The Endocrine Glands 



THE MANIFOLD functions of the body are 

 integrated partly by the nervous system and 

 partly by the endocrine glands. Each endo- 

 crine gland secretes one or more highly ac- 

 tive organic compounds directly into the 

 blood stream, and these hormones control 

 activity in many parts of the body. Com- 

 pared to the rapidly executed commands of 

 the nervous system, hormonal control is 

 more deliberate and sustained. Consequently 

 the endocrine glands are especially impor- 

 tant in determining the slower and more en- 

 during adjustments by which each organ 

 keeps pace with the changing activities of 

 the other body parts. 



The principal glands of the endocrine 

 system are shown diagrammatically in Fig- 

 ure 22-1. Some of these glands — that is, the 

 thyroids, parathyroids, pituitary, and adre- 

 nals — are purely endocrine in function, and 

 these glands possess no ducts. Such ductless 

 glands send all their secretions into the blood 

 stream; in other words, the ductless glands 

 secrete internally, into the blood, rather than 

 externally, into a duct. However, the endo- 

 crine system also includes such duct-possess- 

 ing glands as the pancreas, ovaries, and 

 testes, which secrete both internally and ex- 



PINEAL 

 PITUITARY 



PARATHYROIDS 

 THYROID 



Fig. 22-1. Location 

 human body. 



THYMUS 



PYLORIC 

 T" STOMACH 

 -- ADRENALS 



PANCREAS 



DUODENUM 



OVARY 



OR 



TESTIS 



of the endocrine organs in the 



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