Final answer:
The pulmonary artery is absent in the condition called a patent ductus arteriosus, a congenital defect where the ductus arteriosus remains open, causing a shunt from the aorta to the pulmonary trunk and leading to various symptoms.
Step-by-step explanation:
The condition in which the pulmonary artery is absent is known as a patent ductus arteriosus (PDA). This is a congenital heart defect where the ductus arteriosus fails to close after birth. The ductus arteriosus is a fetal artery that shunts most of the blood away from the nonfunctioning fetal lungs by connecting the pulmonary trunk directly to the aorta. Normally, this artery constricts after birth, allowing all blood leaving the right ventricle to travel to the lungs via the pulmonary arteries.
In the case of PDA, this closure does not occur, which can lead to various symptoms such as dyspnea, tachycardia, and poor weight gain in infants. Treatment options include surgical closure, catheter-based interventions, or medications to encourage the ductus arteriosus to close.