Digestive System 1 Dr. Zahiri

Pharynx Pharynx is a transitional zone between oral cavity and esophagus and trachea It is lined by stratified squamous nonkeratinized epithelium with submucosal glands Pharynx has thin lamina propria In more caudal areas, epithelium may be pseudostratified columnar ciliated with goblet cells Dr. Maria Zahiri

Digestive Tract Digestive tract is consists of: Oral cavity Esophagus Stomach Small Intestine Large Intestine Rectum Anus Dr. Maria Zahiri

Common Structure of Digestive Tract Digestive tract is a hollow tube of varying diameter with wall made up of 4 layers Mucosa Submucosa Muscularis externa Serosa or adventitia Dr. Maria Zahiri

Mucosa Epithelial lining Lamina propria Stomach to colon is simple columnar Other areas are mostly stratified squamous Lamina propria is a loose connective tissue with blood and lymphatic vessels, glands and lymphoid nodules Muscularis mucosa is composed of an inner circular layer and an outer longitudinal layer of smooth muscle Dr. Maria Zahiri

Submucosa Submucosa composed of dense irregular fibroelastic connective tissue with many blood and lymphatic vessels It may have nerve plexus known as Meissner’s submucosal plexus It may contain glands and lymphoid nodules Dr. Maria Zahiri

Muscularis Externa Inner circular layer and Outer longitudinal layer of smooth muscle cells Stomach has inner oblique layer in addition to the other 2 layers Myenteric (Auerbach’s) plexus made up of millions of neurons lies between smooth muscle layers Dr. Maria Zahiri

Serosa or Adventitia Both serosa and adventitia are composed of loose connective tissue rich in blood and lymphatic vessels Adipose tissue often is plentiful Simple squamous layer of mesothelium presented when an organ is intraperitoneal and it is known as serosa Dr. Maria Zahiri

Functions of Epithelium in Digestive Tract It acts as a permeability barrier between gut lumen and blood Transport and digest food Secretes different types of enzymes Absorb nutrients Produce and secrete hormones involved in digestion Dr. Maria Zahiri

Dr. Maria Zahiri

Esophagus Mucosa: has a thick stratified squamous nonkeratinized epithelium Mucous glands known as esophageal cardiac glands are plentiful in lamina propria near the junction with stomach (cardia) and pharynx Muscularis mucosa is unusual consists of a single layer of longitudinally oriented smooth muscle cells Submucosa houses mucous glands known as esophageal glands proper, that are tubuloacinar glands with mucous and serous cells Dr. Maria Zahiri

Esophagous Muscularis externa in upper esophagus has only skeletal muscle fibers Middle esophagus has a mixture of skeletal and smooth muscle cells Lower esophagus has only smooth muscle cells Adventitia covers esophagus until it pierce the diaphragm, after which it is replaced by a serosa At the junction of the esophagus with the stomach: change in the epithelial lining from the stratified squamous epithelium to the simple columnar epithelium Dr. Maria Zahiri

Dr. Maria Zahiri

Gastroesophageal Reflux Disease (GERD) Normal histology of the esophagus Histology from a patient with reflux esophagitis. Dr. Maria Zahiri

Stomach Stomach has 4 regions known as cardia, fundus, body, and pylorus fundus and body are identical histologically Thick muscle layers grind and mix food Secretions of enzymes and acid begin digestion Gastric wall is highly folded display rugae Dr. Maria Zahiri

Dr. Maria Zahiri

Stomach Mucosa Surface epithelium is simple columnar mucous producing cells (does not change throughout the stomach) Produce Alkalin sheat (mucus) against acidic contents of the stomach gastric pits: Surface epithelium invaginates into lamina propria Gastric glands open at the base of pits Cardiac, fundic and pyloric glands differ from each other Lamina propria composed of loose CT with smooth muscle and lymphocytes and occupied mainly by glands Muscularis mucosa consists of inner circular and outer longitudinal smooth muscle layers Dr. Maria Zahiri

Dr. Maria Zahiri

Dr. Maria Zahiri

Gastric Pits and Epithelial lining Simple columnar epithelium of mucus producing cells Cells have a height about 20-40 µm An oval nucleus located in basal cytoplasm Many mucus granules aggregate in apical cytoplasm Thick mucus layer known as visible mucus protects stomach epithelium from autodigestion Junctional complexes at lateral surface attach cells together Regenerative cells are presented at the base of these pits but are numerous in the neck of the glands Dr. Maria Zahiri

peptic ulcer, also known as peptic ulcer disease (PUD) is a distinct breach in the mucosa of the stomach as a result of caustic effects of acid and pepsin in the lumen. Histologically, peptic ulcer is identified as necrosis of the mucosa which produces lesions . It is the most common ulcer of an area of the gastrointestinal tract that is usually acidic and thus extremely painful. Helicobacter pylori is one of the most common causes of peptic ulcer. Ulcers can also be caused or worsened by drugs such as aspirin, ibuprofen, and other NSAIDs (Nonsteroidal anti-inflammatory drugs), ethanol. Dr. Maria Zahiri

