THE BLOOD-VESSELS AND CIRCULATION 



139 



ACTION OF 

 THE HEAKT 



CIRCULA- 

 TION 



Simultaneous. 



Blood forced into ventricles. 



Force not sufficient to cause regurgitation 



into the veins. 

 Valves between the auricles and ventricles 



closed. 



Chorda tendinea tightly stretched. 

 Semilunars forced open. 

 Blood forced into the great arteries. 

 Apex of heart tilted forward against the 



front wall of the chest. 

 From 60 (old age) to 120 (young child) per 



minute. 

 Dull sound closure of tricuspid 'and mitral 



valves, and contraction of ventricles (?). 

 Sharp sound sudden closure of semilunars. 

 Followed by a pause. 



In jerks (pulsations}. 



Very rapid. 



Elastic recoil tends to produce a continuous 



stream in the smaller arteries. 

 Very slow and uniform. 

 In capillaries -) Great resistance offered by the capillary 



walls. 



Much faster than in capillaries. 

 Not so rapid as in arteries. 

 Steady flow. 

 Valves prevent backward flow. 



/ Auricular 

 Contraction 



Ventricular 

 Contraction 



Beating . 



I Sounds 



In arteries 



In veins 



COURSE OF THE 

 BLOOD 



Right auricle 



Right ventricle 



Pulmonary arteries 



Lungs (capillary system) 



Pulmonary veins 



Left auricle 



Left ventricle 



Aorta 



Capillary networks in 

 parts 



Venae cavse. 

 . Right auricle. 



Pulmonary circula- 

 tion. 



all I Systemic circula- 

 , tion. 



QUESTIONS ON LESSON XXIII. 



1. How would you distinguish between arteries and veins? Describe the 



structure of each. 



2. What are capillaries ? Where are they found ? What is the size of a 



capillary ? 



3. What is the use of valves in veins ? How are these valves constructed ? 



4. Name arteries that have valves, and veins that have no valves. 



5. How would you determine the positions of the valves in the veins of your 



own arm ? 



6. Describe fully the action of the heart and its valves. 



