Question

24 hr. (diurnal) the rhythm of our body such as the sleep-wake cycle is regulated by the hormone
(a) Calcitonin
(b) Prolactin
(c) Adrenaline
(d) Melatonin

Answer 1

Hint: The diurnal rhythm is managed by a hormone secreted by the pineal gland which maintains the normal sleep-wake cycle.

Complete answer:
The pineal gland is located on the dorsal side of the forebrain. It has a stalk called a pineal stalk and a small, rounded, reddish structure called the pineal body. The pineal gland secretes a hormone called Melatonin. Melatonin plays an important role in the regulation of 24hr. (diurnal) the rhythm of our bodies. The secretion of the melatonin follows a diurnal cycle i.e., it rises in the evening and throughout the night and drops around noon. Besides, melatonin also influences the metabolism of the body, body temperature, pigmentation of the skin, menstrual cycle as well as defense capability of an individual. - Melatonin hormone delays puberty in humans by opposing the action of LH and FSH and hence, affects the menstrual cycle and working of gonads. - It is also concerned with sleep. - People blind from birth attain puberty earlier than normal, apparently because there is no inhibitory effect of melatonin on functions of gonads.
So, the answer is, ‘Melatonin’.

Note:
- The pineal gland is also called Epiphysis.
- Since melatonin is secreted in response to the darkness it is also called the “hormone of darkness”.
- The melatonin is not stored in the pineal gland rather is directly released into the bloodstream.
- It has its maximum concentration at midnight and a minimum of noon.
- Light reduces the melatonin formation and hence normal rhythm of the sleep- wake cycle.
- It acts like a biological clock.