Digestive System: From General Structure to Stomach PDF

4/13/21 General Structure of the Digestive Tract 5 General Structure of the Digestive Tract The entire gastrointestinal à common structural characteristics: a hollow tube with a lumen of variable diameter a wall made up of four main layers: the mucosa, submucosa, muscularis, and serosa 6 3 4/13/21 T...

4/13/21 General Structure of the Digestive Tract 5 General Structure of the Digestive Tract The entire gastrointestinal à common structural characteristics: a hollow tube with a lumen of variable diameter a wall made up of four main layers: the mucosa, submucosa, muscularis, and serosa 6 3 4/13/21 Tongue - Covered by a nonkeratinizing stratified squamous epithelium supported by a lamina propria associated with interlacing bundles of striated muscle - Serous and mucus glands extend across the lamina propria and the muscles 11 Tongue 12 6 4/13/21 Tongue Mucous and Serous (von Ebner) Glands in the submucosa 17 Tongue and lingual papillae Root of the tongue: filled with masses of lymphoid nodules 18 9 4/13/21 Oral Mucosa 1. Lining Mucosa: lip, cheek, floor of mouth, soft palate, ventral surface of tongue Epithelium - non-keratinized Submucosa contains salivary glands 2. Masticatory Mucosa: gingiva, hard palate Epithelium - keratinized or parakeratinized Submucosa - absent 3. Specialized Mucosa: dorsal surface of tongue 1. Filiform Papillae – keratinized epithelium 2. Fungi form Papillae - non-keratinized epithelium 3. (Foliate Papillae) - rudimentary in human 4. Circumvallate Papillae – non-keratinized epithelium with associated taste buds and von Ebner’s salivary glands 19 Major Salivary Glands 1. Parotid 2. Submandibular 3. Sublingual 20 10 4/13/21 Saliva Secretion About 1,000 ml/day Submandibular Glands 65% Parotid Glands 23% Sublingual Glands 4% Minor Salivary Glands 8% Flow Rate 0.3 ml/min (Unstimulated) Stimulation Autonomic Nervous System Composition Varies with flow rate 21 Composition of Saliva Water Ions: Bicarbonate, potassium, sodium, chloride, etc Glycoproteins: Mucus Proteins: Enzymes – Amylase (parotid gland), nucleases, etc. Cells: pH: Desquamated Epithelial cells Leukocytes ~ 7.0 22 11 4/13/21 Structural and functional Unit of Salivary Gland 23 Myoepithelial Cell 24 12 4/13/21 Esophagus Gastroesophageal junction ESOPHAGUS STOMACH Source: http://library.med.utah.edu/WebPath/jpeg4/GI121.jpg 35 Esophagus Transport food and liquid from the pharynx to the stomach. Overall length: ~25cm 36 18 4/13/21 Esophagus Subdivided into three portions: Upper one third (striated muscle) Middle third (striated muscle and smooth muscle bundles are mixed) Distal third (only smooth muscle) 37 Esophagus - Mucosa 38 19 4/13/21 Esophagus - Lined by a stratified squamous nonkeratinized epithelium - Lamina propria: mucus-secreting esophageal cardiac glands - Muscularis mucosae: variable thickness: a single longitudinal layer of smooth muscle - Submucosa: mucus-secreting esophageal glands proper 49 Esophagus - Muscularis externa: Inner circular layer and outer longitudinal layer - The upper third - skeletal muscle - The middle third - a combination of smooth and skeletal muscle - The lower third - smooth muscle The striated muscles are controlled by the vagus nerve (CN X) The smooth muscles are controlled by nerve fibers derived from the enteric nervous system 50 25 4/13/21 Esophagus - The muscularis externa: peristaltic activity – move bolus of food from the pharynx into the stomach - Two physiological sphincters: the pharyngoesophageal and the gastroesophageal To ensure that the bolus is transported in only one direction, toward the stomach - Adventitia or serosa (after entering the abdominal cavity - the visceral peritoneum) 51 Esophageal Glands Esophageal glands proper - in the submucosa Mucosal and submucosal glands: secrete mucus to lubricate and protect the luminal wall Esophageal cardiac glands 52 26 4/13/21 Esophageal cardiac glands Similar to the cardiac glands of the stomach Found in the lamina propria of the mucosa Present in the terminal part of the esophagus 55 Back to our clinical case… A 69-year-old man with a history of gastroesophageal reflux…...The patient’s esophagus is examined at autopsy (shown in the image) Questions for you: Possible cause of death? 