine

38 Copyright © 2010 Pearson Education, Inc. Gastric Gland Secretions Chief cell secretions Inactive enzyme pepsinogen Activated to pepsin by HCl and by pepsin itself (a positive feedback mechanism) Chief cells also secrete insignificant amounts of gastric lipase

39 Copyright © 2010 Pearson Education, Inc. Gastric Gland Secretions Enteroendocrine cells Secrete chemical messengers into the lamina propria Paracrines Serotonin and histamine Hormones Somatostatin and gastrin

40 Copyright © 2010 Pearson Education, Inc. Mucosal Barrier Layer of bicarbonate-rich mucus Tight junctions between epithelial cells Damaged epithelial cells are quickly replaced by division of stem cells – that reside where the gastric pits join the gastric glands. The surface epithelia are replaced every three to six days

41 Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalance Gastritis: inflammation caused by anything that breaches the mucosal barrier Peptic or gastric ulcers: erosion of the stomach wall Most are caused by Helicobacter pylori bacteria Go to GI Diseases PowerPoint

42 Copyright © 2010 Pearson Education, Inc. Figure 23.16 Bacteria Mucosa layer of stomach (a) A gastric ulcer lesion (b) H. pylori bacteria

43 Copyright © 2010 Pearson Education, Inc. Digestive Processes in the Stomach Physical digestion Denaturation of proteins Enzymatic digestion of proteins by pepsin (and rennin in infants) Secretes intrinsic factor required for absorption of vitamin B 12 Lack of intrinsic factor  pernicious anemia Delivers chyme to the small intestine

44 Copyright © 2010 Pearson Education, Inc. Regulation of Gastric Secretion Gastric Secretion has three phases – (1) Cephalic (2) Gastric and (3) Intestinal. Some are more stimulatory – Cephalic and Gastric and one is more inhibitory – Intestinal Phase Neural (vagus and enteric plexus) and hormonal mechanisms control the secretions 1.Cephalic (reflex) phase: last just a few minutes prior to food entry into the stomach. It occurs even if you don’t actually get the food – if you desire the food and are not depressed or have a lack of appetite

45 Copyright © 2010 Pearson Education, Inc. Gastric Phase Lasts approximately 3–4 hours after food enters the stomach Stimuli for this phase is gastric distention, peptides, and low acidity Gastric Distention activates stretch receptors and initiates both local (myenteric) reflexes and vagovagal – both stimulate acetylcholine release

46 Copyright © 2010 Pearson Education, Inc. Gastrin (1) Gastrin is secreted by G-cells in the Pyloric Antrum in accordance with chemical stimuli and neural stimuli The chemical stimuli for Gastrin secretion are partially digested proteins, caffeine, and rising alkaline pH. High acidity less than a pH of 2 inhibits Gastrin secretion Gastric stimulates release of enzymes, also Histamine from the enterochromaffin cells – but its main targets are the Parietal cells in body of the stomach that secrete HCl- prodding them to secrete increased amounts of HCl

47 Copyright © 2010 Pearson Education, Inc. Gastrin (2) When protein products enter the stomach, the pH generally rises due to the proteins buffering H+. The rising pH stimulates Gastrin which causes HCl to spew out thus denaturing the proteins. The more proteins the more Gastrin. As proteins are decomposed the acidity rises and Gastrin is inhibited

48 Copyright © 2010 Pearson Education, Inc. Gastrin (3) In addition to G-cells being stimulated chemically – they are also stimulated neurally. The parasympathetic turns on secretion via acetylcholine from the Vagus and Sympathetic turns it off The vagus was activated in the Cephalic Phase and Gastric Phase due to stomach distention Emotional upset, fear, anxiety, and anything that triggers the fight and flight response turns off Gastric secretion.

