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
