Lower GI I Flashcards
Layers of the intestinal wall (from inside to outside)
- Mucosa with lamina propria and muscularis mucosa
- Submucosa
- Muscularis layers
- Serosa
Histologic Characteristics of Duodenum
- Villi with wide spatulate or “leaflike” distal shape
- Deep crypts of Lieberkuhn
- Brunner’s glands with excretory ducts in submucosa
Crypts of Lieberkuhn are _______ ______ glands within the _________
simple tubular glands, intestinal mucosa
Crypts of lieberkuhn open between adjacent ______ and extend to ________ _______
villi, muscularis mucosa
Cell of the crypts of Lieberkuhn
Goblet cells
Enterocytes
Paneth cells
Enteroendocrine cells
Enterocytes are _______ epithelial cells
columnar
Characteristics of Enterocytes
- Basal nucleus, perinuclear Golgi, apical brush border
- Produce disaccharidases
- Involved in absorption of proteins, carbohydrates, and lipids
- Enzymes present on apical brush border are important in carbohydrate digestion
- Produce enteropeptidase (enterokinase) which is necessary for the activation of pancreatic zymogens and proenzymes
Enterocytes produce
Disaccharidases and enteropeptidase (enterokinase)
______ is produced by enterocytes and necessary for the activation of pancreatic zymogens and proenzymes
Enteropeptidase (enterokinase)
Characteristics of Paneth cells
- Basal crypt cells
- Prominent eosinophilic granules
- Produce lysozyme to control intestinal flora
basal crypt cells with prominent eosinophilic granules
Paneth cells
Characteristics of Enteroendocrine cells
- Stain with chromium (chromaffin)
- Agyrophilic (respond to silver stains)
- Produce peptide hormones and serotonin
- May produce pancrine or autocrine secretions
- Analogous to unicellular goblet cells
- formed from endodermal stem cells in all regions of the GI tract
Enteroendocrin cells of the crypts of Lieberkuhn produce
peptide hormones and serotonin
What are enteroendocrine cells mode of secretion
paracrine or autocrine secretions
Brunner glands are found in
submucosa of duodenum
Brunner’s glands are responsible for
- Formation of bicarbonate and mucus
- Supplements bicarbonate from the pancreas
- Necessary to neutralize gastric acid
- Supplements bicarbonate from the pancreas
Histological Characteristics of Jejunum
- Villi longer and more narrow than in Duodenum
- Crypts of Lieberkuhn present
- No glands in submucosa
Histologic characteristics of Ileum
- Villi are longer and narrower than in jejunum
- Crypts of Lieberkuhn present
- No glands in submucosa
- Peyer’s patches
Epithelium of large intestine
- Simple columnar epithelium
- Crypts but no villi
Functions of large intestine
- Secretion of mucus for lubrication
- Goblet cell is the prominent cell of the large intestine
- Absorption of fluid
- Formation of fecal mass
- Continuation of digestion initiated in small intestine
Location of M cells (antigen-presenting cells)
Ileum
The epithelial cells of the GI tract are held together by _______ containing the transmembrane proteins ____ and _____, which function to prevent paracellular transport
occluding junctions, claudins and occludins
Characteristics of Paneth Cells
- Basophilic basal cytoplasm
- Supranuclear Golgi complex
- Large, intensely acidophilic apical secretory granules
Paneth cells secrete (what are the functions of each secretion)
Lysozyme- increase permeability of bacteria by degrading peptidoglycan goat
- Defensins to increase membrane permeability of target organism
- Tumor necrosis factor- alpha (proinflammatory cytokine)
- may phagocytize some microorganims and help regulate intestinal flora
What are the three regions of the small intestine
Duodenum
Jejunum
Ileum
______ layer coats intestinal epithelial luminal surface
mucosal
The mucosal layer of intestines is secreted by
goblet cells
The mucosal layer of intestines is made up of how many layer and what are they
It is made up of 2 layers
- Outer layer contains microorganisms
- Inner layer contains:
- Antimicrobial proteins (from Paneth Cells, Enterocytes, and Goblet cells ) that resist microbial penetration
Toll-like receptors are found on the surface of
enterocytes
What are toll-like receptors
They are found on the surface of enterocytes
fxn:
- Type of pattern recognition receptor
- Recognize structurally conserved molecules broadly shared by pathogens but distinguish from host molecules (pathogen associated molecular patterns (PAMPs))
Explain the immune surveillance system with toll-like receptors
- 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)
Explain the immune surveillance system with M cells
- Antigen is taken up by M (microfold) cells associated with Peyer patch in the intestinal mucosa
- —–> Antigens are transported to lymphocytes located in pockets in folds of M cells
- ———-> Antigens are bound to Ig receptors on surface of lymphocytes
- —————> Lymphocytes transfer Ig-bound antigen to dendritic cells in lamina propria
- ——————> Dendritic cells interact with T cells in lamina propria to activate immune response
The bulk of the body’s immune defenses is centered in the
GALT (gut associated lymphatic tissue)
Components of GALT
- Transitory aggregations of lymphocytes, neutrophils, eosinophils
- Permanent structures:
- Appendix
- Peyer’s patches
- Mesenteric lymph nodes
The antigen-presenting cells (APCs) and macrophages of Peyer’s patches phagocytize the antigen and present it to ____ and ______ cells as well as _______
helper and cytoxic T cells as well as B lymphocytes
what is the function of M cells
Associated with Peyer’s patches
- sample particular antigen and present it to antigen-presenting cells in the underlying lamina propria
What are Peyer’s Patches
- A permanent GALT found in the ileum
- Dome-shaped lymphoid structures
- Contain B- and T-cell dependent area
- Possess high endothelial venules (HEVs), which facilitate entrance of lymphocytes into lymphoid organs form the bloodstream
The primary immunoglobulin produced by GALT is ____
IgA (secretory IgA, slgA)
IgA is synthesized and secreted by _____ cells in the lamina proper of the gut and picked up at the ____ surface of enterocytes and transported across the cell
plasma, Basal
while in the enterocyte, slgA is linked to a protein called ______ that inhibits degradation of the saga by proteolytic enzymes in the GI lumen
Secretory component
Secretory IgA, unlike IgG, does not stimulate the _______ but function by
complement system, but functions by coating microorganisms, thus inhibiting microorganisms binding to the epithelium
Rapid cell turnover is a ______ mechanism used by the GI epithelium
Protective (particularly true of stomach and small intestine)
Lining of most GI tract is replaced every ____ days
5
New cells of the small intestine are formed in
the crypts from undifferentiated cells
new cells in the esophagus and anus
are formed in the basal layer of stratified epithelium and migrate through sub-basal levels to be sloughed off into the lumen
Proliferative compartment of large intestine is found in the
base of the crypts
Stem cells are found in what part of the stomach and differentiate into
- stem cells are found in the neck of the gastric glands
- differentiate into
- surface and neck mucus cells (turn over most rapidy)
- Enteroendocrine cells
- Parietal cells
- Chief cells