49 Copyright © 2010 Pearson Education, Inc. Figure 23.17 Presence of low pH, partially digested foods, fats, or hypertonic solution in duodenum when stomach begins to empty Distension; presence of fatty, acidic, partially digested food in the duodenum Brief effect Intestinal (enteric) gastrin release to blood Entero- gastric reflex Release of intestinal hormones (secretin, cholecystokinin, vasoactive intestinal peptide) Local reflexes Vagal nuclei in medulla Pyloric sphincter Stimulate Inhibit 1 1 2 Stomach secretory activity Sight and thought of food Stomach distension activates stretch receptors Stimulation of taste and smell receptors Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors Loss of appetite, depression Emotional upset Lack of stimulatory impulses to parasym- pathetic center Cerebral cortex Cerebral cortex Conditioned reflex Vagovagal reflexes Local reflexes Medulla G cells Hypothalamus and medulla oblongata Vagus nerve Vagus nerve Gastrin release to blood Gastrin secretion declines G cells Overrides parasym- pathetic controls Sympathetic nervous system activation 1 1 1 1 2 2 2 Stimulatory eventsInhibitory events Cephalic phase Gastric phase Intestinal phase Excessive acidity (pH <2) in stomach Distension of duodenum; presence of fatty, acidic, hypertonic chyme, and/or irritants in the duodenum

50 Copyright © 2010 Pearson Education, Inc. Regulation and Mechanism of HCl Secretion Three chemicals (ACh, histamine, and gastrin) stimulate parietal cells through second-messenger systems All three are necessary for maximum HCl secretion Antihistamines block H 2 receptors and decrease HCl release

51 Copyright © 2010 Pearson Education, Inc. Secondary Messenger Systems for HCl release Acetylcholine and Gastrin increase intracellular Calcium levels. Histamine released by the enterochromaffin- like cells in response to Gastrin and to a lesser extent by Ach acts through the cyclic AMP system.

52 Copyright © 2010 Pearson Education, Inc. Figure 23.18 Stomach lumenChief cell Parietal cell Inter- stitial fluid Carbonic anhydrase Alkaline tide HCO 3 – Blood capillary CO 2 Cl – CO 2 + H 2 O H 2 CO 3 HCO 3 – - Cl – antiporter HCO 3 – H+H+ Cl – l K+K+ K+K+ H+H+ H + -K + ATPase HCI

53 Copyright © 2010 Pearson Education, Inc. Regulation of Gastric Secretion 3.Intestinal phase: brief stimulatory effect as partially digested food enters the duodenum, followed by inhibitory effects (enterogastric reflex and enterogastrones) Some actions are excitatory and some are inhibitory As partially digested foods fill the initial part of the small intestine (duodenum). This action stimulates the release of intestinal Gastrin. This stimulates the stomach to continue its secretory activity. However, this action is brief.

54 Copyright © 2010 Pearson Education, Inc. The action is brief due to the fact that as the intestines fill with chyme containing large amounts of H+, fats, partially digested proteins and various irritating substances, the inhibitory component is triggered in the form of the enterogastric reflex The enterogastric reflex is a trio of reflexes that (1) inhibit the vagal nuclei in the medulla (2) inhibit local reflexes and (3) activate sympathetic fibers that cause the pyloric sphincter to tighten and prevent further food entry. The purpose of this inhibitory action is to not fill the duodenum with excess acidity and match the small intestines processing time. Additionally there is a release of several intestinal hormones – termed enterogastrones (Secretin, Cholecystokinin, and Vasoactive Intestinal Peptide). All are inhibitory on the stomach.

55 Copyright © 2010 Pearson Education, Inc. Response of the Stomach to Filling Stretches to accommodate incoming food Reflex-mediated receptive relaxation Coordinated by the swallowing center of the brain stem and mediated by the vagus nerves acting on Serotonin and Nitric Oxide releasing enteric neurons Gastric accommodation Plasticity (stress-relaxation response) of smooth muscle

56 Copyright © 2010 Pearson Education, Inc. Small rippling waves in the body and fundus of stomach where good (food storage) chemical digestion occur Waves get stronger in pyloric antrum. The pyloric region which holds about 30 cc of chyme acts as a dynamic filter that allows only liquids and small particles to pass through the barely open pyloric valve during the digestive process. Normally each peristaltic wave reaching the pyloric muscle squirts only 3 cc or less of chyme into the small intestines. Because the contraction also closes the pyloric valve, which is normally partially relaxed, the rest (27 cc) goes back into the stomach to be better mixed.

