Endocrine glands in man

Endocrine glands lack ducts and are hence, called ductless glands. Their secretions are called hormones. Hormone is a chemical produced by endocrine glands and released into the blood and transported to a distantly located target organ Hormones are non-nutrient chemicals whichact as intercellular messengers and are produced in trace amounts.. Invertebratespossess very simple endocrine systems with few hormones whereas a largenumber of chemicals act as hormones and provide coordination in the vertebrates.
HUMAN ENDOCRINE SYSTEM
The endocrine glands and hormone producing diffused tissues/cells located in different parts of human  body constitute the endocrine system.
Pituitary, pineal, thyroid, adrenal, pancreas, parathyroid,thymus and gonads (testis in males and ovary in females) are the organised endocrine bodies in our body In addition to these, some other organs, e.g., gastrointestinal tract, liver, kidney, heart also produce hormones.
There is enormous diversity in the chemical structure of hormones, but most of them can be divided into four groups:

• Peptides or proteins (e.g., insulin)
• Steroid hormones (derivatives of the steroid cholesterol; e.g., testosterone)
• Amines (derivatives of the amino acid tyrosine; e.g.,epinephrine)
• Iodothyronines (thyroid hormones)