12 Esophagus & Stomach

• 1. Specialized epithelial cells (M-cells) for antigen sampling
• 2. Large aggregations of diffuse and nodular lymphoid tissues (Peyer's patches in ileum)
• 3. Mucus coating traps potential pathogens (eg. bacteria)

• 1. Lumen →
• 2. Mucosa (epithelium, lamina propria, muscularis mucosa)
• 3. Submucosa (may have glands, nerves)
• 4. Muscularis Externa
• 5. will either have an Adventitia or Serosa, depending on where in GI tract you are

• lined by epithelium
• covered by the Lamina Propria: loose CT
• then covered by the Muscularis Mucosa: smooth muscle layer
• all together = MUCOSA (epithelium, loose CT, SM muscle)

• another muscular layer comprised of three components
• 1. muscularis mucosa: thin layer of smooth muscle that can assist in emptying glands
• 2. lamina propria: loose CT that contains immune cells
• 3. luminal epithelium: epithelial layer covering entire luminal surface of GI tract
• contains many of the structural and functional specializations of the different regions of the GI tract
• (eg. intestinal villi, crypts, gastric pits or glands)

• a connective tissue layer that lies between the muscularis externa and the muscularis mucosa
• contains blood vessels, nerves, parasympathetic ganglia, & lymphatics

• muscular layer deep to the serosa that consists of two layers of smooth muscle – an outer one that is longitudinal and inner one that is circular
• wave-like contractions of these opposed muscle layers (peristalsis) results in the efficient propulsion of food
• contractions are regulated by parasympathetic nerves & ganglia (myenteric plexus) that lie between the muscle layers

• outermost layer along most of the GI tract
• consists of two components: 1) simple squamous epithelium (mesothelium) that forms a slippery surface allowing intestines to slide over one another & 2) adventitia made of loose CT
• the serosa contains blood vessel, nerves & lymphatics

the mesentery

• the outermost layer connecting the GI tract to the body wall in regions where there is NO serosa, due to the absence of an epithelium
• most of the esophagus & part of the gall bladder

• In the esophagus it is a stratified squamous epithelium
• throughout the remainder of the tract it is a simple columnar epithelium (gastric epithelium)
• this epithelium is also continuous with the epithelial lining of the ducts and glands of the accessory digestive organs (the pancreas, liver & gall bladder)

• the outer esophagus lining = Adventitia until it crosses the diaphragm
• in the Thorax the outer layer = Adventitia
• within the abdominal cavity it's outermost region consists of a Serosa

in the upper 1/3

in the middle 1/3

lower 1/3

longitudinally

located in between muscle layers of the gut & esophageal wall of the Muscularis Externa

• nerve plexus in the submucosa that innervates the muscularis mucosa to control it’s contraction
• further down in the GI system it controls the emptying of glands

1. esophagus: producing a lubricating/protective mucous




visually the only place there's a submucosal gland deep to a SSNKE = esophagus

2. duodenum (small intestine): neutralizes partially digested acidic chyme (food from the stomach)

• it undergoes an abrupt change from the stratified squamous epithelium (of the esophagus) to the simple columnar epithelium (the gastric epithelium) of the stomach (and subsequently the intestines)

• when acidic contents of the stomach chronically bypass the lower esophageal sphincter (one-way valve), the esophageal SSNKE epithelial cells can undergo a transition to simple columnar epithelium
• METAPLASIA
• associated with the subsequent development of esophageal adenocarcinoma (lethal)

• Cardiac region: short pits & glands; mucous & enteroendocrine cells
• Fundus/Body region: short pits, long glands; thick surface mucous, mucous neck (clear), parietal, chief, & enteroendocrine cells
• fundus also has SM muscle cells running through mucosa to contract it, forcing gland contents into lumen 
• Pyloric region: long pits, short glands; mucous & enteroendocrine cell

• in the stomach by parietal (fried egg) cells
• made in the stomach but used in the gut for the absorption of vitamin B12
• issues with stomach lining or parietal cells can cause Vitamin B12 deficiency & eventually pernicious anemia

• in the stomach where food is also subjected to a grinding action
• outer (longitudinal), middle (circular) & inner (oblique)

1. surface mucous: simple columnar; protective against acid made in stomach

2. mucous neck

3. enteroendocrine

4. parietal: make HCl & intrinsic factor

5. gastric chief: make pepsinogen --> pepsin in acid

the cardiac & pyloric glands contain ONLY the first 3 cell types

the fundic/gastric glands contain all five

• mucous: 3-5 days
• endocrine: weeks
• chief & parietal: 90-200 days (months)

• PAS stained surface mucus & mucous neck cells
• mucus cells making thick bicarbonate mucus that serves to protect the stomach lining

• Parietal cells
• make HCl & Intrinsic Factor
• look like red (eosinophilic) fried eggs
• packed with mitochondria (red dots)
• clear areas in cell represent Intracellular Canaliculus - implies cells were active (secreting HCl)

• purple cells = chief cells
• basophilic because of abundant RER making pepsinogen
• typical protein secreting cells
• have a ton of zymogen granules that contain inactive enzymes: pepsinogen, lipase, chymosin

• when released into acid environment of gut from chief cells, the low pH (<5) causes autocatalytic activity, turning pepsinogen into pepsin
• when pepsin gets to neutral pH of duodenum, it's inactivated

• chronic inflammation of the stomach mucosa leading to loss of gastric glandular cells & their eventual replacement by intestinal & connective tissue
• ability for stomach to secrete substances is impaired (deficiency in intrinsic factor leads to vitamin B12 deficiency, pernicious anemia)
• can be caused by autoimmunity or by Helicobacter pylori infection
• will see lymphocyte infiltration

• bacteria convert urea to ammonia via urease
• this neutralizes acid of the stomach, & allows bacteria to penetrate into mucosal lining
• bacteria have proteins that look similar to stomach lining itself, so when the stomach makes antibodies against the bacteria, it damages self (autoimmune attack to the stomach lining)
• if chronic this can lead to Gastritis

• an cell abundant in the GI tract that requires special staining
• make numerous products including Gastrin, Somatostatin, Ghrelin, Enterochromaffin
• here they're visualized in the pyloric region (end) of the stomach (can see long pits, short glands)

a peptide hormone secreted by Eneteroendocrine (G) cells that stimulates secretion of HCl by parietal cells

• inhibits Gastrin release
• also inhibits release of CCK & Secretin, inhibiting pancreatic & gall
• bladder secretions

• the last part of the stomach overlies the pyloric sphincter, a thickened part of the Muscularis Externa that closes the stomach & only opens when digestion within the stomach is sufficient (material is liquid)
• as the sphincter opens it squirts that fluid into the duodenum (1st part of the SI)