Lecture 7: Histology of the SI and LI

Question 1

What is the plicae circulares?

Answer 1

folds in the jejunum wall with submucosal core, increases surface area

Question 2

Intestinal villi:
Epithelium?
Features?
Contains?

Answer 2

• simple columnar epithelium
• finger like folds on surface in SI with enterocytes and goblet cells in the epithelium
• vessels and lacteals (extension of lymphatics that are important for fat digestion)

Question 3

What is the importance of enterocytes and goblet cells?

Answer 3

Enterocyte: has lots of microvilli (increased SA) and secretes enzymes for digestion

Goblet cells: releases mucus for protection

Question 4

Characteristics of intestinal mucosa:
Epithelium?
Contains?

Answer 4

• simple columnar epithelium

- lamina propia and muscularis mucosae

Question 5

Characteristics of intestinal submucosa:
Type of CT?
Contains?

Answer 5

• dense irregular CT

- NV, lymphatics and glands

Question 6

Characteristics of the intestinal muscularis externa

Characteristics of the intestinal serosa

Answer 6

• inner circular and outer longitudinal muscle layers

- loose CT covered with visceral peritoneum

Question 7

Intestinal glands
Epithelium
Features

Answer 7

• simple columnar epithelium

- tubular glands and continuous with epithelium that covers villi

Question 8

Enteroendocrine cells (intestine):
Function?

Answer 8

-secrete peptide hormones for gut motility, and regulate secretion of enzymes

Question 9

Paneth cells
Found where?
Features
Function

Answer 9

• base of the intestinal glands
• pyramid shaped cells, eosinophilic, granular apical surface (stains differently from the rest of the gland)
• secretes anti-microbial substances like lysozyme and a-defensins

Question 10

Intestinal stem cells
where?
function?

Answer 10

• crypta base of the intestinal gland

- repopulating the epithelium with new cells that move up to the surface

Question 11

M (Microfold) cells:
Found where?
Function?

Answer 11

• epithelial cells found in the ileal mucosa by Peyer patches
• pocket contains immune cells that transport pathogens , apical surface has receptors that bind Gram (-) bacteria

Question 12

Gastroduodenal Junction

Pyloris vs. Duodenum

Answer 12

-transitiion between pylorus and duodenum

Pyloris: thick wall due to the sphincter muscle
Duodenum: Lots of Brunner’s glands deep to the MM

Question 13

Duodenum
Hallmark features
Functions

Answer 13

Brunner’s glands

Brunner’s neutralizes acidic chyme from stomach
hepatopancreatic ampulla collects bile and secretions

Question 14

Jejunum
Hallmark features
Contains?

Answer 14

• Longer finger like villi with lacteal in the core, no submucosal glands
• Lamina propia has lymphoid nodules

Question 15

Ileum

Hallmark features

Answer 15

-shorter finger like villi, Peyer’s patches (lymphoid nodules) with paneth cells at the base of the intestinal glands

Question 16

Ileoceccal Junction

Hallmark features

Answer 16

-ileoceccal valve that propels food into cecum, abrupt transition from small SI villi to glandular LI villi + thickened muscularis externa

Question 17

Colon:
Epithelium?
Hallmark features?

Answer 17

simple columnar epithelium

-tubular intestinal glands (crypts of Lieberkuhn), has glands and goblet cells with no villi

Question 18

Characteristics of colon mucosa:

Colon submucosa:

Colon muscularis externa

Answer 18

• has colonocytes, goblet cells, extensive GALT
• dense irregular CT
• outer layer has taeniae coli forming the haustra of LI, serosa at intraperitoneal portions of the colon

Question 19

Hirschsprung’s Disease
Cause
Clinical
Treatment

Answer 19

RET mutation = failure of NCC migration resulting in lack of ganglionic plexus in distal colon = difficulty of bowel movements due to colon always contracted

• constipation, abd. distention, delayed BM <48 hours post birth
• surgical removal of affected segment

Question 20

What comprises the rectum?

What type of epithelium does the rectum proper have?

Answer 20

Upper part: rectum proper
Lower part: Anal canal

simple columnar

Question 21

Portions of the anal canal (in to out):

Answer 21

Colorectal zone
Anal transitional zone
Squamous zone

Question 22

Epithelium transitions of the anal canal

Answer 22

C zone: simple columnar epithelium
ATZ: simple columnar > startified squamous
Squamous: stratified squamous (continuous with skin)