Lec 30 - Intestines

• List of all the ways in the intestine to increase surface area

  • highly folded small intestine
  • plica circularis (folds in the mucosa and submucosa)
  • villi (folds of the mucosa)
  • microvilli
  • glycocalyx
• Cells of the intestine are called enterocytes
• The epithelium that makes up the small intestine is simple columnar epithelium with goblet cells and microvilli
• The arrow in this image is pointing to plica circularis in the small intestine

  
• Label this image of the small intestine

  A) villi

  B) muscularis mucosa

  C) intestinal glands

  D) submucosa

  E) muscularis externa

  
• The mucosa of the small intestine features villi with a core of lamina propria and intestinal glands
• Inside the lamina propria of the intestinal villi is going to be blood vessels, capillary bed for nutrient absorption and lacteal (blind-ended pouches) for absorbing fats
• The muscularis mucosa in the villi of the intestine helps squeeze lacteals to push contents towards the rest of the lymphatic system
• Label the components of intestinal villi

  A) lacteal

  B) brush border

  C) goblet cell

  D) lamina propria

  E) endothelial cells

  F) muscularis mucosa

  
• The role of the goblet cells in the small intestine is to secrete mucus to cover cell surface and protect cells from acidity and neutralize the acidity
• The cells of the intestinal epithelium

  • enterocyte
  • goblet cell
  • enteroendocrine cell
  • paneth cell
• The enteroendocrine cell in the intestine secretes secretin and cholecystokinin through their basal surface. These effect the liver, gallbladder, pancreas, etc. to initiate the release of other digestive enzymes
• Paneth cells produce a lot of enzymes. They have a basophilic nucleus and lots of rER. Have an eosinophilic apical region
• Most of our digestive enzymes are released as proenzymes. Enterokinases located on the microvilli cleaves the proteins to their active form. This is so enzymes are not just actively digesting all the time without any stimulation
• The highlighted cells are paneth cells

  
• Enteroendocrine cells can only be distinguished from enterocytes by electron microscopy. Notice all the granules at the basal surface of the cell.

  
• Cell renewal in the intestines

  • stem cells are found at bottom of the intestinal glands
  • they are unidirectional - only travel up
  • replace all cell types
  • regenerate quickly (3-6 days)
• The three parts of the small intestine

  • duodenum
  • jejunum
  • ileum
• To distinguish the three portions of the small intestine

  • duodenum contains brunner's glands that secrete mucus. This gives a bubble wrap looking appearance to the submucosa
  • ileum contains peyer's patches which are lymphatic nodules that start in the submucosa and extend into the lamina propria
• The duodenum contains a lot of mucus glands to protect itself from the very acidic stomach chime that drains into here
• Label this section of the duodenum

  A) villi

  B) muscularis mucosa

  C) submucosa

  D) mucus glands

  E) muscularis externa

  
• This section of the intestines in the ileum

  
• Within the peyer's patches of the ileum there are cells called microfold cells. These cells create a hollow chamber that allows immune cells to hide inside the cell to allow them to get really close to the lumen without going into the lumen
• The lamina propria of the ileum will contain a lot of plasma cells. These plasma cells will produce antibodies that get taken up by the enterocyte and get secreted into the lumen to detect antigens
• Within the colon there are no villi. The main role of the colon is electrolyte and water reabsorption. The colon contain haustra, which are out pouching that allow for slower transport and more absorption. The colon also contain tenia coli which are thickenings of the muscularis externa - specifically the longitudinal muscle
• Label the colon

  A) plica semilunaris

  B) haustra

  C) tenia coli

  
• The colon is abundant in goblet cells to help move things along
• These are sections of the colon

  A) tenia coli