IV. GENERAL HISTOLOGY: STRUCTURE OF ORGANS 



An organ consists of two or more kinds of tissue united together in a definite 

 and characteristic way for the performance of specific functions. 



A. STRUCTURE OF THE LIVER 



Examine slide " Necturus liver" (see Holmes, pp. 153-56). The liver may 

 be taken as an example of a rather simply constructed organ, and also as an 

 example of a secreting gland. It consists almost entirely of large cuboidal 

 epithelial cells, arranged in cylindrical columns which branch and connect with 

 each other in a very irregular manner. The columns therefore form a kind of 

 network with numerous large spaces between them. These spaces are capil- 

 laries and in them blood corpuscles will usually be found. A very slender, 

 usually invisible canal runs down the center of each liver column between the 

 cells, and into this canal, which is called a bile capillary, the secretion of the liver 

 cells, known as bile, is poured. The large black spots scattered abundantly 

 through the liver are collections of pigment granules. Large blood vessels, and 

 perhaps some of the bile ducts which collect the bile from the bile capillaries, may 

 be present on the section. Surrounding the liver and penetrating it here and 

 there along the course of the larger blood vessels is a small amount of white 

 fibrous connective tissue. The liver cells have several other highly important 

 functions besides that of secreting bile. 



B. STRUCTURE OF THE INTESTINE 



Examine slide " Necturus intestine" (see Holmes, pp. 148-50). These 

 cross-sections of the small intestine have been stained with Mallory's connective 

 tissue stain in order to produce a marked color contrast between the different 

 layers of the intestinal wall. This stain dyes connective tissue and related sub- 

 stances a deep blue color, and nuclei orange or red. 



i. General structure of the intestinal wall. The wall of the intestine con- 

 sists of four coats. Identify these as follows with the low power, beginning next 

 to the cavity: 



a) The mucous coat (mucous membrane or tunica mucosa], the innermost 

 light-colored layer, containing numerous red or orange nuclei. It is thrown up 

 into folds and is sharply separated from the next layer by its different reaction 

 to the dye. 



b) The submucous coat (tela submucosd), a broad band, stained deep blue, 

 containing frequent spaces and extending up into the folds of the mucosa. 



33 



