Histology of Small & Large Intestines Flashcards
________, _______, and _____ comprise the small intestine and are the principal sites fro digestion of food and absorption of digestion products
duodenum, jejunum, and ileum comprise the small intestine and are the principal sites fro digestion of food and absorption of digestion products
- transverse folds within the SI that have a submucosal core
- cannot lay flat if distended
- visible in jejunum, less so in ileum
plicae circulares
- mucosal folds that project into lumen and cover surface of SI
- covered w/ simple columnar epithelium of enterocytes and goblet cells
- core of loose CT w/ microvasculature and a lacteal
intestinal villi
What is the function of villi and microvilli within the SI?
- enterocytes prod enzymes for digestion/absorption
- goblet cells provide mucus coating to shield from abrasion and bacterial invasion
- villi are covered w/ microvilli to increase absorptive surface area
Describe the characteristics of the mucosa, submucosa, muscularis, and serosa within the small intestines:
- mucosa: simple columnar epithelium w/ tubular intestinal glands, lamina propria and muscularis mucosae
- submucosa: dense irregular CT; neurovasculature, lymphatics, and glands may be present
- muscularis: inner circular and outer longitudinal layers
- serosa: loose CT covered by visceral peritoneum
Describe the innervation of the intestines:
- motility controlled by ANS
- enteric (intrinsic) NS consists of submucosal plexus of Meissner and myenteric plexus of Auerbach:
- sympathetic visceral sensory fibers
- parasympathetic (terminal) ganglia
- pregang and postgang parasympathetics
- regulated by ‘extrinsics’ > pregang parasympathetics (vagus and pelvic nerves) and postgang sympathetics
What is the structure, location, and cell types a/w intestinal glands?
- structure: simple tubular glands lined by simple columnar epithelium
- location: continuous w/ simple columnar that covers intestinal villi; open onto the luminal surface of the intestine at the base of the villi
-
cell types:
1. Paneth cells
2. M (microfold) cells
3. intestinal stem cells
4. enteroendocrine cells
- pyramidal-shaped cells at the base of intestinal glands
- large, eosinophilic secretory granules in their apical cytoplasm
- functions in innate immunity by secreting antimicrobial substances (lysozyme, α-defensins)
- regulate nml bacterial flora via antibacterial action and phagocytosis
Paneth cells
- cells that reside in a niche at crypt base, near Paneth cells
- repopulate epithelial lining
- daughter cells move out of the crypts > differentiate into goblet cells, enterocytes, and enteroendocrine cells
intestinal stem cells (ISCs)
- epithelial cells specialized for transepithelial transport of particles and microorganism (antigen-transporting cells)
- located in the ileal mucosa, overlying Peyer patches
- pocket formed by deeply invaginated membrane and containing lymphocytes and macrophages
M (microfold) cells
What is the specialized function of M cells?
- M cells’ apical surface expresses receptors that bind specific macromolecules and gram-negative bacteria (e.g. E. coli)
- they internalize these particles/microorganisms and transfer them to immune cells
- function as highly specialized antigen-transporting cells
- scattered epithelial cells in the gastric mucosa, named w/ the initial letter of their main hormone prod
- these hormones are of major importance for digestive function
- most of these cells are APUD cells, process amines: amine precursor uptake and decarboxylation activity
- all cells are generally considered to be a part of the diffuse neuroendocrine system (DNES)
enteroendocrine cells
What is the function, types, and hormonal effects of the enteroendocrine cells?
