Final answer:
Pulmonary vasoconstriction is caused by endothelins, platelet secretions, certain prostaglandins, and angiotensin II, as well as by physiological processes regulated by the vasomotor center.
Step-by-step explanation:
The causes of pulmonary vasoconstriction can be attributed to the action of various substances and physiological mechanisms. Contraction of the precapillary sphincter occurs due to the influence of certain regulators, leading to the release of endothelins. These peptides, which are secreted by endothelial cells that line the blood vessels, are potent vasoconstrictors. The presence and activity of platelets can also contribute as their secretions and certain prostaglandins are involved in triggering the constriction of blood vessels. Furthermore, the vasomotor center located in the medulla oblongata plays a critical role in regulating blood flow by sending sympathetic stimulation to smooth muscle in vessel walls, triggering venoconstriction.
Compounds such as angiotensin II also induce vasoconstriction and have a systemic effect on blood pressure. Cocaine, as a stimulant, causes vasoconstriction as well, which is expected to increase blood pressure. In medical conditions like obstructive shock, where there's a blockage in the vascular system, treating the underlying cause is crucial, and management may include addressing pulmonary embolism—a common cause of vasoconstriction due to a clot in pulmonary vessels.