(i) Hormone is called first messenger and cAMP called second messenger.
(ii) Protein hormone is water soluble, it binds to the extrinsic receptor present on the cell surface of the plasma membrane. Hormones when bind to them activates, a membrane bound enzyme adenyl cyclase, which catalyses the conversion of ATP to cAMP.
The cAMPthen activates one more enzyme known as protein kinases. After phosphorylation of protien, alteration of its function occurs which thereby, leads to some metabolic effect.

(1) Melanocytes stimulating –release hormone. Stimulate the function of MSH.
(2) Melanocyte stimulating-inhibiting hormone. It inhibits the release of MSH.

Parathyroid hormone (PTH) increases the Ca2+ levels in the blood. PTH acts on bones and stimulates the process of bone resorption (dissolution/ demineralisation). PTH also stimulates reabsorption of Ca²⁺ by the renal tubules and increases Ca²⁺ absorption from the digested food. It is, thus, clear that PTH is a hypercalcemic hormone, i.e., it increases the blood Ca²⁺ levels. Along with TCT, it plays a significant role in calcium balance in the body

Jet lag is caused by the disruption of the body clock as it is out of synchronisation with the unfamiliar time zone of the two different parts of the world. The body experience different patterns of light and dark than it is normally used to which disrupts the natural sleep - wake cycle.
Melatonin is a hormone that plays a key role in body rhythms and jet lag. After the sun sets, the eyes perceive darkness and alert the hypothalamus to begin releasing melatonin which promotes sleep. Conversely, when the eyes perceive sunlight, they tell the production. It takes several days.

Following are the functions performed by progesterone
(i) Helps in maintaining pregnancy.
(ii) Stimulates the development of secretory alveoli in mammary gland and secretion of milk.
(iii) Its secretion is influenced by luteinising hormone of anterior pituitary.