Lecture 24

Question 1

List the major structural features that increase surface area for absorption in the G.I. tract. (4 of them)

Answer 1

Length of the small and large intestine

Plicae circulares (valves of Kerckring)

Villi

Microvilli

Question 2

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

Answer 2

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)

Question 3

Describe the fine structure of a microvillus. (covering and support structure)

Answer 3

Covered with a glycoprotein and glycocaylyx

Supported by a core of actin filaments within the microvillus that is covered by a formin cap

Question 4

______ fibrils bind these actin filaments to the terminal web intermediate filaments (cytokeratins)

Answer 4

Spectrin

Question 5

_____ and ______ are the 2 membrane-linking proteins that bind these actin filaments to the plasma membrane that covers the villus

Answer 5

Myosin I

calmodulin

Question 6

_____ and _____ are the cross-linking proteins that bind these actin filaments to one another

Answer 6

Villin

Fimbrin

Question 7

Describe the composition of the glycocaylyx that covers the GI tract and identify what secretes the glycocaylyx

Answer 7

A glycolipid coat that contains an array of brush-border enzymes (maltase, sucrase, isomaltase, lactase, lipase, and peptidases)

Produced by small intestinal epithelial cells

Question 8

Describe the shape and contents of the villi in the Duodenum

Answer 8

Villi with wide spatulate or “leaflike” distal shape

Deep crypts of lieberkuhn

Brunner’s glands with excretory ducts in the submucosa

Question 9

Describe the shape and contents of the villi in the Jejunum

Answer 9

Villi have a “finger-like shape” and longer than ileum villi

Crypts of leiberkuhn

NO GLANDS in the submucosa

Question 10

Describe the shape and contents of the villi in the Ileum

Answer 10

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

Question 11

Where can Goblet cells, Enterocytes, Paneth cells, and Enteroendocrine cells all be found? describe the histology of this.

Answer 11

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

Question 12

Describe the tissue they are composed of and the function of Enterocytes

Answer 12

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

Question 13

Describe the function of Paneth Cells and where they are prominent

Answer 13

Paneth cells: basal crypt cells that produce lysozyme to control intestinal flora

Prominent in eosinophilic granules

Question 14

Describe the function of enteroendocrine cells, what they stain with, and what they form from

Answer 14

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

Question 15

True or False: Enteroendocrine cells are analogous to unicellular goblet cells. explain.

Answer 15

True

Question 16

Define Brunner’s glands and explain where they are found.

Answer 16

Found in the submucosa of the duodenum and are responsible for the formation of bicarbonate and mucus

Supplements bicarbonate from the pancreas in order to neutralize gastric acid

Question 17

In terms of the large intestine, state the reason for the secretion of mucus, It’s most prominent cell, what it absorbs, what it forms, and what process it continues.

Answer 17

Secretion of mucus for lubrication

Goblet cells are the prominent cell of the large intestine

Absorption of fluid

Formation of fecal mass

Continuation of digestion initiated in the small intestine