would extend down to about rib 10. The sixth (answer a)intercostals
space is too cranial and tenth (answer b)and twelfth (answer d)inter-
coastal spaces are too caudal.
363.The answer is b.(Moore and Dalley, p 189.)Pulmonary trunk (bifur-
cated) The pulmonary trunk (8) has just bifurcated and will form the left and
right pulmonary artery just inferior to the arch of the aorta. Other labeled
structures are: 1, left ventricle; 7 aortic arch; 8 bifurcated pulmonary trunk
(most likely left pulmonary artery in this image); 9 brachiocephalic artery;
10, left common carotid artery; 11 left subclavian artery; 12 ascending aorta;
13 descending aorta; and 14 right coronary artery (difficult to see).
364.The answer is c.(Sadler, p 178.)The two major changes that occur
at birth in the heart or vessels are that the septum primum closes against
the septum securdum and the ductus arteriosus closes. At delivery, the
blood from the placenta decreases, thus reducing the pressure in the right
atrium. As the air fills the lungs there is increased blood flow to the lungs
and thus increased blood returning to the left atrium. This increase in left
atrial pressure and decrease in right atrial pressure closes the septum pri-
mum against the septum secundum, thus closing the foramen ovale, and
separating the two atrial chambers. In addition there is smooth muscle
constriction within the walls of the ductus arteriosus, also sending more
blood to the lungs. (See figures in answer to question 14 in Embryology:
Early and General.) None of the other answers (answers a, b, d, e)are
correct
365.The answer is b.(Moore and Dalley, pp 79–80.)One would expect a
cracked rib that allows blood from the intercostal vessels to bleed into the
pleural cavity, partially collapsing the left lung, causing the shortness of
breath. Blood in the pleural cavity is an irritant and causes generalized
chest pain. The left-sided, midback pain is from the cracked eleventh rib.
Because only one lung appears to have fluid accumulation and he is young
and exercises regularly; pulmonary hypertension (answer a)is unlikely,
especially give his physical findings and history and sudden onset of symp-
toms. Cardiac tamponade (answer c),which is blood within the pericar-
dial sac, is unexpected. Neither gallbladder pain (answer e), noran
inflamed appendix (answer d)would typically cause chest pain. Note: the
CT of the abdomen is required to rule out damage to kidneys and spleen.
Thorax Answers 489