GI Tract

Question 1

General Structure of the GI Tract

Answer 1

Mesentary
- wall around the tube (protective membrane)

Serosa

• 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

Submucosa

• behind mucosa
• lymphoid nodules and some glands

Question 2

Esophagus

Answer 2

Mucosa

• 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

Question 3

Esophago-gastric Junction

Answer 3

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

Question 4

Cardiac Stomach

Answer 4

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

Question 5

Body and Fundus Stomach

Answer 5

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

Question 6

Pyloric Stomach

Answer 6

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

Question 7

Surface mucous cells

Answer 7

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

Question 8

Mucous neck cells

Answer 8

• under surface mucous cells

- secrete mucous

Question 9

Parietal Cells

Answer 9

• 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

Question 10

Chief Cells

Answer 10

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

Question 11

G cells

Answer 11

• Produce gastrin

Question 12

Enteroendocrine Cells

Answer 12

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

Question 13

HCl Production

Answer 13

• 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

Question 14

Transition from the Stomach to the Intestine

Answer 14

• 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

Question 15

Structure of the small intestine

Answer 15

• 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

Question 16

Duodenum

Answer 16

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

Question 17

Jejunum

Answer 17

• Only surface villi and crypts of lieberkuhn

Question 18

Ileum

Answer 18

• surface villi with crypts of lieberkuhn

Question 19

Peyer’s Patches

Answer 19

• in Ileum
• lymphatic nodules
• immediately underneath mucosa

Question 20

Large Intestine

Answer 20

• 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

Question 21

Appendix

Answer 21

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

Question 22

Teniae Coli

Answer 22

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

Question 23

Recto-Anal Junction

Answer 23

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

Question 24

Cell Renewal in the GI Tract

Answer 24

Stomach

• 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