LEcture 32: Lower GI Flashcards
Distinguish among duodenum, jejunum, and ileum on photomicrograph slides and recognize labeled details, incl. paneth cells.
Duodenum:12”. Villi w/ wide spatulate or leaflike distal shape. Deep crypts of lieberkuhn. Brunner’s glands w/ excretory ducts in submucosa. KNOW BRUNNER’S glands.
Jejunum:villi longer and narrow. NO GLANDS in submucosa. Crypts of lieberkuhn present.
Ileum: SAME as jejunum. Paneth cells found in pic.
Paneth cells: very prominent eosinophilic grannules. These are cells of the crypts. Basal crypt cells. Produce lysozyme to control intestinal flora.
Small intestine is 22ft. Length.
Distinguish among the duodenum, jejunum, and ileum by the shape of their villi and other histological characteristics
Fig 16-5:
Duodenum: wide, spatulate like villi.
Jejunum: long and narrow, finger like projection villi. NO submucosal hands.
Ileum: shorter and fingerlike in shape w/ peyer’s patches in the deeper mucosa. Paneth cells in pic.
Describe the histology of a crypt of lieberkuhn and distinguish the various cell types and their functions.
Deeper parts. Simple tubular glands. W/in the intestinal mucosa. Open adjacent villi and extend to muscularis mucosa. Goblet cells and enterocytes.
Enterocytes: columnar epithelial cells: main absorbing cells of the intestine. Enteropeptidases, enzymes at brush border, etc.
Paneth cells: very prominent eosinophilic grannules. These are cells of the crypts. Basal crypt cells. Produce lysozyme to control intestinal flora.
Enteroendocrine cells:
Define Brunner’s glands and explain where they are found
Found in submucosa of duodenum.
Responsible for bicarbonate and mucus.
- supplements bicarbonate from the pancreas.
- necessary to neutralize gastric acid.
Receiving acid environment from stomach.
List the functions of the large intestine.
- secretion of mucous for lubrication
- goblet cell is prominent cell of the large intestine.
- absorption of fluid.
- formation of fecal mass
- continuation of digestion initiated in small intestine
List the major features that provide a defensive mechanism for segments of GI tract.
Epithelial cells of GI tract are held together by occulding junctions containing claudins and occludins. They prevent paracellular transport.
-Prevent passage of antigens, food particles (allergies) - protective in nature.
GALT also contains lymphocytes for added protection.
Paneth cells
GALT
M cells
Rapid cell turnover of GI epithelium
List functions of paneth cells:
- In mucosal glands, lysozyme to increase permeability of bacteria by degrading peptidoglycan coat.
- Defensins increase membrane permeability of target organisms
- tumor necrosis factor-alpha (proinflammatroy cytokine)
- may phagocytize some microorganisms and help regulate intestinal flora.
**destroys bacteria-defense mechanism
What’re toll-like receptors?
Found on surface of enterocytes.
Recognize structurally conserved molecules broadly shared by pathogens but distinguishable from host molecules (pathogen asso. Molecular patterns (PAMPS)).
Toll-like receptors are non-specific at recognizing pathogens—identify patterns that are different from normal- primitive surveillance system
What is the role of IgA in the immune defense of the GI tract?
PRimary immunoglobulin produced by GALT.
Synthesized and secreted by plasma cells in the lamina propria of the gut
Picked up at the basal surface of enterocytes and transported across the cell.
IgA doesnt signal complement system.
What’re the M cells and what is their role in defense?
M=microfold cells-asso. W/ peyers patches.
Mucosal covering of the dome of peyer’s patches includes specialized M (microfold) cells: sample particulate antigen and present it to antigen-presenting cells in the underlying lamina propria
What’re GALT and peyers patches?
Transitory aggregations of lymphocytes, neutrophils, eosinophils.
Peyer’s patches:
- are permanent while GALT is not.
- domeshaped lymphoid tissue in muscoal layer
- contain HEVs (entrypoints for lymphocytes from blood)
- covering contains M cells.
Compare the epithelium and musculature of the anal canal to other regions of the digestive tract.
ANus: stratified squamous epithelium like upper GI
Pectinate line seperates ectoderm:anus/anal canal.
And rectum:endoderm
