Histology of SI and LI

Question 1

Small Intestine

• parts
• function
• characteristics

Answer 1

Duodenum, jejunum, ileum

Principal site for digestion of food & absorption of digestion products

Pilcae circulares (arrows):

• transverse folds with a submucosal core
  
  • cannot lay flat if distended
  • visible in jejunum, less so in ileum

Question 2

Intestinal Villi

• definition
• cells

Answer 2

Mucosal folds that project into lumen & cover surface of SI

• increase absorptive surface area

Enterocytes: simple columnar cells that produce enzymes for digestion & absorption

Goblet Cells: provide mucus coat to shield from abrasion & bacterial invasion

Core of loose CT with a lacteal

Question 3

Pilica circulares

- where is it seen

Answer 3

foldings of entire mucosa & some submucosa

• absent in duodenum, visible in jejunum, less prominent in ileum
• covered in intestinal villi

Question 4

Villi

Answer 4

fingerlike folds of mucosa projecting into lumen

• covered with microvilli

Question 5

Enterocyte Microvilli

Answer 5

” Striated border”

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

Question 6

Mucosa (SI)

- cell type

Answer 6

simple columnar epithelium with tubular intestinal glands

-lamina propria and muscularis mucosae

Question 7

Submucosa (SI)

- cell type

Answer 7

dense irregular CT

neurovasculature, lymphatics, glands may be present

Question 8

Muscularis (SI)

- cell type

Answer 8

inner circular & outer longitudinal layers

Question 9

Serosa (SI)

- cell type

Answer 9

loose CT covered by visceral peritoneum

Question 10

Innervation of the SI and LI

Answer 10

Motility controlled by the ANS

Question 11

Intrinsic Nervous System

Answer 11

aka enteric nervous system

• submucosal plexus of Meissner & myenteric plexus of Auerbach
  
  • sympathetic visceral sensory fibers
    - parasympathetic (terminal) ganglia
    - preganglionic & postganglionic parasympathetics

Question 12

Extrinsic Nervous System

Answer 12

Preganglionic parasympathetic (vagus and pelvic nerves)

Postganglionic sympathetics

Question 13

Intestinal Glands

• cells ( 4)
• cell type

Answer 13

Simple tubular glands lined by simple columnar epithelium

1) Enteroendocrine cells
2) Paneth Cells
3) Intestinal Stem cells
4) M (microfold) cells

• covers intestinal villi
• open onto luminal surface of the intestine at the base of the villi

Question 14

Enteroendocrine Cell

• location
• function
• hormones

Answer 14

• found throughout the intestinal glands
• secrete peptide hormones to control gut motility, regulate secretion of enzymes, HCl, bile & other components for digestion
• gastrin, secretin, gastric inhibitory polypeptide (GIP), motilin, & cholecystokinin

Question 15

Paneth Cells

• characteristic
• location
• function

Answer 15

-pyramidal-shaped cells

• base of intestinal glands
• found in normal colon in small numbers ( if a lot=> pathological conditions)

function:

• innate immunity by secreting antimicrobial substances
• lysozymes, alpha-defensins, other glycoproteins
• regulate normal bacterial flora via antibacterial action and phagocytosis

Question 16

Intestinal Stem Cells (ISCs)

• location
• function
• cell types

Answer 16

• reside in a niche at crypt base ( near Paneth cells)
• repoplate epithelia lining
• daughter cells move out of crypts
• > differentiate into goblet cells, enterocytes, and enteroendocrine cells

Question 17

M (Microfold) Cells

• characteristics
• cells
• function

Answer 17

specialized cells that overlie Peyer’s patches at other large lymphatic nodules

• has microfold & thin glycocalyx
• has deep pocket-like recess, connected to extracellular space, houses dendritic cells, macrophages, and T & B cells
• apical surface expresses receptors that bind specific macromolecules & gram-negative bacteria
  
  • internalized & transferred to immune cells
  • function as highly specialized ANTIGEN- TRANSPORTING CELLS

Question 18

Gastroduodenal Junction consist of which two organs?

Answer 18

Stomach (pyloris) and Duodenum (SI)

Question 19

Gastroduodenal Junction: Pyloris (stomach)

Answer 19

thick wall due to presence of pyloric sphincter muscle

pyloric glands at base of each gastric pit

Question 20

Gastroduodenal Junction : Duodenum (SI)

Answer 20

abundant Brunner’s glands in submucosa, DEEP to the muscularis mucosae

secretory mucosa with villi

Question 21

Duodenum

• characteristics
• hallmark
• function

Answer 21

• initial segment of SI
• leaf-like villi
• tubular intestinal glands in mucosa

HALLMARK: brunner’s glands in submucosa
- tubuloacinar mucous glands

Function

• produce alkaline secretion
• neutralize acidic chyme
• collect bile and pancreatic secretion via hepatopancreatic ampulla

