Lec 29 - Esophagus and stomach

• The general organization of the GI tract is

  Mucosa

  • epithelium
  • lamina propria
  • muscularis mucosae

  Submucosa

  Muscularis externa

  • inner circular layer
  • outer longitudinal layer

  serosa or adventitia
• The lamina propria in the GI tract is made up of Loose connective tissue, contains WBCs, adipose, nerves, lymph vessels, and blood vessels. It helps with immune and nutrient absorption
• The muscularis mucosae is a thin layer of smooth muscle in the mucosa layer to help control the shape of the lumen
• The submucosa in the GI tract is dense irregular connective tissue. It helps deal with the stretching in all directions
• The inner circular layer and outer longitudinal layer of the muscularis externa collectively work to do peristalsis
• There are two nerve plexuses in the GI tract that collectively form the enteric nervous system

  • myenteric nerve plexus
  • submucosal nerve plexus
• The myenteric nerve plexuses is found between the two layers of the muscularis externa. It controls smooth muscle and peristalsis
• The submucosal nerve plexus is found within the submuscosa. It is responsible for gland secretion and control of the muscularis mucosa
• The enteric nervous system gets input from the autonomic nervous system. But, if you sever the connection, the enteric nervous system can function independently
• Based on the muscle in the muscularis externa, you can tell which region of the esophagus you are seeing in the histological slide

  • upper 1/3 = striated (skeletal) muscle which is under voluntary control because we initiate swallowing
  • middle 1/3 = striated and smooth muscle
  • lower 1/3 = smooth muscle
• In the esophagus, the submucosa will contain esophageal glands and lymphatic nodules (GALT). The esophagus also contains a adventitia until the stomach
• Label this section of the esophagus

  A) mucosa

  B) submucosa

  C) muscularis externus

  D) adventitia

  E) esophageal gland

  F) lymphatic nodule

  
• The esophagus epithelium is stratified squamous non-keratinized epithelium. This performs the barrier function
• The esophagus contains esophageal glands to lubricate as you swallow
• Label the regions of the stomach

  A) fundus

  B) esophagus

  C) cardia

  D) body

  E) pyloric canal

  F) pylorus

  
• The stomach consists of 4 regions

  • cardia
  • fundus
  • body
  • pylorus
• At the gastroesophageal junction, the epithelium has a very obvious change from stratified squamous non-keratinized epithelium to simple columnar epithelium that have a lot of mucus excreting cells

  
• The stomach contains epithelium that invaginates to form gastric pits and gastric glands
• The stomach contains an extra layer of the muscularis externa - the oblique layer
• The mucosa layer of the stomach contains folds called rugae
• The mucosa of the stomach is different in different regions

  • pylorus - really long gastric pits and coiled tubular glands filled with mucin
  • cardia - medium length pits and coiled tubular glands producing mucin
  • fundus/body - short gastric pits and glands with many different cell types
• The pylorus and cardia primarily secrete mucus to neutralize stomach acid
• Label the gastric lumen

  A) gastric pit

  B) surface mucus cells

  C) isthmus

  D) neck

  E) parietal cell

  F) enteroendocrine cell

  G) chief cells

  
• Label the regions of the gastric lumen

  A) gastric pit

  B) gastric gland

  
• Surface mucus cells secrete mucin and bicarbonate to neutralize HCL-. The mucus is viscous and alkaline. They are simple columnar cells with a basal nuclei
• Mucus neck cells have a more watery mucus secretion. Still secrete mucin. Their mucous is soluble in response to nerve stimuli - when something enters the stomach, it sends out a signal

  
• Parietal cells produce and secrete HCl- and intrinsic factor (help absorb B12 in our duodenum). They are abundant in mitochondria and contain canaliculi. They are super eosinophilic and have a large central nucleus

  
• Chief cells are found in the fundic region. They produce pepsinogen and lipase (the enzymes that will do digestion). Pepsinogen and lipase are first secreted as proenzymes that are activated by HCl-. They contain lots of secretory granules. They are very basophilic near their base because they contain lots of rER

  
• Enteroendocrine cells are the hormone producing cells of the stomach. They secrete gastrin into the circulation. Gastrin will stimulate parietal cells to produce HCl-. Secretory vesicles seen at basal side of cell because it secretes into bloodstream not the lumen

  
• Stomach cell turnover is extremely high. Resevior stem cells are found in the isthmus of the gastric gland. They migrate bi-directionally and differentiate into several different cell types. (cell surface renewal - 4-7 days, slow gland cell renewal - weeks)