Lecture 24 Flashcards
List the major structural features that increase surface area for absorption in the G.I. tract. (4 of them)
Length of the small and large intestine
Plicae circulares (valves of Kerckring)
Villi
Microvilli
Describe the histology of the crypt-villus system in terms of it’s core, where the crypts extend to, and the composition of the wall of the villus
Each villus contains a core of lamina propria and the crypts extend down below the bases of the villi
The wall of the villus is composed of a simple columnar epithelium with goblet cells
Each villus contains a capillary plexus and a blind-ending lymphatic (lacteal)
Describe the fine structure of a microvillus. (covering and support structure)
Covered with a glycoprotein and glycocaylyx
Supported by a core of actin filaments within the microvillus that is covered by a formin cap
______ fibrils bind these actin filaments to the terminal web intermediate filaments (cytokeratins)
Spectrin
_____ and ______ are the 2 membrane-linking proteins that bind these actin filaments to the plasma membrane that covers the villus
Myosin I
calmodulin
_____ and _____ are the cross-linking proteins that bind these actin filaments to one another
Villin
Fimbrin
Describe the composition of the glycocaylyx that covers the GI tract and identify what secretes the glycocaylyx
A glycolipid coat that contains an array of brush-border enzymes (maltase, sucrase, isomaltase, lactase, lipase, and peptidases)
Produced by small intestinal epithelial cells
Describe the shape and contents of the villi in the Duodenum
Villi with wide spatulate or “leaflike” distal shape
Deep crypts of lieberkuhn
Brunner’s glands with excretory ducts in the submucosa
Describe the shape and contents of the villi in the Jejunum
Villi have a “finger-like shape” and longer than ileum villi
Crypts of leiberkuhn
NO GLANDS in the submucosa
Describe the shape and contents of the villi in the Ileum
Villi have a “finger-like shape” and are shorter than jejunum villi
M cells (antigen-transporting cells) are found here
Peyer’s patches (lymphoid aggregates that form follicles) are found in the submucosa and lamina propria
Where can Goblet cells, Enterocytes, Paneth cells, and Enteroendocrine cells all be found? describe the histology of this.
They can all be found in a crypt of lieberkuhn
they are Simple tubular glands within the internal mucosa that open between the adjacent villi and extend down to the muscularis mucosa
Describe the tissue they are composed of and the function of Enterocytes
Enterocytes are columnar epithelial cells that have a basal nucleus, perinuclear golgi, and an apical brush border
They produce disaccharidases (break down diasaccharides) and enteropeptidase (enterokinase) which is necessary for the activation of pancreatic zymogens and proenzymes
Describe the function of Paneth Cells and where they are prominent
Paneth cells: basal crypt cells that produce lysozyme to control intestinal flora
Prominent in eosinophilic granules
Describe the function of enteroendocrine cells, what they stain with, and what they form from
Enteroendocrine cells: stain with chromium and are Agyrophilic (respond to silver stains)
They produce peptide hormones and serotonin
(May produce paracrine or autocrine secretions)
Formed from endodermal stem cells in all regions of the GI tract
True or False: Enteroendocrine cells are analogous to unicellular goblet cells. explain.
True
