Histology of Small and Large Intestines

Question 1

Intestinal villi

Answer 1

Mucosal folds that project into lumen and cover surface of SI
Covered with simple columnar epithelium of enterocytes and goblet cells
Villi are covered with microvilli

Question 2

Mucosal layers of SI

Answer 2

Mucosa
Submucosa
Muscularis
Serosa

Question 3

Mucosa of SI

Answer 3

Simple columnar epithelium w/tubular intestinal glands - lamina propria and muscularis mucosae

Question 4

Submucosa of SI

Answer 4

Dense irregular CT - neurovasculature, lymphatics, glands

Question 5

Muscularis of SI

Answer 5

Inner circular and outer longitudinal

Question 6

Serosa of SI

Answer 6

Loose CT covered by visceral peritoneum

Question 7

Intestinal glands

Answer 7

Simple tubular glands lined by simple columnar epi
Enteroendocrine cells
Paneth cells
M (microfold) cells
Intestinal stem cells
Continuous w/simple columnar that covers intestinal villi

Question 8

Enteroendocrine cells

Answer 8

Found throughout intestinal cells
Secrete peptide hormones to control motility, regulate secretion of enzymes, HCl, bile and others
Gastrin, secretin, gastric inhibitory peptide GIP, motilin and cholecystokinin

Question 9

Paneth cell

Answer 9

Large, eosinophilic secretory granules in apical cytoplasm
Functions in innate immunity by secreting antimicrobial substances
Regulate normal bacterial flora

Question 10

Intestinal stem cells

Answer 10

Reside in niche at crypt base, near Paneth cells
Repopulate epithelial lining
Daughter cells move out of crypts and differentiate into goblet cells, enterocytes and enteroendocrine cells

Question 11

M cells

Answer 11

Epithelial cells specialized for epithelial transport of particles and microorganisms
Located in ileal mucosa, overlying peyer patches
Apical surface expresses receptors that bind macromolecules and gram- bacteria
Function as highly specialized antigen transporting cells

Question 12

Duodenum at gastroduodenal junction

Answer 12

Abundant Brunners glands in submucosa, DEEP to the muscularis mucosae- produce alkaline secretion to neutralize acidic chyme
Secretory mucosa with villi
Collects bile and pancreatic secretions via the hepatopancreatic ampulla

Question 13

Jejunum

Answer 13

Long finger-like villi, villus core with a well developed lacteal
No submucosal glands
Lymphoid nodules in lamina propria

Question 14

Ileum

Answer 14

Finger like villi (shorter than jejunum)
Peyers patches** - mucosal lymphoid nodules specific to ileum
Paneth cells found at base of intestinal glands

Question 15

Ileoceccal junction

Answer 15

Food projected through ileocecal valve
Abrupt transition from villi of SI to glandular epithelium of LI
Valve has thickened extension of muscularis mucosae and muscularis externa to prevent refulx

Question 16

Large intestine hallmarks

Answer 16

Openings of tubular intestinal glands (crypts of Lieberkühn)

Intestinal glands, goblet cells but NO intestinal villi

Question 17

Large intestine mucosa

Answer 17

Glandular, simple columnar
Colonocytes, goblet cells, stem cells and enteroendocrine cells
Lamina propria and muscularis mucosase present
GALT is extensive and may penetrate submucosa

Question 18

Submucosa of LI

Answer 18

Dense irregular CT vascularized

Question 19

Muscularis of LI

Answer 19

Inner layer is typical

Outer longitudinal layer arranged into taeniae coli, will form haustra of LI

Question 20

Serosa of LI

Answer 20

Intraperitoneal portions of colon are covered by serosa

Question 21

Glands of colon

Answer 21

Simple columnar epithelium with NUMEROUS goblet cells- hallmark of colon

Question 22

Hirschprungs disease

Answer 22

Aganglionosis in the distal colon
Mutations of RET gene required for migration and differentiation of NCC
Failure of NCC development in both plexuses of a bowel segment
Mostly confined to rectosigmoid region
Sometimes extends to splenic flexure or entire colon

Question 23

Hirschprungs disease presentation

Answer 23

Constipation, poor feeding, abdominal distension

Remove affected colon segment

Question 24

Rectum proper

Answer 24

Upper part

Typical mucosa with tubular intestinal glands, transverse rectal folds

Question 25

Anal canal

Answer 25

Lower part
Anal columns with mucosal folds
Anal sinuses- depressions b/w columns
Anal glands- extend into submucosa and muscularis externa

Question 26

Circumanal glands

Answer 26

Large apocrine glands surrounding anal orifice

Question 27

Anal canal colorectal zone

Answer 27

Simple columnar epithelium identical to rectum

Question 28

Anal transition zone

Answer 28

Simple columnar–>stratified squamous of perianal skin

Question 29

Squamous zone

Answer 29

Stratified squamous epithelium continuous with perineal skin