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Flashcards in GI Tract Deck (24):

General Structure of the GI Tract

- wall around the tube (protective membrane)

- serous producing glands
- internal visceral layer
- outside parietal layer
- Secretion between the two to establish a boundary

2 Layers of Muscle
- Muscularis Externa - longitudinal
- Muscularis Mucosa - goes around the tube

Mucosa layer
- invaginations into the lumen to increase surface area for absorption of proper nutrients
- contains Plica Circularis

- behind mucosa
- lymphoid nodules and some glands



- Epithelial portion - stratified squamous non keratinized
- Some glands
- layer of smooth muscle - muscularis mucosa

Muscularis Externa
- longitudinal muscle
- skeletal muscle and smooth muscle

- lumen in very small compared to other portions of GI tract


Esophago-gastric Junction

- Where the esophagus meets the stomach
- Epithelium changes
- Goes from stratified squamous to simple columnar epithelium which invaginates as gastric pits


Cardiac Stomach

- Simple Columnar epithelium
- Gastric pits - invaginations
- Cardiac Glands - mucous secreting


Body and Fundus Stomach

- Large cavity
- many folds inside the body to expand the surface area (called rugae)
- Gastric pits become deeper and the glands become more complex


Pyloric Stomach

- Deeper gastric pits
- short pyloric glands which are coiled tubular branched
- secretes mostly mucous


Surface mucous cells

- on the surface of gastric pits
- secrete mucous
- serves as protection, preserves the content


Mucous neck cells

- under surface mucous cells
- secrete mucous


Parietal Cells

- Produce HCl and intrinsic factor
- needed for digestion
- When active - they secrete HCl
- there is a rearrangment of intracellular organelles when active
- More microvilli increase the surface are so there is more secretion
- Have a prominent Golgi and a lot of mitochondria due to their secretory nature


Chief Cells

- also called zymogenic cells
- Produce lipase - cleave lipids
- Takes care of any lipid content in the food
- Produce pepsinogen that is made into pepsin


G cells

- Produce gastrin


Enteroendocrine Cells

- Called Argentaffin cells because you use silver stain to find these
- secrete serotonin


HCl Production

- Secreted by parietal Cells
- Production consumes ATP - involves active transport
- Carbonic anhydrase - synthesizes bicarbonate
- Protons are channeled to the outside
- Bicarbonate ion is exchanged with Cl
- Cl is released with H to form HCl


Transition from the Stomach to the Intestine

- Duodenum is the beginning of the small intestine
- Change in mucosa from gastric pits to intestinal villi
- Sphincter- circle of smooth muscle that opens and closes at the end of stomach - Pyloric sphincter
- There is an increase in amount of microvilli for increased surface area for absorption


Structure of the small intestine

- Large number of glands and microvilli

Glands of Liberkuhn
- Goblet Cells - Secrete mucous
- Paneth Cells - secrete serous
- Absorptive Cells- able to absorb whats coming in GI Tract
- Argentiffin - endocrine cells
- Dividing cells constantly push cells upwards for replacement
- lymphocytes that give a connection with immune system

Microvilli contain some of the same cells
- Formed by actin
- Fibrin bridges between filaments of actin
- Villin - protein that forms the top of the microvilli
- smooth muscle inside
- Blood circulation and lymphoid circulation inside
- some nervous connection in submucosa and muscle



- Villi on surface
- short crypts compared to other parts of small intestine
- Long duodenal glands - Brunner's gland - typically branched and extend into submucosa



- Only surface villi and crypts of lieberkuhn



- surface villi with crypts of lieberkuhn


Peyer's Patches

- in Ileum
- lymphatic nodules
- immediately underneath mucosa


Large Intestine

- Colon
- Ileum goes into the cecum of the large intestine
- Ascending to tranverse to descending colon
- Sigmoid colon is the end which attaches to the rectum
- Disapperance of the villi in the large intestine
- both have crypts



- Plenty of lymphoid nodules
- has crypts in mucosa
- typically full of debris which is cleaned by the lymphoid nodules
- no villi


Teniae Coli

- Longitudinal muscle that has accumulated into 3 bands in the large intestine


Recto-Anal Junction

- Rectum lined by simple columnar epithelium and tubular glands changes to stratified squamous epithelium of anus


Cell Renewal in the GI Tract

- Stem cells are not as deep in the pits compared to the small intestine
- undergo mitosis, replacing the ones above and below them

Small and Large intestine
- stem cells are located at the bottom of the pits

Most of the epithelium of GI tract is non keratinized, so it is not very tough