BODY TISSUES 311 



fatty acids in the diet are first incorporated into the body fat before 

 they are oxidized. 



Although depot fats are stored primarily as food reserves, there are 

 secondary benefits. Subcutaneous fats serve as insulators for the body. 

 Lipides serve as shock absorbers in protecting joints, nerves, and other 

 organs against mechanical injury. 



GLANDULAR TISSUES 



Certain tissues in the body are capable of elaborating and discharg- 

 ing secretions of the utmost importance to the welfare of the animal 

 body. These are known as glandular organs, and they possess spe- 

 cialized cells known as gland cells. The glandular tissues do not, of 

 themselves, differ strikingly in chemical composition from other body 

 tissues, but they are of interest because of the chemical substances 

 they elaborate. 



These tissues may be classified into two groups: (1) glands of ex- 

 ternal secretion, with ducts which secrete their chemical materials in 

 such a manner that they may pass from the body, and (2) glands that 

 possess no ducts and secrete their chemical materials directly into the 

 blood stream, whence they are carried to other tissues. The latter are 

 known as ductless glands, endocrine glands, or glands of internal secre- 

 tion. 



Glands of External Secretion 



This group of glands is of great importance to the body since the 

 secretions are used for the digestion of food, the feeding of the young, 

 or the excretion of waste products. External excretory glands related 

 to assimilation are discussed in some detail in other portions of this 

 book. They include the salivary, gastric, intestinal, pancreatic, and 

 liver glands and are discussed in relation to their roles in providing 

 enzymes and activators required for digestion (Chapter 17). 



Sweat glands are located in the external epithelial tissue (skin) and 

 serve as excretory organs, although their role is less significant than 

 that of the kidney. They are tubular coiled glands whose ducts are 

 controlled by smooth muscles which also aid in expulsion of sweat. 

 They are most abundant in the palms of the hands and soles of the 

 feet with lesser numbers in other surface areas of human beings. The 

 foot pads of dogs and cats contain the only sweat glands found in those 

 species. 



