140 STUDENTS HISTOLOGY 



GLANDS 



A gland is an organ frequently subsidiary to and located 

 within other organs whose cells manufacture from the blood pro- 

 ducts to be utilized in the performance of some of the functions of 

 the body, or waste products which are to be excreted. 



Simple glands are tubes or cavities, with connective tissue walls 

 lined with epithelial cells, which are usually placed upon a base- 

 ment membrane. Around, and in close proximity to the lining, 

 is spread a plexus of blood -capillaries. In compound glands, the 

 simple glands (acini or alveoli) are enclosed by connective tissue 

 in groups called lobules, and larger groups called lobes. The 

 same connective tissue is continued to form a capsule over the 

 outside. 



The essential parts of a gland are, therefore: 



1. A duct, or efferent conduit for the secretion. 



2. Parenchyma, or cells engaged in secretion. 



3. A blood -vascular supply. 



TUBULAR GLANDS 



The simplest gland-structure is offered in the form of a tube. 

 Glands are, frequently, little more than tubular depressions in 

 mucous surfaces. Examples are found in the uterus, and small 

 and large intestines. 



COILED TUBULAR GLANDS 



Tubular glands are often greatly elongated, with the blind 

 extremity coiled. This variation presents the simplest differentia- 

 tion between the part of the tube which is secretory, and the duct, 

 or drainage part. With this change in function of the different 

 extremities of the tube will occur a change of epithelium. The 

 cells belonging to the duct-end will usually retain the columnar 

 form; while the actively secreting elements will become enlarged, 

 more nearly filling the tube, and assume a polyhedral form from 

 pressure. 



Examples have already been seen in the sweat-glands of the 

 skin. 



