• Endocrine glands secrete vital chemical substances called hormones. There is a strong impact of hormones upon human behavior. 
• Hormones are responsible for certain behaviours or the absence of reactions.
• Over (hyper) or under (hypo) secretion of hormones may lead to a variety of problems.
• e.g. Hypersecretion of insulin and glycogen hormones by the pancreas reduces blood sugar levels. It results in hyperglycemia, wherein a person lacks energy and motivation, may faint and go to coma. Conversely, in the case of hyposecretion, a person gets diabetes. He becomes quite hungry and feels very tired and restless. He also shows irritated behaviour and faces frequent and uncontrolled urination.

The functions of the five endocrine glands are as follows:

Thyroid gland: It secretes thyroxin which maintains the rate of metabolism.

Parathyroid gland: It secretes parathyroxin which maintains calcium as well as phosphate balance. 

Pancreas: It secretes insulin and glycogen that is responsible for maintaining blood sugar levels.

Adrenal gland: Cortex secretes cortin or cortisone which maintains the level of water, sugar, and sodium. The medulla secretes adrenalin (which is associated with fear) and noradrenaline (which is associated with anger). Medulla plays important role in emotional excitement. 

Gonads (sex gland): Testes in males secrete androgen and testosterone. These hormones are responsible for secondary sex characteristics in males. Their voice becomes hoarse. They also get mustaches and beards. Ovaries in females secrete estrogen and progesterone. These hormones are responsible for secondary sex characteristics in females. As a result, feminine looks develop and menarche begins.