Digestive System PDF

Digestive System © K. Lisk 2024 | Division of Anatomy | University of Toronto Learning Objectives Describe the layers of the GI tract Describe the gross anatomy & histology of the esophagus, stomach, pancreas, liver, small & large intestines Explain the functions & differentiate different components...

Digestive System © K. Lisk 2024 | Division of Anatomy | University of Toronto Learning Objectives Describe the layers of the GI tract Describe the gross anatomy & histology of the esophagus, stomach, pancreas, liver, small & large intestines Explain the functions & differentiate different components of the esophagus, stomach, small & large intestines Describe the gross anatomy & function of the gall bladder Compare & contrast pancreatic islet & acinar cell function 2 Peritoneum A continuous serous membrane that lines the peritoneal cavity & invests viscera Consist of 2 layers of mesothelium; secretes peritoneal fluid Liver s m Sto a Pancre ac h Colon Visceral peritoneum Lines outer surface of viscera Peritoneal cavity Parietal peritoneum Lines inner surface of body wall 3 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.04 th Tortora & Nielsen. (2017). Principles of Human Anatomy. 14 ed. Wiley. Fig. 1.7 Intraperitoneal vs Retroperitoneal Organs Intraperitoneal organs: surrounded by visceral peritoneum & suspended by mesenteries to posterior abdominal wall e.g., stomach & spleen Retroperitoneal organs: develop posterior to peritoneal cavity & are only partially covered by peritoneum e.g., kidneys, aorta, & IVC Secondarily retroperitoneal organs: initially were intraperitoneal, but become attached to posterior body wall through development e.g., ascending & descending colon Kid n Spleen Kidney ey Stomach Digestive tract Dorsal mesentery Secondarily retroperitoneal organ E.g., ascending colon Agur & Dalley. (2020). Grant’s Atlas of Anatomy. 15th ed. Wolters4 Kluwer. Fig 5.13 Drake et al. (2015). Gray’s Anatomy for Students. (3rd ed.). Philadelphia: Elsevier. Fig. 4.7 Mesenteries Double layer of peritoneum with intervening areolar CT; support & stabilize intraperitoneal organs Liver Mesentery proper Sigmoid mesocolon Stomach Transverse mesocolon Colon Several different types/names Pancreas Blood & lymph vessels & nerves are sandwiched between the two folds Peritoneal cavity 5 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.04 Layers of the Abdominal Wall Skin 1. Rectus abdominis 1 2. External oblique 3. Internal oblique 4. Transversus abdominis 5. Psoas major 2 3 Transversalis fascia Peritoneal cavity 4 Superficial fascia 6. Quadratus lumborum Peritoneum 5 Kidney Kidney 6 Renal fascia Transverse section 6 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 10.11 Digestive System Consists of a 2 groups of organs that mechanically & chemically break down food for absorption 1. Gastrointestinal (GI) tract organs; form a continuous tube 2. Accessory digestive organs are connected to the GI tract & include teeth, tongue, salivary glands, liver, gallbladder & pancreas Mouth Salivary gland Pharynx Esophagus Liver Gall bladder Stomach Pancreas Small intestine Large intestine 7 Tortora & Nielsen. (2017). Principles of Human Anatomy. 14th ed. Wiley. Fig. 24.01 Layers of GI Tract Consists of 4 layers (tunics) from esophagus to large intestine 1. 2. 3. 4. Mucosa Submucosa Muscularis externa Serosa or adventitia Epithelium Mesentery Lamina propria Muscularis mucosae Mucosa Submucosa Muscularis externa Serosa View of histological organization Submucosal & myenteric plexuses 8 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.2 Layers of GI Tract Mucosa has 3 components 1. Epithelium: varies 2. Lamina propria: areolar CT with mucosal glands, blood vessels, nerves & lymphatics 3. Muscular mucosae: smooth muscle that alters the shape of the lumen FN: protection, absorption, secretion Submucosa: dense irregular or areolar CT Contains blood & lymphatic vessels & submucosal plexus In some regions lymphatic tissue & submucosal glands Mucosa Submucosa Muscularis externa Serosa 9 Tortora & Nielsen. (2017). Principles of Human Anatomy. 