Jeff is writing a term paper on the role of melatonin. he decides to emphasize the important role that this hormone plays in regards to

The melatonin is a hormone responsible for the regulation of the sleep cycles. this hormone is secreted by the pineal glands.

The amount of the melatonin helps the body to regulate the sleeping pattern. The levels of the melatonin is higher at night and it promotes sleeping. During daytime the level of melatonin is comparatively low.

So, the correct answer is sleeping cycle.

answer; ///i believe the correct answer is (aids) acquired immune deficiency syndrome;

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.