QUESTIONS AND ANSWERS 111 



Describe the circulation of the blood. 



See answer to preceding question. 



Discuss the relative velocity of the blood in the arteries, capillaries and 

 veins. 



Greatest velocity is in the arteries, least in the capillaries, and 

 rising again in the veins. 



Define blood-pressure. Mention (a) factors that increase blood- 

 pressure, (b) factors that decrease blood-pressure. 

 Blood-pressure is the tension on the walls of the blood-vessels 

 derived from the blood current. 



(a) Increase in force of the heart-beat and contraction of the 

 ai-terioles. 



(b) Decrease in the force of the heart-beat and dilatation of the 

 arterioles. 



Where is blood-pressure (a) the highest, (b) the lowest? How is 

 blood-pressure governed? 



(a) In the region of the aorta. 



(b) In the region of the periphery. 



Blood-pressure is governed by the contraction of the heart and 

 the resistance offered by the peripheral vessels ; all being regulated 

 by the vasomotor centre in the brain. 



Describe the flow of blood in the arteries. 



The centre of the vessel is occupied by a column of rapidly 

 moving red cells, while between them and the vessel wall is a clear 

 layer in which the white corpuscles move slowly along, occasionally 

 stopping along the sides, then moving forward once more. 



What is meant by the velocity of the blood? State where this velocity 

 is (a) the greatest, (b) the least. 

 Velocity refers to the rate at which the blood flows through the 

 blood-vessels. The velocity varies inversely as the sectional area of 

 the tubes. Since the total sectional area of the capillaries is greater 

 than that of the arteries or veins, the velocity is least in the capil- 

 laries and greatest in the arteries. 



What causes the flow of blood in the veins? 



Muscular contractions, valves, gravity and the negative pressure 

 in the veins leading directly into the right auricle. 



Why is blood-pressure highest at the beginning of an expiration and 

 lowest' at the beginning of an inspiration? 

 At the beginning of expiration, which is really the height of 

 inspiration, the intrathoracic pressure is greatest, more blood is 



