Circulation of blood through the heart (Fig. 73)
Deoxygenated blood reluming from around the body is carried to the right side of the heart by the major veins: the cruιιkd vena nιvrelatively thick walls which are composed of three layers:
V
1.
Tunica intima - consists of an endothelial lining which Isconiinuous throughout Iheentire circulatory system and is also continuous with theW to the fetus, passing to the foetal liver. The paired Iinibilicol arteries carry deoxygenated bkxxl containing waste products, from the fetus back to the placenta and so Io the circulation of the dam.
As gaseous exchange and nutrient transfer take place in the placenta, bkxxl flow through the lungs and Iiverof the fetus is not as important and there are a number of shunts or by-passes:
In rare cases, the foramen ovale may remain open after birth.This is known as an interventricular septal defect or a ‘hole’ in the heart. Because of the greater pressure in the left ventricle, oxygenated blood passes through the defect from the left to the right side of the heart and pressure builds up on the right side (venous) of the systemic circulation.The animal shows symptoms of right-sided congestive heart failure.
Ioramcn ovale-this is an opening in the septum between the right and left atria and ventricles. Bkx)d passes from the right ventricle to the left ventricle and into the systemic circulation, bypassing the lungs. The foramen ovale closes shortly after birth and the circulation becomes ’adult*. Ductus arteriosus - this is a vessel that forms a connection between the pulmonary artery and the aorta. Bkxxi Hows from the pulmonary artery to the aorta, by-passing the lungs. This closes shortly after birth as the lungs expand but remains as the Iigainnitinn arteriosus.
Ductus venosus- this is a venous shunt within the liver that connects the umbilical vein to the caudal vena cava. The nutrient and oxygen laden bkxxl in the umbilical vein passes directly to Ihecaudal vena cava and so to the fthe prescapular nodes - two on each side lying just in front of (he shoulder joint, at the base of the neck on the cranial edge of the scapula
Superficial inguinal nodes - two nodes on each side lying in the groin, between the thigh and the abdominal wall, dorsal to the mammary gland or penis
Hiplitctil node - lies within the tissue of the gastrocnemius muscle, caudal to the stifle joint.