Cells of Gastric Gland There is 6 different cell types: Surface lining cells Mucous neck cells Regenerative (stem) cells Parietal cells Chief (Zymogenic) cells DNES (APUD or Entroendocrine cells) Dr. Maria Zahiri

Cardiac Region Cardiac region is a narrow band 1.5-3 cm in width, at the gastroesophageal junction It has simple or branched tubular cardiac glands with large lumen at terminus Glands are shallow, slightly coiled Composed mostly of: surface lining and mucous neck cells a few parietal and DNES cells no chief cells Dr. Maria Zahiri

Fundus and Body Gastric pits are narrow and shallow in fundus and body of the stomach Glands are long and straight Many parietal and chief cells are in glands Neck of gland has undifferentiated cells and mucous cells Base of glands have parietal cells, chief cells and enteroendocrine cells Dr. Maria Zahiri

Cells of the Fundus Undifferentiated cells: are narrow columnar cells that located in neck of gland have oval basal nuclei, distinct nucleolus, mitotic figures stem cells surface cells survive 3-7 days and replaced by these cells Dr. Maria Zahiri

have a basal irregular nuclei Mucous neck cells: have a basal irregular nuclei mucous granules, this mucus is soluble and lubricate the gastric contents Dr. Maria Zahiri

Parietal ( oxyntic) cells: located in upper half of glands have eosinophilic cytoplasm and many mitochondria. Produce HCl and intrinsic factor Dr. Maria Zahiri

In EM: Intracellular canaliculi and a tubulovesivular system are prominent features of this cell Dr. Maria Zahiri

Dr. Maria Zahiri

Chief cells (zymogenic) located in deeper portion of the glands They are basophilic due to many ribosomes Produce pepsinogen, renin, gastric lipase and serous Dr. Maria Zahiri

Pernicious anemia (also known as Addison's anemia) atrophic gastritis or autoimmune destruction of gastric parietal cells loss of gastric parietal cells secretion of intrinsic factor absorption of vitamin B12 in the ileum Dr. Maria Zahiri

Dr. Maria Zahiri

manufacture endocrine, paracrine, and neurocrine hormone Enteroendocrine cells "argetaffin cells" ("silver affinity"), APUD (Amine Precursor Uptake & Decarboxylase ) manufacture endocrine, paracrine, and neurocrine hormone Located in the base of glands, in light microscopy appear as clear cell Dr. Maria Zahiri

Pylorus Pylorus has deep and open gastric pits with short coiled glands Mucous neck cells are most predominant which produce mucous and lysozyme Parietal cells and DNES are few G cells Gastrin parietal cell HCl output D cells somatostatin Dr. Maria Zahiri

Stomach Submucosa Submucosa is composed of irregular collagenous connective tissue Contains blood and lymphatic vessels Lymphoid and mast cells and other cells like CT proper are located in submucosa Submucosal plexus is near muscularis externa Dr. Maria Zahiri

Stomach Muscularis Externa Muscularis Externa has 3 layers Internal oblique layer is not well defined except at cardiac region Middle is circular layer (forms pyloric sphincter) Outer longitudinal layer pronounced at cardiac region and body The myenteric plexus is located between the middle and outer layers Serosa Serosa composed of a thin layer of loose CT with covering of wet simple squamous mesothelium Dr. Maria Zahiri

Small Intestine Small Intestine functions in completion of digestion and absorption of nutrients It has 3 segments: duodenum, jejunum, and ileum The surface area of intestine is enlarged by the formation of plicae circularis (Kerckring valve), villi, microvilli, and crypts of Lieberkuhn Villi of lamina propria are leaf-shaped in duodenum, finger- shaped in ileum and jejunum Dr. Maria Zahiri

Small Intestine At the base of villi are simple tubular glands known as crypts of Lieberkuhn Crypts have the following cells: Regenerative cells (stem cells) Absorptive cells Goblet cells Paneth cells M cells Entroendocrine cells Dr. Maria Zahiri

Dr. Maria Zahiri

Absorptive Cells (enterocytes) are tall columnar cells with oval basal nucleus and rich in organelles (RER,SER, GA, endosomes) Apical surface has many microvilli that form striated border Each cell has about 3000 microvilli for increased surface area covered by a thick glycocalyx layer which have enzymatic components Lateral cell membrane form junctional complexes These cells function in terminal digestion and absorption Disacharidase & proteinase Dr. Maria Zahiri