14th ed. Wiley. Fig. 24.2 Layers of GI Tract Muscularis externa: 2 layers of smooth muscle, except in esophagus & stomach 1. Inner circular layer 2. External longitudinal layer Myenteric plexus located between the 2 muscle layers What happens when these layers contract? Adventitia or Serosa: Areolar CT Intraperitoneal organs have a serosa (visceral peritoneum) Mucosa Submucosa Muscularis externa Serosa 10 10 Tortora & Nielsen. (2017). Principles of Human Anatomy. 14th ed. Wiley. Fig. 24.2 Peristalsis & Segmentation Circular muscle: contraction compresses & mixes contents & constricts diameter of lumen (Mixing) Bolus Longitudinal muscle: contraction shortens length of tube Myenteric plexus controls the contraction of these muscles 11 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.3 Esophagus Muscular tube (25cm x 2cm) that runs through the neck & posterior mediastinum Pharynx Secretes mucus & transports swallowed materials from pharynx to stomach Esophagus Passes through diaphragm via esophageal hiatus 12 Tortora & Nielsen. (2017). Principles of Human Anatomy. 14th ed. Wiley. Fig. 24.01 Mucosa Stratified squamous nonkeratinized epithelium Lamina propria contains diffuse lymphatic tissue & esophageal cardiac glands Thick muscularis mucosae Submucosa Dense irregular CT with blood & lymphatic vessels Lots of elastic fibers; assist in closing distended tube **Submucosal glands** C 1/3 skeletal m. Muscular Layer L Circular layer (C) Longitudinal layer (L) 1/3 skeletal m. + smooth m. 1/3 smooth m. Adventitia Adheres to posterior body wall 13 Tortora & Nielsen. (2017). Principles of Human Anatomy. 14th ed. Wiley. Fig. 24.7 Scattered lymphocytes Muscularis mucosae X10 H&E X65 H&E 14 Mescher. (2018). Junqueira’s Basic Histology. 15th ed. Mc Graw Hill. Fig 15.12 Peristalsis Relaxed muscularis externa Progressive, wave like contractions move bolus through the esophagus Circular layer contracts Bolus Longitudinal layer contracts s Bolu Esophageal hiatus Lower esophageal sphincter AKA cardiac sphincter Thickening of circular layer of smooth muscle Portion of esophagus located in peritoneal cavity Frontal section, anterior view 15 Tortora G.J. & Nielsen, M. (2017). Principles of Human Anatomy. 14th ed. Wiley. Fig. 24.9 Gastroesophageal Reflux Disease Lower esophageal sphincter fails to close adequately after food has entered stomach SC SS HCl from stomach irritates esophageal wall Epithelium may change from stratified squamous nonkeratinized to simple columnar Scar tissues builds up; narrowing of lumen SS: Stratified squamous nonkeratinized epithelium SC: Simple columnar epithelium 16 WebPath © 1994-2020 by Edward C. Klatt MD , Savannah, Georgia, USA Stomach Lower esophageal sphincter Muscular, intraperitoneal, Jshaped sac; comprised of 4 regions 1. Fundus Dome shaped area 2. Cardia Rugae formed by folds of mucosa & submucosa accommodate expansion & filling of stomach L Lesser curvature C Lesser omentum attachment Muscularis externa contains 3 layers, additional oblique layer; allows stomach to more effectively mix Transition zone between esophagus & stomach O Rugae 3. Body Greater curvature Greater omentum attachment 4. Pyloric antrum Funnel shaped region Muscular Layers Longitudinal layer (L) Circular layer (C) Oblique layer (O) 17 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.10 Stomach Lower esophageal sphincter Involved in food storage, mechanical & chemical digestion, hormone secretion, little absorption 1. Fundus 2. Cardia After bolus is processed in stomach it is called chyme L C Lesser curvature O Pyloric sphincter, thickening of circular