66 



SECRETION. 



Portiou of one of Brunner's Glands, from 

 human intestine. 



subdivides the main tubule, so as to have several branching 



tubules leading -into it. Often 



p IG ^ these branches again subdivide 



so as to form a group of ulti- 

 mate glandular elements grouped 

 about the main tubule, which acts 

 as a duct. This form of gland is 

 found in kidney, testis, salivary 

 and mammary glands, Brunner's 

 glands (Fig. 15), and in many of 

 the other glandular structures. 



3. Racemose or aggregate glands } 

 in which the glandular structure 

 is divided into lobules or acini. 

 These glands may be regarded 

 as a refinement of the compound 

 tubular variety, and examples are 

 found in the salivary glands and 

 in the Meibomian follicles. 



How is secretion effected by the glands ? 



(1) By physical processes viz. filtration and dialysis the cells 

 are able to separate from the blood-plasma the ingredients which 

 make up the secretion. It is important to remember that the force 

 of dialysis may actually operate against pressure, and is, conse- 

 quently, not a mere negative process ; and, again, the fact that the 

 condition of the blood as to consistency and saline ingredients 

 makes filtration a sort of check-valve upon the permanency of the 

 blood-condition. 



(2) By chemical processes the cells of glands manufacture new 

 substances not found in the blood-plasma and add them to the 

 secretions. These processes are peculiarly noticeable in the fer- 

 ment-producing glands, salivary, peptic, and pancreatic. 



What circumstances affect glandular activity? 



() If the amount of blood passing through a gland be increased, 

 there will be increased activity of the function, and, conversely, as 

 a rule, during functional activity the gland will increase in vascu- 

 larity. The stomach, for example, during digestion is quite en- 

 gorged, and when idle is supplied with much less blood, as is seen 

 by the color deepening during its period of activity. 



(/>) An increase in the motcrinl upon which the gland acts stiinu- 



