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Introduction 



Organs. — Different tissues are grouped together to perform single 

 functions, and are called organs. For example, the stomach contains 

 epithelial tissues, some of which secrete digestive enzymes, muscular 

 tissues which cause movements, nervous tissues which control these 

 movements, vascular tissues to carry food to the cells and waste 

 products away, and finally connective tissues between the various layers. 

 In fact all the types of tissues except the reproductive ones are found 

 in this one organ. Examples of other organs are the brain, heart, and 

 lungs. 



Organ Systems. — Organs concerned with a particular function are 

 grouped into systems. The organ systems of higher animals are 

 as follows : 



Integumentary : 

 Skeletal : 

 Muscular : 



Digestive : 

 Respiratory : 

 Circulatory : 



Nervous : 



Urinary : 



Reproductive : 

 Endocrine : 



Skin and its derivatives. Chiefly protective in function. 



Bones of the body. Chiefly supportive and protective. 



The muscles of the body. Muscles are found attached to 

 bones and in organs wherever movements are necessary. 



Esophagus, stomach, intestine, and accessory glands and 

 structures. This system prepares food for final use by 

 the body cells. 



Lungs and accessory structures. Oxygen and carbon di- 

 oxide are exchanged within the smaller structures of 

 the lungs. 



Blood, heart, arteries, veins, capillaries, and lymphatics. 

 This system brings food and oxygen to the cells and re- 

 moves waste materials. 



Brain and associated nerves. This system coordinates many 

 of the activities of the body. Through the sense organs 

 contact with the outer world is maintained. 



Kidneys and associated structures. By removal of waste 

 materials from the blood, the urinary system is essential 

 in maintaining a favorable internal environment. 



Ovaries, testes, and associated structures. Important for the 

 maintenance of the species. 



The ductless glands of the body. With the nervous 

 system, this system coordinates the many diverse activities 

 of the body. 



Each of these systems will be considered in detail later, but in so 

 doing, it must be remembered that the division of the body into systems 

 is not nearly so complete as this listing would imply. Actually all sys- 

 tems work together in such a manner as to make the organism into 

 a unified whole. 



