Lower GI Normal Structure/Function

Question 1

What are the 3 divisions of the small intestine?

Answer 1

duodenum
jejunum
ileum

Question 2

What is the function of the small intestine?

Answer 2

digest food and absorb end products

Question 3

What are the plicae circulares?

Answer 3

permanent mucosal folds present in the duodenum, jejunum and proximal ileum that increase the surface area by 2-3X

Question 4

What are the villi?

Answer 4

finger like projections of epithelium covered lamina propria that increase surface area by 10X

Question 5

What are the microvilli?

Answer 5

extensions of the epithelial cell apical plasma membrane that increases surface area by 20X

Question 6

What is contained within the villi lamina propria?

Answer 6

central lymphatic channel and capillaries

smooth muscle fibers, loose CT and lymphoid cells

Question 7

What cell types are contained in the crypts of lieberkuhn?

Answer 7

DNES cells, stem cells, paneth cells

Question 8

What cell types are contained in the SI epithelium?

Answer 8

enterocytes, goblet cells, DNES cells

Question 9

What type of epithelium is in the SI?

Answer 9

columnar

Question 10

What is the main function of the enterocyte?

Answer 10

terminal digestion and absorption of water and nutrients
-reesterify FAs into TGs, form chylomicrons, and transport the bulk of the absorbed nutrients into the lamina propria for distribution to the rest of the body

Question 11

What does the glycocalyx coat over the microvilli do?

Answer 11

protect
involved in digestion of disaccharides and dipeptides into monomers for adsorption through peptide hydrolases andd disaccharidases that are abundant on the apical surface

Question 12

What do goblet cells secrete? What does it’s product do?

Answer 12

mucin

lubricates and protects the intestine

Question 13

What does goblet cell mucin contain?

Answer 13

high MW glycoprotein macromolecules

Question 14

What happens to mucin after it was released?

Answer 14

granules become hydrated and expand several hundred fold

Question 15

What is located in the upper half of the crypt of lieberkuhn?

Answer 15

surface absorptive and goblet cells

Question 16

What is located in the basal half of the crypt?

Answer 16

mostly stem cells, DNES cell and paneth cells

Question 17

How often is small intestine epithelium replaced in humans?

Answer 17

every 3-6 days

Question 18

What do paneth cells secrete?

Answer 18

lysozyme & defensins

Question 19

What do defensins do?

Answer 19

neutralize bacterial and viral infections

Question 20

What does shortening of the villi assist with?

Answer 20

emptying the lacteal

Question 21

What is the extensive immune defense system in the form of lymphoid tissue?

Answer 21

GALT

Question 22

What are Peyer’s patches?

Answer 22

a coalescence of lymphoid nodules

Question 23

What are brunner’s glands?

Answer 23

alkaline mucus that neutralizes the pH of the gastric chyme and protects the duodenum, they also contain epidermal growth factor that may be involved in stem cell proliferation in the crypts

Question 24

Which enteric plexus controls secretion?

Answer 24

submucosal (meissner’s)

Question 25

What does the auerbach’s (myenteric) plexus control?

Answer 25

motor innervation to muscularis externa

secretomotor innervation to the mucosa

Question 26

What are the two types of movements in the small intestine called?

Answer 26

mixing and propulsion

Question 27

What are distinguishing features of the duodenum?

Answer 27

25cm
villi are broader, taller and more numerous per unit area
brunner’s glands

Question 28

What are disinguishing features of the jejunum?

Answer 28

villi are narrower, shorter and sparser

more goblet cells per unit area

Question 29

What are distinguishing features of the ileum?

Answer 29

villi are sparsest, shortest and narrowest

peyer’s patches

Question 30

List the regions of the large intestine

Answer 30

cecum
appendix
colon (ascending, transverse, descending, sigmoid)
rectum
anus

Question 31

What does the ileocecal valve do?

Answer 31

prevents reflux of cecal/colonic content back into the ileum

Question 32

What is the surface of the colon like?

Answer 32

smooth, no villi

does have crypts of lieberkuhn

Question 33

What cell type is missing from the colonic crypts that is present in the crypts of the small intestine?

Answer 33

paneth cells

Question 34

What are the differences between small and large intestine crypts?

Answer 34

crypts n the colon are longer and more glandular with an abundance of goblet cells
both have stem cells at the base of the crypts

Question 35

How often is the colonic mucosa replaced?

Answer 35

every 6-7 days

Question 36

What is the taenia coli?

Answer 36

muscularis externa outer longitudinal muscle arranged in three distinct bands that remain partially contracted and cause the large intestine to be puckered in o haustra coli sacculations

Question 37

What are the key features of the appendix?

Answer 37

masses of lymphoid tissues in the mucosa and submucosa

lymphoid tissues often forms follicles with germinal centers

Question 38

What is the terminal 12 cm of the GI tract called?

Answer 38

the rectum

Question 39

What is the rectal mucosa like?

Answer 39

similar to the colon except that the crypts are somewhat deeper and the goblet cells more abundant

Question 40

What change occurs at the recto anal junction?

Answer 40

epithelium transitions from simple to columnar to stratified squamous
(crypts disappear just prior to this junction and are replaced by large circumanal glands

Question 41

What are the two venous plexi found in the submucosa of the anal canal?

Answer 41

internal hemorrhoidal plexus
external hemorrhoidal plexus
*in older people and during pregnancy an increased in the size of the vessels in these plexuses can result in hemorrhoids

Question 42

What is located at the end of the anus?

Answer 42

a ring of thickened smooth muscle called the anal sphincter and distal to this is a circular band of striated muscle called the external anal sphincter