- function: release prod that exert paracrine or endocrine effects
- types:
- “closed” types: cellular apex is covered by neighboring epithelial cells, not exposed to GI lumen
- “open” type: apical end of cell contacts the lumen and has chemoreceptors that sample luminal contents
- hormonal effects:
- regulation of peristalsis and motility
- secretion of digestive enzymes, water, and electrolytes
- sense of being satiated after eating
Duodenum
- mucosa:
- submucosa:
Duodenum
- mucosa: simple columnar epithelia w/ scattered goblet cells
- submucosa: duodenal glands (tubuloacinar mucous glands that prod alkaline secretion), neutralizes acidic chyme
Jejunum
- mucosa:
- submucosa:
Jejunum
- mucosa:
simple columnar epithelia w/ scattered goblet cells;
long finger-like villi, villus core contains well-developed lacteal;
tubular intestinal glands;
lymphoid nodules/follicles in lamina propria
- submucosa: no submucosal glands
Ileum
- mucosa:
- submucosa:
Ileum
- mucosa:
simple columnar epithelia w/ scattered goblet cells
villi typically shorter than jejunum
Peyer’s patches: lymphoid nodules (MALT)
- submucosa: no submucosal glands
Identify where in the body this sample was obtained and identify the labeled structures:
duodenum
V, villi;
C, crypts,
B/DG, duodenal glands;
M,mucosa;
MM, muscularis mucosae;
SM, submucosa;
CM, circular layer;
LM, longitudinal layer;
D, excretory ducts of Brunner’s glands
Identify where in the body the following sample was obtained:
jejunum
Identify where in the body the following sample was obtained:
ileum
Describe the histological structure of the gastroduodenal junction (pyloris and duodenum):
- pyloris: thick wall due to presence of pyloric sphincter muscle; pyloric glands at the base of each gastric pit
- duodenum: abundant duodenal glands in submucosa, DEEP to the muscularis mucosae; secretory mucosa w/ villi
What is the function and histological structure of the LI?
- function: absorbs water, sodium, vitamins, minerals; uptake of sedatives, anesthetics, and steroids
- structure: openings of tubular intestinal glands are hallmark of mucosa; contains goblet cells but NO intestinal villi
Describe the mucosal layers of the LI:
- mucosa:
- glandular, simple columnar epithelium: colonocytes, goblet cells, stem cells, and enteroendocrine cells
- lamine propria and muscularis mucosae are present; GALT is extensive and may penetrate submucosa
- submucosa: dense irregular CT, vascularized
- muscularis: inner layer is typical; outer longitudinal layer organized into taeniae coli, will form haustra of LI
- serosa: covers intraperitoneal portions of colon
Identify the part of the GI in this image:
colon
- glands consisting of simple columnar epithelium w/ numerous goblet cells
- MM: muscularis mucosae
Identify the part of the GI in this image:
colon
Identify the part of the GI in this image:
colon
Identify the part of the GI in this image:
colon
- aganglionosis in the distal colon
- incidence: 1:5000 neonates
- etiology: mutations of the RET gene (required for migration/differentiation of NCC), failure of NCC development in both plexuses of a bowel segment
- types: short-segment disease (85% of cases, confined to rectosigmoid colon); long-segment disease (10%, extends past rectosigmoid region > splenic flexure); total colonic aganglionosis (5%, affects entire colon)
- presentation: constipation, poor feeding, progressive abd distention
- dx: delayed BM <48 hours after birth, rectal biopsy, barium enema
- tx: surgical removal of the affected colon segement, pull through of ganglionic colon segments
Hirschprung’s disease
Describe the histological structure and associated structures of the rectum:
- rectum proper (upper part): typical mucosa w/ tubular intestinal glands, transverse rectal folds
- anal canal (lower part):
- anal columns: mucosal folds
- anal sinuses: depressions between columns
- anal glands: extend into the submucosa and muscularis externa
circumanal glands: large apocrine glands surrounding the anal orifice
What are the anal zones?
- colorectal zone: simple columnar epithelium identical to the rectum (upper 1/3)
- anal transitional zone (ATZ): simple columnar epithelium > stratified squamous epithelium of perianal skin (middle 1/3)
- squamous zone: stratified squamous epithelium c/w perineal skin (lower 1/3)
(at the anus, inner circular layer thickens to form internal anal sphincter)
Identify the area of the GI system this sample was obtained and the label structures:
Identify the area of the GI system this sample was obtained and the label structures:
Identify the area of the GI system this sample was obtained and the label structures:
Identify the area of the GI system this sample was obtained and the label structures:
Identify the area of the GI system this sample was obtained and the label structures:
Identify the area of the GI system this sample was obtained and the label structures:
Identify the area of the GI system this sample was obtained and the label structures:
Identify the area of the GI system this sample was obtained and the label structures:
Identify the area of the GI system this sample was obtained and the label structures:
Identify the area of the GI system this sample was obtained and the label structures:
Identify the area of the GI system this sample was obtained and the label structures:
