110 VETERINAEY STATE BOARD 



(b) The dilatation or stage of dilatation of the heart. 



(c) A cardiac cycle is a complete cardiac movement or heart- 

 beat. It includes the period from the beginning of one heart-beat 

 to the end of another, i.e., the systolic and diastolic movements with 

 the interval between. 



Blood-vessels 



How do arteries and veins differ in (a) structure, (b) function? What 

 arteries carry venous blood and what veins carry arterial 

 blood? 



(a) The walls of veins are thinner than those of arteries and 

 they collapse when empty. They contain less elastic and muscular 

 material and more fibrous tissue than arteries. Veins are provided 

 with valves which are not present in arteries. 



(b) Veins carry impure blood from the tissues to the heart. 

 Arteries carry pure blood from the heart to the various parts of the 

 body. There are two exceptions, viz., the pulmonary artery carries 

 venous blood from the heart to the lungs and the pulmonary vein 

 carries pure blood from the lungs to the heart. 



How does the internal coat of an artery differ from that of a vein? 



Arteries have no valves as do the veins. 



Discuss the forces that cause the blood to circulate in (a) the arteries, 

 (b) the capillaries, (c) the veins. 



(a) Force of the heart's contraction, and the elasticity of the' 

 arterial walls. 



(b) Pressure from arteries and elasticity of the walls. 



(c) Muscular contractions, valves, gravity, and negative 

 pressure in veins leading directly into the right heart. 



Describe the course of the blood from the right auricle back to the 

 same point. What part of this circulation is called the sys- 

 temic circulation? 

 From the right auricle, blood flows through the tricuspid valve 

 into the pulmonary artery, to the lungs, returning to the left auricle 

 through the pulmonary veins, completing the pulmonary circulation. 

 From the left auricle, the blood begins the systemic circulation, 

 passing through the bicuspid valve into the left ventricle, thence 

 through the aortic semilunar valve into the aorta, which divides 

 and subdivides until every part of the body is supplied. Collecting 

 in the veins, it is carried through the anterior and posterior vena 

 cava to the right auricle, whence it started, thus completing the 

 systemic circulation. 



