Explanation

Pineal gland secretes two biogenic hormones i.e., melatonin and serotonin. Melatonin is secreted in a diurnal cycle (the amount changes throughout 24 hour period) where the amount remains low during daylight hours but increases during dark hours. Serotonin Serotonin secretion is induced by light. It act as vasoconstrictor and helps to increase the blood pressure