Histology of SI and LI Flashcards
Small Intestine
- parts
- function
- characteristics
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
Intestinal Villi
- definition
- cells
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
Pilica circulares
- where is it seen
foldings of entire mucosa & some submucosa
- absent in duodenum, visible in jejunum, less prominent in ileum
- covered in intestinal villi
Villi
fingerlike folds of mucosa projecting into lumen
- covered with microvilli
Enterocyte Microvilli
” 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
Mucosa (SI)
- cell type
simple columnar epithelium with tubular intestinal glands
-lamina propria and muscularis mucosae
Submucosa (SI)
- cell type
dense irregular CT
neurovasculature, lymphatics, glands may be present
Muscularis (SI)
- cell type
inner circular & outer longitudinal layers
Serosa (SI)
- cell type
loose CT covered by visceral peritoneum
Innervation of the SI and LI
Motility controlled by the ANS
Intrinsic Nervous System
aka enteric nervous system
- submucosal plexus of Meissner & myenteric plexus of Auerbach
- sympathetic visceral sensory fibers
- parasympathetic (terminal) ganglia
- preganglionic & postganglionic parasympathetics
- sympathetic visceral sensory fibers
Extrinsic Nervous System
Preganglionic parasympathetic (vagus and pelvic nerves)
Postganglionic sympathetics
Intestinal Glands
- cells ( 4)
- cell type
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
Enteroendocrine Cell
- location
- function
- hormones
- 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
Paneth Cells
- characteristic
- location
- function
-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
Intestinal Stem Cells (ISCs)
- location
- function
- cell types
- 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
M (Microfold) Cells
- characteristics
- cells
- function
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
Gastroduodenal Junction consist of which two organs?
Stomach (pyloris) and Duodenum (SI)
Gastroduodenal Junction: Pyloris (stomach)
thick wall due to presence of pyloric sphincter muscle
pyloric glands at base of each gastric pit
Gastroduodenal Junction : Duodenum (SI)
abundant Brunner’s glands in submucosa, DEEP to the muscularis mucosae
secretory mucosa with villi
Duodenum
- characteristics
- hallmark
- function
- 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
Jejunum
- Hallmarks
- location
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
Ileum
- characteristics
- hallmark
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
Ileoceccal Junction
- 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
Large Intestine
- function
- characteristics
- Hallmark
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
Mucosa (LI)
- cell type
- cells
- location
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
Submucosa (LI)
- cell type
dense irregular CT
vascularized
Muscularis (LI)
- characteristics
- inner layer is typical
- outer longitudinal layer organized into taeniae coli, will form haustra of LI
Serosa
lining that covers INTRAperitoneal portions of colon
Colon
- characteristics
- cell type
- hallmark
- simple columnar epithelium
- short microvilli
- dilated intercellular spaces with interdigitating leaflets of cell membrane ( active water transport)
HALLMARK: numerous goblet cells
Veriform Appendix
- characteristics
- layers
- 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
Hirschprung’s Disease
- characteristics
- statistics
- presentation
- diagnosis
- treatment
- 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
Inflammatory Bowel Disease
- symptoms
- types of IBD (2)
- 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
Crohn’s Disease
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
Rectum
- parts
- glands
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
Anal Canal
- Zones (3)
- cell types
- what happens at level of anus?
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
Mucosa of the Recto-anal junction
- cell types
1) non-keratinized stratified squamous
2) Simple columnar with tubular intestinal glands
