Final: Lecture 23 Flashcards
0
Q
Plicae
A
•These are folds of the mucosa, each with a submucosal core
1
Q
The three orders of folding are?
A
- Microvilli, Crypt-villus system, and Plicae
* Increase surface area in the small intestine
2
Q
Crypt-villus system
A
- Each villus contains core of lamina propria
- Extend down between villi below bases of the villi
- Walls composed of simple columnar epithelium with goblet cells
- Crypts and villi constitute glands of small intestine
- Each villus contains a capillary plexus, blind-ending lymphatic reffered to as lacteal
3
Q
Microvilli
A
- Covered with glycoprotein and glycocalyx (contains array of brush-boarder enzymes
- Maltase, sucrase, isomaltase, lactase, lipase, peptidases,
- Produced by small intestine epithelial cells
- Bundles of actin filaments within microvillus is covered by a formin cap
4
Q
Microvilli supported by core of actin microfilaments:
A
- Actin filaments are tied to terminal web intermediate filaments (cytokeratins) via spectrin fibrils
- Bound to plasma membrane covering villus via membrane-linking proteins (myosin I and calmodulin)
- Bound to each other via actin cross-linking proteins (villin and fimbrin)
5
Q
Cells of the Crypts of Lieberkuhn:
A
- Goblet cells
- Enterocytes
- Paneth cells
- Enteroendocrine cells
6
Q
Enterocytes
A
- Columnar epithelial cells with the following characteristics:
- basal nucleus, perinuclear Golgi, apical brush border
- Produce disaccharidases
- Involved in absorption of proteins, carbohydrates, lipids
- Enzymes present on apical brush border are important in carb digestion
- Produce enteropeptidase which is necessary for the activation of pancreatic zymogens and proenzymes
7
Q
Paneth cells
A
- Basal crypt cells
- Prominent eosinophilic granules
- Produce lysozyme to control intestinal flora
8
Q
Enteroendocrine cells
A
- Stain with chromium
- Agryrophillic (respond to silver stains)
- Produce peptide hormones and serotonin
- May produce paracrine or autocrine secretions
- Analogous to unicellular goblet cells
- Formed from endodermal stem cells in all regions of the GI tract
9
Q
Glands of Brunner
A
- Found in submucosa of duodenum
- Responsible for formation of bicarbonate and mucus
- Supplements bicarbonate from pancreas, necessary to neutralize gastric acid
10
Q
Duodenum
A
- Villi with wide spatulate or “leaflike” distal shape
- Deep crypts of Lieberkuhn
- Brunner’s glands with excretory ducts in submucosa
11
Q
Jejunum
A
- Villi longer and narrow
- Crypts of Lieberkuhn present
- No glands in submucosa
12
Q
Ileum
A
- Villi longer and narrow
- Crypts of Lieberkuhn present
- No glands in submucosa
13
Q
Large intestine
A
- Simple columnar epithelium, crypts but no villi
- Functions: secretion of mucus for lubrication, *goblet cell is the prominent cell, absorption of fluid, formation of fecal mass, continuation of digestion initiated in small intestine
14
Q
Exposed bands of longitudinal muscle in the large intestines are ______.
A
•Taeniae coli
15
Q
An appendix epiploica is an aggregate of _______ surrounded by the serosa.
A
•Adipocytes
16
Q
Paneth cells
A
- Characteristics: basophilic basal cyto, supranuclear Golgi complex, large, intensely acidophilic apical secretory granules
- Secrete: lysozyme to increase permeability of bacteria by degrading peptidoglycan coat*
- Defensins to increase membrane permeability of target organisms
- Tumor necrosis factor-alpha (proinflammatory cytokine)
- May phagocytize some microorganisms and help regulate intestinal flora
17
Q
Mucosal Layer
A
- Coats intestinal epithelial luminal surface
- Secreted by goblet cells
- Made up of two layers: other containing microorganisms, inner contains antimicrobial proteins (from Paneth, enterocytes, and goblet cells) that resist microbial penetration
18
Q
Toll-like receptors
A
- Found on surface of enterocytes
- Secreted by goblet cells
- Outer layer contain microorganisms
- Inner layer contains antimicrobial proteins that resist microbial penetration
19
Q
Immune Surveillance System (path 1)
A
- Antigen binds to toll-like receptor on enterocyte surface
- B cell-activating factor produced
- B cells lamina propria mature into plasma cells–>antibodies
20
Q
Immune Surveillance System (part 2)
A
- Antigen is taken up by M (microfold) cells ass. with Peyer patch in the intestinal mucosa
- Antigens transported to lymphocytes located in pockets in folds of M cells
- 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
21
Q
GALT
A
- Components: transitory aggregations of lymphocytes, neutrophils, eosinophils
- Permanent structures: appendix, Peyer’s patches, mesenteric lymph nodes
22
Q
Bulk of the body’s immune defenses centered in _______.
A
•GALT
23
Q
Peyer’s Patches
A
- Dome-shaped lymphoid structures under the mucosal surface
- Contain B and T cell dependent areas
- Possess high endothelial venuels (HEVs), which facilitate entrance of lymphocytes into lymphoid organs from bloodstream
- Mucosal covering of the dome includes specialized M (microfold) cells: sample particulate antigen and present it to antigen-presenting cells in the underlying lamina propria
- Antigen-presenting cells (APCs) and macrophages phagocytize the antigen and present it to helper cytotoxic T cells as well as B lymphocytes
24
Q
The primary immunoglobulin produced by GALT is ___.
A
- IgA
- Synthesized and secreted by plasma cells in lamina propria of the gut
- Picked up at the basal surface of enterocytes and transported across the cell
- While in the cell, IgA is linked to a protein called secretory component that inhibits degradation by proteolytic enzymes in GI lumen
- Secretory IgA, unlike IgG, doesn’t stimulate the complement system, but functions by coating microorganisms, thus inhibiting them binding to epithelium
25
Q
Lining in the stomach and small intestine is replaced every ___ days in humans
A
•5
26
Q
Rapid cell turnover
A
- In esophagus and anus: new cells formed in basal layer of stratified epithelium and migrate through sub-basal levels to be sloughed off into lumen
- In small intestine: new cells formed in crypts from undifferentiated cells
- Large Intestine: no villi, so proliferative compartment found in base of crypts
- Stomach: stem cells are found in the neck of gastric glands, differentiate into surface and neck mucus cells enteroendocrine, parietal, and chief cells
27
Q
Anal Canal
A
- Epithelium returns to stratified squamous
* Skeletal muscle returns as external anal sphincter
