Histology Of The SI And LI Flashcards
The SI is the principal site for what?
Digestion of food and absorption of digestion products
What are pilcae circulares?
Transverse folds with a submucosal core located in the SI
Cannot lay flat if distended
Visible in jejunum but less so in ileum
What are intestinal villi?
Mucosal folds that project into the lumen and cover the surface of the SI
Covered with a simple columnar epithelium of enterocytes and goblet cells
Core of loose CT with microvasculature and a lacteal (absorbs lipids and sends to lymphatics)
What do enterocytes produce?
Enzymes for digestion and absorption
Goblets cells provide what?
Mucus coating to shield from abrasion and bacterial invasion
What are microvilli?
Cover intestinal villi to increase absorptive surface area
Describe the mucosa of the SI
Simple columnar epithelium with tubular intestinal glands
Lamina propria and muscularis mucosa
Describe the submucosa of the SI
Dense irregular CT, neurovasculature, lymphatics and glands may be present
Describe the muscularis of the SI
Inner circular and outer longitudinal layers
What is the outer layer of the SI?
Serosa - loose CT covered by visceral peritoneum
Describe the gastroduodenal junction
Pyloris (stomach)
-Thick wall due to the presence of the pyloric sphincter muscle and pyloric glands at the base of each gastric pit
Duodenum (SI)
-Abundant duodenal glands in submucosa, deep to the muscularis mucosa
-Secretory mucosa with villi
Describe the LI
Absorbs water, Na, vitamins and minerals
Will uptake sedatives, anesthetics and steroids
Openings of tubular intestinal glands are hallmark of the mucosa
What are the hallmarks for the LI?*
Intestinal glands, goblet cells but no intestinal villi
Describe the mucosa of the LI
Glandular, simple columnar epithelium
Colonocytes, goblet cells, stem cells and enteroendocrine cells
Lamina propria and muscularis mucosa present
GALT is extensive and may penetrate submucosa
Describe the submucosa of the LI
Dense irregular CT and vascularized
Describe the muscularis of the LI
Inner layer is typical
Outer longitudinal layer organized into taeniae coli which will form haustra of the LI
Intraperitoneal portions of the colon are covered by what?
Serosa
What are intestinal glands (crypts of Lieberkuhn)?
Simple, tubular glands lined by simple columnar epithelium
Continuous with simple columnar epithelium that covers intestinal wall
Open onto the luminal surface of the intestine at the base of the villi
Includes Paneth cells, M cell, stem cells and enteroendocrine cells
What are Paneth cells?
Pyramidal shaped cells at the base of the intestinal glands
Large, eosinophilic secretory granules in their apical cytoplasm
What are the functions of Paneth cells?
Functions in innate immunity by secreting antimicrobial substances (lysozyme and alpha-defensins)
Regulate normal bacteria flora via antibacterial action and phagocytosis
What are M (microfold) cells?
Epithelial cells specialized for transepithelial transport of particles and microorganism
Located in the ileal mucosa, overlying Peyer patches
Pocket formed by deeply invaginated membrane containing lymphocytes and macrophages
How do M cells function as highly specialized antigen transporting cells?
Apical surface expresses receptors that bind specific macromolecules and gram-negative bacteria (e.g. E. coli)
Internalized and transferred to immune cells
What are intestinal stem cells (ISCs)?
Reside in a niche at crypt base near Paneth cells
Repopulate epithelial lining
Daughter cells move out of the crypts and differentiate into goblet cells, enterocytes and enteroendocrine cells
Describe the innervation of the SI and LI
Motility controlled by the ANS
Enteric (intrinsic) NS consists of the submucosal plexus of Meissner and myenteric plexus of Auerbach
-Sympathetic visceral sensory fibers
-Parasympathetic (terminal) ganglia
-Preganglionic and postganglionic parasympathetics
Regulated by extrinsics —> preganglionic parasympathetics (vagus and pelvic nerves) and postganglionic sympathetics
What is Hirschsprung’s disease?
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
What are the three categories of Hirschsprung disease?
Short segment disease, long segment disease, and total colonic aganglionosis
What is short segment disease?
Aganglionosis confined to rectosigmoid colon
85% of cases
What is long segment disease?
Aganglionosis extends past rectosigmoid colon to the splenic flexure
10% of cases
What is total colonic aganglionosis?
Affects entire colon
5% of cases
What is the presentation of Hirschsprung’s disease?
Constipation, poor feeding, and progressive abdominal distention
How is Hirschsprung’s disease diagnosed?
Delayed BM <48 hours after birth, rectal biopsy or barium enema
What is the treatment for Hirschsprung’s disease?
Surgical removal of the affected colon segment, pull through of ganglionic colon segments
What is the rectum proper?
Upper part
Typical mucosa with tubular intestinal glands
Transverse rectal folds
What is the anal canal?
Lower part of rectum
Anal columns with mucosal folds
Anal sinuses - depressions between columns
Anal glands extend into the submucosa and muscularis externa
What are circumanal glands?
Large apocrine glands surrounding the anal orifice
What are the three different zones of the anal canal?
Colorectal zone, anal transition zone (ATZ), squamous zone
What is the colorectal zone?
Simple columnar epithelium identical to the rectum (upper 1/3)
What is the anal transition zone (ATZ)?
Simple columnar epithelium —> stratified squamous epithelium of perianal skin (middle 1/3)
What is the squamous zone?
Stratified squamous epithelium continuous with perineal skin (lower 1/3)
At the level of the anus, the inner circular layer thickens to form what?
The internal anal sphincter
Describe the mucosa of the duodenum
Simple columnar epithelia with scattered goblet cells
Describe the submucosa of the duodenum
Contains duodenal glands: tubuloacinar mucous glands that produce an alkaline secretion which neutralizes acidic chyme*
Describe the mucosa of the jejunum
Simple columnar epithelia with scattered goblet cells
Long finger like villi; villus core contains a well developed lacteal
Tubular intestinal glands
Lymphoid nodules/follicles in the lamina propria
Describe the submucosa of the jejunum
No submucosal glands present
Describe the mucosa of the ileum
Simple columnar epithelium with scattered goblet cells
Villi typically shorter than jejunum
Peyer’s patches: lymphoid nodules (MALT)
Paneth cells found at base of intestinal glands
Describe the submucosa of the ileum
No submucosal glands