56 28 4/13/21 57 Peer Group Learning: our clinical case… Clinical history: Female 74 years Dyspepsia. Stomach looked normal. Questions for you: describe 1) the organs and 2) Gastroesophageal junction Any possible lesions in relation to the normal… Illustrative specimen only, not from this patient 58 29 4/13/21 Peer Group Learning: our clinical case… Antral, incisura and corpus biopsies taken… https://www.virtualpathology.leeds.ac.uk/slides/library/view.php?path=%2FRes earch_4%2FSlide_Library%2FMFD_Collection%2FFull_Collection%2F30023.svs Question for you: What do you see… 59 Stomach Mixed exocrine-endocrine organ: food digestion and hormones secretion 60 30 4/13/21 Stomach Esophagus Cardia fundus and body Antrum Pylorus Regions: When empty: rugae à longitudinally directed folds, which flatten when the stomach is filled with food 61 Gastric Mucosa SEM of the stomach: numerous small circular or ovoid invaginations of the epithelial à gastric pits (foveolae; P) surrounded by polygonal apical ends of surface mucous cells. X600 The gastric glands of the stomach mucosa deliver their secretions into the bases of the gastric pits 62 31 4/13/21 Gastric Mucosa - Simple columnar epithelium: composed of mucinogen-producing surface lining cell (not goblet cells but produce a thick, viscous mucus: the visible mucus) - Very small number of taste cells (similar to the taste buds of the tongue) Source: Histology: A Text and Atlas Ross,M.H.; Pawlina,W. Lippincott Williams & Wilkins; 6 edition, 2010 63 Gastric Mucosa Mucous cells: Apical part: mucous cup Basal part: the nucleus and Golgi apparatus small amounts of rough endoplasmic reticulum 64 32 4/13/21 Gastric Mucosa Mucous cells Mucus: thick, viscous, gel-like coat. Protection: (1) against abrasion from rougher components of the chyme, (2) from the acidic content of the gastric juice (high bicarbonate and potassium concentration). With prostaglandins (PGE2) à an important role in protecting gastric mucosa 65 Gastric Mucosa - Lamina propria: a loose connective tissue housing smooth muscle cells, lymphocytes, plasma cells, mast cells, and fibroblasts. It contains gastric glands - Muscularis mucosae: a poorly defined inner circular layer, an outer longitudinal layer, and occasionally an outermost circular layer of smooth muscle 66 33 4/13/21 Gastric Mucosa: Luminal surface Most of these cells secrete mucus Tall columnar cells Pits have basally located nuclei and lightly staining cytoplasm 67 Glands of the Gastric Mucosa - Simple, branched, tubular glands in the lamina propria of the cardia, fundus, and pylorus - Each gland consists of an isthmus, which connects the gland to the base of a gastric pit; a neck; and a base 68 34 4/13/21 Glands of the Gastric Mucosa Typically, several glands open into a single gastric pit The base of the gland: usually divides into two and sometimes three branches à gastric glands 69 Glands of the Gastric Mucosa gastric g la nds Gastric glands produce gastric juice (about 2 L/day) 70 35 4/13/21 Cell types: 1. Mucous neck cells 2. Chief cells 3. Parietal cells (oxyntic cells) 4. Enterochromaffin-like cell and G cells are enteroendocrine (APUD) cells 5. Undifferentiated adult stem cells 71 Peer Group Learning: Back to our clinical case… Antral, incisura and corpus biopsies taken… https://www.virtualpathology.leeds.ac.uk/slides/library/view.php?path=%2FRes earch_4%2FSlide_Library%2FMFD_Collection%2FFull_Collection%2F30023.svs Question for you: Can you identify the Glands of the Gastric Mucosa? 72 36 4/13/21 Cells of the Fundic Glands Mucous Neck Cells - Located in the neck of the gland - Short microvilli, apical mucous granules, a prominent Golgi complex, numerous mitochondria, and some basal RER - Produce soluble mucus: a slippery substance that lubricates the lining of the stomach 75 Mucous Surface Cell Mucous (mucigen) granules accumulate in the apical cytoplasm 76 38 4/13/21 Cells of the Fundic Glands Parietal (oxyntic) Cells - Pyramidal cells concentrated in the upper half of the gland - Secrete hydrochloric acid (HCl) and gastric intrinsic factor (necessary for absorption of vitamin B12 in the ileum) - Intracellular tubulo-vesicular system: many mitochondria + secretory intracellular canaliculi (deep invaginations of the apical plasma membrane) lined by microvilli 81 Cells of the Fundic Glands Parietal (oxyntic) Cells When the parietal cells are stimulated to secrete HCl, the number and length of microvilli increase and the complexity of the tubulovesicular system decreases (suggesting that tubulovesicular membranes are incorporated into the intracellular canaliculi, thus lengthening the microvilli) 82 41 4/13/21 Parietal Cells Abundant vesicles and tubules involved in HCl production Numerous giant mitochondria 83 Chief Cells The pepsinogen has been extracted 84 42 