layer, regulates chyme into duodenum Rugae 3. Body Greater curvature Pyloric sphincter 4. Pyloric antrum Muscular Layers Longitudinal (L) Circular (C) Oblique (O) 18 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.10 (simple columnar) * 19 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.12 Histology of Stomach P P Mucosa (M) Simple columnar epithelium Surface mucous cells invaginate into lamina propria forming gastric pits (P) points to muscularis mucosae Longitudinal folds of M & SM create rugae Submucosa (SM) Loose areolar CT, blood vessels (V) & lymphatics Muscularis Externa (ME) 3 layers Serosa (S) X12; H&E Loose areolar CT 20 Mescher. (2018). Junqueira’s Basic Histology. 15th ed. Mc Graw Hill. Fig 15.15 Gastric Secretions 1. Surface mucous cells & mucous neck cells secrete mucins; protects mucosa from acid & helps maintain the acidic conditions 2. Parietal cells secrete intrinsic factor which is needed for vit B12 absorption & HCl which denatures proteins, is antibacterial & breaks down cell walls 3. Chief cells secrete pepsinogen a proenzyme which is converted to the active proteolytic enzyme pepsin by HCl & secretes gastric lipase 4. G cells (enteroendocrine) secrete gastrin into bloodstream; stimulates secretion of parietal & chief cells & contractile activity of gastric muscle 21 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.12 M P P C Surface mucous cells & mucous neck cells (M) Parietal cells (P): large, central nuclei & eosinophilic cytoplasm Chief cells (C): small & basophilic cytoplasm 22 12x & 18x MH 113. © 2005-2024. T. Clark Brelje & Robert Sorenson. Histology Guide. Knowledge Check The following micrograph is from which of the following regions? A. Mouth B. Pyloric region of stomach C. Proximal esophagus D. Gastroesophageal junction CC BY NC 3.0 SA DEED; Regents of the University of Michigan. Slide 155 23 Small Intestine Long tube divided into 3 regions: duodenum, jejunum, & ileum Where most digestion & absorption occurs Duodenojejunal flexure Duodenum ~25 cm Mixes chyme with exocrine secretions Proximal portion intraperitoneal & remaining parts are retroperitoneal Jejunum ~2.5m Chemical digestion & nutrient absorption; intraperitoneal Ileum ~3.6m Controls movement of intestinal contents into cecum of large intestine; intraperitoneal Cecum 24 Tortora & Nielsen. (2017). Principles of Human Anatomy. 14th ed. Wiley. Fig. 24.16 Duodenum No mesentery Jejunum & Ileum Supported by fan-shaped mesentery proper 25 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.04 Small Intestine Mucosa Submucosa Muscularis layer Serosa Circular folds (plicae circulares): permanent, transverse folds of both mucosa & submucosa; increase surface area & function to slow movement of chyme Intestinal villi: finger-like extensions of mucosa only, covered by simple columnar cells Microvilli project from intestinal villi creating a brush border 26 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.14 &.15 Plexuses control movement of chyme & release of secretions in small intestine 27 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.14 Mucosa of Small Intestine Villus Simple columnar epithelium + goblet cells Intestinal glands Lamina propria contains: Capillary networks which carry nutrient rich blood to hepatic portal system Lacteals that carry lipid-protein complexes to venous system Nerves & smooth muscle (not shown) Intestinal glands/crypts extend into lamina propria Enteroendocrine cell produce various hormones e.g., cholecystokinin Paneth cells play a role in innate immunity Stem cells replenish epithelial cells lost in lumen & MALT 28 Pawlina. (2020). Histology a Text & Atlas. Wolter Kluwer. 8th ed. Fig. 17.19 & Tortora & Nielsen. (2017). Principles of Human Anatomy. 