57 Copyright © 2010 Pearson Education, Inc. Gastric Contractile Activity The intensity of peristaltic waves can be changed but the rate is constant – about 3 waves per minute. Pacemaker cells (cells of Cajal) located in the longitudinal muscle layer – automatically depolarize and repolarize setting the cyclic slow waves – also known as the Basic electrical rhythm (BER) The smooth muscle cells are connected by gap junctions to the rest of muscularis – the waves are efficiently transmitted.

58 Copyright © 2010 Pearson Education, Inc. The pacemakers set the maximum rate of contraction, but they do not initiate the contractions or regulate the force. They generate subthreshold depolarization waves, which are then ignited (enhanced by further depolarization and brought to threshold) by neural and hormonal factors. Factors that increase the strength of contractions are the same factors that enhance stomach secretions.

59 Copyright © 2010 Pearson Education, Inc. Gastric Contractile Activity Most vigorous near the pylorus Chyme is either Delivered in ~ 3 ml spurts to the duodenum, or Forced backward into the stomach

60 Copyright © 2010 Pearson Education, Inc. Figure 23.19 1 Propulsion: Peristaltic waves move from the fundus toward the pylorus. 23 Grinding: The most vigorous peristalsis and mixing action occur close to the pylorus. Retropulsion: The pyloric end of the stomach acts as a pump that delivers small amounts of chyme into the duodenum, simultaneously forcing most of its contained material backward into the stomach. Pyloric valve closed Pyloric valve closed Pyloric valve slightly opened

61 Copyright © 2010 Pearson Education, Inc. Regulation of Gastric Emptying The stomach usually empties completely within 4 hours after a meal. The larger the meal (more stomach distention) and the more liquid the meal is – the faster it empties. Fluids pass quickly through the stomach. Solids take longer in that they need to be processed more The rate of gastric emptying depends not only on the stomach but just as much on the small intestines processing time. Too much release into the small intestine (too much stretch) initiates the enterogastric reflex. As chyme enters the duodenum Receptors respond to stretch and chemical signals Enterogastric reflex and enterogastrones inhibit gastric secretion and duodenal filling Carbohydrate-rich chyme moves quickly through the duodenum Fatty chyme remains in the duodenum 6 hours or more

62 Copyright © 2010 Pearson Education, Inc. Gastric Emptying Carbohydrate-rich chyme moves quickly through the duodenum Fatty chyme remains in the duodenum 6 hours or more

63 Copyright © 2010 Pearson Education, Inc. Figure 23.20 Presence of fatty, hypertonic, acidic chyme in duodenum Duodenal entero- endocrine cells Chemoreceptors and stretch receptors Enterogastrones (secretin, cholecystokinin, vasoactive intestinal peptide) Duodenal stimuli decline Via short reflexes Via long reflexes Enteric neurons Initial stimulus Physiological response Result Contractile force and rate of stomach emptying decline CNS centers sympathetic activity; parasympathetic activity Stimulate Inhibit SecreteTarget

64 Copyright © 2010 Pearson Education, Inc. Vomiting and Gastroparesis Vomiting is caused by many factors – with the most common being extreme stretching of the stomach and/or intestines. Other factors are bacterial toxins, excessive alcohol, spicy foods, and certain drugs. Both bloodborne molecules and sensory impulses going to the emetic center in the medulla initiate the events for vomiting.