4/13/21 Cells of the Fundic Glands Chief (zymogenic) Cells - Pyramidal cells residing in the lower half of the gland - Secrete pepsinogen (a precursor of the enzyme pepsin) and the precursors of two other enzymes: rennin and lipase - Abundance of basal rough endoplasmic reticulum (RER), a supra-nuclear Golgi complex, and many apical zymogen (secretory) granules 85 Chief Cells 86 43 4/13/21 Parietal Cells and Chief Cells Chief cells: zymogen granules à stain bright red in H&E preparations With pepsinogen 87 Cells of the Fundic Glands Diffuse Neuroendocrine System (DNES) Cells - = Enteroendocrine cells = APUD cells (amine precursor uptake and decarboxylation cells) - Two major categories: open and closed - Open category: short processes that reach the lumen – chemosensory: testing the luminal content to release specific substances based on the circumstances - Closed category: do not have processes "closed off" from the luminal content 88 44 4/13/21 Cells of the Fundic Glands Diffuse Neuroendocrine System (DNES) Cells - More than a dozen types of cells that house many small hormone-containing granules, usually concentrated in the basal cytoplasm - Each particular enteroendocrine cell is believed to secrete only one hormone - Abundance mitochondria and RER and a moderately well-developed Golgi complex 89 Enteroendocrine Cell 90 45 4/13/21 Cells of the Fundic Glands Diffuse Neuroendocrine System (DNES) Cells 91 Cells of the Fundic Glands Regenerative Cells - Located primarily in the neck and isthmus - Replace all the epithelial cells of the gland, gastric pit, and luminal surface 92 46 4/13/21 Cardiac and Pyloric Glands - Coiled tubular mucus-secreting glands (different from fundic glands) - Lack chief cells 93 Cardiac glands Abrupt transition from the mucosa of the esophagus with its stratified squamous epithelium to the glandular mucosa of the stomach 94 47 4/13/21 Cardiac glands 95 Cardiac glands Composed mainly of mucous cells with pale staining cytoplasm and basally located nuclei Present, but not seen in regular preparations, are stem cells and endocrine cells Present only in a very small segment of the stomach mucosa adjacent to the cardioesophageal junction 96 48 4/13/21 Cardiac glands HOMOGENEOUS population of pale-staining columnar cells with a “bubbly” supranuclear cytoplasm 97 Cardiac glands PAS staining 98 49 4/13/21 Cardiac glands Cardiac gastric glands are primarily mucous à stain very intensely with PAS due to the carbohydrate-rich present in the mucus PAS staining 99 Pyloric glands 100 50 4/13/21 Pyloric glands HOMOGENEOUS population of mucous cells that are similar in appearance to those in cardiac glands The pits are much deeper compared to cardiac glands Stem cells and endocrine cells are also present. Parietal cell may be also found. 101 Gastric Juice - Water and electrolytes - Hydrochloric acid (HCl) - Pepsin (converted from pepsinogen produced by the chief cells) - Mucus - Intrinsic factor (a glycoprotein secreted by parietal cells that binds to vitamin B12) - Gastrin and other hormones and hormonelike secretions: produced by enteroendocrine cells and secreted into the lamina propria à circulation or act locally 102 51 4/13/21 Regulation of Gastric Secretion - Effected by neural activity (vagus nerve) and by several hormones 103 Lymphoid Cells/Nodules 104 52 4/13/21 Lymphoid Cells/Nodules A large number of lymphocytes and plasma cells in the lamina propria between the gastric glands, and, in some areas, aggregated as lymphoid nodules Strands of smooth muscle fibers from the inner layer of the muscularis mucosae extend between the glands toward the surface. The contraction of these strands may help the emptying of the glands 105 Gastro-duodenal Transition Pyloric region of the stomach is characterized by a thick wall due to the presence of the pyloric sphincter muscle à inner circular layer of the muscularis externa 106 53 4/13/21 Peer Group Learning: Back to our clinical case… Antral, incisura and corpus biopsies taken… https://www.virtualpathology.leeds.ac.uk/slides/library/view.php?path=%2FRes earch_4%2FSlide_Library%2FMFD_Collection%2FFull_Collection%2F30023.svs Questions for you: 1- Can you identify the different cell types of the gastric? 2- Can you identify the different regions that each biopsy came from? 107 Peer Group Learning: Back to our clinical case… A silver stain of the patient’s gastric mucosa reveals small curved rods (shown in the image). Questions for you: What are this structures? Are they related to the patient’s chronic gastritis? 108 54