Question 22

Jejunum

• Hallmarks
• location

Answer 22

HALLMARK: long finger-like villi

• tubular intestinal glands
• villus core contain a well-developed lacteal

HALLMARK: no submucosal glands

• lymphoid nodules/follicles in lamina propria
• tubular intestinal glands in mucosa

Question 23

Ileum

• characteristics
• hallmark

Answer 23

finger-like villi ( shorter than jejunum)

tubular intestinal glands in mucosa

HALLMARK: peyer’s patches
- mucosal lymphoid nodules specific to ileum

paneth cells found at base of intestinal glands

Question 24

Ileoceccal Junction

Answer 24

• food is propelled from ileum into cecum through ileoceccal valve
• abrupt transition from villi of SI-> to glandular epithelium of LI
• Valve has thickened extension of muscularis mucosae
  
  • critical function is to limit reflux of colonic contents into ileum
• muscularis (externa) is also somewhat thickened

Question 25

Large Intestine - function - characteristics - Hallmark

Answer 25

function: absorbe water, sodium, vitamins & minerals, will uptake sedatives, anesthetics, steroids Characteristics: opening of tubular intestinal glands (crypts of Lieberkuhn) are hallmark of mucosa HALLMARK: intestinal glands, goblet cells, NO INTESTINAL VILLI

Question 26

Mucosa (LI) - cell type - cells - location

Answer 26

glandular, simple columnar epithelium - colonocytes, goblet cells, stem cells, enteroendocrine cells location - lamina propria & muscularis mucosae are present - GALT is extensive and may penetrate submucosa

Question 27

Submucosa (LI) | - cell type

Answer 27

dense irregular CT vascularized

Question 28

Muscularis (LI) | - characteristics

Answer 28

- inner layer is typical | - outer longitudinal layer organized into taeniae coli, will form haustra of LI

Question 29

Serosa

Answer 29

lining that covers INTRAperitoneal portions of colon

Question 30

Colon - characteristics - cell type - hallmark

Answer 30

- simple columnar epithelium - short microvilli - dilated intercellular spaces with interdigitating leaflets of cell membrane ( active water transport) HALLMARK: numerous goblet cells

Question 31

Veriform Appendix - characteristics - layers

Answer 31

- diverticulum of the cecum with layers similar to those of LI Mucosa - simple columnar epithelium - goblet cells - lymphoid follicles and lymphocytes with lamina propria - extend into submucosa Submucosa - adipocytes - dense irregular CT - inner circular layer is well developed, but outer longitudinal layer is not - covered with serosa

Question 32

Hirschprung's Disease - characteristics - statistics - presentation - diagnosis - treatment

Answer 32

- Aganlionosis in distal colon - Mutation in RET gene (for migration & differentiation of NCC) - failure of NCC development in both plexuses of a bowel segment 1:5000 neonates Presentation: constipation, poor feeding, progressive abdominal distention Diagnosis: delayed BM < 48hrs after birth ; rectal biopsy, barium enema Treatment: surgical removal of affected colon segment, pull through of ganglionic colon segments

Question 33

Inflammatory Bowel Disease - symptoms - types of IBD (2)

Answer 33

- include ulverative colitis & Crohn's Disease symptoms: diarrhea, pain, periodic relapses 1) Ulcerative colitis- affect mucosa of large intestin 2) Crohn's Disease- affect any segment of intestinal tract

Question 34

Crohn's Disease

Answer 34

chronic inflammatory process involving terminal ileum and large intestine - inflammatory cells produce cytokines that cause damage to intestinal mucosa - infiltration of neutrophils into cyrpts of Liberkuhn-> destruction of intestinal glands due to crypt abscesses-> progressive atrophy, ulceration of mucosa

Question 35

Rectum - parts - glands

Answer 35

Parts 1) Rectum proper (upper part): typical mucosa with tubular intestinal glands, transverse rectal folds 2) Anal Canal ( lower part) - anal columns: mucosal folds - anal sinuses: depressions between columns - anal glands: extend into submucosa & muscularis externa Circumanal glands: large apocrine glands surrounding anal orifice

Question 36

Anal Canal - Zones (3) - cell types - what happens at level of anus?

Answer 36

1) Colorectal Zone: simple columnar epithelium identical to rectum ( upper 1/3) 2) Anal transitional zone (ATZ): simple columnar epithelium - > stratified squamous epithelium of perianal skin (middle 1/3) 3) Squamous zone: stratified squamous epithelium continuous with perineal skin (lower 1/3) At level of anus, inner circular layer thickens to form the internal anal sphincter

Question 37

Mucosa of the Recto-anal junction | - cell types

Answer 37

1) non-keratinized stratified squamous | 2) Simple columnar with tubular intestinal glands