65 Copyright © 2010 Pearson Education, Inc. Gastroparesis Gastroparesis, also called delayed gastric emptying, is a medical condition consisting of a paresis (partial paralysis) of the stomach, resulting in food remaining in the stomach for a longer period of time than normal. Normally, the stomach contracts to move food down into the small intestine for digestion. The vagus nerve controls these contractions. Gastroparesis may occur when the vagus nerve is damaged and the muscles of the stomach and intestines do not work normally. Food then moves slowly or stops moving through the digestive tract. paresisparalysisstomach small intestinevagus nerve

66 Copyright © 2010 Pearson Education, Inc. Causes Gastroparesis may be chronic or transient; transient gastroparesis may arise in acute illness of any kind, with the use of certain cancer treatments or other drugs which affect digestive action, or due to anorexia nervosa, bulimia and other abnormal eating patterns.anorexia nervosabulimia Chronic gastroparesis is frequently due to autonomic neuropathy. This may occur in people with type 1 diabetes or type 2 diabetes. The vagus nerve becomes damaged by years of high blood glucose, resulting in gastroparesis. Gastroparesis has also been associated with various autoimmune diseases and syndromes, such as fibromyalgia and Parkinson's disease, and may occur as part of a mitochondrial disorder.autonomic neuropathytype 1 diabetes type 2 diabetes autoimmune diseasesfibromyalgiaParkinson's disease

67 Copyright © 2010 Pearson Education, Inc. Small Intestine: Gross Anatomy Major organ of digestion and absorption 2–4 m (20 feet long in cadaver but 7 -13 feet long in living person); extends from pyloric sphincter to ileocecal valve – approximately 200 square meters of surface area (doubles tennis court) Subdivisions 1.Duodenum (retroperitoneal) 10 inches 2.Jejunum (attached posteriorly by mesentery) 8 feet 3.Ileum (attached posteriorly by mesentery) 12 feet

68 Copyright © 2010 Pearson Education, Inc. The Ligament of Treitz (named after Václav Treitz) connects the duodenum of the small intestines to the diaphragm. It contains a slender band of skeletal muscle from the diaphragm and a fibromuscular band of smooth muscle from the horizontal and ascending parts of the duodenum. When it contracts, the suspensory muscle of the duodenum widens the angle of the duodenojejunal flexure, allowing movement of the intestinal contentsVáclav Treitzduodenumsmall intestinesdiaphragm

69 Copyright © 2010 Pearson Education, Inc. Figure 23.1 Mouth (oral cavity) Tongue Esophagus Liver Gallbladder Anus Duodenum Jejunum Ileum Small intestine Parotid gland Sublingual gland Submandibular gland Salivary glands Pharynx Stomach Pancreas (Spleen) Transverse colon Descending colon Ascending colon Cecum Sigmoid colon Rectum Vermiform appendix Anal canal Large intestine

70 Copyright © 2010 Pearson Education, Inc. Duodenum The bile duct and main pancreatic duct Join at the hepatopancreatic ampulla Enter the duodenum at the major duodenal papilla Are controlled by the hepatopancreatic sphincter

71 Copyright © 2010 Pearson Education, Inc. Figure 23.21 Jejunum Mucosa with folds Cystic duct Duodenum Hepatopancreatic ampulla and sphincter Gallbladder Right and left hepatic ducts of liver Bile duct and sphincter Main pancreatic duct and sphincter Pancreas Tail of pancreas Head of pancreas Common hepatic duct Major duodenal papilla Accessory pancreatic duct

72 Copyright © 2010 Pearson Education, Inc. Structural Modifications Increase surface area of proximal part for nutrient absorption Circular folds (plicae circulares) 1 cm tall – permanent folds of mucosae and submucosa Villi – 1 mm high Microvilli

73 Copyright © 2010 Pearson Education, Inc. Structural Modifications Circular folds Permanent (~1 cm deep) Force chyme to slowly spiral through lumen

74 Copyright © 2010 Pearson Education, Inc. Figure 23.22a Vein carrying blood to hepatic portal vessel Muscle layers Circular folds Villi (a) Lumen

75 Copyright © 2010 Pearson Education, Inc. Structural Modifications Villi (gives a velvety look) Motile fingerlike extensions (~1 mm high) of the mucosa Villus epithelium Simple columnar absorptive cells (enterocytes) Goblet cells In the core of each villus is a dense capillary bed and a wide lymph capillary called a lacteal.

