368 - Multicellular Animals, Especially Man 



for the control of respiration (and heart rate). 

 This is provided hy a special chemoreceptor, 

 the carotid sinus, imbedded in the wall of 

 each internal carotid artery near the point 

 of origin. The cells of this receptor are ex- 

 cited by increases in either CO., or hydrogen 

 ion in the blood that is flowing through 

 the artery. The nerve impulses thus gener- 

 ated are carried via the sensory branches of 



the vagus nerve (p. 467) to the respiratory 

 and cardiac centers, increasing the intensity 

 and frequency of the motor discharges from 

 these vital reflex centers. All in all, there- 

 fore, the body has developed a number of 

 checks and balances upon the breathing 

 mechanism — for this mechanism must be 

 relied upon constantly from the instant of 

 birth to the time of death. 



TEST QUESTIONS 



1. Differentiate between external and internal 

 respiration. Why is it not possible to make 

 such a distinction in very small organisms, 

 like Hydra? 



2. What is a specialized respiratory surface, and 

 what advantages are provided by such a sur- 

 face? 



3. Differentiate between lungs and gills. Ex- 

 plain why gills are poorly suited to terres- 

 trial conditions. 



4. Explain the part played by the diaphragm 

 and intercostal muscles in inspiration and ex- 

 piration. How does a forced expiration differ 

 from the expiration of ordinary breathing? 



5. What is alveolar air? Explain how and why 

 it differs from the external air. 



6. Explain the term "partial pressure" ol oxy- 

 gen. Specify the partial pressure of oxygen: 



(a) in the outside atmosphere at sea level; 



(b) in the alveolar air at sea level; (c) in the 

 outside air at 14,000 ft elevation; and (d) in 

 the alveolar air at 14,000 feet. 



7. What are the symptoms of "mountain silk- 

 ness"? What is the cause ol this condition? 



8. Compare the oxygen-carrying capacity of 

 whole blood with that ol (a) plasma and 



(b) salt solution. How is this difference to be 

 accounted for? 

 9. Describe and explain the difference of color 

 between venous (unaerated) and arterial 

 (aerated) blood. 



10. The binding and freeing of oxygen by hemo- 

 globin is determined by the following equi- 

 librium: 



HHb + 2 ^H-Hb0 2 



Explain how and why this equilibrium is 

 shifted: (a) while the blood Hows through the 

 capillaries of the lung: and (b) while the 

 blood flows through the capillaries of the 

 other parts ol the body. 



11. Carefully explain how- the mechanisms of 2 

 and CO,, transport are intimately interre- 

 lated. 



12. Explain the mechanism of carbon monoxide 

 asphyxia, specifying the best method of resus- 

 citation. 



13. Describe two other types ol asphyxia, citing 

 an example ol each type. 



14. Carefully explain how our breathing move- 

 ments are modified by (a) chemical and (b) 

 nervous factors. 



FURTHER READINGS 



1. Lessons from Higli Altitude, by Joseph Bar- 

 croft; Cambridge, Eng., 1925. 



2. Respiration, by J. S. Haldane; New Haven, 

 1927. 



3. Tlie Wisdom of the Body, by Walter B. Can- 

 non; New York. 1939. 



