GENERAL ZOOLOGY 



It is necessary for warm-blooded animals to conserve their heat when the 

 external temperature drops. Autonomic nervous regulation produces con- 

 striction of peripheral blood vessels. Voluntary regulation is through reduc- 

 tion of exposed body surface by huddling and finding additional protection 

 in nests or sheltered places, seeking of warmer climes by migrating animals, 

 heavier clothing and artificial heat for man. Heat production is raised by 

 increased intake of food, utilization of fat stores, and involuntary muscular 

 activity or shivering. Elevation of the hair in fur-bearing mammals conserves 

 heat, but piloerection in man only produces "gooseflesh." 



Hormones play a part in temperature regulation. The secretion of the 

 thyroid regulates cellular oxidation, an important source of body heat; the 

 basal metabolic rate is normally higher in cold weather. Epinephrine in- 

 creases the availability of glucose, a major source of energy and heat. Ad- 

 renal cortical salt-active hormone controls the concentration of the blood, thus 

 affecting its rate of flow; a more concentrated blood conserves heat because it 

 flows more slowly. 



Fever is, in effect, the result of conservation of body heat when it is phys- 

 iologically unnecessary. Something goes wrong at the thermoregulatory 

 centers in the hypothalamus, but exactly what happens is not known. 



Summary 



The material discussed in this chapter has been selected to acquaint you 

 with the ways in which coordination is accomplished in vertebrates. In the 

 complex adjustments of the internal environment of the cells and of the 

 animal as a whole to its external environment, there is a delicately balanced 

 interplay of autonomic nervous and hormonal mechanisms, modified by the 

 emotions and conscious nervous control. Similarly, we find the several mech- 

 anisms of integration working together in the coordination of the events lead- 

 ing to parenthood: growth and differentiation of the germ cells, behavior 

 patterns in male and female that lead to fertilization of the egg cell and, 

 in many vertebrates, to its incubation and to the care and feeding of the 

 young after hatching or birth. Regulation of intrauterine gestation in placental 

 mammals appears to be entirely hormonal. 



The life of the individual is maintained as a result of the distinctive 

 protoplasmic capacities of metabolism and responsiveness. The life or con- 

 tinuity of the species depends on the capacity of reproduction, the implica- 

 tions of which we must now examine. 



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