136 ANATOMY FOR NURSES [Chap. Mil 



by small ducts into the main duct, which pours the secretion 

 upon the surface. If composed of many tubes, either straight or 

 convoluted, they are called compound tubular glands; if composed 

 of gr()Uj)s of small sacs, they are called racemose glands. 



3. Ductless glands. — This term is applied to a collection of 

 glandular structures that possess no ducts. Whatever secretion 

 or excretion they produce is discharged into the blood, either 

 directly or indirectly by way of the lymphatics. 



SECRETION 



A new substance, the product of a gland, elaborated from 

 the blood by cell action, and intended for use in the body is called 

 a secretion. 



For purposes of study we may divide the secretions into two 

 groups : — 



(1) External secretions. 



(2) Internal secretions. 



External secretions. — This term is used to designate those 

 secretions of glandular tissues which are carried to their destina- 

 tion by a duct. All of the digestive juices — saliva, gastric juice, 

 pancreatic juice, bile, and intestinal juice — are examples of ex- 

 ternal secretions, because thej' are carried off from the respective 

 glands in which they are formed by means of ducts. 



Function. — The function of the external secretions is dealt with 

 in connection with the organs which produce them. 



Internal secretions. — This term is used to designate those 

 secretions of glandular tissues which are not carried off to the 

 exterior by a duct, but instead are discharged into the blood or 

 l\Tnph. The conception is that probably all the ductless glands 

 form secretions which have a profound influence on nutritive 

 changes in the body. Such secretions are called internal secre- 

 tions. It has also been shown that not only the ductless glands, 

 but some at least of the typical glands provided with ducts, may 

 give rise to internal secretions. For example, the pancreas forms 

 the pancreatic juice and discharges it by means of a duct into the 

 small intestine. In addition, it is believed that the pancreas forms 

 an internal secretion which passes into the blood. 



Function. — On account of the difficulty of separating internal 



