Lower GI Histology Flashcards
What are the layers of the intestinal wall?
From inside to outside:
mucosa with lamina propria and muscularis mucosa
submucosa
muscularis layers
serosa
In what layer of the intestine are the villi and crypts found?
mucosa
What lymphatic plexus is found in the villi?
lacteal.
They have branches that surround a lymphoid nodule in the submucosa.
What are characteristics of the duodenum?
It has villi with a wide, leaflike shape
Deep crypths of lieberkuhn
Brunner’s glands with excretory ducts in submucosa
What gland is found only in the muscularis mucosae of the duodenum?
Brunner’s gland
What patch is found only in the submucosa of the ileum?
Peyer’s patches. They are lymphoid aggregates.
What are the crypts of liberkuhn?
Simple tubular glands within the intestinal mucosa.
They open between adjacent villi and extend to muscularis mucosa.
What cells are found in the crypts of lieberkuhn?
Goblet cells
Enterocytes
Paneth cells
Enteroendocrine cells
What are physical characteristics of the crypts of lieberkuhn?
Basal nucleus
Perinuclear Golgi
Apical brush border
What is the function of enterocytes?
production of disaccharidases
Absorption of proteins, carbohydrates and lipids.
Enzymes present on the apical border of the enterocytes are important in what?
carbohydrate digestion
What enzyme produced by enterocytes is necessary for the activation of pancreatic zymogens and proenzymes?
enteropeptidase
What enzyme do paneth cells produce?
lysozyme; it controls the intestinal flora.
Where are paneth cells found?
in the crypt (basal area)
What type of blood component is found in the paneth cells?
eosinophilic granules
What do enteroendrocrine cells produce?
peptide hormones and serotonin.
You are studying the GI tract and obtain a sample of endodermal stem cells. What will these stem cells differentiate into?
enteroendocrine cells.
Where are the glands of Brunner found?
submucosa of duodenum
What are the glands of brunner responsible for?
Formation of bicarbonate and mucus.
They are also necessary to neutralize gastric acid.
What are the histologic characteristics of the jejunum?
Long and narrow villi
Crypts of Lieberkuhn present
No glands in submucosa
What are the histologic characteristics of the ileum?
Long and narrow villi
Crypts of Lieberkuhn Present
No glands in submucosa
The large intestine is comprised of what type of epithelium?
simple columnar
The large intestine contains ____, but no ____
crypts, villi
Why does the large intestine secrete mucus?
for lubrication.
What is the prominent cell of the large intestine?
goblet cells
What are three functions of the large intestine?
Absorption of fluid
Formation of fecal mass
Continuation of digestion initiated in small intestine.
What type of junctions are found between intestinal cells?
Tight junctions.
THey are occluding junctions that contain claudins and occludins.
What do the occluding junctions between the intestinal junctions prevent?
paracellular transport.
If there is a defect in the tight junctions, what is able to pass inbetween the junctions?
lamina propria.
Paneth cells contain what blood componentn?
basophils
Paneth cells contain what type of secretory granules at the apical surface?
acidophilic secretory granules
What do patheth cells secrete
Lysozyme
Defensins
Tumor necrosis factor alpha
You are studying the GI tract and introduce foreign bacteria to it. What enzyme is secreted to attack the bacteria, and what type of cell secretes it?
Lysozyme is secreted by the paneth cells in order to degrade bacteria.
What is the purpose of the secretion of defensins by paneth ells?
It increases membrane permeability of target organisms.
Paneth cells secrete various enzymes and proteins. What is another function of paneth cells?
To phagocytize some microorganisms and help regulate intestinal flora.
What does the mucosal layer coat?
Intestinal epithelial luminal surface.
What are the two layers of the mucosal layer?
outer layer (microorganisms)
Inner layer: antimicrobial proteins that resist microbial penetration.
Where are toll-like receptors found?
on the surface of enterocytes.
What do toll-like receptors recognize?
structurally conserved molecules broadly shared by pathogens but distinguishable from host molecules.
What is the pattern of the immune surveillance syste?
- Antigen binds to toll-like receptor on enterocyte surface.
- B-cell activating factor is produced
- B cells in lamina propria mature into plasma cells -> antibodies.
Once B cells mature into plamsa cells (antibodies), what happens to the antigen?
It is taken up by M cells associated with Peyer patch in the intestinal mucosa.
Once antigens are taken up by M cells, where are the antigens transported?
to lymphocytes located in pockets in folds of M cells.
Once antigens are transported to lymphocytes, what do the antigens bind to on the surface of lymphocytes?
Ig receptors.
Once antigens are bound to Ig receptors on lymphocytes, where is the Ig bound antigen transferred?
to dendritic cells in lamina propria.
When lymphocytes are transferred to dendritic cells in the lamina propria, what do the dendritic cells then do?
interact with T cells in lamina propria to activate an immune response.
Where is the bulk of the body’s immune defenses centered?
GALT
What are the permenant structures in the GALT?
appendix
Peyer’s patches
Mesenteric lymph nodes
What does GALT contain?
lymphocytes
neutrophils
eosinophils
In what region of the villi are peyer’s patches found?
submucosa (under mucosal surface)
What type of cells are found in peyer’s patches?
B and T cells
Peyer’s patches contain high endothelial venules. What do HEVs do?
allow the entrace of lymphocytes into lymphoid organs from the bloodstream.
What is found on the mucosal covering of Peyer’s patches?
M (microfold cells).
They take particulate of an antigen and present it to antigen-presenting cells in the underlying lamina propria.
What do antigen presenting cells do?
phagocytize an antigen and present it to helper and cytotoxic T cells, as well as B lymphocytes.
What is the primary immunoglobulin produced by GALT?
IgA
Where are IgA immunoglobulins synthesized and secreted?
They are secreted by plama cells in the lamina propria of the gut.
They are picked up at the basal surface of enterocytes and transported across the cell.
When in the cell, what is sIgA bound to in order to prevent degradation by proteolytic enzymes?
secretory component protein
What is the function of secretory IgA?
It coats microorganisms, which inhibits microorganisms from binding to the epithelium.
What is a protective mechanism used by the GI epithelium?
rapid cell turnover.
How often is the lining of the stomach and small intestine replaced?
Every five days
In the esophagus, where are new cells formed?
in the basal layer of stratified epithelium.
Where are new cells formed in the small intestine?
in the crypts
Where is the proliferative compartment found in the large intestine?
At the base of the crypt.
What cells in the stomach are responsible for cell turnover?
surface and neck mucus cells
Enteroendocrine cells
Parietal cells
Chief cells.
What does the small intestine consist of?
Duodenum
Jejunum
Ileum