76 Copyright © 2010 Pearson Education, Inc. The villi are large and leaflike in the duodenum and gradually narrow and shorten along the length of the small intestine. A slip of smooth muscle in the villus core allows it to alternatively shorten and lengthen. The pulsations (1) increase the contact between the villus and contents of the intestinal lumen making better absorption and (2) milk lymph along the lacteals.

77 Copyright © 2010 Pearson Education, Inc. Structural Modifications Microvilli Projections (brush border) of absorptive cells Bear brush border enzymes – these enzymes complete the digestive process

78 Copyright © 2010 Pearson Education, Inc. Histology of Intestinal Wall Epithelium of the villus is largely simple columnar absorptive cells bound by tight junctions and richly endowed with microvilli. Goblet cells Between the villi are intestinal pits that lead into tubular glands called intestinal crypts – also known as the crypts of Lieberkühn.

79 Copyright © 2010 Pearson Education, Inc. Intestinal Crypts Intestinal crypt epithelium Primarily composed of secretory cells that produce intestinal juice – a watery mixture containing mucus that serves as a carrier fluid for absorbing nutrients from chyme Enteroendocrine cells – source of the enterogastrones (Secretin and CCK) Intraepithelial lymphocytes (IELs) – these are T-cells that do not need priming – upon encountering antiges they immediately release killing cytokines Release cytokines that kill infected cells Paneth cells – release defensins and lysozyme Stem cells – can differentiate – become specialized absorptive cells, goblet cells, and enteroendocrine cells.

80 Copyright © 2010 Pearson Education, Inc. The stem cells migrate up to become the epithelial cells – the existent epithelial cells undergo apoptosis and are shed from the villus tips, renewing the villus epithelium every two days. but when the stem cells differentiate into Paneth cells – they stay at the base The crypts decrease in number along the length of the small intestine, but the goblet cells become more abundant.

81 Copyright © 2010 Pearson Education, Inc. Figure 23.22b (b) Absorptive cells Lacteal Intestinal crypt Mucosa associated lymphoid tissue Muscularis mucosae Duodenal gland Submucosa Enteroendocrine cells Venule Lymphatic vessel Goblet cell Blood capillaries Vilus Microvilli (brush border)

82 Copyright © 2010 Pearson Education, Inc. Submucosa Typical areolar connective tissue Contains individual and aggregated lymphoid follicles Peyer’s patches (aggregated lymphoid follicles) – increase in number as go towards end of small intestine. They protect distal part against bacteria since normal flora increases there. Also contains proliferating lymphocytes that leave the intestine enter blood stream and then return to home in the submucosa to produce IgA

83 Copyright © 2010 Pearson Education, Inc. Submucosal Duodenal Glands Duodenal (Brunner’s) glands of the duodenum secrete alkaline mucus The glands help neutralize acidic chyme moving in from the stomach When this protection is absent or insufficient – duodenal ulcers can occur The muscularis of the small intestine is bilayered and except for the duodenum which is retroperitoneal and has an adventitia, the external intestinal surface is covered by a visceral peritoneum

84 Copyright © 2010 Pearson Education, Inc. Intestinal Juice Normally secrete 1 to 2 ml of intestinal juice daily – that facilitates transport and absorption of nutrients Secreted in response to distension or irritation of the mucosa by hypertonic or acidic chyme. Slightly alkaline (7.4 – 7.8) and isotonic with blood plasma Largely water, enzyme-poor, due to the fact that enzymes are limited to the intestinal enzymes bound to brush border. It does contain contains mucus – secreted by goblet cells and duodenal glands

85 Copyright © 2010 Pearson Education, Inc. Liver Largest gland in the body Four lobes—right, left, caudate, and quadrate

86 Copyright © 2010 Pearson Education, Inc. Liver Falciform ligament Separates the (larger) right and (smaller) left lobes Suspends liver from the diaphragm and anterior abdominal wall Round ligament (ligamentum teres) Remnant of fetal umbilical vein along free edge of falciform ligament