Goblet Cells are Few in duodenum but many in ileum Unicellular glands that produce mucinogen whose hydrated form is mucin a component of mucus It acts to protect and lubricate epithelium Dr. Maria Zahiri

Regenerative cells Regenerative cells are stem cells that proliferate to repopulate the other cells Their rate of division is high Dr. Maria Zahiri

Paneth Cells Paneth Cells are located in basal area of gland They are exocrine serous, eosinophilic granules containing lysozyme Dr. Maria Zahiri

Microfold Cells Microfold Cells are specialized epithelial cells which are covering lymphoid follicles of Peyer’s patches They are cuboidal cells that can phagocytose antigens and transport them to underlying immune cells Dr. Maria Zahiri

Entroendocrine Cells These are Pale cells with small granules Constitute about 1% of the cells covering villi and intervillar surface Produce paracrine and endocrine hormones These hormones include: glucagon, gastrin, secretin, gastric inhibitory peptide, cholecystokinin, somatostatin, motilin, serotonin, substance P, vasoactive intestinal peptide Dr. Maria Zahiri

Dr. Maria Zahiri

Subepithelial Tissues Lamina propria is composed of loose connective tissue with blood and lymph vessels, nerves, smooth muscle, lymphoid cells and macrophages Lamina propria form core of the villi Muscularis mucosae is typical and enter the villus and extended through its core Submucosa is composed of dense irregular fibroelastic CT Duodenum has Brunner’s glands (mucous glands) Peyer’s patches mostly located in ileum Dr. Maria Zahiri

Peyer’s patches Peyer’s patches mostly located in ileum; there is about 30 patches that are composed of 10-200 lymphoid nodules; usual epithelium is replaced by M-cells Dr. Maria Zahiri

Brunner’s gland Brunner’s gland are branched, tubuloalveolar glands whose secretory portions resemble mucous acini Ducts of them usually pierce the base of the crypts of Libeberkuhn Secrete a mucus, alkaline fluid, and Urogastrone Dr. Maria Zahiri

Enteric Nervous System Enteric Nervous System is consists of Auerbach’s plexus and Meissner's plexus Neurons of Auerbach’s plexus located between layers of the muscularis externa Submucosal (Meissner's) plexus innervates submucosa (parasympathetic) Parasympathetic fibers increase gut activity Sympathetic adrenergic fibers decrease gut activity Dr. Maria Zahiri

Large Intestine(Colon) Mucosa of large intestine has folds except in rectum Colon has no villi Epithelium is columnar with short microvilli The absorptive cells are the most numerous cell type Glands of Lieberkuhn contain goblet cells and a few endocrine cells but there is not any paneth cells Dr. Maria Zahiri

Large Intestine(Colon) Functions of epithelium include water absorption, mucous production and feces formation Lamina propria has lymphoid cells and some nodules An increment in bacterial population Muscularis externa has typical circular layer; longitudinal layer forms 3 bands known as the taeniae coli Dr. Maria Zahiri

Dr. Maria Zahiri

Dr. Maria Zahiri

Appendix Appendix is an evagination of large intestine It has a narrow lumen with abundant lymphoid follicles in submucosa, and lamina propria Its Structure is similar to large intestine but has many more DNES cells It has not any teniae coli Dr. Maria Zahiri

Rectum Rectum resembles the colon but the crypts of Lieberkühn are deeper and fewer The mucosa contains numerous goblet cells The muscularis externa has both inner circular and outer longitudinal smooth muscle layers, no teniae coli Dr. Maria Zahiri

Anal Canal In anal canal the crypts are short and few and in distal half there is no crypts Mucosa has longitudinal folds, the anal columns (rectal columns of Morgagni) Dr. Maria Zahiri

Dr. Maria Zahiri

Anal Canal Epithelium is simple cuboidal from rectum to pectinate line, and stratified squamus nonkeratinaized from pectinate line to the external anal orifice At the anus epithelium changes to epidermis Lamina propria houses anal glands (at rectoanal junction) and circumanal glands (at distal end) Submucosa has plexus of large veins, if these become varicose they can become hemorrhoids Dr. Maria Zahiri

Anal Canal Muscularis externa consists of inner circular and outer longitudinal smooth muscle cells Inner circular layer thickened and form the internal anal sphincter External anal sphincter forms by skeletal muscles of floor of pelvis Dr. Maria Zahiri

Dr. Maria Zahiri

روزگارتان پر از خیر Dr. Maria Zahiri