Histology of the SI and LI

Question 1

Small Intestine

Answer 1

duodenum, jejunum, and ileum

principle site for digestion of food and absorption of digestion products

Question 2

Plicae circulares

Answer 2

transverse folds with a submucosal core
-cannot lay flat if distended
not in duodenum, visible in jejunum, less so in ileum
-foldings of the entire mucosa, and some submucosa
-covered with intestinal villi

Question 3

Intestinal Villi

Answer 3

mucosal folds that project into lumen and cover surface of SI
- increase absorptive surface area

Question 4

enterocytes

Answer 4

simple columnar cells that produce enzymes for digestion and absorption

Question 5

goblet cells

Answer 5

provide mucus coat to shield from abrasion and bacterial invasion

Question 6

lacteal

Answer 6

lymphatic structure in intestinal villi that is important for absorption

Question 7

Villi

Answer 7

Finger like folds of mucosa projecting into the lumen

covered by microvilli

Question 8

Enterocyte microvilli

Answer 8

striated border

• provide amplification of luminal surface
• glycocalyx coat assists in nutrient uptake
• actin microfilament core anchors to other proteins and myosin 1 via terminal web
• terminal web permits contraction of microvilli

Question 9

Intestinal Glands

Answer 9

simple tubular glands lined by simple columnar epi.

1) enteroendocrine cells
2) paneth cells
3) intestinal stem cells
4) microfold (M) cells
- continuous w/ simple columnar that covers intestinal villi
- open onto the luminal surface of the intestine at the base of the villi

Question 10

enteroendocrine cell

Answer 10

found throughout the intestinal glands
-secrete peptide hormones to control gut motility, regulate secretion of enzymes, HCL, bile and other components for digestion

Question 11

Secretin

Answer 11

stimulates bicarbonate secretion by the pancreatic duct

it enhances insulin secretion by B cells of the islet of langerhans

Question 12

Cholecystokinin

Answer 12

it slows down emptying of the stomach by acting on the pyloric sphincter
it stimulates bile release from the gallbladder and teh secretion of pancreatic enzymes

Question 13

gastrin

Answer 13

it stimulates the secretion of the HCL by parietal cells
it stimulates insulin secretion by B cells of the islet of langerhans
also stimulates gastric motility and growth of the mucosal cells

Question 14

Paneth Cells

Answer 14

pyramidal shaped cells at base of intestinal glands

• funcitons in innate immunity by secreting antimicrobial substances (lysozyme, a-defensins, other glycoproteins)
• regulate normal bacterial flora via antibacterial action and phago.
• sometimes found in LI (just a lil)

Question 15

Intestinal Stem Cells (ISCs)

Answer 15

reside in niche at crypt base, near paneth cells
repopulate epi lining
daughter cells move out of the crypts…differentiate into goblet cells, enterocytes, enteroendocrine cells

Question 16

Microfold (M) cells

Answer 16

specialized cells that overlie peyer’s patches and other large lymphatic nodules
-has microfolds and thin glycocalyx
-has a deep pocket like recesss connected to extracellular space, houses dendritic cells, macrophages, and T and B cells
-internalize and transfer pathogens (e coli_ to immune cells
AG TRANSPORTING CELLS

Question 17

Gastroduodenal junction

Answer 17

pyloris: thick wall due to presence of the pyloric sphincter muscle. pyloric glands at base of each gastric pit
duodenum: abundant brunner’s glands in submucosa. DEEP to mm. secretory mucosa w/ villi

basically look at submucosa area..has brunner’s glands? ITS SI starting!

Question 18

Duodenum

Answer 18

initial segment of SI
BRUNNERS glands in submucosa
=tubuloacinar mucous glands…produce alkaline secretion which neutralize the acidic chyme
-collects bile and pancreatic secretions bia the hepatopancreatic ampulla
leaf like villi

Question 19

Jejunum

Answer 19

long finger like villi (typically longest)
-tubular intestinal glands
-villus core contains well developed lacteal
NO SUBMUCOSAL glands
-lymphoid nodules/follicles in the LP

Question 20

Ileum

Answer 20

PEYERS PATCHES!!! =mucosal lymphoid nodules specific to ileum
finger like villi shorter than jejunum typically
paneth cells found at base of intestinal glands

Question 21

Ileocecal junction

Answer 21

food is propelled from ileum into cecum through ileocecal valve
-abrupt transition from villi of SI to glandular epi. of LI
-valve has thickened extension of the MM.
(critical function is to limit reflex of colonic contents into ileum
-mus. externa is also somewhat thickened

Question 22

Large intestine

Answer 22

absorbs water, sodium, vitamins, will uptake sedatives, anesthetics, steroids
openings of tubular intestinal glands (crypts of LIERBURKUHN) are hallmark of MUCOSA
-hall mark: intestinal glands, goblet cells but no intestinal villi

Question 23

crypts of lierberkuhn

Answer 23

openings of tubular intestinal glands of the large intestine. they are the hallmark of the mucosa
-lined by a large number of GCs

Question 24

Hallmark of the colon

Answer 24

glands consisting of simple columnar epi. with numerous goblet cells

Question 25

Hirschprung's disease

Answer 25

aganglionosis in the distal colon - mutations of the RET gene required for migration and differentiation of NCC - failure of NCC development in both plexuses of a bowel segment

Question 26

short segment disease

Answer 26

HIRSCHPRUNGS | 85% of cases..confined to rectosigmoid region

Question 27

long-segment disease

Answer 27

HIRSCHPLUNGS 10% of cases extends past rectosigmoid region --> splenic flexure

Question 28

Total colonic anganglionosis

Answer 28

HIRSCHPLUNGS 5% of cases affects entire colon

Question 29

Hirschplungs disease presentation/diagnosis/treatment

Answer 29

presentation: constipation, poor feeding, and progressive abdominal distention dx: delayed BM < 48 hrs after birth, rectal biopsy, barium enema tx: surgical removal of the affected colon segment, pull through of ganglionic colon segments

Question 30

inflammatory bowel disease

Answer 30

includes ulcerative colitis and crohns disease | -characterized by diarrhea, pain, and periodic relapses

Question 31

Ulcerative colitis

Answer 31

affects the mucosa of the LI

Question 32

Crohns disease

Answer 32

affects any segment of the intestinal tract - chronic inflammatory process involving the terminal ileum, also obs. in LI - inflammatory cells produce cytokines that cause damage to the intestinal mucosa - infiltration of neutrophils into the crypts of lieberkuhn --> destruction of intestinal glands due to crypt abcesses --> progressive atrophy, ulceration

Question 33

Rectum proper

Answer 33

typical mucosa with tubular intestinal glands, transverse rectal folds

Question 34

Anal canal (lower part)

Answer 34

1) anal column- with mucosal folds 2) anal sinuses- depressions btwn columns 3) anal glands- extend into submucosa and muscularis externa circumanal glands, large apocrine glands surrounding the anal orifice

Question 35

Colorectal zone of anal canal

Answer 35

simple columnar epi. identical to the rectum (upper 1/3)

Question 36

anal transition zone

Answer 36

simple columnar epi --> stratified squamous epi of perianal skin (middle 1/3)

Question 37

squamous zone

Answer 37

stratified squamous epi continuous w/ perianal skin (lower 1/3)

Question 38

internal anal sphincter

Answer 38

at the level of the anus, inner circular layer thickens to form the internal anal sphincter