87 Copyright © 2010 Pearson Education, Inc. Figure 23.24a Sternum Nipple Liver Right lobe of liver Gallbladder (a) Bare area Falciform ligament Left lobe of liver Round ligament (ligamentum teres)

88 Copyright © 2010 Pearson Education, Inc. Figure 23.24b Lesser omentum (in fissure) Left lobe of liver (b) Porta hepatis containing hepatic artery (left) and hepatic portal vein (right) Quadrate lobe of liver Ligamentum teres Gallbladder Hepatic vein (cut) Sulcus for inferior vena cava Caudate lobe of liver Bare area Bile duct (cut) Right lobe of liver Sternum Nipple Liver

89 Copyright © 2010 Pearson Education, Inc. Liver: Associated Structures Lesser omentum anchors liver to stomach Hepatic artery and vein at the porta hepatis Bile ducts Common hepatic duct leaves the liver Cystic duct connects to gallbladder Bile duct formed by the union of the above two ducts

90 Copyright © 2010 Pearson Education, Inc. Figure 23.21 Jejunum Mucosa with folds Cystic duct Duodenum Hepatopancreatic ampulla and sphincter Gallbladder Right and left hepatic ducts of liver Bile duct and sphincter Main pancreatic duct and sphincter Pancreas Tail of pancreas Head of pancreas Common hepatic duct Major duodenal papilla Accessory pancreatic duct

91 Copyright © 2010 Pearson Education, Inc. Liver: Microscopic Anatomy Liver lobules Hexagonal structural and functional units Filter and process nutrient-rich blood Composed of plates of hepatocytes (liver cells) Longitudinal central vein

92 Copyright © 2010 Pearson Education, Inc. Figure 23.25a, b (a)(b) Lobule Central veinConnective tissue septum

93 Copyright © 2010 Pearson Education, Inc. Liver: Microscopic Anatomy Portal triad at each corner of lobule Bile duct receives bile from bile canaliculi Portal arteriole is a branch of the hepatic artery Hepatic venule is a branch of the hepatic portal vein Liver sinusoids are leaky capillaries between hepatic plates Kupffer cells (hepatic macrophages) in liver sinusoids

94 Copyright © 2010 Pearson Education, Inc. Figure 23.25c (c) Interlobular veins (to hepatic vein) Central vein Sinusoids Portal triad Plates of hepatocytes Portal vein Fenestrated lining (endothelial cells) of sinusoids Bile duct (receives bile from bile canaliculi) Bile duct Portal arteriole Portal venule Hepatic macrophages in sinusoid walls Bile canaliculi

95 Copyright © 2010 Pearson Education, Inc. Liver: Microscopic Anatomy Hepatocyte functions (see MS Word Liver Functions for complete list) Process bloodborne nutrients Store fat-soluble vitamins Perform detoxification Produce ~900 ml bile per day Stores glycogen

96 Copyright © 2010 Pearson Education, Inc. Liver Regeneration The regenerative ability of the liver is exceptional. It can regenerate to its former size even if 70% is removed. Liver cells secrete VEGF (Vascular Endothelial Growth Factor) which binds to specific receptors on endothelial cells lining the sinusoids. The endothelial cells proliferate and release other growth factors, such as hepatocyte growth factor (HGF) and interleukin 6.

97 Copyright © 2010 Pearson Education, Inc. Bile Yellow-green, alkaline solution containing Bile salts: cholesterol derivatives that function in fat emulsification and absorption Bilirubin: pigment formed from heme Cholesterol, neutral fats, phospholipids, and electrolytes

98 Copyright © 2010 Pearson Education, Inc.

99 Bile Enterohepatic circulation Recycles bile salts Bile salts  duodenum  reabsorbed from ileum  hepatic portal blood  liver  secreted into bile

100 Copyright © 2010 Pearson Education, Inc. The Gallbladder Thin-walled muscular sac on the ventral surface of the liver Stores and concentrates bile by absorbing its water and ions Releases bile via the cystic duct, which flows into the bile duct


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