14th ed. Wiley. Fig. 24.17 Regional Specializations Duodenum Jejunum Mucus secretion Goblet cells Submucosal (Brunner’s) glands Structurally specialized for nutrient absorption; well developed circular folds Circular folds Villi Ileum Lymphoid nodules (Peyer’s patches) & goblet cells 29 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.15 Knowledge Check What region of the small intestine is shown? CC BY NC 3.0 SA DEED; Regents of the University of Michigan. 30 Large Intestine Extends from ileocecal valve to anus (1.5m long & 6.5cm wide) Divided into 3 regions: cecum, colon & rectum Involved in reabsorption of H2O & salts, absorption of vitamins & storage of feces Transverse Colon Descending Colon Ascending Colon Cecum Sigmoid Colon Blind ended sac Rectum 31 Tortora G.J. & Nielsen, M. (2017). Principles of Human Anatomy. 14th ed. Wiley. Fig. 24.01 Right colic (hepatic) flexure Left colic (splenic) flexure Haustra Permits expansion Teniae coli Replace external longitudinal muscular layer (3 strips) Ileocecal valve Cecum Appendix Filled with lymphoid nodules & involved in immune FN 32 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.16 What parts of the large intestine are retroperitoneal (R) vs intraperionteal (I)? Ascending colon: Transverse colon: Descending colon: Secondarily retroperitoneal R or I Transverse colon Secondarily retroperitoneal Sigmoid colon: R or I Sigmoid colon Rectum: R or I Rectum 33 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.04 Rohen et al 2004. Anatomy a Photographic Atlas. 34 Rectum Expandable; filling triggers the urge to defecate Rectum Ends as the anal canal & opens at the anus Epithelium changes: simple columnar à stratified squamous nonkeratinized à stratified squamous keratinized Anal canal Internal anal sphincter Smooth muscle; thickening of inner circular muscular layer External anal sphincter Skeletal muscle Anus 35 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.16 Teniae coli Omental appendices Haustrum * Simple columnar epithelium M Goblet cells (M) Intestinal glands (very deep) (SM) * SM CC-NC-SA 3.0 DEED; Regents of University of Michigan 36 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.18 Control of Large Intestine Regulated by local reflexes in ANS Proximally, fecal material moves slowly by peristalsis; segmentation occurs with haustral churning Mass movements are powerful, peristaltic-like contraction involving teniae coli; occur infrequently (2-3x/day) Rectal distension consciously sensed Voluntary relaxation of external anal sphincter Reflex relaxation of internal anal sphincter 37 Blood Supply Primarily from unpaired visceral branches of abdominal aorta Not shown: esophageal arteries; visceral branches of the thoracic aorta Celiac trunk Superior mesenteric a. Supplies midgut: distal duodenum to left colic flexure Foregut: stomach, pancreas, liver & gall bladder, proximal duodenum 3 branches: 1. Left gastric a. 2. Splenic a. 3. Common hepatic a. Inferior mesenteric a. Supplies hindgut: descending colon to upper rectum 38 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 22.12 Hepatic Portal System Portal veins connects 2 capillary beds IVC Hepatic vv. Drains blood to IVC Hepatic portal v. Carries nutrient rich & O2 poor blood from digestive system to liver Superior mesenteric v. Left gastric v. Splenic v. Inferior mesenteric v. 39 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 22.15 Liver Liver is covered by fibrous CT capsule & visceral peritoneum, except at the bare area Coronary ligament Caudate lobe Bare area Right lobe Left lobe Bare area Falciform ligament Attachment to body wall Round ligament of liver Anterior surface Remnant of fetal umbilical vein Left lobe Porta hepatis Right lobe BVs, lymph, bile ducts & nerves Quadrate lobe Inferior & posterior surface 40 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.19 Functions of the Liver 1. Digestive: Production & secretion of bile; facilitates digestion of fat & buffers acidity in chyme Falciform ligament 2. Metabolic: Regulates circulating levels of nutrients; store fatsoluble vitamins; remove metabolic wastes & toxins 3. Hematological: Synthesizes plasma proteins, phagocytizes debris in blood & blood reservoir (25% of cardiac output) Transverse section 41 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.19 Porta Hepatis 1. Common hepatic duct 2. Hepatic artery proper 3. Hepatic portal vein 42 Histology of Liver Each lobe is divided by CT into 1000s of functional units called lobules Lobules are commonly hexagonal; at periphery are portal triads Portal triads include branches of the hepatic portal vein, hepatic artery proper & bile duct 43 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.20 Hepatocytes Branch of bile duct Central vein Branch of hepatic portal vein Branch of hepatic artery proper Hepatic sinusoid Lined by endothelium with large fenestrae & discontinuous BM Stellate macrophage Blood from the hepatic portal vein & hepatic artery proper drain via the hepatic sinusoids into the central vein; as blood flows through, it is processed by hepatocytes & stellate macrophages Central veins converge to form hepatic veins which empty into IVC 44 Tortora & Nielsen. (2017). Principles of Human Anatomy. 14th ed. Wiley. Fig. 24.14 stellate macrophage Stellate macrophage Perisinusoidal space Perisinusoidal space CC BY NC 3.0 SA DEED; Regents of the University of Michigan. Slide 220 Perisinusoidal space separates hepatocytes from endothelial cells; where functions of the liver take place 45 Pawlina. (2020). Histology a Text & Atlas. Wolter Kluwer. 8th ed. Fig. 18.10 Where does the bile produced by hepatocytes go? Hepatocytes Produce & secrete bile into bile canaliculi à bile ductules à bile ducts Bile canaliculi Branch of bile duct 46 Tortora & Nielsen. (2017). Principles of Human Anatomy. 14th ed. Wiley. Fig. 24.14 Hepatic ducts Collect bile from all bile ducts of liver lobes Gallbladder Common hepatic duct Cystic duct Common bile duct What does bile do & where does it go? FNs in the digestion of lipids in duodenum; stored & concentrated in gallbladder Pancreas Major duodenal papilla 47 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.21 Common bile duct Empty into major hepatopancreatic ampulla (HA) HA Pancreatic duct Hepatopancreatic sphincter Controls the flow of secretions into duodenum Lipid/protein-containing chyme in duodenum stimulates enteroendocrine cells to release cholecystokinin (CCK), which stimulates gallbladder contraction & hepatopancreatic sphincter relaxation 48 Gall Stones Can occur in gallbladder or biliary apparatus Typically formed from condensations of cholesterol or calcium & bile salts Size varies; majority asymptomatic unless it becomes lodged in cystic duct CC BY-SA 4.0; George Chernilevsky 49 Pancreas Located posterior to stomach, in the curve of the duodenum; retroperitoneal organ ~15 cm long & subdivided into a head, body & tail Surrounded by thin fibrous CT capsule; CT septa subdivide it into lobules Involved in endocrine & exocrine functions Which major visceral branches supply it with blood? Tail Accessory pancreatic duct Pancreatic duct Body Lobules Head 50 Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.23 Histology of Pancreas Pancreatic islets: secrete endocrine products e.g., insulin & glucagon Acinar cells: secrete mucin & digestive enzymes e.g., proteases, amylase & lipases Intercalated duct cells: secrete HCO3- ions Martini et al. (2018). Human Anatomy. 9th ed. Pearson. Fig 25.23 Pancreas (rat) chrome-alum hematoxylin and phloxine stain, slide 190B CC BY NC-SA 3.0; Regents of the University of Michigan 51 Mouth Salivary gland Pharynx Esophagus Liver Gall bladder Stomach Pancreas Small intestine Large intestine 52 Tortora & Nielsen. (2017). Principles of Human Anatomy. 14th ed. Wiley. Fig. 24.01