Histology of the SI & LI

Question 1

What are plicae circulares and where are they found?

Answer 1

transverse folds w/ submucosal core

more visible in jejunum of SI

Question 2

Intestinal villi

Answer 2

mucosal folds that project into lumen & cover surface of SI

simple columnar epi w/ enterocytes & goblet cells

Question 3

Role of SI enterocytes

Answer 3

produce enzymes for digestion & absorption

found in epithelium

Question 4

What glands are located in the submucosa of the duodenum?

Answer 4

Brunner’s glands

Question 5

What is the function of Brunner’s glands?

Answer 5

Secretion of an alkaline fluid to neutralize acidic chyme.

Question 6

Describe the 4 layers of SI

Answer 6

mucosa (simple columnar epi w/ enterocytes, GCs, & tubular glands)

submucosa (neurovasc, lymphatics & some glands)

muscularis (inner circular & outer longitud layers)

serosa (CT covered by visc peritoneum)

Question 7

Innervation of SI/LI

Answer 7

motility controlled by ANS

peristalsis/contraction by submucosal plexus (of Meissner) & myenteric plexus of Auerbach

Question 8

What is the structure of intestinal glands?

What cells compose intestinal glands?

Answer 8

simple tubular glands

enteroendocrine cells (secrete hormones)
Paneth cells
M cells
Intestinal stem cells

Question 9

How many submucosal glands do we find in the jejunum?

Answer 9

The jejunum has no submucosal glands.

Question 10

What do we call the lymphatic structure that assists with the absorption of fat in the intestinal villi?

Answer 10

Lacteal

Question 11

Role of enteroendocrine cells

Answer 11

found thru out intestinal glands

secrete peptide hormones to control gut motility, regulate secretion of enzymes, HCl, bile & other components for digestion

Question 12

Location & function of paneth cells

Answer 12

pyramidal shaped cells @ base of intestinal glands (super pink in color b/c lots of secretory granules)

function in innate immunity by secreting anti-microbial substances (lysozymes & alpha defensins) & regulate normal bacterial flora

Question 13

What is the role of M (microfold cells)?

Answer 13

function as highly specialized antigen-transporting cells in ileal mucosa (overlying Peyer patches)

bind macromolecules & bacteria (E coli) to internalize them & transfer to immune cells

Question 14

Histologically speaking, where are intestinal glands found?

Answer 14

Throughout the mucosal layer of the entire small intestine

Question 15

Describe the histology of the gastroduodenal junction

Answer 15

stomach will have thick muscle wall b/c pyloric sphincter muscle & pyloric glands @ base of each gastric pit

duodenum will have many Brunner’s glands in submucosa (deep to muscularis mucosae)

Question 16

Hallmarks of duodenum

Role of duodenum

Answer 16

Brunner’s glands in submucosa (to neutralize acidic chyme)

collect bile & pancreatic secretions via hepatopancreatic ampulla

Question 17

Hallmarks of jejunum

Answer 17

long finger-like villi (tubular intestinal glands & villus w/ lacteals)

NO submucosal glands

lymph nodules in lamina propria

Question 18

Hallmarks of ileum

Answer 18

shorter finger-like villi

Peyer’s patches (muscoal lymphoid nodules specific to ileum)

some paneth cells @ base of glands

Question 19

Histology of ileocecal junction

Answer 19

abrupt transition from villi of SI to glandular epithelium of LI

thickened muscularis

Question 20

Why is the valve @ the ileocecal junction thick?

Answer 20

thickened extension of muscularis mucosae that limits reflux of colonic contents into ileum

Question 21

Hallmarks of LI

Answer 21

GOBLET CELLS
NO intestinal villi
muscoa w/ tubular intestinal glands

Question 22

Why does the LI have goblet cells?

Answer 22

GC produce lots of mucus needed to move hard, solid waste thru tube

Question 23

What do we call the simple columnar cells of the large intestine epithelium?

Answer 23

Colonocytes

Question 24

What layer, in the colon, forms the tinea coli?

Answer 24

The outer longitudinal layer of the muscularis externae

form haustra of LI

Question 25

Why would the GALT of the LI be extensive?

Answer 25

b/c gut is exposed to external environment

Question 26

What is the basic pathophysiology of Hirschsprung’s disease?

Answer 26

Neural crest cells fail to differentiate causing an absence of both plexuses in the colon or bowel segment. This results in absent peristalsis, and leads to megacolon through impactions.

Question 27

Hirschsprung’s disease presentation, diagnosis & treatment

Answer 27

present w/ constipation, poor feeding & progressive ab distension

diagnosed w/ delayed BM<48hrs after birth, rectal biopsy

treatment by removing affect colon segment & pulling through ganglionic colon segments that are properly innervated

Question 28

What is the most common type of Hirschsprung’s disease?

Answer 28

“Short segment disease” – where the issue is confined to the “rectosigmoid region” (rectum and sigmoid colon).

Question 29

What are the three divisions of the anal canal?

Answer 29

The colorectal zone, the anal transitional zone, and the squamous zone.

Question 30

Where does the enteric nervous system end?

Answer 30

At the anal transitional zone of the anal canal

Question 31

Describe histology of the rectum (upper part)

Answer 31

typical muscoa w/ tubular intestinal glands & transverse rectal folds

Question 32

Where are circumanal glands found?

Answer 32

large apocrine glands (release of apical portion of cell) surrounding anal orifice

Question 33

When can you see anal sinuses?

Answer 33

when bowel is empty

Question 34

Where are anal glands found?

Answer 34

Extending into the submucosa and muscularis externa of the anal canal

Question 35

What are the anal columns formed from?

Answer 35

Mucosal folds of the anal canal

Question 36

Describe different zones of anal canal

Answer 36

colorectal zone-simple columnar epi

anal transitional zone-simple columnar & stratified squamous

squamous zone-stratified squamous epi (blending w/ peri-anal skin)